Fermented products are: Fermented products are those whose production involves the action of microorganisms or enzymes which cause desirable biochemical changes and significant modification to the food.
Fermentation processes: • Lactic acid • Alcoholic • Acetic acid • Propionic acid
Fermented foods • Beverages • Dairy products • Cereals • Meat and fish • Fruits and vegetables
Beverages Beer Wine Sake Cider spirits
Dairy products Cheese Yoghurt Kefir Kurut
Cereals Breads Rolls dosa, idli, adai, vada (cereals & legumes) lao-chao, kenkey, ogi injera
Meat and Fish Jerky, country ham, salami, pepperoni pickled meat fish sauce, paak, bagoong
Fruits & vegetables Pickled fruits & vegetables olives sauerkraut
Contribution of the fermented foods: • Enrichment of the human dietary • preservation of substantial amounts of food • enrichment of nutritional value of food (vitamins, proteins, essential amino acids etc] • detoxification of food (flatulence-causing sugars, lectins, phytates etc] • a decrease the cooking time and fuel requirements
Preservation principle: To hinder (delay) the growth of food spoilage microorganisms
Alcoholic fermentation: Simple sugars yeasts > ethanol Saccharomyces cerevisiae
Yeasts involve in fermentation should possess: • Rapid and relevant carbohydrate fermentation ability; • appropriate flocculation and sedimentation characteristics; • genetic stability; • osmotolerance
Yeasts involve in fermentation should possess: • ethanol tolerance • ability to produce elevated concentration of ethanol; • high cell viability for recycling; • temperature tolerance.
Alcoholic fermentation is affected by: • Oxygen supply • sugar content • alcohol content • temperature
Alcoholic fermentation: • Unlimited oxygen supply - cell growth • Limited oxygen supply - alcohol production
Beer A diluted solution of ethanol with a characteristic flavour arising from the use of malt as predominant source of carbohydrates and other yeast nutrients and hops as a source of bitter components.
Kinds of beer • Lager - produced by bottom fermen- ting yeasts ( Saccharomyces uvarum) . • Ale - produced by top fermenting yeasts ( Saccharomyces cerevisiae)
Production of beer: • Malting • Mashing • Boiling of wort with hops • Fermentation • Storage
Malting (preparation of malt): • Soaking barley grains in water at 10-15 0C • Germination of barley grains at 16-21 0C for 5-7 days • Separation germs and sprouts • Crushing the malt
Mashing (preparation of wort) • Mixing malt with water at 38-50 0C (protein hydrolysis) • Saccharafication of malt at 65-70 0C (hydrolysis of starches to simple sugars) • Inactivation of enzymes at 75 0C • Separation of insoluble materials.
Boiling of wort with hops is done to: • concentrate it • sterilize it • inactivate enzymes • extract soluble substances from hops • coagulate and precipitate proteins • contribute antiseptic resins: humulone, cohumulone, adhumulone.
Fermentation of beer • Pitching (inoculation)- 1lbs of yeasts per barrel of wort • Lager beer is fermented at 7-15 0C • Ale beer is fermented at 18-22 0C • Fermentation - 9 days • At the end of fermentation yeasts are skimmed (top-fermenting) or are cropped (bottom-fermenting).
Storage and packaging • after fermentation beer is stored (lagered) at 0 C (several weeks to several months) • clarified or filtered • pasteurized at 60 C shortly • carbonated to CO2 content 0.45-0.52% • packaged to cans or bottles.
Beer defects (off flavour) may be due to: • butyric (Clostridium sp.) or lactic acid fermentation during mashing process. • Inoculum contaminated with wild yeasts or lactic acid bacteria. - Yeasts may produce off flavor. -Bacteria may produce sour taste and/or silky turbitidy.
WINES Products obtained by alcoholic fermentation of grapes, grape juices, fruit juices, berries, rhubarb, honey etc by yeasts.
Kinds of wines • still wines • sparkling wines • artificially carbonated wines
Kinds of wines • Dry vs. sweet wines • Unfortified vs. fortified wines • Red vs. white wines • Grape vs. fruit wines • Table vs. dessert wines
Steps involve in fermentation of wine: • Preparation of must (grape juice, crushed grapes, fruit juice]. • inoculation of must with wine yeasts (2-5% ]. • aeration of must to encourage the growth of yeasts and to facilitate the extraction of pigments from a skin (mixing must twice a day ].
