This set of Fruits Processing Multiple Choice Questions & Answers (MCQs) focuses on “Enzymatic Browning of Fruits”.
1. What factors affect enzymatic browning?
a) Phenolic compounds
b) Temperature
c) pH
d) Phenolic compounds, temperature and pH
View Answer
Explanation: The most important factors that determine the rate of enzymatic browning of vegetables and fruits are the concentration of active polyphenol oxidase and phenolic compounds present, the pH, the temperature and the oxygen availability of the tissue.
2. How does sugar slow enzymatic browning?
a) Reduce oxygen diffusion
b) Increase the oxygen diffusion
c) Reduce carbon dioxide diffusion
d) Increase carbon dioxide diffusion
View Answer
Explanation: The enzymatic browning can be stopped by decreasing the oxidation of poly phenol oxidase. It can also be achieved by lowering the availability of the substrate to which the enzyme can bind. Coating, dipping and brushing in sugar or syrup reduces oxygen diffusion. Therefore it slows the browning reaction.
3. How does salt water prevent enzymatic browning?
a) Inhibit the polyphenol oxidase
b) Activates the polyphenol oxidase
c) Reduce carbon dioxide diffusion
d) Increase carbon dioxide diffusion
View Answer
Explanation: The saltwater was the most effective in slowing the browning in fruits. This is due to the presences of chloride ions in the salt which inhibit the polyphenol oxidase (PPO) enzymes from working properly. The water cuts off the enzyme’s access to oxygen.
4. What is the purpose of enzymatic browning?
a) Ripening
b) Metabolism
c) Protein denaturation
d) Metabolism and protein denaturation
View Answer
Explanation: Different molecules are present in food which also includes enzymes. Enzymes act as biological catalysts. These are the distinctive protein which helps in speeding up chemical reactions. They can cause fruit to ripen and over-ripen, which gives the fruit a brown color.
5. Are these statements about the enzymatic browning true?
Statement 1: Pyrocatechol derivatives are one of the substrate for enzymatic browning.
Statement 2: Enzyme reacts with only air to cause brown discoloration.
a) True, False
b) True, True
c) False, True
d) False, False
View Answer
Explanation: Many natural substrates are involved in enzymatic browning. The most significant are pyrocatechol derivatives, benzoic acid and cinnamic acid derivatives, flavonoids and tannins. The enzyme reacts with both the air and other enzymes in the fruit to cause that brown discoloration.
6. Which of the following is used for measuring the enzymatic browning?
a) Browning indicators
b) Cellulose metabolism
c) Ethylene production
d) Protein denaturation
View Answer
Explanation: The enzymatic browning has been quantified using browning indicators through a biochemical index. For example, polyphenol oxidase activity or physical indicators, such as surface color. In the case of physical indicators based on color, CIE L*a*b* coordinates have been the most extensively used color space.
7. Does vinegar prevent oxidation?
a) True
b) False
View Answer
Explanation: Lemon juice, vinegar and clear soda prevents prevent food from browning reaction. The liquids mentioned are acidic in nature. This results in lower pH on the surface of the food. Salt wateror the brine solution will also help in slowing down the browning reactions in foods.
8. How to control enzymatic browning?
a) Prevention of oxygen exposure
b) Unclarified pectin
c) Use of low temperature
d) Thermal treatment, prevention of oxygen exposure, use of low temperature
View Answer
Explanation: It is very important to regulate and control the enzymatic browning. It can be done by physical and chemical methods. Some of them are heat treatment, using antioxidants, freezing and irradiation. Blanching is an important unit operation in fruit processing, where it inhibits the enzymatic activity.
9. At what pH range does poly phenol oxidase is activated?
a) 5-7
b) 3-5
c) 1-3
d) 4-5
View Answer
Explanation: Polyphenol oxidase acts as a catalyst to speed up the process. It occurs rapidly at warm temperatures when the pH is between 5.0 and 7.0. Polyphenol oxidase is a copper-containing enzyme that catalyzes or causes the oxidation of phenol compounds contained in plant tissues.
10. Which of the following is not used in preventing enzymatic browning?
a) Reducing agents
b) Chelating agents
c) Acidic agents
d) Basic agents
View Answer
Explanation: Reducing agents such as sulphiting agents, ascorbic acid, analogs, cysteine and glutathione are used for preventing browning reactions. Chelating agents such as phosphates, EDTA, organic acids are also used. Acidic agents such as citric acid and phosphoric acid are also preferred.
11. What is phenylalanine ammonia lyase?
a) Reducing agents
b) Chelating agents
c) Enzyme in phenolic biosynthesis
d) Basic agents
View Answer
Explanation: Phenylalanine ammonia lyase is the key enzyme in phenolic biosynthesis. Mechanical injury (wounding) and ethylene can stimulate phenolic metabolism. Phenolic compounds are substrates for poly phenol oxidase. The increased concentration of this enzyme stimulates browning.
Sanfoundry Global Education & Learning Series – Fruits Processing.
To practice all areas of Fruits Processing, here is complete set of 1000+ Multiple Choice Questions and Answers.
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