Microbial Control In Foods Flashcards Preview

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Flashcards in Microbial Control In Foods Deck (54):
1

Examples for biological control of microbial growth ?

Controlled acidification, bacteriocin, probiotics

2

Actions of microbial control agents

Alternation of membrane permeability
Damage to proteins
Damage to nucleic acids

3

Effectiveness of antimicrobial treatment depends on

Number of microbes
Environment
Time of exposure
Microbial characteristics

4

Heat treatments used commercially

Blanching
Pasteurization

5

What is blanching

Briefly pass through boiling water

6

Does pasteurization kill all the pathogens

No

7

Pasteurization -----pathogens
Kill ?
Inactivates ?

Inactivates

8

What is the major site of sub-lethal heat induced injury

Cell membranes

9

Destruction of a pure culture , by moist heat at a constant temperature, results in...

Negative exponential kinetics

10

Bacterial death is

Logarithmic

11

D value aka

Decimal reduction time

12

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

13

1 log reduction means

90% reduction,
10% survival

14

When D value is higher the survivor curve

Is flatter because it takes longer to have 1 log reduction

15

D values are ---- specific

Process
Temperature

16

Z value

Temperature change to result in a 10 fold change in the D value

17

What is autoclave

Steam under pressure

18

Classic method of pasteurization

Milk was exposed to 65 C for 30 min

19

What is the pasteurization method used for milk today

High temperature short time pasteurization (HTST)

20

HTST

Milk is exposed to 72 C for 15 sec

21

Ultra high temperature pasteurization

Milk is treated at 140 C for 3 seconds and then cooled every quickly in a vacuum chamber

22

What is the advantage of milk pasteurization

Pasteurized milk can be stored at room temp for several months

23

Freezing

Temp below 0

24

Freezing can be divided to

Flash freezing
Slow freezing

25

Does flash freezing kill most bacteria

No

26

Why is slow freezing harmful

Ice crystals disrupt cell structure

27

What is lyophilization

Freeze drying

28

Advantage of sublimation

Texture will be less affected

29

What is an essential oil ?

Concentrated hydrophobic liquid containing volatile aroma compounds from plants

30

What kind of essential oils have antimicrobial effects on fresh produce

Clove
Basil
Lemongrass
Thyme

31

What is the effect of emulsifier on emulsion

Stabilize it

32

Why do we ferment foods

-Food preservation
-Change in organoleptic characteristics
-Money

33

Fermentation takes place in the presence or absence of oxygen

Absence

34

What are the major fermentation used

Lactic
Propionic
Ethanolic

35

Most important bacterial starter cultures

Lactate Acid Bacteria
LAB

36

Bacterial started cultures belong to 4 categories

Lactococcus
Streptococcus
Lactobacillus
Leuconostoc

37

How is yogurt produced

By the controlled fermentation of milk by 2 species of bacteria

38

What are the 2 species of bacteria that are used in making yogurt?

Lactobacillus bulgaricus
Streptococcus thermophilus

39

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

40

How does streptococcus thermophilus affect milk

Brings the PH down to 5.5

41

How does lactobacilluls Bulgaria help in making yogurt

It converts lactose to lactic acid

42

At the end of incubation pH may fall to as low as

4.2-4.4

43

-------coagulates the remaining milk proteins causing the yogurt to thicken

Lactic Acid

44

What gives raw yogurt its characteristic flavor ?

Acetaldehyde

45

What is bacteriostatic effect

Low temp Reduces metabolic rate of most microbes so they cannot reproduce or produce toxins

46

What is fermentation ?

Any partial breakdown of carbohydrates taking place in the absence of oxygen

47

How is acetalehye produce

It is a metabolic by product of both species

48

How long is the incubation of yogurt

12 hrs at 32 C

49

How does homogenization make pasteurized milk more stable ?

It makes fat globule smaller

50

What is the liquid portion of milk called after treatment with rennin

Whey

51

Where do they obtain rennin from

From the stomach of young calves

52

What does rennin do

It causes the milk protein ( casein ) to clabber

53

In Cheese making milk is treated with what bacteria

Lactic acid bacteria and enzyme called Rennin

54

Before being sold and eaten, the cheese must age how long ?

From 60 days to several years