Food Microbiology

Introductory Microbiology: Lecture 9 - Food Microbiology

• Food microbiology is a critical area of study impacting food safety and quality.
• Pasteurization methods (HTST and LTLT) influence nutrient composition and taste.
• HTST (High Temperature Short Time): 72°C for 15 seconds.
• LTLT (Low Temperature Long Time): 63°C for 30 minutes.
• HTST is preferred for milk due to less damage to nutrients and sensory characteristics compared to LTLT.
• Microbes significantly impact food via spoilage, illnesses, and food production.
• Spoilage and poisoning are separate phenomena.
• Food spoilage is a continuous process with infection linked to these processes (but different microbes involved).
• Visual inspection of food cannot predict poisoning.

Learning Objectives

• Understand how microbes contribute to food spoilage and the factors influencing this process.
• Understand how food can be a vector for transmission of pathogenic microorganisms.
• Understand how microorganisms cause illnesses due to food consumption.
• Learn microbes' roles in food production, preservation, and consumption.
• Recognize that food spoilage is a component of both food production and potential infection.

Impact of Microbes on Food Safety and Quality

• Microbes significantly impact food.
• Food spoilage affects food quality.
• Foodborne illnesses directly affect human health.
• Microbes are essential for food production processes.

Microbial Growth and Food Spoilage

• Microbial growth in food alters its appearance and quality.
• Microbial growth is a predictable, successive process.
• Different food types undergo different spoilage processes.
• Toxin production is possible.
• Microbial growth is affected by intrinsic (food-related factors) and extrinsic (environmental factors) influences.

Intrinsic Factors

• Food composition (carbohydrates, proteins, fats).
• Mold predominates in carbohydrate-rich foods, hydrolyzing them.
• Tomatoes are particular susceptible to food degradation.
• Ergotism (hallucinogenic alkaloids) is associated with Claviceps purpurea in grains.
• Various chemical reactions affect foods during microbial decomposition.

Intrinsic Factors (continued)

• pH (impacts microbial community composition, chemical reactions).
• Water activity (lower water activity inhibits microbial growth).
• Oxidation-reduction potential (altered by cooking).

Antimicrobial Substances

• Coumarins (fruits, vegetables).
• Lysozyme (cow's milk, eggs).
• Aldehydic and phenolic compounds (herbs, spices).
• Allicin (garlic).
• Polyphenols (green, black teas).

Microbial Product-Based Inhibition

• Bacteriocins (bactericidal proteins active against related species).
• Bacteriocins can influence susceptible bacteria by:
  • Disrupting proton motive forces.
  • Creating pores in cell membranes.
  • Disrupting protein or RNA synthesis.
• Examples include nisin from Lactococcus lactis and various bacteriophages.

Extrinsic Factors

• Temperature (lower temperatures retard microbial growth, higher temperatures promote growth).
• Relative humidity (higher relative humidity promotes microbial growth).
• Atmosphere (oxygen promotes growth).
• Modified atmosphere packaging (MAP).
• Use of packaging technologies like shrink wrap and vacuum atmospheres.

Controlling Food Spoilage

• Modern food microbiological era started in 1857 (Louis Pasteur).
• Goal of preservation methods: eliminate/reduce spoilage microbes while maintaining quality.
• Specific preservation methods: heat for different time periods.
• Shorter heating times result in better flavor preservation.

Removal and Reduction of Microorganisms

• Removal/reduction of microbes is common in water, wine, beer, juices, and soft drinks.
• Filtration is a method commonly used.
• Refrigeration retards growth but doesn't eliminate all microbes.
• Extended storage may lead to spoilage/bacterial/growth.
• Microbes still grow below -10°C.

High Temperature Preservation (Canning)

• Food heating in special containers at 115°C for 25-100 minutes.
• Kills most spoilage microbes, but not necessarily all food-related microbes.

Food Handling Contamination

• Contamination during food handling is a concern for safety.

Food Safety Considerations (and Questions)

• Questions about the safety of specific food products (e.g. Surströmming).

Water Activity

• Dehydration techniques (e.g., lyophilization) to produce freeze-dried foods can eliminate bacterial growth.
• Food preservation impacts directly with reduced water and increased solute concentration.
• Xerophilic organisms can tolerate reduced water levels, grow at low water activities.

Chemical-Based Preservation

• GRAS (generally recognized as safe) chemical agents: Organic acids, sulfites, ethylene oxide gas, sodium nitrite—inhibiting spore formation in meats—forming nitrosamines, pH affecting effect of chemical preservative.
• Salt is a common food preservative.

