Food spoilage
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Microbial growth and food spoilage results from microbes altering food, rendering it unsuitable for consumption. Different foods undergo specific spoilage processes due to their unique microbial loads and compositions. Approximately 1/3 of the world's food is lost to spoilage each year. Minimizing contamination through good management practices and preservation procedures can help reduce food spoilage. Different types of microbes degrade the chemical components of foods in characteristic ways, impacting appearance, flavor, and other qualities. Specific foods are prone to spoilage by certain microorganisms depending on their nutrients and conditions.
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Food spoilage
- 2. Microbial Growth and Food Spoilage • food spoilage • results from growth of microbes in food • alters food visibly and in other ways, rendering it unsuitable for consumption • involves predictable succession of microbes • different foods undergo different types of spoilage processes • toxins are sometimes produced • algal toxins may contaminate shellfish and finfish
- 3. • Change in appearance, smell or taste • Economic loss • Reduced quality • Higher prices • E.g. fruits, vegetables, meat, dairy products contains- • Microorganisms- airborne, soil borne, food borne, waterborne, human handling
- 4. Food Spoilage •Approximately 1/3rd of all food manufactured in world is lost to spoilage •Microbial content of foods (microbial load): qualitative (which bugs) and quantitative (how many bugs) •Shelf life •Non-perishable foods (pasta) •Semiperishable foods (bread) •Perishable foods (eggs)
- 5. General Principles •Minimize contamination by: •Good management processes •Acceptable sanitary practices •Rapid movement of food through processing plant •Well-tested preservation procedures
- 6. Spoilage •Meat •Cutting board contamination •Conveyor belts •Temperature •Failure to distribute quickly •Fecal bacteria from intestines •Fish •Polluted waters •Transportation boxes
- 7. Spoilage •Poultry and Eggs •Human contact •Penetration by bacteria •Milk and Dairy Products •Lactobacillus and Streptococcus species that survive pasteurization (sour milk) •Breads •Spores and fungi that survive baking •Grains •Fungi produce toxins
- 8. Chemistry in Microbial Spoilage of Foods • Food (Plant or Animal) composed of- carbohydrates proteins fats vitamins and minerals • These serve as good media for the growth of many different microorganisms • Microorganisms produces changes in food- appearance flavour odour and some other qualities These changes are due to degradation of the chemical constituents of the food.
- 9. Carbohydrate foods (plant products) + Carbohydrate fermenting microorganisms • Acids • Alcohol • Gases Protein foods (animal products) + Proteolytic microorganisms • Amino acids • Amines • Ammonia • H2S Fatty foods (oils and fats) + Lipolytic microorganisms • Fatty acids • Glycerol Mechanism of microbial degradation of different kinds of foods
- 10. Microbiology of Spoilage of Specific Foods Cereal Grains - wheat, corn, rye, rice • Microbes enter from field or storage environment • High in carbohydrates and proteins • But microbes do not grow due to low aw if harvested and stored properly • Under moist conditions- microorganisms is stimulated and cause spoilage. • Tropical climates- common moulds- • Rhizopus stolonifera • Penicillium • Aspergillus • Alternaria • Fusarium
- 11. Bread -staple baked food made up of flour, water and salt leavened by yeast Saccharomyces cerevisiae • Ingredients used are generally the source of spoilage microorganisms • Most contaminants are killed during baking (100’C for 9mins) • Some molds and endospores producing bacteria survive • Rhizopus nigricans; commonly called the bread mold fungus Low water activity prevents growth of bacteria. Exceptions- Aerobic, spore-forming rods of genus Bacillus B. subtilis, B. pumilis and B. mesentericus
- 12. Cakes -Molds Sources- ingredients- sugar, nuts and spices Airborne Human handling High humidity Bacterial spoilage is rare due to high sugar conc.
- 13. Fresh Vegetables -88% water -8.6% carbohydrates -9% proteins -0.3% fats -<1% vitamins, nucleic acids and other constituents All these support the growth of molds, yeasts and bacteria. Fresh Fruits <85% water 0.9% proteins 0.5% fat 13% carbohydrates
- 14. Juices -pH of 4.0 or below (fruit juices) -pH of 4.5 or above (vegetable juices) -Lactobacillus, Leuconostoc and Acetobacter are common spoilage agents.
- 15. Assignment Write short notes microbial spoilage of food for: 1. Cereal Grains 2. Bread 3. Fruits and Vegetables 4. Juices 5. Meat- Raw meat; Fresh meat; Ground meats 6. Poultry 7. Eggs 8. Fish 9. Milk 10. Tea 11. Coffee 12. Cocoa • Constituents /Compositions • Common spoilage condition • Common spoilage agents Note: Scientific names should be in italics or underlined if hand written.
Editor's Notes
- that makes it unacceptable to the consumer To producers, distributors and consumers The population varies considerably depending upon the kind of food and infection
- Yeasts- live in apple juice; converts carbohydrate into ethyl alcohol –alcoholic taste and smell Bacteria- Food protein into amino acids which on further breakdown give foul smell Breakdown of carbohydrate- Sour taste in food is due to acid formation. Swelling of cans is due to gas formation. Rancid odour or taste in spoiled butter is due to the breakdown of fats to fatty acids.
- Heat resistant and survive baking