Microbes in food fermentation- Food Microbiology
- 2. Bread • Microorganisms – leaven, flavour compounds, conditioning of dough • Bread rises due to carbon dioxide produced through fermentation of sugars by baker’s yeast • Wild yeast, coliform bacteria, saccharolytic Clostridium sp., heterofermentative lactic acid bacteria • Any alcohol produced evaporates during baking • Characteristic flavor of sour dough bread due to the addition of lactic acid bacteria to bread making ingredients
- 3. Traditional Indian Fermented Foods • Dahi • Idli, dosa • Dhokla • Nan, bhatura and kulcha – from fermented wheat dough
- 4. Fermented Leafy vegetables • Ziang sang/Ziang dui – Nagaland and Manipur, prepared during winter season • Preparation – 2-3 day old withered leaves of hangam(Brassica sp) – crushed, soaked inwarm water, squeezed to remove water, placed in container for 7-10days at 20-30C. Juice extracted (Ziang dui), paste sundried(Ziang sang) • Sinki –fermented radish- L.plantarum, L.brevis, L.fermentum • Gundruk – fermented leaves of mustard, rayo-sag, cauliflower, radish • Goyang-fermented leaves of wild plant magane-saag – L.plantarum, L.brevis, Lactococcus lactis, Enterococcus faecium, Pediococcus pentosaceus • Anishi –leaves of edible yam • Khalpi – cucumber - L.plantarum, L.brevis, Leuconostoc fallax
- 5. Fermented Fish products • Ngari • Hentak • Tungtap • Gnuchi Fermented beans • Kinema • Hawaiijar • Tungrumbai • Ankhone
- 6. • Fermented milk – cultured buttermilk, yogurt, Bulgarian buttermilk, acidophilus milk, kefir, kumiss, skyr and taette • Cultured sour cream • Cultured buttermilk and sour cream – mixed cultures – one for lactic acid(Streptococcus lactis), other for flavor (Leuconostoc mesenteriodes) • Bulgarian buttermilk – L. delbrueckii • Yogurt – mixed – S. thermophilus and L.delbrueckii • Kefir – kefir grains – aggregate – L.brevis and yeast • Kumiss – mare’s milk – lactics and yeast • Acidophilus milk – therapeutic properties for intestinal disorders- pure culture of L acidophilus grown in sterilized milk • Sweet acidophilus milk – nonfermented – frozen concentrate of bacteria added • Taette – ropy butter milk- ropy variety of S. lactis • Skyr – semisolid fermented milk – S. thermophilus and L. delbrueckii Fermented dairy products
- 7. • Lactic acid fermentations by lactic acid bacteria • Tastes of yogurt, pickles, sharp cheeses and some sausages due to production of lactic acid by lactic acid bacteria • Cheese, yogurt and other fermented milk products • Milk is sterile in cow’s udder • Rapidly becomes contaminated during milking and handling • Lactic acid bacteria generally reside ON the udder • Aesthetic features of milk change due to production of acid • Causes milk proteins to coagulate or curdle • Sour flavor Fermented dairy products
- 8. • Cheese production • Can be made from milk of wide variety of animals • Cow’s milk most common • Cheeses classified as very hard, hard, semi-soft and soft • Classification passed on percentage of water content
- 9. Microorganisms in Food and Beverage Production • Cheese production • Cottage cheese easiest cheese to make • Pasteurized milk inoculated with starter culture • Culture causes milk proteins to coagulate • Coagulated proteins called curd • Curd heated and cut into small pieces to facilitate drainage of liquid waste • Waste termed whey
- 10. • Cheese production • Most other cheeses undergo further microbial processing termed ripening or curing • Cottage cheese is unripened • Enzyme rennin is added to fermenting milk to hasten protein coagulation • Curds salted after whey is separated and pressed and ripened to encourage changes in texture and flavor • Ripening can take weeks to years • Longer ripening produces more acidic sharper cheese • Certain organisms produce certain characteristics » Propionibacterium shermanii Swiss cheese » Penicillium roquefortii Roquefort, and gorgonzola
