POST-MORTEM CHANGES AND QUALITY ATTRIBUTES OF MARINATED

FILETS WHEN SUBJECTED TO ULTRA-RAPID AIR CHILLING

by

NEERAJ SHARMA

(Under the direction of Romeo T. Toledo and Rakesh K. Singh)

ABSTRACT

Direct water immersion chilling is used widely in the poultry plants because of higher

heat transfer rate. However, post-mortem state of poultry muscle, extent of water uptake by

carcasses prior to deboning, and marination has been one of the largest sources of

inconsistency in marinated product quality and has become a problem for producers of

marinated broiler meat.

The effect of Ultra-rapid air chilling on carcasses compared to water chilling on the pH, R-

values, % expressible moisture, cook yields, tenderness, color, calpain activity, and cook

yield of marinated filets were investigated. In addition, the surface heat transfer coefficients

were calculated when the carcasses were subjected to Ultra-rapid air chilling process, which

would be helpful in designing of chilling cabinets.

Results showed that carcasses subjected to Ultra-rapid air chilling had higher pH and

%expressible moisture when compared to water chilled carcasses. No difference was

observed in the R-values, cook yields, tenderness, color, and calpain activity between the

chilling processes. Furthermore, air chilled filets marinated in Sodium Tri Polyphosphate

(STPP) and cooked after 24 h of storage at 2oC gave higher yields when compared to water

chilled filets. Higher yields may accounted to usual loss of mass during the air chilling

process and higher water holding capacity due to the formation of thin crust of ice on the

surface of the carcass.

In conclusion, physical and chemical properties namely pH, % expressible moisture,

tenderness, cook yields in marinade filets and quality attributes of marinated broiler muscle

are influenced by the air chilling process.

INDEX WORDS: Air chilling, dry chilling, Ultra-Rapid Air chilling, marination, cook yield,

Broilers, Rigor-mortis.

POST-MORTEM CHANGES AND QUALITY ATTRIBUTES OF MARINATED

FILETS WHEN SUBJECTED TO ULTRA-RAPID AIR CHILLING

by

NEERAJ SHARMA

B.S., ACHARYA N.G. RANGA AGRICULTURAL UNIVERSITY, 2004

A Thesis Submitted to the Graduate faculty of The University of Georgia in partial

fulfillment of the Requirements for the Degree

MASTER OF SCIENCE

ATHENS, GEORGIA

2006

© 2006

Neeraj Sharma

All Rights Reserved

POST-MORTEM CHANGES AND QUALITY ATTRIBUTES OF MARINATED

FILETS WHEN SUBJECTED TO ULTRA-RAPID AIR CHILLING

by

NEERAJ SHARMA

Major Professor: Rakesh K. Singh

Committee: Romeo T.Toledo Windham, W.R.

Elecronic Version Approved: Maureen Grasso Dean of the Graduate School The University of Georgia December 2006

iv

DEDICATION

I would like to dedicate this work to …..

…….my beloved parents and siblings for providing support and love during pursuing my degree

………all my friends

v

ACKNOWLEDGEMENTS

I would like to thank my project advisors Dr. Toledo and Dr. Singh from bottom of my

heart for being my mentors and guiding me all through my Master’s. Under my professors

supervision I have grown up more as a research and started to understand the nuance of doing

research. My whole perspective of looking at the problem has changed completely and this

whole intellectual thinking is contributed by my professors. During my two years of stay in

FPRDL lab. amount of knowledge imbibed is immense and I would like thank Dr. Toledo for

giving me space in his laboratory. It is also that time of the year where Dr. Toledo is retiring; all

I want to say is not just the FPRDL lab. but also whole of UGA is going miss you.

My hunger to do research was doubled every time I go to the laboratory since we had a

very loving and caring motherly face called Mrs. Toledo who would not only discuss and help

me in research but also fix us sumptuous food whenever she was around. My 25% of my

research completion can be accredited in her name.

I would like thank Dr.Windham for serving on the committee and correcting me

whenever I was diverting from the subject. Without his knowledge of understanding things I

would not have completed my thesis writing.

I would like to thank Dr. Fletcher who helped me in setting up the experiments, taught

me different techniques. He is one of those few professors who are humorous and witty that I

have come across at the UGA.

I would like to thank my lab. mates PJ, Vijendra, Litha, Heather, Deepti, Dr. Lee, Carl

Ruiz, Ben, Jegan and raghu for being with me and sharing there thoughts about research.

vi

I would also like to take this opportunity to thank all my parents for supporting me and all my

Jamestown, Family Housing, Raintree, Carousal and Rivermill friends for keeping me engaged

in other activities during the leisure time.

vii

TABLE OF CONTENTS Page

ACKNOWLEDGEMENTS……………………………………………………………….....v

CHAPTER 1 PURPOSE OF THE STUDY …………………………………......1

2 POST-MOPRTEM BIOCHEMICAL, TEXTURAL CHANGES IN BROILER MUSCLE

AFTER ULTRA-RAPID AIR CHILLING AND QUALITY ATTRIBUTES OF AIR

CHILLED MARINATED BREAST FILETS ……………………………………………24

3 STUDY ON SURFACE HEAT TRANSFER COEFFICIENTS DURING THE

ULTRA – RAPID AIR CHILLING PROCESS ………………58

4 CONCLUSIONS ….………...….67

1

CHAPTER 1

PURPOSE OF THE STUDY

Webster’s dictionary defines chilling as “to make something cold”. Chilling is an important step

in primary poultry slaughter operations. USDA regulations require carcasses to be chilled to

4.4oC or lower in 4, 6, or 8 h for carcasses weighing less than 4, 4 to 8, or over 8 pounds (<1.8,

1.8 to 3.6, or >3.6 kg), respectively. Direct water immersion chilling is used widely in the United

States because of the rapid heat transfer. However, extensive bird-to-bird contact via water

increases the potential for spreading bacteria between carcasses. Further, Post-mortem state of

poultry muscle, extent of water uptake by carcasses prior to deboning, and marination has been

one of the largest sources of inconsistency in marinated product quality and has become a

problem for producers of marinated broiler meat. This research has the major objectives of

elucidating post-mortem changes in poultry meat as affected by the method of chilling. The

focus is to determine if the time for rigor resolution can be accelerated by air chilling and if

consistent marinade retention can be achieved on further processing if there is no water absorbed

during chilling. The justification for an alternative to water immersion as a method of chilling is

avoidance of bird to chlorine contact, reduction of cross-contamination and possibly

improvement in textural properties of birds deboned after a very short post-mortem. The

approach used to meet the objectives involved (1) heat transfer studies to determine chilling time

and techniques for accelerating the rate of chilling (2) Determine the effect of Ultra-Rapid air

chilling on acceleration of rigor development and rigor resolution in elucidating physical and

bio-chemical post-mortem changes in broiler muscles as a function of chilling procedure and 3)

determining effect of ultra-rapid air chilling on quality attributes of marinated filets.

2

LITERATURE REVIEW

History of chilling

Chilling which comes soon after inside-outside wash of eviscerated broiler carcasses is of

foremost importance in broiler processing to control the rate of microbial growth. The idea of

chilling poultry carcasses in U.S was first developed by Benjamin (1923), whereas in U.K. air

and contact (plate) cooling of uneviscerated carcasses was established in mid 1950s as the most

common industrial practice (James et. al., 2005). The U.S. Department of Agriculture (1972)

defines chilling as a processing step which aids in the preservation of many food commodities,

and is required for poultry. The primary methods of chilling used in the poultry industry are

water-immersion chilling and dry chilling (Allen et al., 2000). The quantity of ice required to

cool the poultry carcass from 38oC (100oF) to 0oC (32oF) is about 0.38Kg of ice per kg of

poultry, but for all practical purposes most of the processing plants use 0.4 to 1.0 kg per kg

(A.S.H.R.A.E., 1971). However, the European Union in the late 1960s new regulations which

allowed direct air chilling using liquid nitrogen as the cooling medium for poultry carcasses and

banned ice-water immersion chilling due to concerns over food safety and economic perspectives

relative to moisture uptake by the chilled carcasses.

Previously, water chilling in U.S. was performed by placing the birds in vats with ice and

water, or slush-ice and permitting them to remain in the medium until the interior of the breast,

beginning at a median, ventral position between the anterior end of the sternum reaches a

temperature of 4.4oC or below (Kennet and Miller, 1958). This process took a few hours (5-10 h)

to reach the desired internal temperature. Continuous high capacity on-line chilling systems were

developed in the 1960’s to reduce the chilling time. Since then all the poultry plants started using

the continuous chilling instead of still vat chilling method.

3

Types of Chilling:

The most common methods of chilling poultry are: (1.) immersion, (2.) Spray (evaporative)

chilling, (3.) Air chilling and (4.) Cryogenic coolants used in a limited number of studies (Arafat

et. al, 1978).

According to the U.S. Department of Agriculture regulations, poultry carcasses can be chilled in

cold running tap water, crushed ice, slush ice, or slush ice agitated with compressed air or a

circulating pump or in an on-line-chiller.

