preservation of fish and aquatic products ii 2 preserving reducing the free-water drying salting ...
Post on 15-Jan-2016
225 Views
Preview:
TRANSCRIPT
PRESERVATION OF FISH AND AQUATIC PRODUCTS II
2
PRESERVING
Reducing the free-water Drying
Salting
Smoking
Chemical means Fermentation
Pickling
3
DRYING
Removal of water from fish (to reduce water activity) to extend shelf life
Requires input of heat (evaporate water) Sun, wind, flame, electrical etc.
Requires removal of water in the form of vapor
4
DRYING PROCESS
5
Center HeatSurfacemoistureevaporates
Morewater
Lesswater
Water diffusion
Morewatervapor
Lesswatervapor
DRYING PRINCIPLES
Drying occurs in two phases Phase 1 (constant rate period)
Water removed from surface
Phase 2 (falling rate period) Water is removed from muscle
Water migrates to the surface (diffusion)
Water evaporates at surface (requires heat)
Water is removed from the atmosphere surrounding the fish surface
6
7
8
9
10
11
Advanced automated driers
Problems with dried fish If environmental T is warm and fish is too wet
Molds (Aw>0.75) Grow very well when drying in tropical areas
Aerobic spoilage bacteria (if non-salted)
If salted (solar salt) can get halophiles growing Pink colonies Major problem with salted and dried cod
Pests Insect parts and eggs a major quality problem Flies (Dipteria) lay eggs and can spread disease
Less problem with fish pre-drying Salting can deter flies Some use insecticides on fish!
Rodents and birds are a constant problem
12
Problems with dried fish (cont.) Lipid oxidation (rancidity)
Protein denaturation Get muscle fragmentation
If drying is too rapid we can get “case hardening”: water-impermeable skin at the surface
Case hardening Flesh soft on the inside and spoiled by bacteria (extreme putrid
odor)
13
SALTING
Salting - traditional method
Reduces water activity (aw) to retard microbial spoilage and chemical reactions
Salt penetrates into the muscle and binds the water.
At 6-10% in the meat will spoilage
14
Different grades of salt, from 80-99.9% purity Purer salt leads to less problems
less contaminants (less water uptake, bitterness)
less halophilic bacteria (salt tolerant)
Some salts can have up to 105 of bacteria
At least 95% purity should be used Impure salts about 80% NaCl
Solar salt most impure (major source of halophiles)
Can purify by washing briefly with water (calcium and magnesium dissolve sooner than NaCl)
Finer salts are ideal for brines (dissolve rapidly) Larger size salt preferred during dry salting
15
16
Fish in saturated salt brine at 0.75
17
Methods of salting
Brine salting (15-25% solution) Fish immersed in solution of salt
Frequent stirring necessary
Replacement of salt in brine may be needed
Need to supply fresh brine to new batch of fish
Dry salting (3-4 parts fish to 1 part salt) Salt rubbed into fish surface and fish left uncovered to dry
Not recommended in tropical regions due to insects and rodents
18
Methods of salting (cont.) Kench salting
Salt rubbed on split fish and stacked. Pickle formed which leaks away
Pickle salting Same as above but pickle is not removed. Fish are packed in water
tight containers
Pickle is from water and blood leaking from the muscle as salt penetrates
Need about 30% salt for this to occur
Salt brine injection Fish injected with salt solution and phosphates, then soaked in salt
solution for 2 days (10 C=50 F) and then kench salted
19
20
Mackerel being dry-salted
Head, gut and wash fish
Soak in 10% brine for 30 min
Drain
Dry salt fish in shallow boxes
Stack fish up first one skin down, last one skin up
Leave for about 12 h (or up to 30 days)
Wash salt crystals away with 10% brine or seawater
Dry fish during day
Pile fish up overnight
Pack product21
Process example (salted groundfish):
22
Typical cod salting operation (kench salting)
Splitting the cod
23
Salting the cod
24
Maturation period in salt
25
Drying the cod
26
Drying fish the old way (still widely done)
27
Quality inspection and packaging
28
Injection
29
Distributing the fish
30
2 day soaking period in salt
31
Fillet sorting/grading and packaging
32
Pickle salting
Early stagesLate stages
Factors influencing the salting process Thickness -> thicker = slower NaCl uptake Fat content -> more = slower NaCl uptake Quality -> older = faster NaCl uptake Salt concentration and quality Temperature
More rapid salt penetration at higher temps
More chance of spoilage (normally in center of fish, turns into a smelly paste)
Storage Keep cool, dry and well ventilated Have plenty of insect/rodent traps The saltier the product the longer the shelf-life
33
34
35
Smoking
Old preservation method.In developed countries, used for flavor and color
Flavors
Water
Smoke(Hot air)
PREPARATION
Start with good quality seafood.
