This set of Dairy Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Bacteria”.
1. Milk secreted in the udder is virtually sterile.
a) True
b) False
View Answer
Explanation: When milk is secreted in the udder it is virtually sterile. Milk, even before it leaves the udder it is infected by bacteria which enter through the teat channel.
2. Which of the following is not a source of infection in milk?
a) Milker and cow
b) Litter
c) Ambient air
d) Heat
View Answer
Explanation: When cows are milked by hand, bacteria can get into the milk via the milker, the cow, the litter and the ambient air. Hence, milker and cow are primary source of infection.
3. Which of the following is the characteristic of good quality milk?
a) CFU<1000000 per ml
b) CFU>1000000 per ml
c) CFU=1000000 per ml
d) CFU>1500000 per ml
View Answer
Explanation: CFU is Colony Forming Units. For milk to be classed as top quality, the bacteria count, the CFU, should be less than 100 000 per ml.
4. Lactic acid bacteria ferment which of the following forming lactic acid?
a) Sucrose
b) Glucose
c) Lactose
d) Fructose
View Answer
Explanation: Lactic acid bacteria prefer lactose as a source of carbon. They ferment lactose to lactic acid.
5. Which among the following is not a bacterial group which occurs in milk?
a) Lactic acid bacteria
b) Coliform bacteria
c) Putrefaction bacteria
d) Carboxylic acid bacteria
View Answer
Explanation: The groups of bacteria which occur in milk can be divided into lactic acid bacteria, coliform bacteria, butyric acid bacteria, propionic acid bacteria and putrefaction bacteria.
6. Which bacteria is responsible for ripening Emmenthal cheese?
a) Lactobacillus helveticus and Lb. bulgaricus
b) L.acidophilus
c) Bifidobacteria
d) Streptococcus diacetylactis
View Answer
Explanation: Lactobacillus helveticus and Lb. bulgaricus are the bacilli responsible for ripening Emmenthal cheese. They are added to cheese milk as a pure culture together with Str. thermophilus.
7. Coliform bacteria leads to _________
a) Off-flavor and smell
b) Gas formation
c) Off-flavor, smell and gas formation
d) Fruity taste
View Answer
Explanation: Coliform bacteria can cause serious trouble in cheese making. Besides causing off flavor, the relatively strong gas formation will result in an unwanted texture.
8. Presence of coliform in milk pipelines after pasteurization indicates __________
a) Excessive hygiene
b) Poor sanitation
c) Rusting
d) Coating
View Answer
Explanation: Coliform bacteria are found in milk and pipelines after the pasteurizer, this is a sign of reinfection. It indicates that cleaning and disinfection routines need to be improved.
9. Which bacteria are also known as “The cheese destroyer”?
a) Propionic acid bacteria
b) Coliform
c) Lactic acid bacteria
d) Butyric acid bacteria
View Answer
Explanation: Clostridium tyrobutyricum and Clostridium butyricum are both butyric acid bacteria also known as “cheese Destroyers”.They are responsible for spoilage of cheese.
10. Non bacterial ropiness or sliminess in milk and milk products may be due which of the following reasons?
a) Stringiness due to mastitis and in particular by fibrin and leucocytes from the cow’s blood
b) Sliminess resulting from the thickness of the cream
c) Stringiness due to thin films of casein or lactalbumin during cooling
d) Cleanliness
View Answer
Explanation: Stringiness due to mastitis and in particular by fibrin and leucocytes from the cow’s blood; sliminess resulting from the thickness of the cream and Stringiness due to thin films of casein or lactalbumin during cooling may contribute to non bacterial ropiness in milk.
11. The yoghurt is made from ________
a) Lactobacillus bulgaricus
b) Streptococcus thermophilus
c) S. cremoris
d) Mixed culture of Lactobacillus bulgaricus and Streptococcus thermophilus
View Answer
Explanation: Yogurt is a cultured milk product. It is made from Lactobacillus bulgaricus and Streptococcus thermophilus.
12. Cheese cancer of Swiss and similar cheese is caused by?
a) Oospora Crustacea
b) Oospora caseovorans
c) Oospora aurianticum
d) S. cremoris
View Answer
Explanation: Oospora caseovorans spoils swiss cheese and is hence responsible for cheese cancer. These organisms spoil the cheese.
13. Bacteria which cause diseases in humans, animals and plants are called __________
a) Anaerobic bacteria
b) Aerobic bacteria
c) Pathogenic bacteria
d) Non pathogenic bacteria
View Answer
Explanation: Organisms which produce diseases are called pathogenic bacteria. These organisms bring about disease in human beings, animals and plants by attacking and breaking down living cells and producing poisonous substances.
14. What is pigment or color production by bacteria called?
a) Cytogenesis
b) Phytogenesis
c) Chromogenesis
d) Chemogenesis
View Answer
Explanation: The process of color production is called chromogenesis. The organism causing the production is referred to as chromogenic.
15. Which of the following species of Clostridium is responsible for the formation of dark green to black colors in cheese?
a) Clostridium tyrobutyricum
b) Clostridium sporogenes
c) Clostridium herbarum
d) None of the mentioned
View Answer
Explanation: Clostridium herbarum gives the dark green to black color in cheese. It is one of the species of clostridium.
Sanfoundry Global Education & Learning Series – Dairy Engineering.
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