1. Immersion chilling: The continuous on-line chillers fall into four categories: a.) Drag chillers,

b.) Parallel- flow tumble chillers, c.) Counter flow tumble chillers, and d.) Oscillating vat chillers

(Kotula et al., 1960). Veerkamp & Hofmans (1974) reported the empirical relationship

describing heat removal in immersion chilling of poultry carcasses as:

∆H/∆Hi = (-0.09logα′ + 0.73)*logt – (0.0194logα′ - 0.187)*logG + 0.564*logα′ - 2.219 ……1.1)

Where α′ = Apparent heat transfer coefficient (W/m2K),

G = Mass of the carcass (kg),

t = Cooling time (s)

∆Hi = the maximum amount of heat to be removed and ΔH is the heat removed at time t.

a. Drag chillers: Consists of two vats in which carcasses suspended on the shackle are dragged

through the cooling medium. The first vat is a 15.24 m. trough containing water at 41oF. The

second vat is S-shaped with 200 lineal feet filled with water at a temperature of 0o to 1oC

maintained by addition of slush ice. Drag chillers have proven to induce very slow heat transfer

and the equipment cost was high.

b. Parallel- flow chillers: Depending upon the number of birds to be processed per hour, two

metal tanks about 7.92 m long each are generally used. A revolving cylindrical drum tumbles the

4

birds in the coolant, and a current of recirculated water moves the carcasses forward along the

drum. The first tank contains tap water and second tank uses slush ice.

c. Counter-flow tumble chillers: These chillers use air-agitation or a high speed current of water

from recirculating pumps to maintain a constant uniform temperature, and control the water

uptake. The heat transfer mechanism is similar to that in the parallel-flow system except that the

water circulates in a direction opposite to the movement of carcasses.

d. Oscillating Vat Chillers: These chillers are divided into two tanks. The first tank uses tap

water to pre-cool the carcasses and ice is used in the second tank to maintain the temperature of

water at 1o to 2o C. The tanks are placed side by side on concentric rollers and rocked side to side

to agitate the contents.

2. Spray Chilling: Spray or evaporative chilling system is popular in Europe because of the

perceived higher levels of hygiene. During spray chilling, water is sprayed continuously on the

surface of the carcass while they are suspended in a stream of refrigerated air. Since evaporation

occurs from the water sprayed on the carcasses the overall mass loss by carcasses is reduced

while the heat transfer is increased by the water evaporating from the surface of the carcasses

(James et al., 2005). Although this process is referred to as evaporative air chilling, it should not

be confused with true evaporative chilling of poultry as described by Klose (1975).

3. Air chilling: In this process the carcasses are exposed to a stream of refrigerated air or air

cooled by liquid nitrogen or CO2 in either a blast freezer or chilling room depending upon the

size of the poultry plant. The chilling time and weight loss are inversely related to each other. It

was also found that carcasses hung in a vertical position are cooled faster than carcasses in a

horizontal position (Vacinek, 1973). In air chilling carcass weight loss of about 1 to 1.5% are

commonly seen.

5

Cook & Sair (1938) described an equation that relates chilling time to carcass weight and

chilling air temperature as follows:

t= -5+ 11.22*log10 (Tp - Ta) +0.5183*W ………………………(1.2)

Where, t = time in hours to cool to -16.66oC above the air temperature,

Tp = Initial carcass temperature (oC),

Ta = air temperature (oC),

W = Weight of the bird in kg.

However the above equation holds only for large birds and high air velocities, hanging details,

and other conditions are not mentioned.

Benefits of Air chilling

1. Air chilling systems are used to produce an unadulterated and cleaner product because water

uptake is minimal and there is no transfer of microflora among the birds processed. These

systems are designed to maintain hygienic conditions during the process.

2. It has been assumed that during air chilling drying of the surface of carcasses reduces the

water activity thus retarding microbial growth and hence prolongs self life. However, the

opposite has been observed by Thomas (1977) suggested that perhaps higher bacterial counts on

air chilled carcasses counteracted the inhibition of growth by a reduced water activity.

3. The texture of air-chilled and cooked meat is similar to that of the water-immersed and cooked

product.

4. There is an improvement in the flavor of the poultry meat when nitrogen or carbon dioxide is

used as a chilling medium (Lillard, 1982).

6

Physical, chemical and functional properties of breast meat

Two most important properties of poultry breast meat are appearance (color) and water-

holding capacity. The color of raw or cooked breast filet is the primary determinant of

acceptability of meat in the market place, while water holding capacity strongly influences the

color of raw meat and the texture of the cooked product. A loss in the water holding capacity of

poultry meat gives meat a pale color often referred to as a Pale, Soft and Exudative (PSE) like

condition which is a common syndrome in porcine and turkey muscles (Bianchi, 2005). Pale

meat can be encountered in commercial processing plants and in retail stores as light white-

yellow discolored breast meat turning to a pale gray discoloration during storage and

distribution. There is no significant growth of microbes associated with this syndrome

(Boulianne and King, 1995). Sams (1999) reported that further processing of pale meat induces

an additional defect called ‘crackling’ in which gaps appear in the interior of the cooked meat.

Petracci and Fletcher (2002) reported that short aging times post-mortem affected the color

values. Meat thickness (Sandusky and Heath, 1996; Bianchi and Fletcher, 2002) and color

measurement position on the fillet (Goshaw et al., 2000) have also shown to affect the meat color

measurement. Measured values of the water holding capacity can guide the technologist in

product formulation and process control. However, Alvarado and Sams (2002) reported that

further-processed PSE meat will have excessive water accumulation in packages during cooking

giving an unacceptable appearance and quality.

Postmortem glycolysis results in the accumulation of lactic acid and a decline in pH of

muscle from near to 7.0 at death, to almost 5.5 after 24 h of storage in the walk-in-cooler. The

amount of glycogen present in the muscle determines the ultimate pH values post-mortem. A

rapid glycogen depletion result in the formation of lactic acid and lactic acid level post-mortem

7

is due to stress experienced by birds before slaughter (Ngoka and Froning, 1982). Breast meat

with higher pH appeared darker (Livingston and Brown, 1981). These findings were confirmed

by Yang and Chen (1993) and Cornforth (1994) who stated that the breast meat appeared darker

because a high pH meat has higher water binding capacity. The high water binding capacity will

have effects on the taste, tenderness and rate of post-mortem depletion of glycogen (rigor

development and rigor resolution).

Generally, pH is measured electrochemically using a metal or glass electrode and

variations in pH are recorded using different types of meters and probes. pH measurements are

accurate only when the pH of the muscle has reached a constant value, e.g. after 24 h storage of

the muscle. Another method very commonly used on muscles undergoing rigor is

homogenization of meat in potassium chloride and iodoacetate solution to arrest glycolysis

(Bendall, 1973) and the pH is measured using a glass electrode.

Rigor Mortis

Rigor mortis is considered as the first step in the conversion of muscle to meat. This can

be characterized by progressive stiffening of the muscle and is a temporal process occurring

during the postmortem glycolysis. Bate-Smith (1948) reported that start of rigor mortis occurs

when ATP concentration in muscle drops to ½ to 1/3 of its initial value. ATP is the only energy

source in aerobic or anaerobic metabolism. Anaerobic metabolism does not have a considerable

effect on the rate of postmortem depletion of ATP as measured by R-value (Sams et al., 1989).

Aerobic metabolism takes the pathway of glycolysis, respiration (citric acid cycle and electron

transport) and utilizes oxygen to efficiently produce ATP compared to the anaerobic process.

Anaerobic process occurs when the muscle experiences an oxygen debt and the metabolism takes

a glycolysis pathway that leads to the accumulation of lactate.

8

AEROBIC PROCESS:

1 Glucose Unit + 36 Pi + 36 ADP + 6O2------- 36 ATP + 6 CO2 + 24 H2O………………. (1.3)

ANAEROBIC PROCESS (Glycolysis):

1 Glucose Unit + 3 ADP + 3 Pi --------- 3 ATP + 2 Lactate + 2 H+ + 3 H2O……………… (1.4)

In the nonliving or postmortem period, the changes in meat muscle can be divided into two

stages: postmortem pre-rigor and postmortem post-rigor

Pre-rigor:

Rigor development is faster in avian than in mammalian muscle. Pre-rigor is a condition

of carcass muscle that is progressively becoming stiff as rigor mortis proceeds. This period is

generally said to be 3 to 5 h after chilling of avian carcasses. During the postmortem pre-rigor

stage ATP decreases with time following death and this is accompanied by an increase in the

fixed actomyosin cross bridges in the muscle. There is also a change in the concentrations of

hydrogen ion (H+)(expressed as pH) and Creatine Phosphate (CP), the compound that serves as a

reservoir of the high-energy phosphate necessary to regenerate ATP from ADP. The

concentration of ATP does not decrease soon after postmortem but rather remains at

compositional levels for a brief period due to the regeneration of ATP from CP and continued

anaerobic glycolysis.

ADP + CP ----- (Creatine Kinase) ATP + Creatine………………………………………….. (1.5)

Shear values of early harvested pre-rigor breast fillets is greatly decreased by restraining

the wings during rigor mortis development, known as muscle tensioning (MT). However, the

decrease in shear values due to MT is not low enough for the meat to be considered tender by

consumers (Papa et al., 1989; Janky et al., 1992). However, electrical stimulation (ES) when

combined with MT showed significantly lower shear values than no treatment or MT alone and

9

product tenderness was acceptable. Birkhold and Sams (1993) showed that high current stunning

delayed early rigor development compared to the low voltage stunning, but had little effect on

the final meat quality (Craig and Fletcher, 1997).

