45. What is being described by \'water activity (Aw)\'\"? Would an Aw of 0.65 gr

Question

45. What is being described by 'water activity (Aw)'"? Would an Aw of 0.65 growth of most bacteria? Explain. (2 pts) 46. Answer one of the following questions [45a or 45b]. (1 pt) a) Rank the following detergents regarding their antimicrobial ability from the least effective to the most effective. cationic detergent nonionic detergent ? anionic detergent least effective most effective b) Why are ethyl and isopropyl alcohols the most common alcohols used as disinfectants in the laboratory? 47. Define Photoreactivation' and briefly discuss how the process works. (2 pts)

Explanation / Answer

45) Water activity is used in predicting the growth of bacteria, yeast, and mold. Water activity (aw) refers to the unbound water i.e., the water molecules that is not bound to the food molecules. It is described as the ratio between the vapor pressure of the solution (of solutes in water) to the vapor pressure of the solvent.

Growth of micro-organisms is greatly affected by the level of water activity in food. Inhibition of growth occurs if the water activity is less than the organism's minimum water activity that is neccessary for growth. Water activity of 0.65 means the vapor pressure is 60 percent of that of pure water and therefore will support the growth of osmophilic yeast. Bacteria requires high water activity of 0.85 - 1.00

46) a) Cationic detergents are the most effective detergents for antimicrobial activity. Ex- Quaternary ammonium compounds, ("quats") are bacteriostatic, fungistatic, and sporistatic. They are highly effective against gram-positive bacteria and moderately active against gram-negative bacteria.

Anionic detrgents are less effective than cationic detergents. Ex - Sodium lauryl sulfate

Non ionic detergents are least effective as they are neutral or carry no charge.

b)  They denature (bacterial) proteins so they are effective against microorganisms like bacteria, fungi, viruses. They work by oxidising bacterial protoplasm, coagulates or denatures proteins and dissolves lipid and disrupts cell membrane.

47) UV radiation mediated damage, pyrimidine dimeras, are repaired by a light dependent system termed as Photoreactivation. The process involves an enzyme, DNA photolyase. When stimulated by light with a wavelength between 300 and 500nm, the enzyme binds to pyrimidine dimers and converts them back to the original monomeric nucleotides

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