chaters 40 and 41 - Ch 40 & 41: Ch 40 & 41: Food...

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Unformatted text preview: Ch 40 & 41: Ch 40 & 41: Food & Industrial Microbiology Microbially Produced Foods Microbially Produced Foods Fermented milk products Breads Yogurt Sour cream Buttermilk Cheeses Yeast­risen Sourdough Other fermented foods Fermented meats Vegetables Summer sausage Pepperoni Country ham Sauerkraut, olives, pickles Tofu Miso Soy sauce Soy products Alcoholic beverages Wines Beers Distilled liquors Coffee & Tea Fermented Milk Products Fermented Milk Products Uses lactic acid fermentation pathways Mesophilic ­ buttermilk and sour cream Lactobacillus sp. and Lactococcus sp. Thermophilic – yogurt Lactocbacillus sp. and Streptococcus sp. Manufacture of Cheeses Manufacture of Cheeses 1. Coagulate the milk & form the curd Industrially: Directly add clotting enzymes engineered from microbes (e.g. proteases like rennin) Traditionally: Use heat to begin protein denaturation and microbial acids and enzymes to help 2. Separate the curd from whey 3. Shape the curd 4. Ripen with fungus or bacteria for flavor & texture Ripening of Cheeses Ripening of Cheeses Uses lactic or proprionic acid fermentation pathways Initial fermentation occurs by Lactobacillus sp. and Lactococcus sp. Other microbes (including molds) contribute to the ‘flavoring’ and appearance of the cheese curd during ripening Bleu cheese ­ the blue vein and flavor in this cheese is due to the growth of Penicillium roqueforti whose spores are mixed with the curds before final processing Swiss cheese – holes and flavor produced by Proprionibacterium sp. which produces gas during the ripening of the newly formed (soft) curd) Camembert – hard crust around cheese is formed by Penicillium camemberti; hard cheese is softened inside the ‘shell’ by enzymes; Brie is a similar style of cheese Fermentation of Meats Fermentation of Meats Uses lactic acid fermentation pathways Pediococcus sp. and Lactobacillus sp. are involved Unique flavors come from acidic end­products Quick production now by adding lactic acids (and other flavors) directly to the meat instead of awaiting bacteria to produce them naturally Aged beef: Sides of beef are left in a cool, but not refrigerated larder Bacterial and fungal species grow on surface of meat and produce acids and proteases which degrade the muscle tissue to tenderize the beef Initially CO2 is produced by yeasts and some bacteria during an aerobic respiration period where the cells multiply rapidly Alcohol Production Alcohol Production Puts the leavening (or rise) in breads or the fizz in soda/beer Rapid growth depletes O2 and metabolism switches over to fermentation and ethanol production Wine begins as mostly juice (sugary) extracts of grapes and some other fruits depending on wine variety Beer begins as an extract of barley and wheat grains (called malt) Heat must be used to release enzymes in the grains which convert the starchy contents into sugars that are accessible for fermentation Hops are flavoring ingredients that give it a citrusy flavor or a bitter flavor depending on the variety used Darkness of beer is controlled by roasting of barley grains (or wheat) prior to heat converting the starches to sugars Bottled wines and beers that are naturally carbonated undergo a second aerobic respiration by yeasts (and second minor fermentation) Alcohol Production Alcohol Production A small amount of sugar is added to the finished product Remaining yeasts undergo aerobic respiration once more in a sealed vessel The CO2 produced in this reaction cannot escape capped bottles and carbonates the beverage­ termed krauzening in the beer industry Distilled spirits are fermented much like beer, however the final product is distilled to produce a more potent potable by boiling off the water remaining in the alcohol Vinegars are produced when alcohol is further fermented by microbes like Acinetobacter sp. Wine Fermentation Wine Fermentation Beverage Sources for Alcohol Sources for Alcohol Fermentation Source of sugar Wine Beer Whiskey Tequila Rum Sake Gin Vodka Mead Fruits Barley, Rice, Corn Rye, Corn, Barley Agave Cactus Sugarcane, Molasses Rice Corn Potatoes, Corn Honey Other Tasty Fermentables Other Tasty Fermentables Sauerkraut: cabbage which has been fermented by Leuconostoc sp. and Lactobacillus sp. Pickles: cucumbers are placed in a brine solution and fermented by Leuconostoc sp., Lactobacillus sp. and Pediococcus sp. Olives: fresh olives are pickled much like cucumbers by the same genera as pickles Soy sauce: fermentations by Aspergillus sp. (a mold) in a mixture of soybeans and wheat produces soy sauce Natto, or sticky beans: fermented by Bacillus natto beginning with fresh soybeans Miso: a mixture of brown rice and soybeans is fermented by fungal species Other Tasty Fermentables Other Tasty Fermentables Cocoa beans and vanilla pods are harvested and subjected to fermentation by the natural flora of the plants Tea is produced by a fermentation of the green tea leaves and which are dried before brewing Coffee beans are fermented prior to roasting to remove their fleshy pulp, leaving the desired bean Some coffees are fermented in quite unconventional manners before the beans are dried and roasted Luwak coffee Red ripe coffee beans are eaten by the luwak (jungle cat in the civet family) and during their digestion are changed by the animals digestive juices The beans pass thru the animal’s digestive tract and are collected (and thoroughly cleansed!) from the animal’s droppings before being dried and roasted Luwak coffee beans sell in very specialized markets for $600 per pound! Probiotics Probiotics Microbial therapeutic foods – provide a health benefit beyond basic nutrition For lactose intolerant folks who like dairy products­ there are a number of dairy products which contain live cultures of Acidophilus sp., Lactobacillus sp. and/or Bifidobacterium sp. Microbes can temporarily colonize alimentary tract and help human host to digest lactose ingested There are also tablets/capsules which are essentially freeze­dried microbes that can be taken before meals Some dairy products are available as lactose­free: These products are subjected to fermentation before consumption to remove any lactose present in the product Microbial growth often causes spoilage of foods Food Spoilage Food Spoilage Characterized by unpleasant changes in taste, texture, smell and appearance of foods Pathogenic bacteria as well as non­pathogenic bacteria are responsible for spoilage Pathogens growing in foods which do not cause a perceptible change in food can still result in disease (infection or intoxication) Prevent spoilage by altering the conditions of the foodstuff to prevent microbial growth: Increasing solute concentration (sugar, salt content) Lowering or raising pH Adding preservatives Altering storage conditions (O2 availability, temperature) Irradiation Filtration of liquids Pasteurization Prevent spoilage by eliminating microbes from the foodstuff: ...
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This note was uploaded on 03/24/2009 for the course MIBO 3500 taught by Professor Dustman during the Fall '09 term at University of Georgia Athens.

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