international journal of food science & technology volume 34 issue 4 1999 [doi...

7/22/2019 International Journal of Food Science & Technology Volume 34 Issue 4 1999 [Doi 10.1046_j.1365-2621.1999.00284

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Effect of gelatin dip on the oxidative and colourstability of cooked ham and bacon pieces during frozenstorage

R. Villegas, T. P. OConnor,* J. P. Kerry & D. J. Buckley

Department of Food Science and Technology, University College, Cork, Ireland

(Received 6 May 1998; Accepted in revised form 29 April 1999)

Summary Samples of cooked ham and bacon were dipped in water or 2, 4 or 6% gelatin solutions.Samples were then packed in oxygen permeable or vacuum packaging lm and stored at

18 C for seven months. Lipid oxidation (TBARS) and colour stability (Hunter a* val-ues) were assessed monthly. The gelatin coating exerted benecial effects on oxidative and

colour stability.Keywords Colour deterioration, fat oxidation, packaging effect.

Introduction

Modern trends in convenience foods have result-ed in the increased consumption of frozen foodssuch as pizzas which can be prepared rapidly bythe consumer. Meat toppings used in these prod-ucts are susceptible to oxidative and colour dete-

rioration during frozen storage which limits theshelf-life of these products. Lipid oxidationresults in off-avours and odours, loss of polyun-saturated fatty acids, fat-soluble vitamins andpigments and reduced consumer acceptability(Gray et al ., 1996).

Gelatin is a protein resulting from partialhydrolysis of collagen using acid or alkali treat-ment followed by or accompanied with heating inthe presence of water (Eastoe & Leach, 1977).The principal raw materials used commerciallyfor gelatin manufacture are pork skins andbovine hides, skins and bones (Gennadios et al .,1994). Enzymatic processing is an alternative toacid or alkali hydrolysis for conversion of colla-gen to gelatin producing a higher purity, betterphysical properties and a more narrow molecular

weight distribution (Hinterwaldner, 1977).Research interest in edible coatings made from

proteins, polysaccharides and lipids has intensi-ed in recent years. These coatings can helpmaintain and improve the quality of fresh, frozenand processed muscle foods by reducing moistureloss, lipid oxidation and colour deterioration,

sealing in volatile avours, acting as carriers forantimicrobial and antioxidant food additives andreducing oil uptake during frying of breaded andbattered products (Gennadios et al ., 1997).

Gelatin has been proposed, in patent disclo-sures as early as 1869 (Harvard & Harmony,1869) and 1895 (Morris & Parker, 1895), as apreservative coating for meat and other foods.Gelatin coatings have also been used to carryantioxidants. Klose et al . (1952) reported thatturkey steaks sprayed with an aqueous gelatinsuspension of various antioxidants had 6090%lower peroxide values in skin and meat fat thanuncoated controls during frozen storage at

12 C for six months. Marggrander & Hofmann(1997) conducted studies to assess the effects of spraying pork belly cuts with a 10% solution of gelatin on changes in physicochemical and senso-ry properties during frozen storage for up to 18months. Gelatin coating reduced lipid oxidation

International Journal of Food Science and Technology 1999, 34 , 385389

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(peroxide value and TBARS) and improvedretention of avour, taste and aroma duringfrozen storage. Further patents have been grant-ed for acidic, aqueous solutions of gelatin and ametaphosphate polymer (Keil et al ., 1960) and

aqueous solutions of metal gelatinates (Keil,1961) as coatings on processed meats such assausages, Canadian bacon and boned hams whichoffer protection against mould growth, lipid oxi-dation and handling abuse.

The objective of the present work was to inves-tigate if application of a gelatin coating by dip-ping would delay the progress of lipid oxidationand preserve colour in frozen meat pieces suitablefor use as pizza toppings.

Materials and methods

ChemicalsAll chemicals used were Analar grade, obtainedfrom British Drug House, Poole, Dorset, UK,and Sigma Chemical Co. Ltd., Poole, Dorset,UK. Gelatin (from pork) was obtained fromDGS STOESS, Germany. The gelatin was pre-pared by acid hydrolysis of collagen and had abloom value of 200 bloom grams.

Meat

Cooked ham and raw bacon rashers (both 3mm

thickness) were obtained from a local commercialprocessor (Galtee Meats, Mitchelstown, Co.