Table 40.3: Major Groups of Chemicals Used in Food Preservation

• Provides a list of food preservatives using various examples of usage and levels.

Food Safety and Radiation Techniques

• Radappertization is used for extending shelf life or sterilization of specific foods (meat, seafood, fruits, vegetables).
• Killing microbes in moist foods by producing peroxides (from water) by ionizing radiation.
• Electron beams are used to kill microbes, but do not penetrate foods as deeply as gamma radiation.

Food Packaging

• Modified atmosphere packaging (MAP) controls microbial growth by altering gases in stored food.
• Other methods include using impermeable materials and vacuum technologies.
• Using polylactic acid as an alternative to plastic.

Types of Food-Borne Disease

• Foodborne infections: pathogens growing in food.
• Common pathogens: Noroviruses, E. coli, Campylobacter jejuni, Salmonella, Listeria monocytogenes.
• Food intoxications: toxins from microbes growing in food.

Foodborne Diseases (Continued)

• Breakdown in hygiene can cause transmission of pathogens.
• Fecal-oral route is a major transmission pathway.
• Fomites are materials that can carry infection (clothes, utensils).

Specific Foodborne Pathogens

• Salmonella, E. coli O157:H7, Campylobacter, Giardiasis, Listeria, Norovirus, Staphylococcal Food Intoxication, Aflatoxin, common pathogens leading to food illness.

Food-Borne Infection

• Pathogens are ingested, grow, and invade tissues.
• Raw foods (e.g., sprouts, raspberries, seafood) are important sources of contamination.
• Pregnant women, young, old, and immunocompromised people are at higher risk for foodborne infections.

Food-Borne Intoxication

• Ingestion of toxins produced by microorganisms.
• Does not require microbial growth (in food) to produce symptoms (e.g., Staphylococcus aureus toxins, botulism, C. perfringens, Bacillus cereus toxins, mycotoxins).
• Various types of fungus-derived toxins: Aflatoxins, fumonisins can affect grains, nut products, corn, and fish/shellfish.

Microorganisms and Food Production

• Most food production processes involve fermentation.
• Major fermentations are lactic, propionic, and ethanolic fermentations.

Fermented Milks

• Most fermented milk products involve lactic acid bacteria (Lactobacillus, Lactococcus, Leuconostoc, Streptococcus).
• Gram-positive, aerotolerant, survive under acidic conditions.

Fermented Meat and Fish

• Sausages, hams, bologna, salami are fermented meats; fish (sushi), rice, vegetables, and tuna are fermented food.
• Fermented meats are prepared for human consumption.

Effects of Culture on Meat and Products

• Curing agents in fermented sausages work to prevent the growth of various pathogens (e.g in raw/ready to eat ham; Semi-processed raw meats use strains of bacteria that improve longevity.

Wines and Champagnes

• Enolgy (wine production; crushing grapes, separating liquid from grapes).
• Treatment with sulfur dioxide fumigant.
• Saccharomyces cerevisiae or S. liposideus is used for consistent wine results.

Beers and Ales

• Cereal grains as fermentation sources for beers and ales.
• Using Malt (germinated barley grains).
• Mashing, adding hops.
• Inoculation (pitching) of wort with yeast.
• Top and bottom yeasts.

Production of Breads

• Involves growth of yeast (Saccharomyces cerevisiae) under aerobic conditions.
• Maximizing CO2 production causes bread dough to rise.
• Other microbes are used in specific bread types, like sourdough.
• Spoilage can occur due to Bacillus species in bread.

Major Types of Cheese and Microorganisms (Table 40.6)

• Contains a list of various cheeses along with the causative microorganisms.

Cheese as an Ecosystem (page 45)

• Explains different aspects of cheese production from fresh cheese to aged cheese.

Probiotics and Standardization

• Probiotics are live microorganisms that benefit the host.
• Specific requirements exist to confer health benefits.
• Examples: Lactobacillus, Bifidobacterium.

Good and Bad Bacterial Flora

• Various bacteria are present in the human gut.
• Bifidobacterium, Lactobacillus, Escherichia coli (some strains), beneficial varieties.
• Campylobacter jejuni, enterococci faecalis, Clostridium difficile are also present.

Summary

• Microorganisms are essential for food production and are also components that can cause food-related damage or illness.
• Many various food sources impact health depending on their composition and microbial growth.

Test your knowledge on the processes of microbial growth and its impact on food. This quiz covers various aspects including intrinsic and extrinsic factors, putrefaction, and types of food spoilage. Perfect for students and enthusiasts of food science and microbiology.