food

MICROBIOLOGY OF FOOD

INTRODUCTION

  • Presenter: Dr. Glyn Barrett

  • Email: glyn.barrett@reading.ac.uk

  • Location: Health and Life Sciences (HLS) building, University of Reading

LEARNING OUTCOMES

  • Differentiate Intrinsic and Extrinsic Factors

    • Ability to distinguish intrinsic factors (internal characteristics of food) from extrinsic factors (external environmental influences) that affect food spoilage.

  • Microbial Growth Composition

    • Explanation of how food composition dictates the type of microbial growth that may occur on it.

  • Physical and Biological Features

    • Identification of two physical and two biological characteristics of food that influence spoilage.

  • Pathogen Entry

    • Comprehension of mechanisms through which pathogens infiltrate the food chain.

  • Microbial Contributions to Food Industry

    • Recognition that microbes not only hinder food safety but also play a significant role in food production.

A BRIEF HISTORY

  • Bread and Beer Production

    • Current evidence suggests these practices date back approximately 8,000 years.

  • Recognition of Food Poisoning

    • Documented acknowledgment around 900 AD.

  • Development of Canning

    • Invention credited to Nicolas Appert in 1795, particularly influenced by the needs during the Napoleonic Wars.

  • Evolution of Food Microbiology

    • Transition to a recognized scientific field occurring between 1854-1864, notably involving contributions from Louis Pasteur.

FOOD-BORNE ILLNESS (FBI)

  • Economic Impact

    • Estimated yearly cost of food-borne illness is $6.9 billion.

  • Centers for Disease Control and Prevention (CDC) Estimates:

    • 48 million reported cases annually.

    • Roughly 128,000 hospitalizations stemming from these cases.

    • About 3,000 deaths connected to food-borne illnesses.

  • Common Pathogens

    • Major pathogens include Campylobacter, E. coli, and Salmonella.

    • thes enter the food by conntamination

MICROORGANISMS IN FOOD

  • Classification of Microorganisms:

    • Pathogenic Microorganisms: Cause diseases and health issues.

    • Spoilage Microorganisms: Lead to undesirable changes in food's smell, taste, or appearance. - economic losses

    • Fermentation Microorganisms: Also known as beneficial microbes, they produce desirable food products through fermentation processes.

    • Neutral Microorganisms: Have no significant effect on the food.

MICROBIAL GROWTH AND FOOD SPOILAGE

  • Controlling Factors of Microbial Growth:

    • Intrinsic Factors

    • Properties related to the food itself, including:

      • pH

      • Water content

      • Nutrient content

      • Natural antimicrobial substances

    • Extrinsic Factors

    • Environmental conditions influencing spoilage, such as:

      • Temperature

      • Relative humidity (rH)

      • Gas composition

      • Pressure

CONTROLLING GROWTH STRATEGY

  • Principles:

    • F - Food

    • A - Acidity

    • T - Temperature

    • T - Time

    • O - Oxygen

    • M - Moisture

INTRINSIC FACTORS

  • Carbohydrates

    • In carbohydrate-rich foods:

    • Molds generally predominate due to an average poH of around 5 (e.g., breads with high moisture).

    • High nutrient content supports mold growth during storage in non-airtight conditions.

    • occurs during hydolysis when carbohydrates arfe broken down into similar compounds.

  • Proteins and Fats

    • In protein and fat-laden foods such as meats and dairy:

    • Bacterial growth, particularly Putrefaction, is common, leading to breakdown of proteins (proteolysis) and foul-smelling byproducts.

    • Spoilage in unpasteurized milk can lead to lactic acid production that lowers pH, followed by spoilage due to putrefaction.

    • Rancidity can also occur due to short-chained fatty acid production in butter.

  • pH Growth Range in Foods

    • Organisms thrive in different pH ranges, for example:

    • Vibrio spp. and Campylobacter spp. thrive at lower pH values.

    • E. coli and Salmonella spp. are found at neutral pH.

  • Physical Properties

    • Physical properties like grinding increase microbial growth by increasing surface area and distributing microbes more easily.

    • The outer skins of fruits and vegetables can inhibit microbial growth.

EXTRINSIC FACTORS IMPACTING MICROBIALw GROWTH

  • Temperature:

    • Low Temperatures: Refrigeration (<5°C) slows microbial growth but does not eliminate it, as seen in organisms like Listeria monocytogenes.

    • High Temperatures: Canning at temperatures of 115°C can kill spoilage organisms but may not eliminate all microorganisms.

  • Relative Humidity: High humidity levels foster microbial growth.

  • Atmosphere: The presence of oxygen facilitates growth; modified atmosphere packaging (MAP) limits oxygen availability by using shrink wrap and vacuum technologies.

TEMPERATURE AND GROWTH

  • Types of Microbial Growth Based on Temperature:

    • Psychrophiles: Thrive in temperatures from 1-20°C (e.g., Pseudomonas, Flavobacterium).

    • Psychrotrophic: Can grow in refrigeration conditions but prefer warmer temps (e.g., Listeria monocytogenes).

    • Mesophiles: Most human pathogens, prefer temperatures between 20-40°C (e.g., E. coli, Salmonella, Clostridium botulinum).

    • Thermophiles: Favor temperatures above 45°C (e.g., Geobacillus stearothermophilus).

the danger zone is the temp between 5 and 60 degrees celcius.

FOOD PRESERVATION STRATEGIES

  • Pasteurization reduces pathogens and the number of spoilage organisms through specific heat treatments.

  • Water Availability: Dehydration techniques such as lyophilization (freeze-drying) eliminate bacterial growth.

  • Chemical Preservation: Use of Generally Recognized As Safe (GRAS) compounds like organic acids and sulfites.

  • High Hydrostatic Pressure (HHP): Application of pressures from 100-800 MPa without significant temperature change to alter cell membranes.

  • Irradiation (Radappertization): Use of gamma radiation to kill microbes and extend shelf life without rendering food radioactive.

  • Microbial Inhibition: Bacteriocins and natural antimicrobials derived from natural substances like garlic and spices

TYPES OF FOOD-BORNE DISEASE

  • Roughly 48 million cases annually in the U.S. with a significant number of hospitalizations and deaths.

  • Major pathogens include Noroviruses, Campylobacter jejuni and Salmonella.

  • Foodborne Infections and Intoxications: Defined by the means of transmission; the fecal-oral route plays a crucial role.

  • infections - invade and multiple in the host

  • intoxinations - consuming toxins produced by the microbes

EXAMPLES OF SPECIFIC FOOD-BORNE DISEASES

  • Listeriosis: Affected demographics include pregnant women and immunocompromised individuals.

  • E. coli O157:H7: Known for severe symptoms, including hemolytic uremic syndrome, especially dangerous to children and the elderly.

SOURCES OF FOOD CONTAMINATION

  • Various routes including animals, humans, wildlife, processing plants, sewage, etc. can contaminate food products. Key sources include:

    • Poultry

    • Cows

    • Meat products

    • Contaminated water and vegetables.

FOOD PRODUCTION AND FERMENTATION

  • Fermented Products: Rely on lactic acid bacteria such as Lactobacillus.

  • Types of Fermented Products: Cheese varieties, fermented milks, and various traditional fermented foods from different regions.