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PRESERVATION OF FISH AND AQUATIC PRODUCTS II 2 Reducing the free-water Drying Salting Smoking Chemical means Fermentation Pickling PRESERVING 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 Heat Center Surface moisture evaporates More water Less water Water diffusion More water vapor Less water vapor 5 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 DRYING PRINCIPLES 6 7 8 9 10 Advanced automated driers 11 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”: waterimpermeable skin at the surface Case hardening Flesh soft on the inside and spoiled by bacteria (extreme putrid odor) 13 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 SALTING 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 Fish in saturated salt brine at 0.75 16 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 Mackerel being dry-salted 20 Process example (salted groundfish): 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 product 21 Typical cod salting operation (kench salting) Splitting the cod 22 Salting the cod 23 Maturation period in salt 24 Drying the cod 25 Drying fish the old way (still widely done) 26 Quality inspection and packaging 27 Injection 28 Distributing the fish 29 2 day soaking period in salt 30 Fillet sorting/grading and packaging 31 Pickle salting Early stages Late stages 32 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 Smoking Old preservation method. In developed countries, used for flavor and color Flavors Smoke (Hot air) Water 35 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 SMOKE Smoke is absorbed by a liquid, and concentrated. Rapid, uniform, but different than “real” smoke 44 NATURE OF SMOKE Mixture 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 VAPORS Antioxidants: high boiling phenols Smoldering fire is better Bactericidal: formaldehyde, acetic acid, creosote. Also heat, drying, salt. Reduces bacteria, fungi, viruses 46 SAFETY Smoke 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 GENERATION Wood: 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 HUMIDITY Surface moisture is needed for smoke absorption. 60 % RH optimum Skin-side absorbs less smoke. Too high RH: slow drying. 50 SMOKE VELOCITY Faster 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 Breakdown can synthesize vitamins 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 Anaerobic breakdown of an organic substrate by an enzyme system in which the final hydrogen acceptor is an organic compound Example: NADH2 Pyruvic acid (CH3-CO-COOH) NAD Lactic acid (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 – DEFINITIONS Sugars … Acids … Alcohols, Aldehydes Proteins … Amino acids … Alcohols, Aldehydes Lipids … Free fatty acids … Ketones FOOD FERMENTATIONS – BIOCHEMISTRY 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 38(Glucose) ATP 6 CO2 + 6 H2O + 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. Fig. 9.18 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Respiration vs. fermentation FERMENTATION: • An organic compound is the final electron acceptor • Glucose is converted to one or more 1-3 carbon Examples: compounds CH O 2 CH -CH OH + 2CO + 2 ATP 6 12 6 (Glucose) 3 2 2 (ethanol) C6H12O6 2 CH3-CHOH-COOH + 2 ATP (lactic acid) C6H12O6 CH3-CHOH-COOH + CH3-CH2OH + CO2 + 1 ATP 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. Fig. 9.17a Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Carbohydrates, fats, and proteins can all be catabolized through the same pathways. Fig. 9.19 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings 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 •molds Aspergillu s Penicilliu m Geotrichum Rhizopus Candida 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 Natural fermentation Create conditions to inhibit undesirable fermentation yet allow desirable fermentation Examples: Vegetable fermentations CONTROLLED VS. NATURAL FERMENTATION Vegetables + salt 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) CONTROLLED VS. NATURAL FERMENTATION Traditional Fermentation Incubation under specific conditions Raw material with indigenous microflora Final product = desirable m/o’s = undesirable (pathogen or spoilage) m/o’s 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. Controlled Fermentation Add starter culture Raw material Incubation under specific conditions Final product 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. 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 Controlled Fermentation: pure cultures Add pure microbial culture Raw material Incubation under specific conditions Pure culture Final product Controlled Fermentation: “backslop” method Add product (or byproduct) from a recent successful fermentation Raw material Final product from a previous fermentation (traditional or controlled) Incubation under specific conditions Final product 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 = 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 FERMENTATION 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 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. FERMENTATION 88 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. EFFECTS OF FERMENTATION 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 (6) fermenting temperature, (7) pH of the fermentation mixture, (8) the presence of enzymes, (9) presence/concentration of carbohydrates, (10) the length of fermentation. VARIABLES 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. QUALITY (FERMENTATION) 92 QUESTIONS? 93