Steps involve in fermentation of wine: • Active fermentation: - red wines 24 -27 0C; 3-5 days; - white wines 10-21 0C; 7-14 days; • separation of fermented juice from residue (pomace); • placing fermented juice under light CO2 pressure • secondary fermentation: 21-29 0C, 7-11 days. • aging of wines.
Problem solving Calculate the% [w/w] of EtOH in wine. Assume that at fermentation starting point 30 kg of must contained 26% of sucrose. The fermentation ceased at 2% concentration of sugar. The yield of conversion of sugar to ethanol was 94%.
Calculation steps: C6 H12O6 2 C2 H2 OH + 2 C02 1. Calculate the amount of sugar in must. M1 = 30 * 0.26 = 7.8 kg
Calculation steps: 2. Calculate the final weight of must (M) at the end of fermentation process. M = M0 - M2 + M3 M0 - initial weight of must; M2 - weight of fermented sugar; M3- weight of produced alcohol.
Calculation steps: 3. Calculate the weight of sugar in wine. M4 = M * 0.02 4. Calculate the weight of sugar fermen- ted to alcohol. M2 = (7.8 - M4 ) * 0.94
Calculation steps: 5. Calculate the weight of produced alcohol. C6 H12O6 2 C2 H2 OH + 2 C02 180 92 M2 M3 --------------------------------- M3 = 92 * M2 /180 = 92 * ( 7.8 - M4)/180 = 92 * ( 7.8 - M * 0.02) * 0.94/180
Calculation steps: 6. Calculate the final weight of wine (M) M = M0 - M2 + M3 M = 30 - (7.8 - 0.02*M)+ + 92*(7.8 - 0.02*M) *0.94/180 M = 26.22 kg of wine
Calculation steps: 7. Calculate the weight of produced ethanol. M3 = 92 * (7.8 - 26.22 *0.02) * 0.94/180 M3 = 3.495 kg of ethanol
Calculation steps: 8. Calculate [ % ; w/w) of ethanol in wine. [%] = M3/M * 100 [%] = 3.495/26.22 *100 [%] = 13.3%
Factors affecting the wine spoilage: • Acidity - the lower the pH the less likely the wine will spoil. Molds, yeasts, acetic acid bacteria would not be stopped by any pH normal to wines: most wines - pH 3.5-4.0; • Sugar content < 0.1%; • Ethanol content . 14% • Temperature - spoilage most rapid at 20-30 oC.
Production of ethanol • Starch pretreatment: -gelatinization, -liquefaction, -saccharification • Fermentation • Distillation
Lactic Acid Fermentation • Lactobacilli • Streptococci (dairy streptococci) • Pediococci • Leuconostocs
Benefits from Lactic Acid Fermentation • Alteration of flavour, texture, and appearance • enhancement of nutritional value • retardation of food spoilage and reduction of microbial contamination • probiotic effect- prolongation of life: (Metchnikoff 1908) due to lactase, metabolism of dietary cholesterol, detoxification of potential carcinogens.
Sequence in changes in raw milk in relation to acid concentration
Are fermented foods safer than fresh foods? • Cases of microbial food-borne infection have been reported in association with fresh cheese, sausages, fermented fish and fermented cereals. • Cases of microbial food intoxications due to mycotoxin contaminated raw material, production of microbial toxins, production of mycotoxins by fungal have been reported. • Toxic by-products (ethyl carbamate and biogenic amines) may be produced.
Toxic by-products of fermenta tion: • Ethyl Carbamate: a carcinogenic and mutagenic compound which results from the esterification of ethanol with carbamic acid (NH2COOC2H5- also known as urethane) • Biogenic amines - a mildly toxic substances. 100-200 ppm; >1000ppm is supposed to elicit toxicity.
Major risk enhancing factors: • Use of contaminated raw materials. • Lack of pasteurization. • Poorely controlled natural fermentations. • Sub-optimal fermentation starters. • Inadequate storage and maturation conditions. • Consumption without prior cooking
How can these risk be minimized • By ensuring wholesomeness of raw materials. • Optimization of starter cultures by conventional selection and mutation or by recombinant DNA manipulations. • Good hygienic practices during manufactu- ring • Adequate storage