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APPLIED MICROBIOLOGY

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Microbes Found in Food

20% of E.R. visits are foodborne illness Grains

– Claviceps purpurea mildew– Aspergillus– Rhizopus

Produce– Pseudomonas – Salmonella on cantaloupes

Meats/Poultry– Salmonella, Clostridium, Staphylococcus– Helminths– Molds

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Microbes Found in Food (cont.)

Fish/Shellfish– Vibrio cholerae, V. parahemolyticus– Salmonella

Milk– Staphylococcus aureus (milk handling)– Pseudomonas– Mycobacterium bovis

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Preventing Disease and Food Spoilage

Canning– Commonest method– Moist heat under pressure– Balances flavor/safety

Thermophilic (flat sour) food spoilage– Bacillus stearothermophilus

Avoid temperature abuse to cans

– Acid taste, no gas production

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Canning

Mesophilic food spoilage– Improper cooking– Flaws in cans

• Gas often seen– Botulism is a risk in canned meats

– Home canners need to follow USDA guidelines

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Food preservation (cont.)

Refrigeration/ Freezing– Frig. – few days only – bacteriostatic– Freezing – also bacteriostatic

• Softer textures due to ice crystals• May enhance thawed food spoilage

Drying– Removal of 90% or more of moisture– Microbes may not be killed– Osmotic control with salt/sugar adds

bacteriocidal effects

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Preventing Disease and Food Spoilage

Irradiation– Safe but expensive– X-rays, γ-rays– Public education is

needed

Chemical Preservatives– Organic acids– Ozone– Ethylene oxide for dried

foods

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Pasteurization

Destroys vegetative pathogens High Temperature Short Time (HTST)

– 72oC, 15 secs

Low Temperature Long Time– 70oC, 30 mins

Ultra High Temperature (UHT)– 88oC, 3 secs– Refrigeration not needed

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Microbes as Food

Fungi– Yeast supplements– Limited tolerance by

humans Algae

– Chlorella– Shortened food chain– Some disease risks from

sewage growth Bacteria

– Spirulina– 65% protein– South America

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Microbes in Food Production

Bread– Saccharomyces

cerevisiae– Carbon dioxide

bubbles create leavening

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Cheese manufacture Add rennin to milk (curd) Add Lactobacillus bacteria

(anaerobic acid fermenters)– Immature cheese – cottage

cheese Allow ripening (aging) to

decrease water, increase flavor

Classified by consistency– Very hard – Parmesan, Romano– Hard – Cheddar, Swiss– Semi-hard – Stilton, Danish Blue– Soft – Camembert, Brie

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Cheese production

Dairy/Cheese

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Alcoholic Beverages — Beer

Beer/Ales– Starch from rice,

wheat, barley– Malting of grains, – Hop addition– Yeast

Saccharomyces cerevisiae

– Alcohol is filtered, pasteurized (diluted)

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Alcoholic Beverages — Wine

Wine– Monosaccharides from fruit

juice– Yeast added after

sulfites/pasteurization– Filtration, clarification, wood

aging

Spirits– Alcoholic mash is “distilled”

to boil off alcohol– Fruit or grains may be used

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Industrial Fermentation

Valuable commodities– Acetone/ glycerol– Vitamins– Antibiotics, vaccines– Monoclonal Ab, human insulin (Humulin)

Metabolic Processes are modified for commercial production by– Altered nutrition/ environment

• Citric acid from molds in iron free media– Altered gene regulation

• Overproducers of penicillin– Recombinant genes

• Humulin from bacteria

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Industrial and Pharmaceutical Microbiology

Challenges– Toxicity to microbes– Extraction from cells– Aeration

Reactor Types– Continuous– pH, temperature,

nutrient levels are maintained