Post-rigor:

Post-rigor is a condition where carcass muscle has completed rigor mortis development

i.e. greater than 3 to 5 h after chilling in poultry meat. No change in tenderness was reported in

muscle deboned 24h post-chill. (Lyon et al, 1992).

Cold Shortening:

In poultry, cold shortening occurs in a prematurely excised or otherwise altered breast

meat (Papinaho and Fletcher, 1996). Cold shortening occurs most extensively at 0oC, while

muscle pH is greater than 6.7 whereas, rigor shortening occurs most extensively at 40oC, when

the muscle pH had fallen to 6.2 (Dunn et al., 1993b, c).

Factors effecting Rigor:

1. Electrical Stimulation: Supposed to accelerate rigor mortis development and reduce the aging

time before deboning can be carried out without affecting textural properties of the boneless

meat.

2. Gas Stunning: Gases like Argon produce anoxia at a more advanced level of rigor mortis by

slowing the rapid decrease in pH.

3. Temperature: Poultry meat incubated at 40oC or higher soon after evisceration expedited rigor

mortis and resulted in tough meat after cooking.

Aging and Texture:

Reports were published as early as the beginning of the century that the tenderness of

meat changes after storage (Lehman, 1907). Aging, defined as storing intact carcasses at

10

refrigerated temperatures prior to deboning or cooking, has two phases. First is rigor mortis

development, where there is a gradual shift from aerobic to anaerobic pathways, adenosine

triphosphate (ATP) is depleted, and actomyosin is formed during the post-mortem (Hamm,

1982). In poultry meat, this period lasts for 4-6 h post-mortem. The second phase, termed as

rigor mortis resolution, affects structural degradation of the myofibrillar protein matrix and

results in improved meat tenderness (Lawrie, 1991). During aging, in addition to proteolysis,

increase in post-mortem ionic strength due to decreased protein interactions and increased

solubility of myofibrillar proteins contributes to aging induced tenderness (Wu and Smith, 1987).

Eating quality like appearance, texture and flavor has a direct correlation with consumers

buying a poultry product. Meat tenderization is described as enzymatic in nature and involves

endogenous proteolytic systems (Carlo et al., 2006). Endogenous peptidases play a major role in

meat tenderness and soften the myofibrillar structure during post-mortem (Ouali, 1992).

Numerous factors such as breed, age, sex, nutrition, bird management, sarcomere length, skeletal

restraint and proteolytic activity affect the tenderness in the cooked chicken muscle (Stadleman,

1967; Nakamura at al., 1975; Ricard and Touraille, 1988; Chambers et al., 1991; Pearson, 1987).

Similarly, Dunn et al. (1995) reported that type of chilling and temperature influenced the

textural variability of broiler breasts. de Fremery and Pool (1960) demonstrated that chicken PM

muscle incubated at 0oC produced tougher cooked meat than muscle incubated at 10oC and 20oC,

while muscle incubated at 40oC turned out to give toughest cooked meat of all. Khan (1971) has

also reported that holding muscle at 37oC during the onset of rigor mortis resulted in tough

cooked meat

11

Prediction of Heat and Mass transfer

Many food processing operations include cooling and freezing and transient convective

heat transfer between a fluid medium and the solid food item (Dincer, 1993). According to

Newton’s law of cooling, heat transfer coefficient (h) is the parameter that is used to calculate

the heat flux (q) from the surface of an object as a result of the temperature difference between

the surface of the object (Ts) and the temperature of the fluid flowing across the object (T∞)

(Harris, et. al.,2003).

Q = h (Ts-T∞) ………………………………………………. (1.6)

Thus surface heat transfer coefficient is very important in designing equipment in which

convection heat transfer is used to process foods and beverages.

Factors that affect the heat transfer coefficients are velocity of the fluid past the surface

of the product, the physical and thermal properties of the fluid, the dimensions of the solid, the

roughness of the product’s surface and, in some cases, gravity or other body forces. If the flow

regime of the fluid is unstable, a dimensionless heat transfer variables (Nusselt number

correlations) are used to present the results of the heat transfer measurements (Harris, et al.,

2003). Under laminar flow conditions it is possible to derive heat transfer coefficients

analytically by solving the mass, energy and momentum conservation equations (Incropera and

de Witt, 1996).

Tarlea and Chiriac (2003) presented three main methods of theoretical modeling of the

refrigeration process: the graphical methods, analytical methods, and the numerical methods. The

most important numerical methods used now are: finite differences method and finite element

method. Harris et al. (2003) measured local heat transfer coefficients using special sensors which

depended on air velocity, turbulence intensity and sensor position. Metallic chicken and

12

mathematical modeling were used to estimate the value of the surface heat transfer coefficient

without considering simultaneous convective mass transfer (Kyhos and Nesvadba, 1999).

Calpain Activity

Proteolytic enzymes are widely distributed in the animal kingdom. These endogenous

proteolytic enzymes consist of calpains and calpastatin, the major proteolytic system responsible

for initial myofibrillar protein degradation resulting in ante-mortem muscle atrophy and post-

mortem meat tenderization (Goll et al., 1983; Koohmaraie, 1988, 1992a, b). Cathepsins were

first discovered in the year 1950 by De Duve et al.

Calpains, the Ca2+- dependent cysteine proteinases discovered in the rat brain by Guroff

(1964), are said to explain variability in the meat tenderness. Later, calpains received much more

attention due to their ability to alter the z-line density; a modification often observed post-

mortem, even if this change is not correlated with tenderness (Taylor et al., 1995). Traditionally,

two calpain isoforms have been identified; (μ-) calpain and milli (m-) calpain, which are

activated at the micro molar and milli-molar calcium concentration, respectively (Prigge et al.,

1998). Studies on meat during the last 15 to 22 years have indicated that the calpains have a

major role in postmortem proteolysis that lead to increased tenderness (Koohmaraie, 1988, 1992;

Goll et al., 1992 a, b; Taylor et al., 1995a).

Highly polymorphic protein named calpastatin inhibits calpains and cathepsins and is

inhibited by cystatins (Dubin, 2005; Sentandreu et al., 2002). Etherington et al. (1990) noted and

verified that μ-calpain is inactivated by Electrical Stimulation (ES) effect in aged carcasses but

not m-calpain. Hwang and Thompson (2001) showed that in beef longissimus dorsi muscle the

adverse effect of rapid glycolysis on meat tenderness appeared to be associated with the early

reduction in μ-calpain, while the levels of calpastatin remained relatively high.

13

History of Marination

Marination is performed on whole as well as deboned carcasses and this step can come

soon after chilling process or after certain period of storage in a cooler at 2oC or after deboning.

Marinade when added to meat is meant to improve tenderness, water holding capacity, cook

yields, improvement of product shelf life and improvement in palatability. In general, marinade

solution consists of water, phosphate and salt but might also consists of water binders to improve

cook yields, flavoring substances and antimicrobial agents in minute quantities. Tenderness of

meat products, along with juiciness, flavor and color are the main eating quality characteristics

that influence the consumers overall judgment of quality (Wood, Nute, Fursey, & Cuthberston,

1995). Marination is defined as soaking of meat in liquids like vinegar, oils in combination with

spices or salt to improve the flavor of the meat and extend the shelf-life or at least masks off-

flavors. Tumbling or massaging for a period of 15-30mins may also be used (Northcutt, 1999).

If the tumbling time is small marinade pick up is less and if tumbling is prolonged, a rubbery

texture is formed in a final product. USDA recommends 0.5% as upper level of phosphate

concentration in the final product where as for salt there are no such restrictions. Higher

concentration of salt raises the water holding capacity in the final product, but excessive salt may

reduced sensory acceptability and may raise concern on consumers with restricted sodium

dietary intake. The upper limit of salt concentration in whole muscle chicken products is around

0.8%.

As a common industry practice marination is carried out in a vacuum tumbler, a massager

or the marinade solution may be injected into the meat. In boneless chicken meat both injection

and tumbling may be used to improve marinade dispersion into the meat (tumbling under

14

vacuum improves marinade pick up). Bone-in chicken is marinated by injection because

tumbling or massaging can break bone and result in bone fragments in the marinated product.

Functions of Phosphates & Salt:

Phosphates are alkaline in nature, which when used in meat products increases both pH

and ionic strength [(factors that are known to increase protein extraction) Schmidt and Trout

(1982)] with the extent of increase depending on the type and concentration of phosphate used.

The commonly used phosphates in the industry are Tetra Sodium Pyrophosphate (TSPP), Tetra

Potassium Pyrophosphate (TKPP), Sodium Tripolyphosphate (STPP), Monosodium phosphate

(MSP), Hexametaphosphate, and phosphate glass. Hamm (1970) summarized on the effect of

phosphate on the increase in Water holding capacity as due to (a) an increase in pH (b) an

increase in ionic strength, (c) the ability of phosphates to bind to meat proteins, and (d) the

ability of phosphates to prevent the association of actin and myosin into actomyosin.

In recent years the detriment of a high dietary salt intake to human health has been

proposed by health professionals. Salt contains 40% of sodium which has been attributed to be a

cause of hypertension in humans. Xiong and Brekke (1989) stated that salt in poultry meat

marinades caters to the solubilization of protein which swells the isolated myofibrils thereby

increasing the water holding capacity by forming a three dimensional, continuous gel network

when the protein is heat-set by cooking.

