Fermentation: Desirable Effects of Microbes 17 Fermentation: Desirable Effects of Microbes

Objectives Describe the types of microbes that impact the food supply. List factors that impact the growth of single-celled organisms. Differentiate among yeast, bacterial, and mold fermentation. Identify food products that are a result of fermentation.

Microorganisms Microbiology is the study of living organisms too small to be seen by the unaided human eye Organisms that are only visible through a microscope are called microorganisms or microbes They multiply rapidly, and transfer easily from one surface to another

Types of Single-Celled Organisms Microbes that have a positive use in foods are bacteria, yeasts, and molds Bacteria are members of the Monera kingdom Yeasts and molds are members of the Fungi kingdom Microbes depend on outside sources of food to grow and multiply

Bacteria Bacteria are single-celled organisms that multiply through cell division Their cells have no nucleus and are filled with a gelatinous liquid called cytoplasm Bacteria are up to 3 micrometers long classified by shape, cell wall structure, and oxygen needs continued

Bacteria Bacteria have these basic shapes Bacilli have a rod shape Cocci have a spherical shape Spirilla have a spiral shape ©Sebastian Kaulitzki/Shutterstock.com continued

Bacteria Bacteria have 2 types of cell wall structures identified by the ability to be stained by a crystal violet dye, called Gram’s stain Gram-positive bacteria turn violet; gram-negative turn red continued ©Janice Haney Carr, Centers for Disease Control and Prevention

Bacteria Bacteria can be categorized by oxygen needs Aerobic bacteria must have oxygen to function Anaerobic bacteria function best in an oxygen-free environment Facultative bacteria can function in either type of environment continued

Bacteria Aerobic bacteria spoil cabbage, but submerging cabbage in salt water does not allow aerobic bacteria to grow the anaerobic bacteria can multiply and develop the flavor and texture of sauerkraut Bacteria’s growth rate depends on pH, air, temperature, and food supply

Fungus A fungus is a plant that lacks chlorophyll Fungi are not always single-celled have a nucleus in their cells are widely distributed in nature and help organic matter decay Examples include mushrooms, molds, mildews, rusts, smuts, and yeasts continued

Fungus Fungi are classified by their structure and reproduction methods Basic structure of most fungi is made of filaments or tubes called hyphae, which have elongated cells or chains of cells that absorb nutrients from the environment intertwine and form a branched network called a mycelium continued

Fungus Mycelium reproduces by creating spores, the reproductive cells of fungi Spores develop in a sac- or balloon-like structure that explodes when full Spores are microscopic and resistant to harsh environments ©Goodheart-Willcox Publisher continued

Fungus Molds are fungi that form a mycelium structure with a fuzzy appearance Many give off an antibiotic that kills bacteria likely to be growing in the same area Mushrooms, toadstools, and puffballs reproduce through a basiodiocarp, a spore case with a stem, a cap, and gills located under the cap continued

Fungus Yeasts are fungi with a single-celled structure that produce alcohol and carbon dioxide They form mycelium structures on soil or plants, but reproduce in animals by budding ©Goodheart-Willcox Publisher

Common Characteristics of Microbes grow rapidly and are good sources of edible protein for animals can enhance or add to the nutritional value of food can enter a dormant or inactive state to protect themselves from a harsh environment reproduce when the environment supports growth needs continued

Common Characteristics of Microbes A pure culture is a large volume of one type of microbe grown purposely At food processing plants, large volumes of microbes are used in the development of such foods as pickles, cheese, and beverages When a pure culture is mixed with a food source, a starter is made

Microbial Enzymes Enzymes produced by microbes are the source of most changes in food products Microbes excrete digestive enzymes to break down large macromolecules for transport through the microbe’s cell wall Microbes can then absorb the fragments and use them for fuel continued

Microbial Enzymes Microbes can be classified by the organic molecules they use as a food source Proteolytic microbes release proteases that change proteins into amino acids and are used to clot milk, tenderize meat, and remove pulp from cacao beans Lipolytic microbes produce enzymes that digest fats and are used to flavor cheese, remove egg yolk, and clean up oil spills continued

Microbial Enzymes Halophilic microbes require high concentrations of salt to function are used to produce bean cake and many other Asian foods ©Andrew L./Shutterstock.com

