This set of Food Microbiology Multiple Choice Questions & Answers (MCQs) focuses on “Microorganisms Growth Factors – pH”.
1. The pH of egg white increases up to 9.2 due to the loss of ____
a) CO2
b) N2
c) O3
d) SO2
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Explanation: Carbon dioxide is acidic in nature and it diffuses through the pores in the egg shells. Increase in pH also depends on the carbonate and bicarbonate ions whose concentrations are determined by the partial pressure of carbon dioxide in the atmosphere. Oiling the eggs prevents the diffusion of CO2, thereby making it less alkaline.
2. Fermented _____ is called Hákarl and is a famous dish from Iceland.
a) Lobster
b) Oyster
c) Seaweed
d) Shark
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Explanation: Fermented shark is one of the very rare alkaline dishes. It has a pH of about 10-12 and has a very high ammonia content. The shark meat is poisonous when fresh as it contains large amounts of urea and trimethylamine oxide, but it can be consumed after fermentation.
3. Under chill conditions, meat survives for a longer period than fish.
a) True
b) False
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Explanation: Microbes such as Shewanella are able to spoil fish but not meat because they are pH sensitive (pH<6.0). The pH value of meat (5.2-5.6) is lower as compared to that of fish (6.2-6.5). This contributes to the longer storage period of meat.
4. Soft drinks contain _____ acid.
a) Hydrochloric
b) Sulfurous
c) Phosphoric
d) Nitric
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Explanation: Phosphoric acid (H3PO4) is used to give soft drinks a sharp taste. It is also added as a preservative to lessen the growth rate of microbes.
5. What is one factor due to which microbes can be inhibited by weak acids?
a) Temperature of the acid
b) Concentration of undissociated acid
c) Inorganic or organic acid
d) Volume of acid
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Explanation: Weak acids undergo partial dissociation. Strong acids do have an effect on the pH proportionally, but they are less effective as compared to weak lipophilic acids at the given pH. This is due to the fact that microbes are inhibited not only by the high extracellular proton concentration but also due to the concentration of undissociated acid.
6. Which one of the following is a high-acid food item?
a) Avocados
b) Tofu
c) Potato
d) Blueberries
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Explanation: Blueberries have a pH of approximately 3.1-3.4. The main acid found in them is citric acid which is about 77-87% of all the acids present in the fruit. Blueberries also contain succinic and tartaric acids among others.
7. After Rigor Mortis sets in after the death of an animal, the usual 1% _________ is converted to lactic acid.
a) Glycogen
b) Starch
c) Cholesterol
d) Cellulose
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Explanation: After death, respiration stops and the body starts producing ATP via anaerobic glycolysis due to shortage of oxygen. Hence, as the glycogen depletes, lactic acid is formed due to anaerobic glycolysis.
8. Gram-negative bacteria are more sensitive to low pH than Gram-positive bacteria.
a) True
b) False
View Answer
Explanation: Gram-negative and Gram-positive bacteria have different reactions to low pH because of their different characteristics. The main difference is the structure of the cell wall. Gram-negative bacteria have thinner outer layers as compared to Gram-positive.
Sanfoundry Global Education & Learning Series – Food Microbiology.
To practice all areas of Food Microbiology, here is complete set of Multiple Choice Questions and Answers.
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