Food technology Flashcards
How long does it take bacillus cereus to incubate and what does it cause?
Emetic toxin: 1-5 hours causes vomiting for 24h (Rice and pasta)
Diarrhoeal toxin: 8-16h and causes V&D for 24h (meat, sauce)
How long does it take campylobacter spp to incubate and what does it cause?
2-5d
Diahorrea
Raw milk, chicken
How long does it take clostridium perfringens to incubate and what can cause it?
12-18h
cooked meats
How long does it take salmonella to incubate and what can cause it?
12-72h
Meat, eggs and dairy
How long does it take staphylococcus aureus to incubate and what can cause it?
2-4h
Any food handled by a carrier
What are the intrinsic properties of food that affect microbial growth?
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)
Name some natural antimicrobial substances
Milk: lactoferrin, conglutinin, lactoperoxidase
Eggs: Lysozyme
What is oxidation and reduction?
Oxidation - loss of an electron
Reduction- gain
Eh is dependent on ………
pH
What is Eh’
Eh if pH is 7.0
What water activity do most bacteria grow at?
Over 0.8
What temperatures do psychotrophs grow at?
Grow well at or below 7’C
Optimum between 20-30’C
What temperature do psycrophiles grow at?
Optimum 15’C or lower
What temperature do mesophiles grow at?
Grow well between 20-45’C
Optimum between 30-40”C
What temperature do thermophiles grow at?
Grow well at and above 45’C
Optimum between 55’C and 65”C
What is the d value?
The time taken for the population to pass through a log cycle (where 90% of the population is killed) at a certain temperature
Thermal processing of 1D causes a ……. death of the population.
2D? 3D?
90%
99%
99.9%
What is the Z value?
The temperature change that is required to change the D value by a factor of 10
What gasses can be added to packaging to prevent microbial growth?
CO2: MAP
Ozone: But not in high lipid foods as can cause rancidity as it is a strong oxidising agent
What are organoleptic changes?
Changes in the food taste/texture/appearance due to the growth of microorganisms
What are the chemical changes that can cause food spoilage?
Oxidation of fats - rancidity
Oxygenation of myoglobin that causes browning of meat , Mbo2 becomes MetMB (metmyoglobin)
What is freezer burn?
Moisture leaving the food as it migrates the coldest part of the freezer, caused by poor packaging
Why is nitrite added to fermented sausages?
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
Why is sugar added to fermented sausages?
Sugar content is x2 or x3 to give sufficient lactic acid production to reach pH 4.8
