Lecture 10

Lecture 10 - © E.Garcia 2010 FST 1 – Main topics –...

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Unformatted text preview: © E.Garcia 2010 FST 1 – Main topics – Lecture 10 Food Spoilage About 1/3 of the world’s food supply is lost to spoilage! There are several causes of food spoilage, including: ‐ Chemical reactions, such as lipid oxidation ‐ Enzymatic reactions, such as enzymatic browning ‐ Loss of water, germination, sprouting, etc ‐ Microbial Spoilage Food is considered spoiled when its sensory characteristics make it unacceptable to the consumer. These may include changes in color; development of off flavors, off odors; slime; changes in texture. Microbial Spoilage can be caused by bacteria and fungi (yeasts and molds). Bacteria are single‐celled organisms, and occur in a variety of shapes, including spheres, rods, spirals. Often they occur in pairs, chains, or clusters. bacillus (plural bacilli), rod shape spirilla Streptococcus coccus (plural cocci), spherical Staphylococcus Yeasts are unicellular fungi. Molds are multicellular fungi composed of threadlike filaments called hyphae. Large numbers of hyphae from a fuzzy mass (mycelium). Spoilage is affected by the food environment, which consists of ‐ intrinsic factors: food pH and composition, water and other nutrients ‐ extrinsic factors: temperature; air / gases; presence of other bacteria Microbial growth When conditions are appropriate – water, pH, oxygen, nutrients, temperature – bacteria multiply. BINARY FISSION Food Preservation methods are carried out by controlling these factors. Yeasts and Molds are a common cause of spoilage of fermented dairy products. They grow well at low pH. Most common molds found in cheese are Penicillium spp. Milk is nutritious and highly perishable. It is a good growth medium for many microorganisms. Examples of problems resulting from microbial growth in milk Defect Sour flavor Coagulation Bitter flavor Associated microorganism(s) Lactic Acid bacteria Bacillus spp Bacillus and others Product(s) Lactic acid, etc Casein destabilization Bitter peptides Milk Pasteurization is a heat treatment that destroys pathogenic microorganisms, and affects (↓) the growth rate of spoilage microorganisms. Meats origin of contamination. In the muscles of healthy live food animals bacteria are present in very low numbers. Large numbers of microorganisms occur on the hide, hair. After slaughtering, there are many potential risks of contamination through contact of the meat with external surfaces (such as hide), gastrointestinal tract / fecal material; handling, knives/utensils, etc. Fruits and vegetables may harbor a wide range of microorganisms. Potential sources of contamination include: soil (a natural reservoir of microorganisms); water (irrigation, rain); air/wind (disperse spores); postharvest processing, etc. Food Deterioration ‐ Prevention ‐ adequate food processing and preservation ‐ appropriate packaging ‐ appropriate food storage ‐ food additives A food additive is any substance added to food. Most food additives are used to limit food spoilage. These are preservatives. Preservatives may slow food spoilage (microbial or chemical), maintain food freshness. Food additives are regulated by federal authorities and international organizations to ensure their safety. Readings 1. Mold on Foods (pdffile posted on the course web page) 2. Temperatures&Food‐USDA (pdf file posted on the course web page) Video U.S.: Hamburger Confidential ‐ nytimes.com/video http://www.youtube.com/watch?v=859ZHzK9_X4 Bacteria multiply rapidly between 40°F and 140°F (“Danger Zone”), doubling in number in as little as 20 minutes. To keep food out of this danger zone, keep cold food in the refrigerator or in coolers. Set your refrigerator no higher than 40°F and the freezer at 0°F. Keep hot food in the over, in heated chafing dishes, or in warming trays, and/or slow cookers. Source: Dietary Guidelines for Americans (2005) ...
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