Factors which affect the action of salt and phosphate are: 1) initial meat pH 2) time after

death or extent of rigor development 3) temperature; and 4) mode of application (tumbling or

needle injection).

15

Water Holding Capacity

Water Holding capacity affects the economic value and meat quality of meat and meat

products, because it affects the water change during transportation and storage, drip loss during

thawing, weight loss and shrinkage during cooking and the juiciness and tenderness of the meat

(Lawrie, 1985; Gault, 1985). As reported by Essary and Dawson (1965) moisture absorption per

unit weight is higher in small carcasses than in larger carcasses. If the carcasses are cut up prior

to water chilling moisture retention by parts is as follows: neck> back> thigh> wing>

breast>drumstick (Katz and Dawson, 1964).

Water holding capacity in meat and meat products is determined by 1) using external

forces to drive out the water like the filter press method and by centrifugation 2) letting the water

drip out of the raw meat in a standardized way over a certain time period like the ‘Honikel bag

method’ or the EZ-drip loss, or 3) heating the meat and measuring the cooking loss (Honikel,

1989; Honikel and Hamm, 1994; Rasmussen and Andersson, 1996; Christensen, 2002). Press

filter method is good with a small number of samples and is easy to perform but when there is a

large number of samples the procedure becomes laborious and results are unstable. The other

procedure which was recently developed is video image analysis (VIA) which uses computers

and a simple formula to calculate the WHC (Irie, Izumo and Mohri, 1996). VIA measures WHC

rapidly and accurately when compared to Press filter method.

Cooked Meat:

A wide range of aging times post-mortem may be used on the raw meat before and after

deboning prior to cooking. Tray packed or ice packed products may undergo several days of

aging after deboning prior to cooking where as, processors who sell cooked products or

individually quick frozen fillets allow virtually no aging after deboning prior to cooking or

16

freezing (McKee, Hirschler and Sams, 1997). Cooking is indirectly related to eating quality as

the end point of cooking (cooking time or internal temperature) will define the cooked product

tenderness. Generally, poultry meat is cooked until the internal temperature reaches 176oF,

where temperature is monitored using a thermocouple. If the meat is undercooked, a pink or

bloody color persists in the product. On the other hand, the meat may be fully cooked and under

certain conditions, the pink color persists giving consumers the perception of an undercooked

product. Pink color defect in cooked products has been a problem in the meat industry for over

more than 30 years (Pool, 1956; Trout, 1989). A few important causes of pink meat are:

1) Carbon monoxide or nitric oxide generated in gas-fired ovens (pool, 1956); 2) irradiation

pasteurization (Coleby et al., 1960; Mead and Roberts, 1986); 3) nitrates or nitrites in the bird’s

diet (Froning et al., 1967); 4) different concentration of muscle myoglobin in meat (Froning et

al., 1968a); 5) lower than target end-point cooking temperature and 6) fluctuating frozen storage

temperature (Helmke and Froning, 1971).

17

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21

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inhibitos in meat tenderness. Trends in Food Sci. and Technol. 56:1130-1135.

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color of chicken meat. Poultry Sci. 46:1261. (Abstr.)

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affected by age, sex and strain. Poultry Sci. 47:1827(Abstr.)

Helmke, A., and Froning, G. W. 1971. The effect of endpoint cooking temperature and storage

on the color of turkey meat. Poultry Sci. 50:1832-1836.

23

Gault, N. F. S. 1985. The relationship between water holding capacity and cooked meat

tenderness in beef muscles as influenced by acidic conditions below the ultimate pH. Meat Sci.,

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Co-operative Extension Service, College of Agricultural and Environmental Sciences. The

University of Georgia, Athens, GA.

24

CHAPTER 2

POST-MOPRTEM BIOCHEMICAL, TEXTURAL CHANGES IN BROILER MUSCLE

AFTER ULTRA-RAPID AIR CHILLING AND QUALITY ATTRIBUTES OF AIR

CHILLED MARINATED BREAST FILETS

______________________ Sharma Neeraj, Toledo RT, Singh RK and Fletcher DL. To be submitted to Journal of Poultry Science

25

ABSTRACT The effects of Ultra-rapid air chilling on carcasses compared to water chilling on the pH, R-

values, % expressible moisture, cook yield, tenderness, color and Calpain activity were

investigated. A total of 48 birds were processed. After final washing of eviscerated birds, 24

birds were subjected to air (40 min at -20oC) and 24 to water immersion chilling (0oC, 50 min).

Eight birds at each time period (2 h, 4 h & 24 h post-mortem) were analyzed for biochemical

attributes. Ultra-rapid air chilled birds showed higher pH for all three times chosen post mortem

compared to the water-immersion chilled birds. There was no significant difference in the R-

values and Calpain activity at any given time post-mortem between the two chilling methods.

There was no difference in shear values and color at 24 h post mortem while there was a

significant difference in the % expressible moisture and cook yield at 24 hr post mortem between

the two chilling methods. The results suggest that time post-mortem for resolution of rigor can be

accelerated by the frozen crust formed on carcass chilled in -20oC dry air.

Quality attributes of marinated breast fillets from Ultra-rapid air chilled and conventionally water

chilled carcasses were studied. Breast filets from 324 whole carcasses air or water chilled and

aged 1, 5, and 23 h post-chill were marinated in a basic marinade solution consisting of Sodium

Tripolyphospahte and salt at different concentrations such as 10%, 15% and 20%. A 22.73 kg

capacity rotary vacuum tumbler was used. Tumbing was for 25 min and marinated fillets were

stored 24 h before measurement of the retention values. All marinated samples were steamed

cooked 24 h after marination and the following data were collected: marinade absorption,

marinade retention and cook yield.

Results indicated that as aging period increases the marinade absorption and retention

also increases with time post-chill except at target marinade pick up of 10%. Air chilled breast

26

filets at the marinade target levels of 10% at 1 h pos-chill time intervals and later cooked after

24 h of storage showed significant difference at p<0.05 and breast filets deboned after 5 h and 24

h showed no significant difference. Whereas at target level of marinade pick up of 15% and 20%

at 1 h and 5 h showed significant difference at p<0.1, at 24 h time period for 15% pick up

showed significant difference at p<0.05 but there was no significant difference at 24 h time

period for 20% pick up . In other experiment heat transfer co-efficient of the whole carcass was

calculated which would further used be in designing the equipment.

27

Introduction

In 2004 the US production of live broiler was 45.8 billion pounds, which was 4 percent

more than that in 2003. Ninety percent of broilers are sold as parts and while the rest are

marketed as whole birds (W.P. Roenigk, 2005). Since the demand for fabricated pieces is high

and early harvesting would reduce production cost of energy, labor and storage, processors are

striving for shortening the hold time post-chill in the processing plant. However, unaged birds

post-mortem may be unacceptably tough and cook yields may also be lower than that for fully

aged birds (Walker et al. 1994; Skarovsky and Sams, 1999). Birds are considered to be fully

aged birds are at least 4 to 6 h old after rigor completion (Dawson et al., 1987).

Researchers have used several different approaches to mediate rigor development and to

prevent toughening. Some of these are electrical stimulation (ES) with different voltage levels,

and amperages (Thompson et al., 1987; Froning and Uijttenboogaart, 1988; Lyon et al., 1989;

Sams et al., 1989); combined muscle tensioning + electrical stimulation (MT, Papa and Fletcher,

1988). Walker et al. (1994) reported that high voltage ES + MT significantly reduced the shear

value relative to 1-h post-chill control meat. It has been reported that both low and high voltage

ES systems accelerated rigor mortis development (Thompson et al., 1987; Lyon et al., 1989;

Sams, 1990). Lee et al. (1979) reported that electrically stunned birds showed delays in post-

mortem gylcolysis or reduced levels of lactic acid, higher Adenosine triphosphate (ATP),

Creatine phosphate (CP), and pH levels, but lower lactate level than unstunned control birds.

Chilling is an important step in the primary poultry slaughter operations and USDA

requires the broilers to chill to 4oC within four hours post-mortem. Considering the fact that there

is extensive bird-to-bird contact via water in direct immersion chilling, increasing the potential

for spreading bacteria between carcasses, and aging front halves or whole carcasses has become

28

an important cost consideration, researchers have been investigating the merits of ultra-rapid air

chilling to accelerate the rigor development, rigor resolution and avoid cross-contamination of

birds with pathogenic microorganisms. Air chilling, which is hardly used in the US is a popular

method to chill the poultry meat in Europe. The European Union regulations do not specify a

time to chill the poultry carcass, but specifies only a maximum final meat temperature of 4oC to

be achieved as soon as possible before transportation or cutting. In previous work, Chilling air

temperature ranged between -7 and 2oC (James et al., 2005). Chilling with air at sub-freezing

temperature induces crust-freezing which might be useful in reducing the aging time post-chill

by affecting rigor mortis development, and thereby reducing toughening when deboning is

carried out with short aging times post-chill. Air chilling may also influence the effectiveness of

ES to improve meat tenderness particularly when cooling rate is slow under conditions of

chilling with air temperature above freezing (Dunn et al., 1995).

