Food technology

Question 1

How long does it take bacillus cereus to incubate and what does it cause?

Answer 1

Emetic toxin: 1-5 hours causes vomiting for 24h (Rice and pasta)
Diarrhoeal toxin: 8-16h and causes V&D for 24h (meat, sauce)

Question 2

How long does it take campylobacter spp to incubate and what does it cause?

Answer 2

2-5d
Diahorrea
Raw milk, chicken

Question 3

How long does it take clostridium perfringens to incubate and what can cause it?

Answer 3

12-18h

cooked meats

Question 4

How long does it take salmonella to incubate and what can cause it?

Answer 4

12-72h

Meat, eggs and dairy

Question 5

How long does it take staphylococcus aureus to incubate and what can cause it?

Answer 5

2-4h

Any food handled by a carrier

Question 6

What are the intrinsic properties of food that affect microbial growth?

Answer 6

Nutrient content of the food
Natural antimicrobials
pH and its ability to resist a pH change
The oxidation/reduction potential (Eh) of the food
Water activity of the food (aw)

Question 7

Name some natural antimicrobial substances

Answer 7

Milk: lactoferrin, conglutinin, lactoperoxidase
Eggs: Lysozyme

Question 8

What is oxidation and reduction?

Answer 8

Oxidation - loss of an electron

Reduction- gain

Question 9

Eh is dependent on ………

Answer 9

pH

Question 10

What is Eh’

Answer 10

Eh if pH is 7.0

Question 11

What water activity do most bacteria grow at?

Answer 11

Over 0.8

Question 12

What temperatures do psychotrophs grow at?

Answer 12

Grow well at or below 7’C

Optimum between 20-30’C

Question 13

What temperature do psycrophiles grow at?

Answer 13

Optimum 15’C or lower

Question 14

What temperature do mesophiles grow at?

Answer 14

Grow well between 20-45’C

Optimum between 30-40”C

Question 15

What temperature do thermophiles grow at?

Answer 15

Grow well at and above 45’C

Optimum between 55’C and 65”C

Question 16

What is the d value?

Answer 16

The time taken for the population to pass through a log cycle (where 90% of the population is killed) at a certain temperature

Question 17

Thermal processing of 1D causes a ……. death of the population.
2D? 3D?

Answer 17

90%
99%
99.9%

Question 18

What is the Z value?

Answer 18

The temperature change that is required to change the D value by a factor of 10

Question 19

What gasses can be added to packaging to prevent microbial growth?

Answer 19

CO2: MAP
Ozone: But not in high lipid foods as can cause rancidity as it is a strong oxidising agent

Question 20

What are organoleptic changes?

Answer 20

Changes in the food taste/texture/appearance due to the growth of microorganisms

Question 21

What are the chemical changes that can cause food spoilage?

Answer 21

Oxidation of fats - rancidity

Oxygenation of myoglobin that causes browning of meat , Mbo2 becomes MetMB (metmyoglobin)

Question 22

What is freezer burn?

Answer 22

Moisture leaving the food as it migrates the coldest part of the freezer, caused by poor packaging

Question 23

Why is nitrite added to fermented sausages?

Answer 23

It surpasses the natural gram -ve flora and promotes the growth of streptococci, micrococci, and lactobacilli that are present normally in meat

Prevents discolouration of the meat and oxidative rancidity

Question 24

Why is sugar added to fermented sausages?

Answer 24

Sugar content is x2 or x3 to give sufficient lactic acid production to reach pH 4.8

Question 25

What is the D value of botulinum at 121’C

Answer 25

0.21 minutes

So 12 x0.25 = 2.52 minutes is sterilisation time for canned foods

Question 26

Why does milk for yogurt need to be free from antibiotic residues?

Answer 26

Otherwise the flora of the yogurt cannot grow, the pH of the yogurt will not drop and it will not set