Scientific Names for Microbes Microbes are classified by 2 Latin names The genus name is always capitalized indicates a family of organisms that have similar characteristics The species name is never capitalized identifies the type of microbe within the family continued

Scientific Names for Microbes Example: Lactobacillus acidophilus Lacto refers to milk Bacillus refers to bacteria with a rod shape Acidophilus indicates bacteria that give off acid Lactobacillus acidophilus is a rod-shaped bacteria that lives in or feeds on milk and produces an acid

Factors Affecting Microbe Growth Microbes need a food supply Because microbes are composed of carbon, oxygen, nitrogen, and hydrogen, they need a food supply containing all 4 chemicals The food supply needed depends on the enzyme systems the organism can make Microbes also need minerals and vitamins to aid with enzyme activity continued

Factors Affecting Microbe Growth Microbes need water Some microbes can remain alive, but dormant, in dried conditions A safe water activity (aw) for most food storage is considered 0.70 or lower Water activity can be lowered by removing water, adding solutes, or by freezing continued

Factors Affecting Microbe Growth Microbes need a certain pH Each microbe has a preferred range, but can survive at pH levels above and below it ©Goodheart-Willcox Publisher continued

Factors Affecting Microbe Growth Microbes prefer a moderate temperature Freezing slows enzyme activity and cell reproduction, while heating can kill microbes Most microorganisms die at 5°C to 12°C above the temperature for maximum growth Food processors balance temperatures needed to kill microbes against the affect heating has on food quality and production costs continued

Factors Affecting Microbe Growth Pasteurization is a process in which a liquid is heated until pathogens are destroyed High temperatures for a brief period are less damaging to flavor Food scientists can grow cultures of microbes if they know the preferred food supply, water activity, pH, and temperature

Fermentation Fermentation is an enzymatically controlled change in a food product caused by the action of microorganisms Changes result from digestive enzymes released by the microbes the release of by-products, such as carbon dioxide, acetic and lactic acids, and ethanol continued

Fermentation The primary product of a microbial reaction is energy By-products can change the color, texture, flavor, aroma, and pH of a food Fermentation occurs when nutrients broken down by digestive enzymes are absorbed by microbes for growth and energy

Yeast Fermentation Yeast is needed in all yeast breads, alcoholic beverages, and vinegars Saccharomyces cerevisiae is often used Sugar is its main source of energy It also feeds on honey, molasses, or corn syrup Quick-rising yeast may be used in some breads

Yeast Fermentation: Bread Yeast is affected by steps in the bread-making process Warm liquid activates yeast Mixing distributes yeast evenly Kneading the dough develops the gluten Proofing allows the yeast to produce enzymes that break down sugars, releasing alcohol and carbon dioxide continued

Yeast Fermentation: Bread In the bread-making process carbon dioxide becomes trapped in pockets throughout the dough, gluten stretches, and the dough rises the dough continues to rise during baking and a crust forms Bread products contain flour, yeast, salt, and water

Yeast Fermentation: Wine Wine is the fermented juice of plant products such as grapes, honey, various fruits and dandelions Sulfur dioxide (SO2) or potassium metabisulfite is added to inhibit unwanted microbe growth Juices are held in anaerobic conditions for up to 4 weeks in oak barrels or stainless steel tanks continued

Yeast Fermentation: Wine Wine fermentation is complete when bubbling from CO2 production stops Wine is then aged in barrels or vats to slowly develop the characteristic flavors ©Rusian Rizvanov/Shutterstock.com

Yeast Fermentation: Other Alcohols Yeast is used in the fermentation of other alcoholic beverages Beers are made from fermented barley Bourbon is made from corn Rum is made from sugar cane or molasses Brandy is distilled wine or fermented fruit juice Liqueurs and cordials have a brandy base with sugar and flavorings added

Bacterial Fermentation Lactic acid fermentation is one of 3 main types of bacterial fermentation refers to the many fermented foods—vegetables, meats, and dairy products—produced by bacteria whose by-product is lactic acid produces the other by-products of acetic acid, formic acid, and carbon dioxide

Bacterial Fermentation: Sauerkraut Sauerkraut results from the lactic acid fermentation of cabbage submerged in brine, a salt and water solution The salt controls water activity and pulls water with dissolved sugar and nutrients to the surface Bacteria feed on the sugar and release carbon dioxide and lactic acid into the brine