Tenderness, one of the attributes that characterize the eating quality of meat is measured

either using instrument or consumer panel on the cooked meat. If the poultry meat is deboned

early (0 to 2h of post-mortem), 50-80% of the meat will be tough and if deboned after 6h, 70-

80% of the meat will be tender. Warner-Bratzler, a ‘V’ shaped shear apparatus measures the

force to cut through the cooked sample whereas, Lee-Kramer apparatus has multiple blades to

accurately measure the tenderness of intact sample. Sensory evaluation of tenderness involves a

group of trained panelists or a large panel of untrained consumers.

Cooking is carried on the whole, bone-in cut-up or boneless poultry meat. Most

processors cook poultry using forced air convection, steam cooking or cooking in the hot water

until the internal temperature reaches 78oC. Internal temperature is monitored with a

thermocouple inserted into the thickest part of the breast fillet. Usually the meat is very tender if

29

it is cooked for a longer time at a low temperature but this process usually results in lowered

yields. Furthermore, endpoint internal temperature is greater than 78oC, moisture retention is

reduced and higher % loss can result. On the contrary, cooking for short period of time at high

temperature in a steam or hot air atmosphere could result in higher moisture retention and %yield

but the meat would be tough. Cooking is the primary means for inactivating pathogenic

microorganisms therefore undercooking, though it increases yields and produces a juicier

product, is not recommended for ready to eat meat. Short time cooking under conditions when

the rate of heat transfer is rapid and the meat is restrained to avoid muscle fiber contraction, such

as in a clam shell grill generally produces a more tender product than those a hot air or steam

cooked product.

Marination technology is widely used to improve the tenderness and juiciness of red

meat, poultry meat and fish products. Since the beginning of 1950s popularity of marination has

grown due to the demand in the market for ready-to-cook poultry meat in as bone-in parts or

boneless meat. The spaces between the thick and thin filaments of the myofibrils is said to affect

the marinade pick up in the all the muscles types. Allen et al. (1998) reported that amount of

marinade pick up and Water holding capacity (WHC) of “darker than normal” fillets is greater

than “lighter than normal” fillets.

Simple marinade ingredients include phosphates, salts and the complex marinade might

also include sugars, starch, spices and color in small amounts. In simpler terms marination can be

defined as soaking of meat in a solution of Phosphates, curd, salt, seasoning, spices and other

flavoring ingredients for several hours (still marination). Since still marination has a

disadvantage in excessive time, reduced amount of marinade pick up and retention, recent

commercial marination processes utilize atmospheric and vacuum tumblers, injectors and

30

massagers. Above described equipment assists in tenderization by disrupting of some muscle

fibrils due to the applied mechanical action this muscle fibril disruption and solubilization of

protein increases the percent marinade pick up and retention.

Phosphates are one of the vital ingredients in the marinade and have a great effect on

complete absorption and retention of water. However, the concentration in the final product is

restricted to below 0.5%. Although there are no regulatory restrictions on salt content, effective

solubilization of myofibrillar proteins by salt occurs in the range of 0.8 to 2% while excessive

saltiness may be perceived by consumers when salt content is > 1%. Hamm (1970) summarized

on the effect of phosphate on the increase in Water holding capacity as due to (a) an increase in

pH, (b) an increase in ionic strength, (c) the ability of phosphates to bind to meat proteins, and

(d) the ability of phosphates to dissociate actomyosin into actin and myosin. So, phosphates

along with salt are said to improve the cooking yield and water-holding capacity, tenderness and

palatability.

Even after the addition of phosphates and salts in the marinade solution, inappropriate

mechanical manipulation of the meat may result in incomplete absorption of marinade and poor

marinade retention thus absorbed marinated will be released by the meat as purge. Purge is

liquid separation from the muscle and affects the final cook yields. To improve on these aspects

other functional ingredients like starch are added in very small amounts into the marinade

solution which not only maximizes the final cook yield but also improves palatability.

The objective of the present study is to determine the effect of ultra-rapid air chilling on

acceleration of rigor development and rigor resolution, elucidate physical & biochemical post-

mortem changes in broiler muscles as a function of chilling procedure and effect of ultra-rapid

air chilling of broiler carcasses on marination pick up, retention and cook yield of boneless breast

31

fillets form these birds excised after different times post-chill. Water chilled carcasses were also

processed for comparison

Materials and Methods

Materials

Broilers (7-wk-old) were raised in large groups on litter at the poultry Research Center,

the University of Georgia, Athens. Feed was withdrawn 12 h before the slaughter without

expulsion of water. In each replication, 48 birds were hung on the shackle line and then stunned

by immersing their heads in an electrified 1% NaCl up to the neck. Immediately after stunning,

birds were killed by bleeding through a unilateral neck cut for 90 s. Birds were electrically

stimulated at 15 volts and 60 Hz for 18 s per chicken. After exsanguinations, birds were sub-

scalded (62°C, 45s), and de-feathered with a mechanical in-line picker, and manually

eviscerated. Half of the carcasses were conventionally chilled using a static immersion chilling

system (< 4°C, 1 h) and the remaining half were shackled by the wings on the rack and air

chilled in the air chilling cabinet (< 4°C, 15-50 min). Ultra rapid air chilling was done in air

cabinet maintained at -20oC using liquid nitrogen. After chilling the carcasses were analyzed

after 2 h, 4 h and 24 h of storage at 2°C.

The air chilling system used in the experiments was an insulated stainless steel air

chilling cabinet equipped with a set of two high speed fans which take in air from the chamber

into a plenum and discharge the air through a system of channels over the carcass. Spray nozzles

injecting liquid nitrogen cooled the air at the intake side of the fans. Air temperature and deep

breast temperature were monitored every 15 sec with thermocouple connected to a data logger.

Carcasses entered the cabinet at an average deep breast muscle temperature of 29°C and it took

approximately 40 min at -20°C to get the carcass temperature to less than 4oC. Soon after

32

chilling, i.e. after 1 h of post-mortem period, samples were pooled from the right breast filet for

various analyses. Whole birds from 2, 4 and 24 h of storage at 2oC post-chill were dipped in

liquid nitrogen (-80°C) and stored frozen until analyzed for R-values (3g) and Calpain activity.

Methodology of marination experiments

A total of 324 whole carcasses where collected from the poultry processing plant and

transported to Food science building, UGA. 162 whole carcasses were water chilled and were

collected at the exit from the chiller of the poultry processing plant. The other 162 carcasses

were removed from the evisceration line of the processing plant just after the final outside wash

step. The carcasses were shackled by the wings and air chilled in the air chilling cabinet (< 4°C,

15-50 min.) at pilot plant of food science building, UGA. Ultra rapid air chilling was done in an

air chilling cabinet using liquid nitrogen (-20° C) to cool the air. The liquid nitrogen spray was

not applied directly on the birds but on air drawn into the plenum shrouding the high speed

circulation fans. Chilling was terminated when the deep breast temperature reached 4 C. After

chilling the carcasses were transferred into a 2°C walk-in cooler. After one hour of storage post-

chill twelve filets were randomly excised from carcasses, and the same sampling process was

used for each of the three time periods post-chill. Breast fillet samples were marinated

immediately after they were removed form the carcasses.

Twelve breast filets were cut and weighed from the six randomly selected whole

carcasses of the water chilled process and air chilled process put in vacuum bags with the

specific concentration of marinade, vacuum sealed and put in a 22.73 kg capacity vacuum

tumbler and 26.5 inches vacuum was drawn using a high capacity vacuum pump (Soge Vac

model UV 25, Leybold Vacuum, Export PA). Marination was conducted by tumbling the filets in

the marinade solution of 10%, 15%, 20% STPP for 25minutes at 9 rpm in a 7oC processing

33

room. Immediately after tumbling the bags were cut, weight of the filets were noted and

marinade retention and cook yields were calculated after storing for 24 h in a walk-in

cooler(2oC). All the experiments at different concentration levels of marinade were repeated

thrice.

The filets after storage of 24 h were weighed and cooked for 20 min at 98 2oC in steam,

allowed to sit for 2 min and weighed to calculate the cook yields.

Methods

Chilling time and weight loss/gain

Three thermocouples were used for monitoring the deep breast carcass and one other

thermocouple was used to monitored air temperature inside the cabinet. The deep breast and air

temperature were monitored every 15 s with thermocouple which was connected to a data logger.

Carcasses entered the cabinet at an average deep breast muscle temperature of 29°C and it took

approximately 40 min at -20°C to get the carcass temperature to less than 4oC. For calculation of

weight loss and gain, the carcasses were weighted before and after the chilling process.

pH

pH was measured using the iodoacetate method as described by Jeacocke (1973) as

modified by Sams and Janky (1986). Samples (approximately 2.0 g) were placed in 10 ml of a

solution of sodium iodoacetate (5 mM) and potassium chloride (150 mM) adjusted to pH 7.0.

The samples were homogenized for 30 s, with a 5 s interval using a homogenizer (Polytron

homogenizer, Kinemetica A6, Switzerland). An electrode was inserted into the homogenate and

the pH was recorded.