Whole, headed, gutted, split, fillets, chunks,
Salting
Brine (2-5%), spices, sugar
Air drying (a few hours)
36
PREPPING
BRINING
DRY BRINING
RACKING
INTO THE SMOKER
FINISHED!
SMOKING TEMPERATURE
1. Cold smoking
Room temperature (<90 F)
Not cooked
Perishable product
2. Hot smoking
Temperature (>150 F)
Cooked
43
LIQUID SMOKESmoke is absorbed by a liquid, and concentrated.
Rapid, uniform, but different than “real” smoke
44
NATURE OF SMOKEMixture of particles and vapors.
1. Vapors
More than 200 chemicals
Carbonyls, organic acids, phenols, organic bases, alcohols, hydrocarbons, others.
Impart color and flavor enhancement
45
VAPORSAntioxidants: high boiling phenols
Smoldering fire is better
Bactericidal: formaldehyde, acetic acid, creosote.
Also heat, drying, salt.
Reduces bacteria, fungi, viruses
46
SAFETYSmoke has carcinogenic substances.
Polycyclic aromatic hydrocarbons (PAH):
Benz(o)pyrene. Thermally generated.
1-60 ppm in food.
Lower smoke generation T is better.
Use liquid smoke, or electrostatic filters.
Nitrosamines
Nitrous oxide in smoke: very low concentrations in food
47
SMOKE GENERATIONWood:
Sawdust or wood chips heated to form smoke, but no flames.
Hardwood. Oak, mahogany, teak, hickory, redwood, cedar, pitch-pine.
Resinous wood: bitter taste.
48
SMOKE GENERATION
Temperature:
High T: cooking, rapid drying, reaction between smoke and food.
Dry surface: less smoke absorption.
Optimum smoke generation = (550°F).
At higher T more smoke, but less active components.
49
RELATIVE HUMIDITYSurface moisture is needed for smoke absorption.
60 % RH optimum
Skin-side absorbs less smoke.
Too high RH: slow drying.
50
SMOKE VELOCITYFaster smoke= better penetration
Absorbed smoke near surface is replenished.
Stagnant film on surface decreased, and diffusion path shortened.
51
SMOKED QUALITY
Flavor: Low T is better.
Nutritive effects: loss of vitamins
Phenols react with sulfhydryl groups
Carbonlys react with amino groups
Texture: Drying, smoke-protein interactions
Color: carbonyl-amino reactions
Phenolics
52
FOOD FERMENTATION
UI Snack Bar
What are fermented foods?
Foods or food ingredients that rely on microbial growth as part of their processing or production
FOOD FERMENTATION Metabolic activities occur during fermentation that:
Extend shelf life by producing acids Change flavor and texture by producing
certain compounds such as alcohol Improve the nutritive value of the
product by: Microorganisms can synthesize
vitamins Breakdown indigestible materials to
release nutrients, i.e., bound nutrients
FERMENTED FOODS
Foods fermented by yeast MaltBeer
Fruit (grapes) Wine
Rice Saki
Bread dough Bread
Foods fermented by mold Soybeans Soy sauce
Cheese Swiss cheese
Foods fermented by bacteria Cucumbers Dill pickles
Cabbage Sauerkraut
Cream Sour cream
Milk Yogurt
FOOD FERMENTATIONS – DEFINITIONS
Anaerobic breakdown of an organic substrate by an enzyme system in which the final hydrogen acceptor is an organic compound
Example:
NADH2 NAD
Pyruvic acid Lactic acid
(CH3-CO-COOH) (CH3-CHOH-COOH)
Biological processes that occur in the dark and that do not involve respiratory chains with oxygen or nitrate as electron acceptors
FOOD FERMENTATIONS – BIOCHEMISTRY
Sugars … Acids … Alcohols, Aldehydes
Proteins … Amino acids … Alcohols, Aldehydes
Lipids … Free fatty acids … Ketones
Respiration vs. fermentation
Refer to how cells generate energy from carbohydrates
RESPIRATION:• Glycolysis + TCA (Kreb’s) Cycle + Electron Transport• O2 is final electron acceptor• Glucose is completely oxidized to CO2
C6H12O6 + 6 O2 6 CO2 + 6 H2O + 38 ATP (Glucose)
Some organisms (facultative anaerobes), including yeast and many bacteria, can survive using either fermentation or respiration.
