Food Microbiology Lecture Review

Food Microbiology: The Ugly - Food Spoilage

• Foodborne illness has a significant economic and social impact, affecting public health and the economy.

• In Australia, there are an estimated 2 to 4 million cases of foodborne diseases per year, costing $2 to $3 billion due to healthcare expenses, lost productivity, and other associated costs.

• In the USA, the scale is about 10 times larger due to a larger population and broader food distribution networks, resulting in even greater economic and health burdens.

• Foodborne microbial diseases are often regarded as "iceberg diseases" because many cases with mild symptoms go unreported, leading to an underestimation of the true burden of these diseases.

Impact on Industry: Food Recalls

• Food recalls occur when manufacturers, retailers, or health authorities find food potentially misleading or harmful, posing risks to public health and consumer confidence.

• Undeclared allergens are a major cause of recalls, particularly for individuals with food allergies, but microbial contamination, such as Salmonella or E. coli, is also a significant factor.

• Recalls lead to economic losses due to investigation, destruction of food, and temporary consumer loss, affecting both the company and consumers.

Commonly Involved Foods

• Animal-based food products are most commonly involved in foodborne disease outbreaks, particularly eggs and egg products, due to potential contamination with pathogens like Salmonella.

• Leafy vegetables have become a growing concern in recent years due to recalls and outbreaks caused by pathogens like Salmonella and E. coli, often linked to irrigation water or soil contamination.

Food Preparation Settings

• Restaurants account for a large percentage (46%) of foodborne disease outbreaks due to various factors, including improper food handling and hygiene practices.

• Primary production and private residences are also important settings, where unsafe practices during food preparation and storage can lead to illness.

• The food service industry is more involved in outbreaks than the food manufacturing industry, possibly because they employ fewer people with food safety expertise, leading to less stringent control measures.

• Cruises can also experience outbreaks due to confined environments and common areas, facilitating the rapid spread of pathogens among passengers.

Main Organisms of Foodborne Illness

• Salmonella is a common and important pathogen, causing a significant number of foodborne infections worldwide.

• Other organisms include Bacillus cereus, norovirus, hepatitis A virus, Listeria monocytogenes, and E. Coli, each with distinct characteristics and health implications.

• Listeria monocytogenes is particularly dangerous for infants, the elderly, and pregnant women, as it can cause severe consequences like stillbirth and miscarriage due to its ability to cross the placental barrier.

• Some strains of E. Coli can be very harmful, especially to children, causing kidney failure and death due to the production of potent toxins.

• Newer strains of pathogens are emerging, making it an ongoing concern that requires constant monitoring and research.

Factors Contributing to Foodborne Outbreaks

• Food contaminated with pathogenic organisms above acceptable levels, representing a direct threat to consumer health.

• Food obtained from unsafe sources (e.g., seafood from polluted water, contaminated vegetables), leading to the introduction of harmful microbes into the food chain.

• Contamination from improperly cleaned equipment, creating breeding grounds for pathogens that can easily spread to food.

• Inadequate processing control (e.g., under-roasting chicken), failing to eliminate or reduce pathogens to safe levels.

• Poor hygiene of food handlers, allowing the transfer of microbes from hands and surfaces to food.

• Cross-contamination of pathogens from raw to cooked food, leading to the spread of bacteria to ready-to-eat items.

• Inadequate cooking of food, failing to kill harmful bacteria and parasites.

• Slow cooling of cooked products, providing an opportunity for bacteria to multiply to dangerous levels.

• Storage of food in the temperature "danger zone" (between 4^{\circ}C and 60^{\circ}C), promoting rapid bacterial growth.

• Storing cooked food too far in advance of consumption, increasing the risk of microbial contamination and spoilage.

• Use of leftover products without proper reheating (preferably over 70^{\circ}C), potentially causing illness if pathogens have grown during storage.

Mechanism of Foodborne Illness

• Pathogens must compete with the existing microorganisms in the human biome, affecting their ability to colonize and cause disease.

• Two major mechanisms by which pathogens cause disease:

  • Production of toxins (exotoxins and endotoxins), leading to various symptoms depending on the type of toxin.

  • Live microbial cells evading the human defense system, causing infection and tissue damage.

• Exotoxins are toxins released outside the microbial cell and can be:

  • Enterotoxins: Irritate the intestinal system, leading to gastroenteritis.

  • Cytotoxins: Kill cells, damaging organs.

  • Neurotoxins: Affect the nervous system (e.g., Clostridium botulinum toxin).

• Endotoxins are toxic components of bacterial cell walls (lipopolysaccharides) that are released when bacteria die, triggering an inflammatory response.

Intoxication vs. Infection

• Intoxication: Bacteria grow in food and produce exotoxins before consumption. Symptoms appear quickly (3-6 hours) due to the rapid action of pre-formed toxins.

• Infection: Live bacterial cells must be present in high numbers and adhere to the intestinal wall. Symptoms appear later (at least 12 hours) as the bacteria multiply and invade the body.