34

R-Values

The ratios of adenine:inosine nucleotide (R-values) in the muscle tissue of broiler carcass

was measured according to the procedure of Honikel & Fisher (1977). Briefly, nucleotides were

extracted from 2-g samples by homogenization for 30 s (Waring Blender homogenizer) in 1 M

perchloric acid (1:10 w/v). The homogenate was then filtered and one aliquot (0.1 ml) of the

supernatant was diluted in 4.9 ml of 0.1 M phosphate buffer pH 7.0. Absorbance was determined

at 250 nm and 260 nm with a spectrophotometer (Hitachi M V-200), using phosphate buffer as

reference. The R value corresponds to the ratio between the concentration of adenine

phosphatidyl compounds (ATP, ADP, AMP and others) and the concentration of a major

breakdown product, inosine monophosphate (IMP). It was calculated as the ratio between the

absorbance at 250 nm (IMP) and the absorbance at 260 nm (ATP), and served as a monitor of

ATP depletion.

Enzyme extraction (Total calpain activity)

Total calpain activity was determined using the assay procedures described by

Veeramuthu and Sams (1999). Meat from the frozen bird samples were excised and pooled (5 g

per bird, birds/sample) The 20 g pooled meat sample was homogenized in 2.5 times volume of

50 mM Tris, 10 mM 2-Mercaptoethanol (MCE), 1.0 mM EDTA, 0.2% triton X-100 at pH 8.5.

Following centrifugation (34,000 X g 1 h), the extract was dialyzed against 40 mM Tris, 0.5 mM

EDTA, 10 mM 2-MCE at pH 7.5. Following a second centrifugation (34,000 X g 1 h) the

samples were incubated for 1 h at 25oCin a 100 mM Tris, 1 mM of sodium Azide, 5 mM calcium

chloride, 5 mg/mL casein, 1 mL of 2-MCE/L (pH 7.5). The reaction was terminated by adding

2.0 mL of 5 % TCA to each tube, vortexed and centrifuged for 30 min at 2000Xg. The

absorbance of each tube was measured by using a spectrometer (UV-1601 Shimadzu) at 278 nm.

35

Expressible Moisture:

The Filter paper press method (Wierbicki and Deatherage 1958) was used for measuring

the water holding capacity of air and water chilled meat after 24 h of storage time. Samples (300

mg ± 5) of intact meat from the cranial of the right filet were placed on a previously weighed

(0.0001 g accuracy) filter paper (Whatmann no. 1, 9 cm diameter). Afterwards, the filter paper

with meat sample was placed between two plexiglas plates. A load of 1.0 kg was applied for 1

min and damp filter paper was rapidly weighed accurately after removing the compressed meat

sample. Mean of two replicates was taken as the average value of water holding capacity and

expressed as percentage of released water (expressible moisture, EM) and calculated as:

EM= (damp paper wt-dry paper wt)x 100/sample wt

Color:

Color of the samples was measured by the procedure described by Fletcher (1998). Color

is one characteristic that determines broiler breast meat quality. The color values for lightness

(L*), Redness (a*), Yellow (b*) were measured using a portable Minolta reflectance colorimeter

(Minolta Corp., Ramsey, NJ 07446) and using illuminant source C. Color was measured in

triplicate on the cranial, medial surface (bone side) in an area free of obvious color defects

(bruises, blood spots, or surface discolorations).

Cook yield:

The cooking yield was determined by the method describe by Papa and Fletcher (1988).

After 24 h of aging period the left breast filet was excised from the carcass and cooked in an

autoclave at 98±2oC for 20 min. The cooked breast filets were allowed to equilibrate at room

temperature for 5 min before weighing. Cook yield was calculated as mass cooked sample x

100/mass before cooking.

36

Shear value:

The shear value was determined by the method describe by Papinaho and Fletcher

(1996). Cooked meat was evaluated by measuring the shear values using an Instron Universal

Testing Machine equipped with an Allo-Kramer shear cell. A 25 mm diameter core was removed

from the thickest part of each filet for determination of shear force. The core samples were

exactly weighed, and sheared with the blades at the right angle of the fibers (for the whole meat)

using a 500 kg load cell and cross head speed of 500 mm/min. Shear values were reported as

kilograms shear per gram of sample.

%Marinade Pick up:

Immediately after tumbling vacuum bags were cut and filets were put in a colander for 2

min, undisturbed and weighed for marinade absorption (Wt0h). The drained filets were then

placed in the polyethylene zip lock bags and stored under refrigeration (2oC) for 24 h to allow

equilibrium of the absorbed marinade in the muscle.

MA = ((Wt0h – Wt initial)/Wt initial)*100 …………..2.1

Marinade retention (MR):

All the samples that were stored for 24 h after calculating the marinade absorption were

taken out and weighed to calculate the % marinade retention.

MR = ((Wt 24 h – Wt initial)/Wt initial) *100 …………..2.2

Cook yield

After storing the samples for 24 h of the each time period the filets were weighed and

cooked for 20 min at 98±2oC in steam and weighed again to calculate the cook yield.

% cook yield = ((Wt 24h – Wt initial) /Wt initial)* 100 …………..2.3

37

Statistical analysis:

All the experiments were replicated three times. Data were analyzed by ANOVA using

the Statistical tool, SAS jump software.

Results and discussion:

Chilling time

Carcass subjected to ultra-rapid air chilling (-20oC) took around 35-40 min to get the

deep breast temperature to less than 3oC (fig.2.1).Where as, static water chilling took around 55

min during our experiments and this was similar to some of the earlier studies reported by

Esselen (1954). Carcasses chilled quickly at -20oC showed higher cook yields and better shear

values.

Weight Loss/gain:

Table.2.1 shows the percent weight loss/gain during the air and water chilling processes

for poultry carcass. A 4.5% weight gain was observed during the water chilling process.

However, as expected, 1.12 % weight loss occurred during air chilling due to the moisture

evaporation from the skin. Our results are similar to those of earlier studies reported by others.

Young and Smith, (2004) observed a weight gain of 11.7 % during water immersion chilling of

poultry carcass. Skarovsky and Sams, (1999), and Vacinek and Toledo (1973) reported 1.88 %

weight loss during air chilling of poultry carcasses.

pH:

A lower pH resulting from rapid metabolism causes extensive protein changes. The pH

values of broiler carcass meat declined most rapidly in water chilled carcass than in the air

chilled carcasses. From time 0 to 24 h post mortem, the mean pH decreased from 6.45 to 5.83

38

during water chilling process, while the decrease in the air chilling process was from 6.45 to

5.92. After subjecting to different chilling processes a significant difference (P<0.05) was seen in

the pH at the all the time periods (Fig. 2.2). This rapid decrease is consistent with previous

studies which showed accelerated post mortem pH decline in poultry muscle was from 6.22 to

5.76 during water chilling (Froning et al. 1978; Kannan et al., 1997; Mckee and Sams, 1997).

R-value:

The R-value is an indirect measure of ATP depletion in the muscle. During rigor mortis

development, ATP in the muscle is depleted and R-value, a ratio of inosine:adenosine containing

compounds, increases. The R-value data are presented in Fig. 2.3 indicate that through 0 hr to 24

h of post-mortem storage, there was no significant (≤ 0.5%) difference between R–values of air

and water chilled poultry carcasses. Some previous studies also indicated that the R-values of

breast muscles reach 0.95 to 0.97 within 15 to 30 min post mortem and 1.2 to 1.3 within 2 to 4 h

post mortem ultimate R-value reported was 1.35 (Papa and Fletcher, 1988).

Enzyme assay (Total Calpain activity):

Fig. 2.4 shows the total calpain activity of the water and air chilled samples after 2 and 4

hrs post-mortem. A slightly higher calpain activity of air chilled samples might be due to the

early release of free calcium in the tissue, and combined with high muscle pH, increased calpain

activity increased. This could possibly improve product tenderness. Total calpain activity results

were lower than values reported by Veertamuthu (1999) probably because calpains are known to

be inhibited by the presence of cathepsins.

Expressible Moisture:

The water holding capacity is the opposite of the expressible moisture values. The latter

represents loosely held water in the tissue while the former represents the amount of the water in

39

the tissue retained after mechanical pressure is applied to the tissue. Table 2.2 shows the

expressible moisture in meat samples from air chilled and water chilled poultry carcasses 24 h

post mortem at 2°C. EM was 25% for the water chilled samples, and 15.65% for the air chilled

samples. These results are consistent with the higher weight gain of water chilled carcasses

compared to a weight loss in the air chilled carcasses. The water absorbed during water chilling

process is loosely held in the tissue therefore it is easily expressed. It is interesting that the

difference in EM between the water chilled and air chilled carcasses is almost the same as the

weight gain by the water chilled carcasses. Denbow et al. (2001) reported an EM value in water

chilled broiler of 23.5%.

Color:

Color is one of functional property which influences the broiler breast meat quality. No

significant difference (≤ 0.5) in color was observed between air and water chilled meat samples

(Table 2.3). Earlier Allen et al. (1997) reported that L-values of dark meat as 43.7 and light meat

as 51.6.

Cook Yield: No significant difference (<0.5) was found in cook yields at 24 h time period between

fillet samples from air and water chilled carcasses (Table 2.4). The % cook yield values obtained

were in accordance with the previous findings of Mc Neal and Fletcher (2002).

