Introduction to Food Microbiology - Food Microbiology - Lecture Slides, Slides for Microbiology. Shoolini University of Biotechnology and Management Sciences


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Introduction to food microbiology

Introduction to food microbiology

A brief history Topics in food microbiology

Survey of microbes

People have “practiced” food microbiology for thousands of years

History of food microbiology

• 8-10,000 years ago – Food preservation

• Ca. 4,000 years ago – Fermented foods

• 1600s – Early observations with microscopes

• 1700s – Spontaneous generation was challenged (in

experiments involving food)

1800s –The Golden Age of Microbiology -Cell theory -Spontaneous generation disproved -Proof that fermentation is a biological process -Germ theory of disease -Canning invented -Discovery of organisms that cause foodborne illness -Techniques for studying microbes


• 1849 John Snow: cholera spread through water contaminated with feces

• Several waterborne pathogens isolated

More pathogens isolated from food, diseased animals, feces

Foodborne pathogens

Salmonella enteriditis- isolated from meat as well as person who ate it

Staphylococcus Clostridium botulinum • Isolated in late 19th century • Koch’s postulates in action!

Techniques in microbiology

• Pure culture technique • Microscopy • Staining, esp. Gram stain • Sterile microbiological media (liquid and solid) • Aseptic technique • Methods to control microbial growth • Biochemical tests to distinguish microbes • Studying beneficial microbes as well as pathogens

Molecular genetics and biotechnology

• Rapid identification • Genetic engineering • Understanding mechanisms of resistance,

biochemical processes, etc.

Limitations of microbiological techniques

• Most microbes cannot be grown in the laboratory

• Microbes do not grow in isolation • Most microbes have not even been


Topics in food microbiology

• Fermentation/probiotics – Fermented foods and important metabolites

• Making fermenting strains more stable – Resistant to viruses – Enhance fermentation capacity

• Understanding probiotics and their effect on the body (the microbiome)

Food spoilage

• Which microbes, and under what conditions? • What are the metabolites (products)? • How do they work in the cold? • How can they be controlled?

Foodborne pathogens

• Detection • Identification • Control • How do we monitor and share information? • Are we making the problem worse?

– Antibiotic resistance – Are we introducing pathogens through our


What kinds of microbes are found in food?

• Bacteria • Fungi (yeasts and molds) • Viruses

• Protozoans, algae, helminths to a lesser extent • (Helminths=worms) • Protozoans and helminths are considered


Classification of organisms

Where are viruses and prions?

Prokaryotes vs eukaryotes

prokaryotes • Smaller cells • No nucleus or organelles • Single-celled • Bacteria and archaea

• Viruses and prions are not cells so are not considered alive

eukaryotes • Larger cells • Cells have nucleus and

organelles • Can be single-celled or

multicellular • Plantae, Animalia, Fungi,



• Binomial name: genus and species – Ex. Salmonella typhimurium; S. typhimurium

• Subspecies: – Lactococcus lactis ssp. lactis, (soft cheese) – L. lactis ssp. cremoris (hard cheese)

• Serovar, pathovar, biovar

Yeasts and molds

• Yeasts: single-celled eukaryotes

• Molds: multicellular structure (filaments, spores) required for reproductions

• Can be used to make foods but also involved in spoilage

Saccharomyces cerevisiae:

• Carbon dioxide and ethanol

Molds can grow almost anywhere

• Food spoilage • Toxins • Allergens • Food processing • Different genera grow on different foods

Rhizopus- fruits, vegetables, bread – Geotrichum- dairy mold – Penicillium-spoils almost everything, but also used

to make cheese

Viruses infect cells

Hepatitis A- infects humans

Can cause disease Interfere with food processing

Protozoans, algae, helminths

• Protozoans can cause parasitic disease (Giardia, Cryptosporidium, Toxoplasma)

• Algae- photosynthetic protists – Contaminants, food products, toxins

• Helminths- parasites – Roundworms, tapeworms- contaminated food

Life cycle of a tapeworm (helminth)

Bacteria (“eubacteria”)

• We will spend much lecture time, and most lab time, working with them

• Classification is complicated and changing all the time

• Most bacterial species have not been described, but many have been very well studied

Major classification criteria

• Gram-positive or Gram-negative


Bacterial classification, continued

• Aerobes, anaerobes, fermenters • Spore formers, non spore formers • What metabolic products do they produce?

– Acids, alcohols, gases- and which ones? • What do they use for food?

– Carbohydrates, lipids, proteins • Under what conditions do they grow?

– Temperature range, pH range, availability of water Do they cause disease? What kind?

What should a food microbiologist know?

• Characteristics of the different types of microbes • How to identify and enumerate them • Factors that affect their growth (innate and

introduced) • Fermentation vs spoilage • How microbes cause disease • That the field of food microbiology is a work in


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