Food Microbiology: Chapter 28
Importance of Food Microbiology
Preservation of food products is crucial to prevent disease.
According to the CDC, common pathogens causing foodborne illness:
E. Coli
Salmonella (both are types of bacteria)
Norwalk virus (causes flu-like symptoms)
Foodborne Illness Cases
Both raw foods (fruits, vegetables) and processed foods can be implicated.
Many cases go unreported due to mild symptoms.
Common symptoms include diarrhea and vomiting.
Individuals with mild diarrhea typically do not seek medical help, leading to underreporting.
Monitoring of Food Products
Food products are monitored by:
FDA (Food and Drug Administration)
USDA (United States Department of Agriculture)
The monitoring strategy uses the Hazard Analysis and Critical Control Point (HACCP) system:
Identifies specific points in processing where contamination may occur.
Methods for Prevention of Disease
Canning
Involves heating with pressurized steam in a vessel called a retort.
Follows the 12D treatment system:
12 decimal reduction of Clostridium botulinum.
Aimed at reducing Clostridium botulinum by 12 log units.
Clostridium botulinum is the bacterium responsible for botulism.
Challenges with canning:
Endospores: Highly resistant forms of bacteria.
Low-acid foods can lead to safe conditions for Clostridium botulinum.
Indicators of spoilage: Bulging cans (gas production) and bad odors suggest microbial replication.
Aseptic Packaging
Used in conjunction with sterilization techniques such as ultraviolet light.
Irradiation
Utilizes radioactive cobalt-60 to kill bacteria and insects.
Doses of irradiation:
Low dose: Less than 1 kg, used for treating insects on fruits/vegetables.
Mid dose (pasteurizing dose): 1 to 10 kg, effective for bacteria on meats.
High dose: Greater than 10 kg, typically used for spores in spices.
On average, spices can contain over 1,000,000 bacteria per gram.
High-Pressure Preservation
Involves using pressurized water to lyse microbes.
High pressure applied is about 87,000 PSI.
Limitations: Not all food products can tolerate high pressure; those that do may have reduced shelf life.
Benefits of Microbes in the Food Industry
Dairy Production:
Cheese production involves casein protein and enzyme renin.
Cheese curd formation is catalyzed by lactic acid bacteria under acidic conditions.
Yogurt is made by inoculating milk with Streptococcus thermophilus and various lactobacilli species.
Yeast Fermentation:
Bread rises due to CO2 production from yeast.
Wine production from fermentation of grapes.
Beer production through fermentation of grains leading to ethanol and CO2.
Industrial Microbiology
Biotechnology in Industrial Microbiology
Biotechnology aims for an open system in bioreactors.
Unlike closed systems, open systems maintain constant conditions:
pH
Aerobic/anaerobic environments
Temperature
Nutrient supply
Bioreactor: The vessel where microbes and nutrients interact under controlled conditions.
Role of Genetically Modified Strains
Often, genetically modified strains of microbes are used to optimize product yield, and products are termed metabolites:
Primary Metabolites:
Typically alcohols produced during the log phase of growth (also known as tropho phase).
Secondary Metabolites:
Include antibiotics (e.g., penicillin) produced during the stationary phase (referred to as ideophase).
Examples of Biotechnological Products
Amino Acids:
Example: Lysine, added as a supplement in various food products.
Citric Acid: Produced by microbes and has various uses.
Vitamins:
Example: Vitamin B12 produced by Pseudomonas species.
Antibiotics: Various antibiotics can be produced through microbial action.
Alternative Fuels:
Conversion of biomass into fuel using microbes, termed bioconversion.
Examples include methane and ethanol.
Conclusion
The lecture briefly covered the importance of food microbiology, methods for the prevention of foodborne diseases, and the contributions of microbiology to food production and biotechnology.