Etiket Arşivleri: CLM 206

Food Chemistry Example Exam ( CLM206 )

CLM206  FOOD CHEMISTRY

1) Table sugar is which type of sugar?

  1. a) Fructose b) Galactose c) Glucose     (d) Sucrose

2) Please fill in the gaps in sentences below.

  • Attraction among water molecules is more than polar-polar in nature. The O atoms are small and very electronegative. As a result, the positive H atoms (protons) are very attractive to the negative O atoms of neighboring molecules. This O- – -H – O strong attraction is called a ………………………… (hydrogen bond).

  • …………………. reactions, ……………… changes, and ……………… growth may occur readily in foods with high water contents. (Chemical reactions, enzymatic changes, and microbial growth)

  • Proteins are polymers of ………….. which are made up of carbon, hydrogen, oxygen and nitrogen and some may also have sulfur. (amino acids)

  • When many amino acids bond together to create long chains, the structure is called a protein. It is also called a …………… because it contains many peptide bonds. (polypeptide)

  • ……………….. are the major class of dietary lipids including fats & oils which made up of 3 units known as fatty acids and 1 unit called glycerol. (Triglycerides)

  • The body can synthesize all of the fatty acids it needs from carbohydrates, fat or protein except for two: …………………………….….. and ……………………..………(Linoleic acid and Linolenic acid).

3) Why do cut apples, pears, bananas and potatoes turn brown?

Answer: Apples and other produce (e.g., pears, bananas, peaches, potatoes) contain an enzyme (called polyphenol oxidase or tyrosinase) that reacts with oxygen and iron-containing phenols that are also found in the apple. The oxidation reaction basically forms a sort of rust on the surface of the fruit. You see the browning when the fruit is cut or bruised because these actions damage the cells in the fruit, allowing oxygen in the air to react with the enzyme and other chemicals.

The reaction can be slowed or prevented by inactivating the enzyme with heat (cooking), reducing the pH on the surface of the fruit (by adding lemon juice or another acid), reducing the amount of available oxygen (by putting cut fruit under water or vacuum packing it), or by adding certain preservative chemicals (like sulfur dioxide). On the other hand, using cutlery that has some corrosion (as is seen with lower quality steel knives) can increase the rate and amount of the browning by making more iron salts available for the reaction.

4) How many types of browning reactions are there? Briefly define/explain them.

5)Which statement is true (T) or false (F)?

T: Denatured proteins have a greater tendency to aggregate.

F: Chemical reactions, enzymatic changes, and microbial growth may occur readily in foods with low water contents.

T: Rates of deteriorative changes and microbial growth at normal food storage conditions often depend on water content and water activity.

T: Amino acids contain carbon, hydrogen, nitrogen and sometimes sulfur and serve as the monomers to make peptides and proteins.

T: Unsaturated fatty acid is a fatty acid with one or more points of unsaturation. They are found in foods from both plants & animal sources.

T: Fat-soluble vitamins are more likely to be toxic to your health if taken in excess, because they are stored in the body, where as water-soluble are excreted.

F: More unsaturated a fat is the more solid it is at room temperature.

F: Starch is most common storage polysaccharide in plants and composed of 10–30% amylopectin and 70-90% a-amylose depending on the source.

F: Lactose (maltose) produced by the partial hydrolysis of starch (either salivary amylase or pancreatic amylase).

T: The functions of fat in food: provide calories (9 per gram), provide satiety, carry fat-soluble vitamins & essential fatty acids, contribute aroma & flavor.

T: Water is eaten, absorbed, transported, and utilized by cells.

F: Polysaccharides are large molecules that may consist of hundreds, or even thousands of amino acids.

T: Most carbohydrates are found naturally in bound form rather than as simple sugars.

T: Carbohydrates have an empirical formula CnH2nOn or (CH2O)n. Since this formula is essentially a combination of carbon and water.

T: Lipids include fats, oils, waxes, and cholesterol. In the body, fat serves as a source of energy, a thermal insulator, and a cushion around organs; and it is an important component of the cell. Since fats have 2.25 times the energy content of carbohydrates and proteins, most people try to limit their intake of dietary fat to avoid becoming overweight.

T: There are 20 amino acids found in the body. Eight of these are essential for adults and children, and nine are essential for infants. Essential means that we cannot synthesize them in large enough quantities for growth and repair of our bodies, and therefore, they must be included in our diet.

6) How many types of browning reactions are there? Briefly define/explain them.

Answer:

a.Enzymatic (polyphenoloxidase).

b.Caramelization.

c.Lipid Browning.

d.Vitamin C Browning.

e.THE MAILLARD REACTION

Briefly define/explain them.

7) What are the factors affecting the Maillard reaction?

Answer:

  1. Rapidly accelerated by temperature

  2. Significant acceleration at intermediate water activities

  3. Sugar type

Pentose>hexose>disaccharide>>polysaccharide

  1. Protein concentration (free amines)

  2. Inhibited by acid / amines are protonated and used up, pH drops

  3. Sulfur dioxide

8) Fill in the blank.

………………..is a phenomenon that involves transformation of a well-defined, folded structure of a protein, formed under physiological conditions, to an unfolded state under non-physiological conditions. (Denaturation)

……………….represents the ratio of the water vapor pressure of the food to the water vapor pressure of pure water under the same conditions (The water activity)

…………………..is a common phospholipids and often used as an emulsifier in foods such as margarine, chocolate & salad dressings. (Lecithin)

…..…………..are heteropolysaccharides found in the pulp of fruits (citrus, apples) and used as gelling agents (to make jellies) (Pectins)

…..……participate in biological transport, cell-cell recognition, activation of growth factors, modulation of the immune system. (Carbohydrates)

……..……maintains biological activities of proteins, nucleotides, and carbohydrates, and participates in hydrolyses, condensations, and chemical reactions that are vital for life. (Water)

…………commercially obtained from sugar cane or sugar beet. (Sucrose)

9) Describe the correlation between water activity and growth of microorganism in foods.

10) Explain the interaction mechanism of water with non-polar substances of foods.

11) Discuss the browning reactions of food. Explain the merits and demerits of these reactions.

12) Describe the general characteristics of auto-oxidation of lipids.

13) Differentiate between hydrolytic rancidity and oxidative rancidity.

14) Comment on safety of heated and oxidized fat.

15) What do you understand by denaturation of proteins. Explain its implications and name the physical and chemical agents causing denaturation of proteins.

16) Define aw. Explain the effect of temperature on aw. Discuss correlation between aw and stability of foods.

17) Explain the importance of hydrolysis reaction of carbohydrate in food industry.

18) Describe the structure function relationship of polysaccharides and their implications infoods.

19) Describe the emulsifying and foaming properties of food proteins.

20) What are the factors affecting the rate of autooxidation reaction?