Food Industrial Microbiology PDF

CHAPTER 16.1 -16.5 Food and Industrial Microbiology Copyright © 2024 by W. W. Norton & Company, Inc. Introduction § The fermentation industry reaches back to 5,000 BCE. Wine and bread have been made since the Neolithic age. § Today, microbial products and enzymes are made by bacteria grown in giant...

CHAPTER 16.1 -16.5 Food and Industrial Microbiology Copyright © 2024 by W. W. Norton & Company, Inc. Introduction § The fermentation industry reaches back to 5,000 BCE. Wine and bread have been made since the Neolithic age. § Today, microbial products and enzymes are made by bacteria grown in giant fermentation vessels. 2 16.1 Microbial Foods § Certain kinds of microbial bodies have long been eaten as food. Examples include the fruiting bodies of fungi and the fronds of marine algae. § Single-celled algae and cyanobacteria are also used as food supplements. § These microbes can provide important sources of protein, vitamins, and minerals. 3 Edible Fungi § Mushrooms: fungal fruiting bodies Source of proteins and minerals Include: ― Underground truffles ― Button and portobellos § Less than 1% of mushrooms are poisonous. 4 Edible Algae and Cyanobacteria § Several kinds of seaweed are cultivated § Red alga forms large multicellular fronds cultured for nori. 5 Bacteria are Inedible as Isolated Organisms, Because Nucleic Acid is Often too Concentrated for Food 6 Fermented Foods: An Overview Virtually all human cultures have developed varieties of fermented foods, which are food products modified biochemically by microbial growth. 7 Fermented Foods: An Overview § The purposes of food fermentation include: 1. To preserve food: by limiting microbial growth 2. To improve digestibility: by breaking down fibers 3. To add nutrients (such as vitamins) and flavor molecules 8 Microbes Used in Fermented Foods § Traditional fermented foods usually depend on indigenous flora (found naturally in the food) or starter cultures (from a previous fermentation) 9 Microbes Used in Fermented Foods § Commercial food-fermenting operations use highly engineered microbial strains to inoculate their cultures 10 16.5 Industrial Microbiology § Industrial microbiology is the commercial exploitation of microbes. § It includes food production and preservation. § Also the production of: Vaccines and insulin Microbial enzymes GMO plants and animals 11 Microbial-based Production can Improve Current Methods § Less costly and less waste or negative effects on environment § There are two fundamentally different sources of products 1. Cloned genes from human, animal, or plant sources 12 Insulin Production via E. coli 13 Insulin Production via E. coli 14 Insulin Production via E. coli insulin purified medicine 15 Insulin Production via E. coli 16 Microbial-based Production can Improve Current Methods § Less costly and less waste or negative effects on environment § There are two fundamentally different sources of products 1. Cloned genes from human, animal, or plant sources 2. Native microbial products from newly discovered species in the environment ― Bioprospecting 17 Bioprospecting: Search for Organisms with Commercial Application One important aspect is “mining the genome.” 18 Bioprospecting: Search for Organisms with Commercial Application Cloned genes are transferred into an industrial strain § Genetically stabile § Easy to genetically manipulate § Inexpensive growth requirements § Safe to handle § High level of protein expression § Ready harvesting of product 19 16.2 Acid- and Alkali-Fermented Foods § Many food fermentations produce acids or bases. § An acid or base serves as an effective preservative. The pH change is unlikely to be reversed. 20 Acidic Fermentation of Dairy Products § Milk fermentation begins by lactic acid fermentation with Lactobacillus and Streptococcus. Acidification of milk during fermentation causes proteins, especially caseins, to denature and coagulate to form a semisolid curd. 21 Acidic Fermentation of Dairy Products § Additional coagulation occurs following degradation of these proteins by proteases such as rennet § The curd separates from the liquid portion, called whey 22 Cheese Production 23 Flavor Molecules In all fermented foods, microbial metabolism generates by-products (secondary metabolites) that confer a characteristic aroma and flavor 24 Varieties of Cheese § Cheeses are divided into categories based on steps in production. Soft, unripened cheeses (cottage cheese and ricotta) Semihard, ripened cheeses (Muenster) Hard cheeses (Swiss cheese and cheddar) Brined cheeses (feta and Gouda) Mold-ripened cheeses (Brie and Camembert) 25 Acid Fermentation of Vegetables § Many kinds of vegetable products are based on microbial fermentation. § Soybeans Microbes remove substances that decrease nutritional value. Mold: Rhizopus—tempeh Mold: Aspergillus—miso, soy sauce 26 Acid Fermentation of Vegetables § Cabbage, cucumbers, olives Pickling: fermentation in brine (high salt) ― Sauerkraut, pickles, kimchi 27 Chocolate from Cocoa Bean Fermentation § Chocolate, the product of the cocoa bean, requires one of the most complex fermentations of foods. No “starter culture” has yet been standardized. 