Question

92. Which is wrong about preservation of foods by using salts and sugars?  

A. works by creating a hypertonic environment

B. prevents the growth of Gram negative bacteria better than Gram positive bacteria.

C. leads to plasmolysis of bacteria

D. sugars are more effective than salts in disrupting the osmotic pressure in the bacterial environment

93. Which of the following methods will not sterilize?      

A. Ethylene oxide for 1 to 6 hours                                                                                                                                                                                             

B. Dry heat at 171˚C for 1 to 2 hours                                                                                                                         

C. 121˚C at 15 lb/in pressure for 15 to 20 minutes                                                                                        

D. 100˚C boiling water for 30 minutes                                                                                                                    

94. Which of the following is bactericidal?                                                                                                                         

A. membrane filtration          

B. Ionizing radiation                                                                                                

C. Freeze-drying                        

D. Deep freezing  

Answer 1

92.Ans. Sugars are more effective than salts in disrupting the osmotic pressure in the bacterial environment.

Explaination: Salts produce ions in aqueous medium by dissociation into its constituent ions. But sugars do not produce ions and hence per mole effectiveness (degree of dissociation) is more in salts than sugars. Hence, salts are more effective in disrupting the osmotic pressure in bacterial environment.

93.Ans. 100°C boiling water for 30 minutes

Explaination: Some bacterial and fungal spores are able to tolerate 100°C temperature and hence do not get killed at this temperature. Hence, boiling at 100°C is not an effective method of sterilization.

94.Ans. ionizing radiation

Explaination: Bactericidal agents kill bacteria unlike bacteriostatic which inhibit growth of bacteria. Ionizing radiation kills bacteria by disrupting DNA; for example UV radiation used in laminar flow is to kill bacterial spores.