This set of Food Microbiology Multiple Choice Questions & Answers (MCQs) focuses on “Fermented Dairy Products – Yogurt/Curd/Dahi”.
1. Although yogurt gets its flavor from acetaldehyde, lactate, diacetyl and acetate, _________ gives 90% of its flavor.
a) Acetaldehyde
b) Lactate
c) Diacetyl
d) Acetate
View Answer
Explanation: The cocci bacteria present in the yogurt starter are responsible for the majority of the initial acid production. The production takes place at a higher rate when 2 species of bacteria (rods and cocci) are mixed together. This also yields more acetaldehyde. This is what gives yogurt the sharp acidic and walnut-like taste.
2. According to Louis Pasteur’s discovery, which organism is responsible for souring of milk?
a) Salmonella
b) Lactobacillus
c) Escherichia coli
d) Rhizobium
View Answer
Explanation: Lactobacillus is a harmless bacterium that uses lactose (milk sugar) as an energy sources and synthesizes lactic acid as a by-product. Salmonella is a genus of bacteria that is harmful and causes typhoid, food poisoning, gastroenteritis etc. E. coli bacteria are found in the guts of peoples and animals. Rhizobium is a genus of nitrogen-fixing bacteria.
3. For the growth of species, fermentation is carried out at 316.3 K.
a) True
b) False
View Answer
Explanation: The above temperature is the optimum temperature for the balanced growth of both, Streptococcus and Lactobacillus. The acidic and flavor components are perfect when the growth is balanced. When the temperature is above 316.3 K, it facilitates the growth of Lactobacillus more than Streptococcus and this leads to more acid production and less flavor. When the temperature is below 316.3 K, it is vice versa and it leads to more flavor and less acid.
4. Heating milk helps to destabilize ______ for good gel formation.
a) Water
b) Lactic Acid
c) Lactose
d) Casein
View Answer
Explanation: Casein is the main protein found in milk. Destabilization of this protein helps in its coagulation. The coagulation is also caused by acids produced by the bacteria. The coagulation of proteins gives yogurt its thickened, creamy texture.
5. Acetaldehyde can be produced from glucose or from _______
a) Tyrosine
b) Valine
c) Threonine
d) Leucine
View Answer
Explanation: Streptococcus sp. help in the production of acetaldehyde from glucose via the pyruvate pathway. Lactobacillus sp. can help produce acetaldehyde from threonine. Threonine is the product of proteolysis in milk.
6. ____________ has the ability to polymerize glucose.
a) Formate lyase
b) β-galactosidase
c) Casein
d) Threonine
View Answer
Explanation: β-galactosidase is a constituent of some strains of Str. thermophilus. It has the ability to polymerize glucose to produce oligosaccharides and glycan. Glycan is the component that gives yogurt its viscous texture. This step can also be called Slime Formation.
7. The growth of Streptococcus and Lactobacillus is symbiotic in nature.
a) True
b) False
View Answer
Explanation: Initially there is rapid growth of the cocci in the presence of dissolved oxygen to produce formic acid and carbon dioxide. This provides anaerobic conditions for the growth of the bacilli which produce amino acids required for the growth of the cocci.
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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