Microbial Spoilage Part 2

Question 1

Why is milk a great growth media for bacteria?

Answer 1

• High water content
• Near-neutral pH
• Available nutrients

Question 2

Milk has a low amount of available __________

Answer 2

amino acids

Question 3

Several milk spoilage bacteria can rely on __________ or ________ for energy generation

Answer 3

proteolysis and lipolysis

Question 4

What is the most common carbon source for bacterial spoilage in milk?

Answer 4

Lactose

Question 5

What is the main source of nitrogen for bacterial growth?

Answer 5

caseins proteins

Question 6

Major inhibitors of microbial growth in milk are __________ and ____________

Answer 6

lactoferrin and lactoperoxidase

Question 7

How does lactoferrin limit bacterial growth?

Answer 7

Lactoferrin binds iron, making iron a limiting factor for bacterial growth in milk. Lactoferrin is of great importance in limiting bacterial growth in human milk, which is low in citrate. However, there is more citrate cow’s milk. Citrate binds iron, which limits the ability of the lactoferrin to limit bacterial growth

Question 8

How does lactoperoxidase limit bacterial growth?

Answer 8

The lactoperoxidase system is the most effective microbial inhibitor in cow’s milk. Lactoperoxidase survives pasteurization. It catalyzes the oxidation of thiocyanate (when hydrogen peroxide is present) and in the process creates hypothiocyanite, which is a highly reactive oxidant, and is antimicrobial

Question 9

Psychrotrophic bacteria that spoil both raw and pasteurized milk are generally ___________

Answer 9

aerobic Gram-negative rods

Question 10

The bacteria most associated with milk spoilage ___________ are unable to ferment lactose

Answer 10

Pseudomonas sp

Question 11

When does milk spoilage by LAB occur ?

Answer 11

when the milk is temperature abused, and is stored at temperatures sufficiently high for Gram-positive acid-producers to outgrow psychrotrophic bacteria

Question 12

TRUE OR FALSE: dairy products almost always use starter cultures

Answer 12

TRUE

Question 13

_______ is produced by plants, and increases produce maturity

Answer 13

Ethylene

Question 14

The main limitation preventing the growth of bacteria in fruits and vegetables is ___________________

Answer 14

the pH (as low as pH 2.0 in some citrus fruits)

Question 15

How are nuts preserved?

Answer 15

By lowering the water activity to below 0.7

Question 16

Most nut spoilage is independent of microbiology and is caused by ____________

Answer 16

oxidation of the nut fats

Question 17

Peanuts are ground nuts or tree nuts

Answer 17

ground nuts

Question 18

___________is a ubiquitous invader, and production of mycotoxin is a major issue

Answer 18

Aspergillus Flavus

Question 19

Microbiological contamination of cereal grains occurs when…..

Answer 19

the grains are growing

Question 20

What interventions limit the growth of microbes in cereal grains?

Answer 20

drying and good storage practices