Effective Dose

• The dose (number of cells or amount of toxin) is important, as it determines the likelihood and severity of illness.

• The severity (virulence) of the microorganism and the health status of the consumer are key considerations, as they influence the body's ability to fight off infection.

• At-risk groups (children, the elderly, those with poor health, and pregnant women) require a much lower dose due to their weakened immune systems.

Prevention

• Prevention is the most important strategy, as it reduces the occurrence of foodborne illnesses and protects public health.

• Food safety risk assessment should be conducted to identify potential hazards and implement control measures throughout the food production chain.

• Food safety programs should be developed and implemented throughout the food supply chain, ensuring adherence to guidelines and regulations.

• Consumer education on food safety handling at home is essential, empowering individuals to take responsibility for their food safety.

• Food Standards Australia and New Zealand (FSANZ) develops food standards and safety programs, providing guidelines and regulations for the food industry.

• Acceptable risk: Cannot have a zero-tolerance policy due to cost; food standards and safety are already very good in Australia and other developed countries.

The Positive Role of Microbes in Food Technology

Learning Outcomes

• Appreciate the diversity of fermented food products worldwide, recognizing their cultural and economic significance.

• Name at least two major types of microbes commonly involved in food fermentation, understanding their roles and applications.

• Identify the main roles of different microbes in wine, cheese, and tempeh making, gaining insights into the science behind food fermentation.

Beneficial Contribution of Food Microbes Interaction

• Industrialized fermented food products (bread, beer, wine, soy sauce, etc.), contributing to global food production and availability.

• Traditional fermented products (cocoa, coffee, tempeh). Small scale operation, often at home, reflecting local customs and traditions.

• Microbes are widely used in the production of food ingredients (vinegar, citric acid, amino acids, vitamins, polysaccharides, colors, etc.), enhancing food quality and functionality.

• Probiotic bacteria are added to yogurt (bifidobacterium, lactobacillus casei, etc.), promoting digestive health and overall well-being.

• Biocontrol cultures can be used to control pests in agriculture and horticulture, reducing the reliance on chemical pesticides.

• Starter culture industry produces yeast for baking and wine making, as well as bacteria for fermentation, ensuring consistent and reliable results.

Benefits of Food Fermentation

• Desirable sensory qualities (flavor), enhancing the taste and aroma of food products.

• Preservation, extending the shelf life of food and reducing waste.

• Safety, inhibiting the growth of spoilage organisms and pathogens.

• Increased nutritional value (vitamin production), improving the nutritional content of food.

• Other health benefits (probiotics, immune system boost, pathogen combat, reduce irritable bowel symptoms, reduce allergenicity, reduce cholesterol, cancer prevention), offering potential therapeutic effects.

• Psychological impact (enjoyment), contributing to food satisfaction and pleasure.

• Economic impact (new industries), creating opportunities for innovation and growth.

Major Microbes Involved in Food Fermentation

• Lactic Acid Bacteria: Utilize sugar to produce lactic acid; involved in fermented meat, vegetables, yogurt, and cheese.

• Yeasts: Involved in alcoholic beverages and bread making; produce carbon dioxide in bread.

• Filamentous Fungi (Mold): Involved in soy sauce and tempeh production.

• Acetic Acid Bacteria: Produce acetic acid, the principal component of vinegar.

Example 1: Wine Fermentation

• Scientific study started with Louis Pasteur, who elucidated the role of yeast in alcoholic fermentation.

• Major groups of microbes:

  • Yeasts: Primary (alcoholic) fermentation; produce alcohol and flavor.

  • Lactic Acid Bacteria: Malolactic (secondary) fermentation.

  • Filamentous Fungi (Mold): Spoilage (negative) or botrytis wine (positive).

  • Acetic Acid Bacteria: Souring of wine (negative).

• Saccharomyces cerevisiae (used in both wine and baking).

• Yeasts numbers extremely high during fermentation (10^8 cells per mL).

• Flavor metabolites include alcohols, esters, organic acids, and sulfur compounds.

Where the yeast come from

• Naturally present yeast in nature, where you can do a natural fermentation or add starter culture. So relying on this yeast to start fermentation.

• Natural fermentation produces the best quality wine.

• Added starter culture offers qualite consistent

• Malolactic fermentation improves wine taste.

• Filamentous improve qualite. It may inhibit alcohol fermentation. Botrytis wines is a special wine

• Acetic acid is how wine vinegar is made.

Example 2: Cheese Fermentation

• Making starts with milk

• Milk is added with L Actic Avid bacteria

• This process typically last 30 min to Ihour

• Rennet will then be added (enzyme produced from microorganisms), curd is now formed.

• During first milk fermentation, is consumed by lactic acid, which will then become lactic acid. In the meantime creates also flavoring. We know exactly what bacteria is in here, because we added it.

• Depending on the type of cheese, these would be matured for a period of time.