Shear value:

One of the most important quality characteristics of broiler meat is texture, which

depends not only on processing variables but also no other factors such as breed of bird, age, pre-

harvest history, transportation and pre-process holding conditions. If all other factors are the

same prior to processing, texture can be significantly affected by electrical stimulation and time

40

between slaughter and deboning. Texture of water and air chilled meat deboned 24 h post

mortem measured as shear value was not significantly different at p< 0.5% (Table 2.5). Meat

having shear values between 3.0 – 6.0 kg/g are generally considered to be tender as reported

earlier by Lyon and Lyon 1990, and Fletcher, 1997. Our ranges of shear values are in agreement

with their findings.

Marinade absorption and retention

The breast fillets from water and air chilled and marinated after 1 h, 5 h and 23 h of post-

chilling at 10, 15 and 20 % of marinade concentration showed that as the rigor time increased

there was increase in amount of marinade absorption and retention (Tables 2.6, 2.7, 2.8, 2.9,

2.10, 2.11, 2.12, and 2.13). Previous results have shown that STPP treatment significantly

increased marinade absorption and retention (Farr and May, 1970; Mahon, 1962; Trout and

Schmidt, 1984; Young and Lyon, 1986; Young et al.) and our results are in agreement with the

published literature. It was reported that Ultra-rapid air chilled carcasses have higher pH which

can be accounted for slower rate of heat transfer due to the formation of thin curst of ice on the

surface of the carcass during the chilling process which actually affected the increase in % of

marinade absorption and retention when compared to the water chilled carcasses. The other

reason for the increase in the % marinade absorption and retention might be due to loss of

moisture during the air chilling process.

Cook yield

Filets that were marinated at target pick up of 10% at different time intervals (1 h, 5 h,

and 23 h) stored for 24 h and steam cooked showed following results. Significant difference at

p<0.05 between treatments (air and water chilled samples) at 1 h time interval, no significant

difference was seen at p<0.05 and .10 between the treatments for the breast filets which were

41

deboned at 5 h time period and breast filets deboned at 23 h time period showed significant

difference at p<0.01 between the treatments (Tables 2.14, 2.15, 2.16). Between the time intervals

of the treatments there was a significant difference at p<0.05 for the breast filets that were

marinated at the target pick up of 10%. Filets that were marinated at target pick up of 15% at

different time intervals (1 h, 5 h, and 23 h) stored for 24 h and steam cooked showed following

results. Significant difference at p<0.10 was seen at the 1 h & 5 h post-chill time intervals

(Tables 2.17, 2.18, 2.19) and 23 h post-chill time interval showed significant difference at p<0.05

between treatments (air and water chilled samples) and. Breast filets marinated at target pick up

of 15% showed significant difference at p<0.05 between all the post-chill time intervals (1 h, 5 h

and 23 h). Filets that were marinated at target pick up of 20% at different time intervals (1 h, 5 h,

and 23 h) stored for 24 h and steam cooked did not show significant difference at 0.05 or 0.1

between treatments at the post-chill intervals of 1 h & 23 h but showed significant difference at

10% between the treatments at 5 h time interval (Table 2.20, 2.21, 2.22). The reason for higher

cook yields may be accounted towards better water holding capacity in air chilled samples due to

the formation of thin crust during the ultra-rapid air chilling process. Between the post-chill time

intervals (1 h, 5 h and 23 h) of the treatments breast filets that were marinated at the target pick

up of 20% showed no significant difference at p<0.05 and 0.1.

Conclusions

Ultra-rapid air chilling significantly influences the pH and water holding capacity when

compared to conventional water chilling due to slow rate of heat transfer as a thin crust of

freezing occurs on the surface of the carcasses during the chilling process. Crust freezing on the

surface of the carcass during the air chilling process was supposed to show higher calpain

activity but in actual terms both the processes had the almost the same amount of enzyme

42

activity. Air chilled carcasses had a slightly red discoloration on the wings but no difference was

found in the L*a*b values of the breast filets between the air and water chilled samples. Ultra-

rapid air chilling on poultry carcasses did not show a significant difference in marinade pick up,

marinade absorption and cook yields by breast filets when compared to the water chilled poultry

carcasses at all the post chill time periods (1 h, 3 h and 23 h). These disproves the hypothesis that

the formation of thin crust on the surface of the carcasses during chilling in sub-freezing

temperature air would yield better water holding capacity than the water chilled process.

43

-40

-30

-20

-10

0

10

20

30

40

0 2 4 6 7 9 11 13 14 16 18 20 21 23 25 27 28 30 32 34 35 37 39

Time (min.)

Chi

lling

tem

pera

ture

(C)

DEEP BREAST TEMP.1(C)DEEP BREAST TEMP.2(C)DEEP BREAST TEMP.3(C)AIR TEMP.(C)

Fig.2.1. Relation between the deep breast temperature (C) and time (min)

44

Table. 2.1. Percent change in weight of poultry meat after air and water chilling

C % St n

Water chilling 4.45 0.12

Air Chilling -1.13 0.09

hilling method Wt. Gain/loss andard Deviatio

45

5.5

5.6

5.7

5.8

5.9

6

6.1

6.2

6.3

1 3 23Time(h)

pH

Air chilledWater chilled

Fig.2.2. Changes in pH values of poultry meat after air and water chilling process

46

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1 3 23Time(h)

Spec

tom

eter

(O.D

) rea

ding

AirchilledWaterchilled

Fig.2.3. R-values of air and water chilled poultry meat during storage

47

Table. 2.2. %Expressible moisture of air and water chilled poultry meat after storage

(24 h)

C % e St n

Water 24.36 4.27

Air 18.49 3.27

Table. 2.3. Color of air and water chilled sample at 24 h time period

Table. ields b er an ples at 24 h time period

Chilling method %cook yield Standard Deviation

Water 75.67 1.89

Air 80.16 1.8

Table. 2.5. Shear value of air and wa illed poultry meat after storage (24 h)

Chilling method L a b

Water 52.58 3.53 5.24

Air 50.63 3.45 5.02

Chilling method Shear Values(kg/g) Standard Deviation

Water Chilling 3.48 0.52

Air Chilling 3.64 0.57

hilling method Expressible moistur andard Deviatio

2.4. % Cook y etween wat d air chilled sam

ter ch

48

Table. 2. s de h po arin d stored for

Chilling Method t (g) % Pick up Wt aft h (g) %R ion

Water 1144 8.49 1236 8.06

Table. 2.7. B filets debon t 5 h pos ll marinate 10 % target pick up and stored for 24 h

Chilling method Initial Wt (g) %P k up Wt after 24 h (g) %Retention

Water 1311 8.57 1417 7.73

Air 1323 8.57 1426 8.03

Table. 2.8. Breast filets deboned at 23 h pos ill mari

stored for 2

Chilling method Initial Wt (g) %Pick up Wt after 24 h (g) %Retention

Water Chilling 1133 8.32 1219 7.71

Air Chilling 1272 8.49 1374 8.06

6. Breast filet boned at 1 st-chill m ated at 10 % target pick up an 24 h

Initial W er 24 etent

Air 1208 8.82 1307 8.13

reast ed a t-chi d at

ic

t-ch nated at 10 % target pick up and

4 h

49

Table. 2.9. Breast filets deboned at 1 h post-c ari 15 % target pick up and

stored for 24 h

1292 9.86 1396 8.04

Air 1331 10.82 1450 9.64

able. 2.10. Breast filets deboned at 5 h post-chill marinated at 15 % target pick up and

ored for 24 h

hill m nated at

Chilling method Initial Wt (g) %Pick up Wt after 24 h %Retention

Water

T

st

Chilling method Initial Wt (g) %Pick up Wt after 24 h %Retention

Water 1334 10.81 1453 8.88

Air 1218 12.05 1351 10.89

able. 2.11. Breast filets deboned at 23 h post-chill marinated at 15 % target pick up and

ethod Initial Wt (g) %Pick up Wt after 24 h %Retention

T

stored for 24 h

Chilling m

Water 1313 11.75 1453 10.68

A 1 ir 1304 2.47 1451 11.29

50

able. 2.12. Breast filets deboned at 1 h post-chill marinated at 20 % target pick up and

Chilling tial W ick up ntion

T

stored for 24 h

method Ini t (g) %P Wt after 24 h %Rete

Water 1280 11.58 1399 9.37

Air 1301 11.57 1423 10.22

Table. 2.13. Breast filets deboned at 5 h post-chill marinated at 20 % target pick up and

stored for 24 h

method Initial Wt (g) %Pick up Wt after 24 h %Retention Chilling

Water 1382 12.59 1520 10.06

Air 1410 12.83 1569 11.32

Chilling method Initial Wt (g) %Pick up Wt after 24 h %Retention

Table. 2.14. Breast filets deboned at 23 h post-chill marinated at 20 % target pick up and

stored for 24 h

Water 1360 13.30 1512 11.22

Air 1271 14.58 1434 12.93

51

able. 2.15. Breast filets deboned at 1 h post-chill marinated at 10 % target pick up stored

