11 - Microbes and Food

Question 1

What are the 4 types of food micro-organisms?

Answer 1

Fermentation microbes
Probiotics
Pathogens (food poisoning)
Spoilage microbes

Question 2

What are some fermentation microbes and their uses?

Answer 2

Mold - aspergillus - lactic acid in soy sauce
Bacteria - lactobacillus - lactic acid in cheese, yoghurt
Yeasts - saccharomyces - ethanol + CO2 in beer, ethanol in wine, carbon dioxide in bread

Question 3

What are probiotics?

Answer 3

Live microorganisms which when administered in adequate amounts confer a health benefit on the host (humans, animals) in terms of gut health or immunity

Most probiotics are bacteria - bifidobacteria, lactobacilli
Common food carrier - yoghurt
Tablets as dietary supplements available

Question 4

What are prebiotics and synbiotics?

Answer 4

Prebiotics - Non-digestable substances that provide a beneficial effect on the host by selectively stimulating growth of probiotic bacteria

Most are carbohydrates e.g., inulin

Synbiotics (not ‘sym’) - preparations of probiotics + prebiotics, potentially best health effect

Question 5

What is food poisoning and its components?

How to prevent food poisoning?

Answer 5

Food poisoning - food borne illnesses, including food infection or food intoxication

Food infection - ingestion of foods containing pathogens (largely prevented by cooking)

Food intoxication - ingestion of foods containing microbial toxins (may be heat resistant)

Prevention - personal hygiene, food handling practices, sufficient cooking

Question 6

What is food spoilage and what are the 4 types?

Answer 6

Changes to the original nutritional value, texture, flavour of the food

Microbial spoilage
Chemical spoilage - oxidation, off-odour, no safety issue
Biochemical spoilage - enzymatic reactions, off-odour from lipid breakdown, no safety issue
Physical spoilage - creaming off in whole milk, wheying off in yoghurt, no safety issue

Question 7

How is food spoilage a relative term?

Answer 7

A buttery aroma - undesirable in lager beer but desirable in dairy products
CO2 - yoghurt spoilage but is an attribute in kefir (milk fermented with yeast and lactic acid bacteria)
Holes - undesirable in certain types of cheese but desirable in others

Question 8

Is spoiled food unsafe?

Answer 8

Not necessarily, but

Unsafe spoiled food does not necessarily look or smell or taste spoiled
It is prudent to assume spoiled (esp. off-odour) as unsafe, unless confirmed as chemical, biochemical or physical spoilage

Question 9

What are the conditions for optimal microbial growth?

Answer 9

Temperature
pH
Water and/or lack of (salt and sugar binds water, making it unavailable for micro-organism)
Oxygen and/or lack of
Nutrients available

Question 10

Why is storing food at room temperature for too long not advisable?

Answer 10

Many microbes that cause food poisoning or food spoilage thrive at temperatures between 15-45°C (mesophiles).

Question 11

What are the effects of pH on the different microorganisms?

Answer 11

Acidic food - prone to molds spoilage
Acidic food, high sugar - prone to yeasts spoilage
Low-acid food - prone to bacteria spoilage

Question 12

What intrinsic and extrinsic factors of food determine types and number of micro-organisms in food?

Answer 12

Intrinsic factors

• water activity
• pH
• physical structure
• available nutrients e.g., certain carbohydrates

Extrinsic factors

• temperature
• relative humidity
• oxygen or lack of

Question 13

How does the end product of food depend on intrinsic and extrinsic factors?

Answer 13

Intrinsic and extrinsic factors affect whether food spoilage or fermentation of foods will occur

e.g., vegetables left on their own vs vegetables + salt, reduced pH, high sugar

Question 14

What do the types of microorganism that populate our gut depend on?

Answer 14

Gut environment

• pH
• secretion of intestinal fluids
• oxygen gradients

Types of food/drugs we ingest e.g., fiber, antibiotics

Environment e.g., urbanised, farms

Question 15

How does the gut microbiome develop with age?

Answer 15

GI tract is fetus is sterile

Babies that are solely breastfed tend to have a more stable, less diverse bacterial community with higher proportions of bifidobacteria than formula-fed babies

After introduction of solid food, gut microbiota composition develops towards the adult pattern with increased diversity

Old age - decline in microbiota diversity, reduced numbers of bifidobacteria

Question 16

What is the importance of micro-organisms in our health?

What are the benefits of having a healthy gut?

Answer 16

Major bacterial species in the gut is dependent on diet

As little as 3 weeks diet is sufficient to modify gut microbe populations

A healthy gut microbiome involves a large diversity of different microbes, especially beneficial microbes such as bifidobacteria

Benefits:
Inhibit harmful bacteria growth
Aids digestion and absorption
Stimulate immune functions
Production of vitamins e.g., vitamin K

Question 17

Besides reducing our glycemic response, what else does fiber affect?

Answer 17

Dietary fiber is the major source of ‘food’ for our gut microbes, which can determine our health status and risk to diseases

It is important to maintain a diversity of good gut microbes by choosing from a variety of fiber-rich food