Cork). The bacon was cooked at 200 C for 20min in a fan-assisted oven, allowed to cool andthen cut into 5 cm squares. The cooked ham wasalso cut into 5 cm squares. The meat pieces weredipped into water (control) or 2, 4 or 6% gelatin

solutions at room temperature before being pack-aged either aerobically or under vacuum. Vacuumpackaging was carried out using a WebomaticType D463 vacuum packer (Webomatic VacuumPackaging Systems, Werner Bonk, Mausegett 59,Bochum, Germany). The vacuum packagingmaterial consisted of Cryovac polyamide/polyeth-ylene 20/70 low oxygen permeable multiex lms(Cryovac, W.R. Grace Europe Inc., Lausanne,Switzerland) (45 ml m 2 24 h 1 at standard tem-perature and pressure (STP)). Aerobically pack-aged samples were wrapped with oxygenpermeable (60008000 ml m 2 24 h 1 at STP)polyvinyl chloride lm (Wrap Film Systems Ltd.,Haleseld 14, Telford, England). Samples werethen stored at 18 C in the dark until requiredfor analysis. Oxidative status and colour stabilitywere monitored after 0, 1, 2, 3, 4, 6 and 7 monthsof storage.

Determination of lipid oxidation

Lipid oxidation in meat was assessed by measur-ing thiobarbituric acid-reactive substances(TBARS) using the method of Ke et al . (1977).

TBARS were expressed as mg malonaldehyde/kgsample. Measurements were carried out on a sam-

Gelatin dip and stability of frozen ham and bacon R. Villegas et al.


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Table 1 Effect of gelatin on the oxidative stability of cooked ham aerobically or vacuum packed and stored at 18C

Storage period (months) in aerobic packageTreatment 0 1 2 3 4 6 7

TBARS*

Control 0.39 (0.03) 0.53 (0.03) 0.67 (0.02) 0.87 (0.02) 0.86 (0.09) 1.71 (0.02) 3.08 (0.00)2% gelatin 0.39 (0.03) 0.49 (0.05) 0.60 (0.04) 0.78 (0.03) 0.88 (0.08) 1.42 (0.06) 1.53 (0.01)4% gelatin 0.39 (0.03) 0.41 (0.05) 0.51 (0.06) 0.52 (0.02) 0.65 (0.03) 0.66 (0.02) 1.62 (0.03)6% gelatin 0.39 (0.03) 0.47 (0.05) 0.45 (0.08) 0.44 (0.03) 0.63 (0.04) 0.67 (0.05) 1.40 (0.03)

Storage period (months) in vacuum packageTreatment 0 1 2 3 4 6 7

TBARS*Control 0.39 (0.03) 0.40 (0.05) 0.48 (0.06) 0.46 (0.05) 0.51 (0.02) 0.70 (0.06) 1.34 (0.02)2% gelatin 0.39 (0.03) 0.44 (0.09) 0.48 (0.05) 0.50 (0.06) 0.50 (0.08) 0.48 (0.05) 1.22 (0.01)4% gelatin 0.39 (0.03) 0.36 (0.02) 0.40 (0.01) 0.38 (0.07) 0.40 (0.00) 0.45 (0.01) 0.83 (0.04)6% gelatin 0.39 (0.03) 0.43 (0.07) 0.39 (0.04) 0.40 (0.14) 0.39 (0.06) 0.38 (0.04) 0.84 (0.01)

*TBARS Thiobarbituric acid reactive substances (mg malonaldehyde/kg sample)Mean (S.D.), n 4

Fishers LSD ( p 0.05) 0.14


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ple size of four pieces of meat at each point. Forthis particular TBARS analysis values in excess of 1.0 approximately correspond to rancidity levelswhich would be detected by a trained sensorypanel.

Colour analysis

Hunter a* values were determined using aMinolta Chromameter (Model CR-300, MinoltaCamera Co., Osaka, Japan). Colour was analyzedby placing the calibrated hand-held probe of the

Minolta Chromameter in contact with the meatpieces. Colour measurements were determined in

triplicate on a sample size of six pieces of meat ateach analysis point.

Statistical analysis

Data were analyzed using the MINITABStatistical Package (Minitab Inc., State College,Pennsylvania, US) by two-way analysis of vari-ance ( ANOVA ) followed by Fishers LSD test(Snedecor & Cochran, 1967).

Results and discussion

Gelatin had a signicant effect ( p 0.05) in low-



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Table 2 Effect of gelatin on the colour stability of cooked ham aerobically or vacuum packed and stored at 18 C


Hunter a* values 1

Control 20.44 (1.20) 14.88 (3.10) 13.85 (2.40) 12.62 (1.50) 12.09 (2.38) 11.65 (2.32) 5.66 (2.34)

2% gelatin 20.44 (1.20) 17.25 (2.10) 18.70 (2.74) 18.16 (1.50) 19.00 (2.10) 16.47 (1.71) 14.05 (3.17)4% gelatin 20.44 (1.20) 19.91 (3.29) 19.50 (1.29) 17.55 (1.23) 19.50 (1.45) 16.27 (2.34) 14.35 (2.01)6% gelatin 20.44 (1.20) 19.87 (2.18) 20.40 (1.88) 18.24 (1.49) 20.14 (1.53) 18.71 (3.11) 12.53 (2.20)