28 Chocolate from Cocoa Bean Fermentation in Three Stages 29 Chocolate Manufacturing 30 16.3 Ethanolic Fermentation: Bread and Wine Ethanolic fermentation converts pyruvate to ethanol and carbon dioxide § Performed by yeast The most prominent is Saccharomyces cerevisiae. ― Baker’s yeast or brewer’s yeast 31 Preparation of All Forms of Yeast Bread 1. A starter culture of yeast is included in the dough. The yeast can be commercial baker’s yeast, or it can be sourdough starter. 32 Bread Dough is Leavened by Microbial CO2 2. The dough is kneaded to develop a fine network of air pockets. CO2 causes bread to rise. ― Easier to chew and digest ― More gluten → more rise Ethanol is removed by baking. 33 Alcoholic Beverage: Beer § Beer production is one of the most ancient fermentation practices and is depicted in ancient Egyptian tombs dated to 5,000 years ago. Today, most beer is produced commercially by fermenting barley using giant vats. 34 Alcoholic Beverage: Beer § Saccharomyces cerevisiae § Beer derives from alcoholic fermentation of grain. Barley grains are germinated, allowing enzymes to break down the starch for yeast Secondary products generate the special flavors of beer ― Different yeast strains can produce different flavors 35 Alcoholic Beverage: Wine § Wine derives from alcoholic fermentation of fruit, usually grapes. The grapes are crushed to release juices The yeast ferments glucose to alcohol 36 16.4 Food Spoilage and Preservation § Humans have always competed with microbes for food. Because meat perished so fast, it made economic sense to share the kill immediately and consume it all as soon as possible. Vegetables might last longer, but eventually they succumbed to mold and rot. 37 16.4 Food Spoilage and Preservation § Later societies developed preservation methods that enabled humans to survive winters and dry seasons. Drying, smoking, and canning of food 38 16.4 Food Spoilage and Preservation § Modern food preservation depends on antimicrobial agents as well as physical preservative measures. 39 Food Spoilage and Contamination § Food spoilage refers to microbial changes that render a product unfit for consumption. Acids -> sour taste Oxidation of fats -> rancidity Decomposition of proteins -> putrefaction Alkalinity -> bitter taste § “Food contamination,” or food poisoning, refers to the presence of human pathogens. 40 How Food Spoils - Dairy § Dairy products can be soured by excessive fermentation or made bitter by bacterial proteolysis. 41 How Food Spoils - Meat § Meat and poultry are putrefied by decarboxylating bacteria, which produce amines with noxious odors. 42 How Food Spoils - Seafood § Seafoods spoil rapidly because their unsaturated fatty acids rapidly oxidize. Psychrotrophic bacteria produce the fishy-smelling trimethylamine. 43 How Food Spoils - Plant § Plant foods spoil by excess bacterial or mold growth. Pathogens can destroy food crops before harvest. 44 Pathogens Contaminate Food § Intestinal pathogens spread readily because microbes can be transmitted through food without signs of contamination § The U.S. Centers for Disease Control and Prevention estimates there are 76 million cases of GI illness each year (¼ Americans) 45 Food-Borne Pathogens Emerge from the Environment and Agriculture § Listeria monocytogenes invades the cells of the intestinal epithelium Psychrotroph 46 Toxin Production by Food-Borne Pathogens § Clostridium botulinum toxin inhibits fusion of synaptic vesicles, thus preventing activation of muscle cells causing paralysis Deadliest known neurotoxin on the plant Can be found in some improperly canned foods 47 Physical Means of Food Preservation § Dehydration (freeze-drying) Removal of water prevents bacterial growth § Refrigeration and freezing Slows microbial growth, but may select growth of psychrotrophs § Pasteurization Most effective for extending the shelf life of liquid foods with consistent, well-understood microbial flora 48 Physical Means of Food Preservation § Ionizing radiation Effectively sterilizes food for long-term storage but raises concerns regarding its potential effects on food chemistry and the hazards of the process for personnel involved 49 Two or More Means of Preservation are Commonly Used in Combination Survival curves of Escherichia coli O157:H7 in eggplant salad stored at 5°C at various pH levels. Pathogen dies faster 50