Food Microbiology

Front 1

What is the difference between natural and artificial contamination?

Back 1

When micro-organisms are present in food, it is contaminated. The contamination can be natural, if the microbia are attached to foods growing in the field,(yeasts on the skins of grapes).
Artificial, if it occurs as a consequence of handling or processing the food.

Front 2

Is milk easily contaminated?

Back 2

Milk is an excellent growth medium for microbia. Most milk and dairy products are pasteurized for 30 min/62C(holding method)or 15-17 sec/72C(flash method). These methods usually kill all pathogens in milk or dairy products, with particular attention to the organisms that cause Tbc and Q fever, since these are among the most heat resistant bacteria known.

Front 3

What are some dairy products produced by the natural fermentation of milk?

Back 3

The natural fermentation of milk yields fermented milk products that fall into 2 classes; fermented milk and cheeses.

Front 4

What is meant by fermented milk?

Back 4

Fermented milks include buttermilk, in which strains of Strep. lactis have produced acid from the CHO. Sour cream is another product, in which strptococci produce acid to make the cream sour.
Yogurt is another form of fermented milk. Here, species of lactobacillus and Streptococcus ferment the components of milk and produce a custardlike sourlike milk product rich in bacteria.

Front 5

What cheeses can be produced from fermented milk?

Back 5

Cheese products are produced from casein, the protein of milk. The casein is either precipitated either by bacterial action or by the enzyme rennet added to the milk. The precipitated protein is unripened cheese, such as cottage cheese or pot cheese. Further growth of microorganisms in the milk curds produces ripened cheeses. Examples would be hard cheeses like cheddar, American and Swiss(holes in the Swiss cheese are due to gas holes produced by growing microorganisms. Soft ripened cheeses are Camembert and bleu cheese. Bleu cheese is produced by the growth of penicillium species in the milk curd.

Front 6

Which microorganisms are involved in the pickiling process of food production?

Back 6

Here microorganisms grow and ferment the food in a salty environment while producing large amounts of acid from available CHO. Species of Leuconostoc and Lactobacillus are commonly used in this process.

Front 7

How is sourkraut produced?

Back 7

Cabbage is grated and salted, and allowed to ferment naturally(bacteria are already present among the leaves).

Front 8

How are pickled cucumbers produced?

Back 8

Salt is added to fresh cucumbers and the naturally occurring bacteria ferment the vegetable CHO over a period of weeks. Different spices are added.

Front 9

What are the sources of contamination in meat and fish products?

Back 9

Contaminations usually affect only the surface of the meat, but fish tissues may be affected on their skin and in their deeper tissues, because the tissues are fairly loose.
Meat is more easily contaminated when it is ground for hamburger or sausage because the chopped meat has many air pockets contaminated with bacteria formerly on the surface.

Front 10

Because canned food is held for long periods of time, the potential for food spoilage is high if the food contents have not been sterilized. TRUE/FALSE

Back 10

TRUE.

Front 11

Gas spoilage is produced by primarily by species of the genus Clostridium. TRUE/FALSE

Back 11

TRUE. Flat sour spoilage is due to members of the genus Bacillus. Acid spoilage may be produced by acid producing organisms such as lactobacilli, or from the foods acid reacting with the metal of the can.

Front 12

How is temperature regulation used for food preservation?

Back 12

The refrigerator or the freezer can be used to preserve the food by reducing the metabolism and enzyme activity going on in the microorganisms.

Front 13

At refrigerator temperatures of 4-8C, fresh vegetables can be preserved, and leftovers and dairy products can be held free of excessive spoilage. TRUE/FALSE

Back 13

TRUE. Freezer burn is a type of dehydration.

Front 14

Which chemicals are used in the food preservation process?

Back 14

Salt, has been widely used as a preservative because it draws water out of foods by osmosis.
Sugaring and smoking meats are other time honored practices. Smoking deposits chemical preservatives in foods and dehydrates them.
Sodium proprionate is used for breads and bakery products. Benzoic acid is used for soft drinks. Sulfur dioxide is used for certain fruits and vegetables and sorbic acid for jams, jellies and a number of other foods.