Hunter a* values 1


1Hunter a* values Indicator of rednessMean (S.D.), n 6


Table 3 Effect of gelatin on the oxidative stability of cooked bacon aerobically or vacuum packed and stored at 18 C


TBARS*



TBARS*Control 0.58 (0.01) 0.78 (0.07) 0.85 (0.09) 0.81 (0.06) 0.82 (0.09) 0.93 (0.02) 0.91 (0.01)2% gelatin 0.58 (0.01) 0.60 (0.06) 0.57 (0.01) 0.62 (0.09) 0.62 (0.02) 0.62 (0.02) 0.73 (0.02)4% gelatin 0.58 (0.01) 0.62 (0.05) 0.64 (0.02) 0.59 (0.07) 0.60 (0.09) 0.60 (0.09) 0.74 (0.05)6% gelatin 0.58 (0.01) 0.54 (0.05) 0.56 (0.07) 0.50 (0.03) 0.58 (0.06) 0.58 (0.06) 0.61 (0.09)

*TBARS Thiobarbituric acid reactive substances (mg malonaldehyde/kg sample)Mean (S.D.), n 4



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ering TBARS in cooked ham (Table 1) both inoxygen permeable packages and vacuum pack-ages at all storage periods with the exception of month 1. This effect was more apparent as stor-age time increased and at higher concentrationsof gelatin. TBARS values were higher in aerobicpackaging than in vacuum packaging.

The colour of cooked ham (Hunter a* values)deteriorated more rapidly in oxygen permeablepackaging than vacuum packaging (Table 2).Gelatin treatment signicantly ( p 0.05) reducedcolour deterioration at months 4, 6 and 7 in bothtypes of packaging and at months 2 and 3 in aer-

obic packaging.Similar trends were observed with cooked

bacon. Control samples had signicantly ( p 0.05) higher TBARS values compared to gelatintreated samples at all storage times in both aero-bic and vacuum packaging (Table 3). TBARS val-ues were higher in the aerobically packagedbacon. Hunter a* values for the cooked baconalso deteriorated more rapidly when stored inoxygen permeable packaging (Table 4) particular-ly in the control samples. Gelatin treatment sig-nicantly ( p 0.05) reduced colour deteriorationin both types of packaging. Gelatin exerted bene-cial effects even in vacuum packaged productsas presumably it reduced oxidative reactions dueto any trace amounts of residual oxygen in thepacks.

Gelatin lms have been reported to have goodoxygen barrier properties (Gennadios et al ., 1994;Krochta & de Mulder-Johnston, 1997). Our data

suggest that these oxygen barrier properties canhelp reduce lipid oxidation and colour deteriora-tion during frozen storage of meat products.Dipping in gelatin solutions represents a simpleand inexpensive method of prolonging the shelf-life of meat toppings in consumer products suchas frozen pizzas.

When considering the use of edible lm coat-ings such as gelatin, it is important to ensure thatthe coating wets and spreads on the food surfaceand forms a coating with adequate adhesion,cohesion and durability upon drying (Krochta &de Mulder-Johnston, 1997). These properties are

affected by the edible lm formulation and by themethod of application of the lm. Whitman &Rosenthal (1971) were granted a patent for solu-bilization of gelatin in polyhydric alcohols such aspolypropylene or ethylene glycol, glycerol or sor-bitol to generate coatings which were quick-set-ting and exhibited good barrier and exibilityproperties at low temperatures.

Conclusions

Gelatin coating improved oxidative and colourstability of cooked ham and bacon during frozenstorage.

References

Eastoe, J.E. & Leach, A.A. (1977). Chemical compositionof gelatin. In: The Science and Technology of Gelatin(edited by A. G. Ward & A. Courts). Pp. 73107. NewYork: Academic Press.



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Table 4 Effect of gelatin on the colour stability of cooked bacon aerobically or vacuum packed and stored at 18 C


Hunter a* values 1

Control 19.18 (1.25) 16.48 (1.68) 15.39 (1.95) 13.25 (1.13) 13.34 (2.70) 12.73 (1.50) 8.90 (2.50)

2% gelatin 19.18 (1.25) 18.14 (0.81) 17.66 (1.69) 15.10 (1.93) 16.10 (0.64) 15.75 (1.40) 14.20 (2.70)4% gelatin 19.18 (1.25) 18.25 (1.63) 18.04 (1.39) 17.60 (1.34) 17.50 (1.53) 15.99 (1.71) 13.66 (1.50)6% gelatin 19.18 (1.25) 19.33 (0.59) 18.02 (1.96) 16.46 (1.52) 16.24 (1.38) 16.37 (1.58) 14.99 (2.70)


Hunter a* values 1


1Hunter a* values Indicator of rednessMean (S.D.), n 6



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