Table. 2.16. Breast filets deboned at 5 h post-chill marinated at 10 % target pick up stored

for 24 h and steam cooked

Table. 2.17. Breast filets deboned at 23 h post-chill marinated at 10 % target pick up stored

r 24 h and steam cooked

Chilling Method Green wt. (g) Cook Wt. (g) %Cook Yield

Water 1133 936 82.46

Air 1272 1119 84.78

Chilling Method Green wt. (g) Cook wt (g) % Cook Yield

Water 1311 1127 85.67

Air 46

Chilling Method Green wt. (g) Cook wt (g) %Cook Yield

er 144 4 7

Air 1208 1036 85.76

T

for 24 h and steam cooked

1323 11 86.17

Wat 1 95 83.3

fo

52

Table. 2.18. Breast filets deboned at 1 h post-chill marinated at 15 % target pick up stored

for 24h an d

Table. 2.19. Breast filets deboned at 5 h post-chill marinated at 15 % target pick up stored

for 24 h and steam cooked

Table. 2.20. Breast filets deboned at 23 h post-chill marinated at 15 % target pick up stored

for 24 h and steam cooked

Chilling Method Green wt. (g) Cook wt (g) % Cook Yield

Water 1313 1128 85.91

Air 1304 1150 88.23

Chilling Method Green w . (g) Cook w (g) % Cook Yield

Water 1334 1128 84.57

Air 1218 1075 87.87

Chillin thod Green wt. (g) Cook wt (g) % Cook Yield

Water 1292 1057 81.89

Air 1331 1134 84.09

d steam cooke

t t

g Me

53

Table. 2.21. Breast filets deboned at 1 h post-chill marinated at 20 % target pick up stored

for 24 h and steam cooked

oned at 5 h post-chill marinated at 20 % target pick up stored

r 24 h and steam cooked

able. 2.23. Breast filets deboned at 23 h post-chill marinated at 20 % target pick up stored

for 24 h and steam cooked

Chilling Method Green wt. (g) Cook wt. (g) % Cook Yield

Water 1280 1039 81.17

Air 1301 1083 82.72

C d G C %

Table. 2.22. Breast filets deb

fo

hilling Metho reen wt. (g) ook wt (g) Cook Yield

Water 1382 1153 83.51

Air 1410 1226 85.91

T

Chilling Method G C % reen wt. (g) ook wt. (g) Cook Yield

Water 1360 1141 83.88

Air 1271 1082 85.08

54

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tr

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58

CHAPTER 3

STUDY ON SURFACE HEAT TRANSFER COEFFICIENTS DURING THE ULTRA –

RAPID AIR CHILLING PROCESS

_______________________ Sharma Neeraj, Toledo RT and Singh RK. 2006. To be submitted to the Journal of Poultry Science

59

ABSTRACT

The purpose of the study was to calculate heat transfer coefficients between the carcasses which

were wet and dry before the ultra-rapid air chilling process. The results obtained had an effect on

the heat transfer time during air chilling.

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Introduction

During the ultra-rapid air chilling process there is a loss of moisture up to 5% depending on the

air temperature, time of chilling. Chilling time is affected not only by chilling air temperature but

the size of the birds, air velocity and orientation of air flow relative to the bird. The knowledge of

surface heat transfer coefficient can be used in designing the equipment which to optimize

chilling time and minimize moisture loss (Landfeld and Houska, 2004). Surface heat transfer

coefficient is calculated using heat flux from the surface of an object at measured temperature

difference between the surface of the object (Ts) and temperature of the air in the cabinet (Ta).

Knowing the surface heat transfer coefficient, unsteady state heat transfer models may be used to

optimize air temperature and velocity to reduce chilling time and minimize moisture loss.

Although a slight loss in weight may occur during the air chilling process, this loss can be

compensated by improved marinade uptake and retention if the meat is later further processed by

marination .

Factors that affect the heat transfer coefficients are velocity of the fluid past the surface

of the product, the physical and thermal properties of the fluid, the dimensions of the solid, the

roughness of the product’s surface and, in some cases, gravity or other body forces. If the flow

regime of the fluid is unstable, a dimensionless heat transfer variables (Nusselt number

correlations) are used to present the results of the heat transfer measurements (Harris, et al.,

2003). Under laminar flow conditions it is possible to derive heat transfer coefficients

analytically by solving the mass, energy and momentum conservation equations (Incropera and

de Witt, 1996).

The purpose of the study was to: Predict heat transfer coefficient using the heat flux

sensor during the process of ultra-rapid air chilling.

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Materials and Method

Method

Measurement of heat flux during ultra-rapid air chilling

Nine 7 – week old broilers (three replicates of 3 carcasses each) that were electrically

stunned, mechanically picked, eviscerated semi-automatically were picked randomly after

inside-outside wash and transported to food science department, UGA for ultra-rapid air chilling.

Two of the three carcasses were mounted with the heat flux sensor in the center of the breast and

then shackled, hung on the rack and transferred in to air chilling cabinet. The deep breast

temperature was monitored using a thermocouple which was connected to data logger saving

device. The temperature in the cabinet was maintained to -20oC until the deep breast temperature

was less than 4oC. In the other experiment another nine carcasses (three replicates of 3 carcasses

each) after getting transported from the processing plant were wetted for 15 s in water and then

subjected to -20oC air chilling process.

Results and discussion

Surface Heat transfer coefficients

Fig. 3.1 shows time- temperature profile in the air chilling process. Fig 3.2 and 3.3 shows

the surface heat transfer coefficients with respect to time on the carcasses. Fig. 3.2 shows the

average value of the surface heat transfer coefficient when the carcass surfaces were not wetted

before ultra rapid air chilling was 190 W/(m2*K) and average surface heat transfer coefficient

when the carcass surface was wetted in water for 15 s. before the air chilling process was 227

W/(m2*K) (Fig. 3.3). During the air chilling process the average mass loss observed during the

ultra rapid chilling process was 1.41 %.

Conclusions

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Heat transfer coefficients were higher when carcass surface was sprayed with water prior

to air chilling compared to a dry surface. The difference could be due to cooling by evaporation

of the surface moisture which added to the convective heat transfer between the warm bird

surface and the cool air. Thus, chilling can be accelerated by incorporating a water spray in the

air chilling process.

63

-25

-20

-15

-10

-5

0

5

10

15

20

25

0.25 1.5 2.7

5 45.2

5 6.5 7.75 9

10.25 11

.512

.75 1415

.25 16.5

17.75 19

20.25 21

.522

.75 24

Time (min)

Tem

pera

ture

(C)

Air temp.deep breast temp.

Fig. 3.1. Time – Temperature profile during the air chilling process

64

0.00E+00

5.00E+01

1.00E+02

1.50E+02

2.00E+02

2.50E+02

3.00E+02

3.50E+02

4.00E+02

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Time (min)

SHTC

W/(m

^2*K

)

SHTC2SHTC1

Fig.3.2. Results representing the Surface heat transfer coefficient – time during the air chilling

process for the unwetted carcasses

*SHTC1 – Surface heat transfer coefficient of the first carcass

*SHTC2 – Surface heat transfer coefficient of the second carcass

65

0

50

100

150

200

250

300

350

00.7

5 1.5 2.25 3

3.75 4.5 5.2

5 66.7

5 7.5 8.25 9

9.75

10.5

11.25 12

12.75 13

.514

.25 1515

.75 16.5

17.25 18

Time (min)

SHTC

(W/(m

^2*K

))

SHTC1SHTC2

Fig.3.3. Results representing the Surface heat transfer coefficient – time during the air chilling

process for the wetted carcasses

*SHTC1 – Surface heat transfer coefficient of first carcass

*SHTC2 – Surface heat transfer coefficient of second carcass

66

References:

Harris, M. B., Willix, J., Carson, J. K., Lovatt, S. J. 2003. Development of a method for

measurement local heat transfer coefficient on carcass-shaped object. IIR/IIF Internationl

congress of refrigeration, Wasington, DC, USA, Proceedings of the ICR2003 ISBN 2-913149-

32-4, CD-ROM.

Landfeld, Ales., Houska, Milan. 2004. Prediction of Heat and Mass transfer during passage of

the chicken through the chilling tunnel. J. Food Engineering 72: 108-112.

67

CHAPTER 4

CONCLUSION

Meat deboned before complete resolution of rigor becomes objectionably tough due to

irreversible muscle fiber shortening as muscle attachment to the bone is severed while muscle

contracts during rigor. So usually minimum of six hours is required after killing for complete

resolution of rigor for broiler meat. Introduction of ultra-rapid air chilling was found useful in

reducing the aging time post-chilling for rigor resolution which indeed has effect on the physical,

chemical properties of broiler muscle. Texture of the meat which represents the physical property

of meat is greatly influenced by the % expressible moisture and carcasses that were subjected to

air chilling showed tender meat due to higher % expressible moisture. The pH values of the

broiler carcasses meat declined more rapidly in water chilled than in air chilled carcasses which

shows that depletion of glycogen is faster in water chilled carcass. Curst freezing during the air

chilling process does not influence activity of calpains and since the rigor time lasts only for few

hours in the poultry meat the role of calpains is not very evident in the process of tenderization.

In the other study, it was found that marination of filets at different target pick ups (10%, 15%

and 20%) with one level of marinade (STPP) after subjecting to chilling process increased the

cook yields at all the time intervals and more interestingly air chilled carcasses showed

significantly higher yields. Higher yields could be due to loss of moisture during the chilling

process and due to higher pH as formation of thin crust of ice on the surface of the carcass.

Combinations of other marinades at different target pick up levels have to be used to see if there

is any significant effect on the cook yields. In the study of Heat transfer coefficients we found

68

that carcasses whose surface was wet showed faster heat transfer due to higher heat transfer

coefficients.