- 11. • Yogurt • Pasteurized milk is concentrated slightly then inoculated with starter culture • Mixture is incubated for several hours at 40° C - 45° C for several hours • Thermophilic bacteria grow rapidly at higher temperatures • Produce lactic acid and other end products • Contribute to flavor • Controlled incubation ensures proper levels of acid and flavor compounds
- 12. • Acidophilus milk • Sweet acidophilus milk retains flavor of fresh milk because it is not fermented • Culture is added immediately before packaging • Bacteria are added for purported health benefits • Prevent and reduce severity of some diarrheal diseases Microorganisms in Food and Beverage Production
- 13. • Pickled vegetables • Pickling originated as way to preserve vegetables • Particularly cucumbers and cabbage • Pickling uses naturally occurring lactic acid bacteria residing on vegetables • Unlike fermentation of milk products which relies on starter culture
- 14. • Fermented meat products • Traditionally were produced by letting small numbers of lactic acid bacteria to multiply to dominance • Natural fermentation of meat inherently risky • Incubation that initiates fermentation can support growth and toxin production of pathogens » Clostridium botulinum and Staphylococcus aureus
- 15. • Alcoholic fermentations by yeast • Some yeasts ferment sugars to produce ethanol and carbon dioxide • Yeasts are used to make variety of alcoholic beverages as well as vinegar and bread • Alcoholic beverages include • Wine • Beer • Distilled spirits
- 16. • Wine • Product of alcoholic fermentation of naturally occurring sugars in juices of fruit • Most commonly grapes • Commercially made wine produced by crushing selected grapes • Stems are removed and solids collected • Entire grape used in red wines • Juice only used in white wines • Solids removed after one day and juice fermented to produce rose wines
- 17. • Wine • Fermentation must be carefully controlled to ensure proper reactions • Sulfur dioxide is added to inhibit growth of natural microbial population • These convert alcohol to acetic acid (vinegar) and most responsible for spoilage • Fermentation process is initiated by addition of selected strains of yeast • At completion of fermentation wine siphoned several times to separate juice from sediment • Wines then aged in oak barrels • Wine is filtered for clarification then bottled
- 18. • Beer • Production of beer is multistep process • Designed to breakdown starches in grain to produce simple sugars • Sugars are fermented • Yeast lack enzymes to convert grains to alcohol • Malted barley (malt) contains enzymes • Malt and starch, sugars and other adjuncts soaked in warm water • Termed mashing • Enzymes in malt act on starches converting to fermentable starches • Spent grains removed • Remaining liquid called wort
- 19. • Beer • Hops are added to wort • Gives beer distinct bitter taste • Also has natural antimicrobial substances • Hops/wort mixture boiled • Extract flavor of hops • Concentrate wort • Inactivates enzymes and precipitates proteins • Wort centrifuged to remove solids and cooled • Brewer’s yeast added to initiate fermentation • Bottom fermenters clump and sink to bottom of fermentation tank • Produces lager beers • Top fermenters distributed throughout • Produces porter and stout beers
- 20. • Distilled spirits • Fermentation process nearly same as beer • Wort is not boiled • Degradation of starch continues through fermentation • When fermentation is complete ethanol is purified and distilled • Different types of spirits made with different substrates • Rum fermentation of molasses • Scotch whiskey fermentation of barley the aged • Tequila fermentation of agave plant
- 21. • Vinegar • Aqueous solution of at least 4% acetic acid • Product of oxidation of ethanol • Strictly aerobic process • Fermenting bacteria are obligate aerobes • Organisms can tolerate high concentration of acid • Vinegar generator produces available oxygen to hasten oxidation • Sprays alcohol on biofilm of acid bacteria on wood chips • Alcohol trickles down and is oxidized by bacteria