Bacterial Fermentation: Pickles Cucumbers are turned into pickles by heating them in a spiced vinegar solution, refrigerating in an acid brine, or fermenting them with lactic acid bacteria Commercial pickling involves washing the cucumbers in a chlorine solution placing them in a brine with a pure culture of Lactobacillus added

Bacterial Fermentation: Other Foods Other foods that can be pickled include vegetables such as watermelon rinds, beets, cauliflower, okra, and onions, and even eggs The lactic acid fermentation of olives is a process similar to making pickles except olives are washed in a lye solution to remove bitter flavor compounds

Bacterial Fermentation: Olives Lactic acid neutralizes any lye remaining and sugar is added to start the fermentation process Green or Spanish olives are picked before being ripe, then cured, pitted, and stuffed with pimento Black or ripe olives are picked at a riper stage

Bacterial Fermentation: Meats Lactic acid fermentation is used to make dry and semidry sausages Increased acid tenderizes the meat and adds a tart flavor Fermentation, smoking, and drying prevent spoilage Sugar provides food for lactic acid, and spices and salt add desired flavor

Bacterial Fermentation: Cultured Dairy Products Cultured dairy products include sour cream, yogurt, and buttermilk Streptococci are the fastest lactic acid producers, which enables milk to acidify quickly, thus reducing prep time and contamination risk Leuconostoc and Lactobacilli are added to produce the desired flavors continued

Bacterial Fermentation: Cultured Dairy Products Milk for cultured dairy products is pasteurized and bacteria is added The action of bacteria on lactose forms lactic acid, which denatures the proteins and causes them to coagulate Texture is also affected by temperature, pH, fermentation time, and added enzymes used Cooling stops the fermentation process

Bacterial Fermentation: Cheese Milk is pasteurized, then rennin and lactic acid bacteria are added to form curds Curds are cut into small cubes and heated to help the whey separate from them Whey is drained off and collected for use as an additive in other processed foods Curds are rinsed and salted continued

Bacterial Fermentation: Cheese Curds are mixed with cream to make cottage cheese put in presses to squeeze out excess moisture for making aged cheese During aging or ripening, cheeses wrapped with wax are placed in curing rooms Different bacteria or molds are responsible for the characteristic flavor of cheeses continued

Bacterial Fermentation: Cheese The sharpness of cheese refers to the strength of flavor and aroma Sharpness develops as cheese ages Cheeses that age longer tend to have firmer consistency have more crumbly textures melt into sauces more readily

Mold Fermentation Molds create a wide range of by-products antibiotics, flavor compounds, and enzymes Fermented foods important to Asian cuisine include soy sauce, a fermented mix of soybeans and wheat tempeh, a soybean cake of cooked, mashed soybeans pressed into blocks, inoculated with Rhizopus molds, and wrapped in banana leaves

Two-Step Fermentation Cheese, soy sauce, and sourdough bread require lactic acid fermentation plus other microbes in a second step For cheese, lactic acid is needed to form the product, then microbes develop the flavors and textures For sourdough bread, lactic acid ferments the yeast starter, then yeast fermentation proceeds continued

Two-Step Fermentation Acetic acid fermentation follows yeast fermentation Yeast release alcohol as they break down sugars, then acetic acid fermentation begins Acetobacter bacteria feed on the alcohol and release acetic acid Vinegar is produced by acetic acid fermentation continued

Two-Step Fermentation Acetic acid fermentation produces candied citron from citron lemons for use in baked goods turns cacao beans into chocolate ©stockcreations/Shutterstock.com

Benefits of Fermentation Microbes help preserve some foods Milk keeps for about a week under refrigeration Cheese can keep for months when properly stored Fermentation offers a wider range of food options

Nutritional Changes in Fermented Foods Changes vary depending on the microbes used other ingredients added impact of fermentation on bioavailability Fat and calcium concentrations are higher in cheese than in milk Pickling adds salt through the brine, which increases the sodium content

Recap Bacteria, yeasts, and molds have positive uses in foods Factors that affect microbe growth are food supply water pH temperature continued

Recap Yeasts, bacteria, molds, or other microbes can ferment foods Examples of foods products that result from fermentation are yogurt, cheese, cottage cheese pickles soy sauce sauerkraut