Lecture 3: Food consumption & food chemistry

Question 1

What are phospholipids?

Answer 1

Contain only two fatty acids esterified to glycerol and instead of the third, a polar group containing phosphoric acid and a nitrogen group

Question 2

What is the most common Emulsifier?

Answer 2

Phospholipids.

Question 3

What are the other components of Lipids?

Answer 3

Sterols (cholesterol)
Tochopherols
Vitamins
pigments

Question 4

What is the role of lipids in food?

5 things

Answer 4

1. Nutrients:
   - Sourse of essential fatty acids
   - Add caloric density and provide satiety
2. Carries flavors and fat soluble vitamins
3. Contribute to texture and mouthfeel
4. Heat transfer medium (frying)
5. Emulsifiers

Question 5

What are the undesired reactions in fats?

Answer 5

Fats can be a source of an off-flavour when degeneration occurs (oxidation & rancidity)

Question 6

What is Hydrolytic rancidity?

Answer 6

Free fatty acids are liberated when fat and water interact

Question 7

What is a Oxidative rancidity?

Answer 7

A biochemical reaction between fats and oxygen in which:

• long fatty acid chains degrade
• Shorter chain fatty acid are released which are odorous.

Question 8

What is added to foods to prevent oxidation?

Answer 8

Antioxidants such as 
BHT
BHA
Vit C
Vit E

Question 9

How much water is in Lettuce, Watermelon, and raw hamburger?

Answer 9

Lettuce: 96%
Watermelon: 93%
Raw Hamburger: 54%

Question 10

What is the first major function of water in food?

Answer 10

Flavors, Vitamins, minerals may be dissolved in water in foods

Question 11

What is the second major function of water in food?

Answer 11

Moisture provides lubrication for mastication and swallowing

Question 12

What is the thrid major function of water in foods?

Answer 12

Influences texture of fruits and vegetables and tenderness of meat.

Question 13

What is the fourth function of water in foods?

Answer 13

Facilitates heat transfer through foods during processing

Question 14

What is the fifth major function of water in foods?

Answer 14

Supports growth of spoilage and pathogenic micros.

Question 15

Is all of the water in a food available for microbes?

Answer 15

No, only some water is free, as water may be tied up by chemical constituents such as salt.

Question 16

Why can Salted Cod be left un-refrigerate while polish sausage has to be refrigerated dispate the fact that they have the same moisture content

Answer 16

Salted Cod is 14% salt and thus the water is chemically tied up.

Question 17

What is water activity?

Answer 17

Water activity is a dimensionless ratio

in food

Question 18

when a(w) is close to 0 there is ____ moisture available

Answer 18

little

Question 19

When a(w) is close to 1.0 there is _________ moisture available.

Answer 19

Lots

Question 20

The higher the a(w) the higher the amount of _____ water to interact with microorganisms and take part in chemical deteriorative reactions

Answer 20

free

Question 21

a(w) less than 0.6 you should see no __________&________ growth

Answer 21

Microbial & Bacterial

Question 22

a(w) less than 0.9 you should see no ________ growth

Answer 22

bacterial growth

Question 23

Pw is known because of the relationship between _______ & ________

Answer 23

Temperature and water

Question 24

What is a Water Sorption isotherm?

Answer 24

it is used to predict reactions in foods based on a foods water activity.

Question 25

True or false:

Each food has its own water sorption isotherm

Answer 25

True

Question 26

What are the characteristic of foods with an a(w) of 0.25 or less?

Answer 26

Moisture content: low

Textural attributes: dry, crips

Stability levels: High

Question 27

What are the characteristics of food with an a(w) of 0.50 -0.75?

Answer 27

Moisture content: Intermediate

Textural attributes: chewy, moist

Stability levels: intermediate stability

Question 28

What are the characteristics of food with an a(w) of 0.75-1.0

Answer 28

Moisture content: high

Textural attributes: soft, juicy

Stability levels:
Fresh - low
processed - high stability

Question 29

How do you reduce a(w) in foods?

Answer 29

addition of salts and sugars, as small compounds tie up moisture.

Question 30

What is the secound most common way to reduce the a(w) of foods?

Answer 30

concentration
Evaporation
Dehydration processes

Question 31

Can fresh water be removed from foods? how or how not?

Answer 31

Yes it can be removed rather easily

it is removed through squeezing, cutting, and pressing

Question 32

Can bound water be removed from foods? how or how not?

Answer 32

No it cannot be remove from foods easily.

it is not free to act as a solvent for molecules, although it can be frozen at very low temperatures.

Question 33

What is the application of a(w)?

Answer 33

Food scientists use it to predict reactions in foods based on food’s water activity.