5. Microbiology of food

Question 1

What is the ugly, the bad and the good of foods

Answer 1

The ugly: pathogenes, food borne outbreaks.

The bad -quality: bad smell and taste, consumer confidence.

The good: fermentation, protective cultures, probiotics.

Question 2

What are the method for best before - use by (4)

Answer 2

1) Based on intrinsic properties of foodstuff
2) Define: risk and quality parameters
3) Check out: predictive microbiology and shelf life studies.
4) Limiting factor? Risk (use by), quality (best before)

Question 3

Give examples of what growth can cause.

Answer 3

The digestion of raw material and the product may cause: formation of organic acids, enzymes, alcohols. Formation of volatile compounds-unwanted odour. Unappetizing slimy food. Gas production-blown packaging, explosion risk. Deterioration in nutritional value. Colour changes.

Question 4

Name sources (3) for microorganism as agents for food spoilages.

Answer 4

Natural flora (microbiota) of food material.

Microbiota introduced by processing and handling.

Contamination from atmosphere, soil and water.

Question 5

What is some EXTRINSIC, IMPLICIT, INTRINSIC AND PROCESSING factors affecting food.

Answer 5

Extrinsic factors: Temperature, humidity, atmosphere (gaseous environment).

Implicit factors: specific growth rate, mutualism, antagonism, commensalism.

Intrinsic factors: nutrient, pH and buffering capacity, redox potential, water activity (aw), antimicrobial compounds.

Processing factors: Slicing, washing, packing, irradiation, pasteurization.

Question 6

Describe aerobes and anaerobes

Answer 6

Aerobs:
obligate: require O2 faculative: Not required
Microerophilic: low
levels

Anaerobs:
Aerotolerant: not require
Obligate: O2 haemful

Question 7

Describe harmful deterioration of fresh fish.

Answer 7

Is rapid. Unwanted odors due to formation of TMA (trimethylamine) Fish meat easily into/are eaily digested. Fish bacteria are psychotropic and thrive in cols. Low content of glycogen high pH ~6.5. Low temperature very important.

Question 8

Describe the use of lactobacillus

Answer 8

Increased storage stability, smell, taste and texture changes.

Ex of lactic acid producers: Lactobacillus, streptococcus, Lactococcus, leuconostoc. +Starterculture. Carbohydrates metabolized to lactic acid (pH 3.5-5.5).

Question 9

Describe spores.

Answer 9

spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, fungi and protozoa.[1] Bacterial spores are not part of a sexual cycle but are resistant structures used for survival under unfavourable conditions.

Withstands: high T, freeze dry, extreme pH…

Question 10

What is the D-value ?

Answer 10

What is D-value? The time(min) it takes at a certain temperature to kill 90% (1 log) of bacteria

Question 11

What is the Z-value?

Answer 11

What is Z-value? The change of temperature required to change D-value to a tenth.

Question 12

What is bacillus subtilis causing?

Answer 12

Bacillus subtilis dominates (b. pumilus, b licheniformis). Soil, plants parts, coarse flour, malt, yeast, gluten. 12-24 hours (10 miljons). Amylaze metabolize the inner part of the bread. Sweet fruity smell, sticky, discoloured giblets (EPS). Increased due to the reduced use of preservatives and increasing the involvement of “fibers”.

Question 13

What is chalk moulds?

Answer 13

“Chalk moulds”

Form flour or chalk like coatings on bread, fast growth (within a few days), visible growth before the smell (glue, acetone) is added. Can grow as mould with hypha (pseudomycel). Ex. Pichia (hyphopochia) burtonii, saccharomyces fibuligera, Saccharomycopsis fibibuligera.

Question 14

What are some factors affecting the shelf life?

Answer 14

Internal: pH, aw, antimicrobial substances.

External: hygiene, storage T, packining, logistic chain.

Question 15

Describe the criteria for microbiological in food.

Answer 15

Microorganism, toxin or metabolite. In which foods. Where in the food chain, it is to be applied. Maximum levels-limit. Sampling plan-sample size and sample size. Reference analysis method. Action if the criterion is exceeded. Food safety criteria and process hygiene criteria.

The criteria are divided into two categories – UNSAFE! UNFIT!
1. Food safety criteria -> with binding output product criteria for pathogens.

2. Process hygiene criteria -> which indicates flaws in the production process and which should lead to improvements in management.