For facultative anaerobes, pyruvate is a fork in the metabolic road that leads to two alternative routes.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 9.18
Respiration vs. fermentation
FERMENTATION:• An organic compound is the final electron acceptor• Glucose is converted to one or more 1-3 carbon compounds
Examples:
C6H12O6 2 CH3-CH2OH + 2CO2 + 2 ATP
C6H12O6 2 CH3-CHOH-COOH + 2 ATP
C6H12O6 CH3-CHOH-COOH + CH3-CH2OH + CO2 + 1 ATP
(Glucose) (ethanol)
(lactic acid)
During lactic acid fermentation, pyruvate is reduced directly by NADH to form lactate (ionized form of lactic acid).
Lactic acid fermentation by some fungi and bacteria is used to make cheese and yogurt.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
In alcohol fermentation, pyruvate is converted to ethanol in two steps.
First, pyruvate is converted to a two-carbon compound, acetaldehyde by the removal of CO2.
Second, acetaldehyde is reduced by NADH to ethanol.
Alcohol fermentation by yeast is used in brewing and winemaking.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 9.17a
Carbohydrates, fats, and proteins can all be catabolized through the same pathways.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 9.19
Respiration vs. fermentation
Some cells can respire and ferment sugars for energy. The cell will do one or the other depending on the conditions. Example: Saccharomyces cerevisiae (baker’s, ale and wine yeast).
Some cells can only respire or only ferment sugars for energy.Example: Lactic acid bacteria produce energy by fermentation.
Important organisms
• lactic acid bacteria
Lactobacillus Carnobacterium
Leuconostoc Enterococcus
Pediococcus Lactococcus
Streptococcus Vagococcus
•yeasts
Saccharomyces sp. (esp. S. cerevisiae)
Zygosaccharomyces Candida
• molds
Aspergillus
Penicillium
Geotrichum
Rhizopus
Typical fermentation process
•substrate disappears as cell mass increases
•sugar, then other small molecules, then polymers used
•primary metabolic products (acids) accumulate during growth •pH drops if acids produced
•growth and product formation stop as substrate is depleted
•microbial succession depends on substrate and acid levels
Food Fermentations
In food fermentations, we exploit microorganisms’ metabolism for food production and preservation.
Where do the microorganisms come from to initiate the food fermentation?
Two ways to initiate a food fermentation…....traditional & controlled fermentations
CONTROLLED VS. NATURAL FERMENTATION
Natural fermentation Create conditions to inhibit undesirable fermentation
yet allow desirable fermentation
Examples: Vegetable fermentations
Vegetables + salt
CONTROLLED VS. NATURAL FERMENTATION
Controlled fermentation Deliberately add microorganisms to ensure desired fermentation
Example: fermented dairy products Lactose … Lactic acid
Starter culture
Lactics or Lactic starter or Lactic acid bacteria (LAB)
Traditional Fermentation
Raw material with indigenous microflora
Incubation under specific conditions
Final product
Disadvantage: Process and product are unpredictable depending on source of raw material, season, cleanliness of facility, etc.
Advantage: Some flavors unique to a region or product may only be attained this way.
= desirable m/o’s= undesirable (pathogen or spoilage) m/o’s
Controlled Fermentation
Raw material
Advantage: – uniformity, efficient, more control of process and product Disadvantage: Isolating the right strain(s) to inoculate is not always easy. Complexity of flavors may decrease.
