Microbial Control In Foods Flashcards
Examples for biological control of microbial growth ?
Controlled acidification, bacteriocin, probiotics
Actions of microbial control agents
Alternation of membrane permeability
Damage to proteins
Damage to nucleic acids
Effectiveness of antimicrobial treatment depends on
Number of microbes
Environment
Time of exposure
Microbial characteristics
Heat treatments used commercially
Blanching
Pasteurization
What is blanching
Briefly pass through boiling water
Does pasteurization kill all the pathogens
No
Pasteurization —–pathogens
Kill ?
Inactivates ?
Inactivates
What is the major site of sub-lethal heat induced injury
Cell membranes
Destruction of a pure culture , by moist heat at a constant temperature, results in…
Negative exponential kinetics
Bacterial death is
Logarithmic
D value aka
Decimal reduction time
What is D value ?
Time necessary at T to reduce the population by 90%
Or time necessary at T for the survivor curve to transfer one log cycle
1 log reduction means
90% reduction,
10% survival
When D value is higher the survivor curve
Is flatter because it takes longer to have 1 log reduction
D values are —- specific
Process
Temperature
Z value
Temperature change to result in a 10 fold change in the D value
What is autoclave
Steam under pressure
Classic method of pasteurization
Milk was exposed to 65 C for 30 min
What is the pasteurization method used for milk today
High temperature short time pasteurization (HTST)
HTST
Milk is exposed to 72 C for 15 sec
Ultra high temperature pasteurization
Milk is treated at 140 C for 3 seconds and then cooled every quickly in a vacuum chamber
What is the advantage of milk pasteurization
Pasteurized milk can be stored at room temp for several months
Freezing
Temp below 0
Freezing can be divided to
Flash freezing
Slow freezing
Does flash freezing kill most bacteria
No
Why is slow freezing harmful
Ice crystals disrupt cell structure
What is lyophilization
Freeze drying
Advantage of sublimation
Texture will be less affected
What is an essential oil ?
Concentrated hydrophobic liquid containing volatile aroma compounds from plants
What kind of essential oils have antimicrobial effects on fresh produce
Clove
Basil
Lemongrass
Thyme
What is the effect of emulsifier on emulsion
Stabilize it
Why do we ferment foods
- Food preservation
- Change in organoleptic characteristics
- Money
Fermentation takes place in the presence or absence of oxygen
Absence
What are the major fermentation used
Lactic
Propionic
Ethanolic
Most important bacterial starter cultures
Lactate Acid Bacteria
LAB
Bacterial started cultures belong to 4 categories
Lactococcus
Streptococcus
Lactobacillus
Leuconostoc
How is yogurt produced
By the controlled fermentation of milk by 2 species of bacteria
What are the 2 species of bacteria that are used in making yogurt?
Lactobacillus bulgaricus
Streptococcus thermophilus
How does curd form in yogurt ?
The sugar in milk called lactose is fermented to lactic acid and it is this that Caucasus the characteristic curd to form
How does streptococcus thermophilus affect milk
Brings the PH down to 5.5
How does lactobacilluls Bulgaria help in making yogurt
It converts lactose to lactic acid
At the end of incubation pH may fall to as low as
4.2-4.4
——-coagulates the remaining milk proteins causing the yogurt to thicken
Lactic Acid
What gives raw yogurt its characteristic flavor ?
Acetaldehyde
What is bacteriostatic effect
Low temp Reduces metabolic rate of most microbes so they cannot reproduce or produce toxins
What is fermentation ?
Any partial breakdown of carbohydrates taking place in the absence of oxygen
How is acetalehye produce
It is a metabolic by product of both species
How long is the incubation of yogurt
12 hrs at 32 C
How does homogenization make pasteurized milk more stable ?
It makes fat globule smaller
What is the liquid portion of milk called after treatment with rennin
Whey
Where do they obtain rennin from
From the stomach of young calves
What does rennin do
It causes the milk protein ( casein ) to clabber
In Cheese making milk is treated with what bacteria
Lactic acid bacteria and enzyme called Rennin
Before being sold and eaten, the cheese must age how long ?
From 60 days to several years