Final product
Incubation under specific conditions
Add starter culture
Controlled Fermentations: Starter cultures
Two main starter culture types are used to inoculate the raw material:
1.Pure microbial cultures prepared specifically for a particular food fermentation. (More details on these later.)
2.“Backslop” method = Using some of the product from a previous successful fermentation to inoculate the next batch of raw material.
Controlled Fermentation: pure cultures
Final product
Incubation under specific conditions
Raw material
Pure culture
Add pure microbial culture
Controlled Fermentation: “backslop” method
Final product
Incubation under specific conditions
Add product (or byproduct) from a recent successful fermentation
Raw material
Final product from a previous fermentation (traditional or controlled)
Mainly used in home applications in the U.S. – home production of yogurt and sourdough
Summary
• Why we ferment foods
• Microbial energy metabolism: respiration vs.
fermentation• Traditional fermentations – indigenous microflora
• Controlled fermentations – starter culture added
Food products
from milk:
cheese, yogurt, sour cream, buttermilk
lactic acid bacteria (lactobacilli, streptococci)
meats:
fermented sausages, hams, fish (Asia)
lactic acid bacteria (lactobacilli, pediococci), molds
beverages:
•beer (yeasts make ethanol)
•wines (ethanol fermentation from grapes, other fruits)
•vinegar (ethanol oxidized to acetic acid)
•breads:
•sourdough (yeast + lactobacilli)
•crackers, raised breads (yeasts)
single cell protein:
how cheaply and efficiently can cells be grown? waste materials as substrate (bacteria, yeast, molds) sunlight and CO2 (algae)
uses in animal feeds (frequently) or human foods
prefer protein to whole cells high nucleic acids --> kidney stones,
ORGANIC ACIDS
Primary Metabolites Organic acids are. (primary products of
metabolism). During the log phase of growth the products
produced are essential to the growth of the cells. Secondary metabolites:
(Secondary products of metabolism) During the stationary phase some microbial cultures
synthesize compounds which are not produced during
the trophophase* and do not appear to have any
obvious function in cell metabolism.(idiophase*)
FERMENTATION
Fermentation = treat with microbes
– Desirable microbes digest food first
– Preserves food (depending on microorganism)
Makes food inedible for undesired microbes
– Alcohol, acid buildup
– Makes food digestible
Breaks down indigestible fibers
Adds nutrients
Microbially produced vitamins
85
FERMENTATION
In developed countries, fermentation is used to provide desired tastes and / or flavors. Preservation is a secondary benefit.
In developing countries, and the Far East, fermented aquatic products provide a significant portion of the protein need.
86
FERMENTATION
Since sauces and pastes prepared in these areas are salty and spicy, they provide a significant departure from a rather bland cereal diet.
Because the high salt content limits the consumption, sauces and pastes used as flavor/taste enhancers often served over rice.
FERMENTATION
Fermented aquatic products are prepared by salting and then fermenting.
Salting selects desired bacteria,eliminating spoilers, prevents
putrification.
Controlling oxygen content determines characteristics. The most common putrefactive microorganisms on fish are inhibited at salt contents above 6 to 8 percent.
88
EFFECTS OF FERMENTATION
Microorganisms (bacteria, yeasts, or molds), and digestive enzymes decompose the product into a soluble protein portion and a high ash portion.
The fermentation process has several benefits. The product is far more stable than the original raw product, and there is often a volume reduction.
89
VARIABLES
(1) the microflora in the fish and salt,
(2) the proteolytic enzymes in the fish,
(3) initial quality of the product,
(4) presence or absence of oxygen,
(5) nutritional state of the fish,
90
VARIABLES
(6) fermenting temperature,
(7) pH of the fermentation mixture,
(8) the presence of enzymes,
(9) presence/concentration of carbohydrates,
(10) the length of fermentation.
QUALITY (FERMENTATION)
Calcium, magnesium, sulfate ion impurities= bitter flavor, tough texture light color.
Several techniques are available for increasing the rate of fermentation:
(1) using higher temperatures, (2) adding concentrated chemical enzymes, (3) bacterial seeding, and (4) acid additions.
92
QUESTIONS?
93
top related