Final answer:
Jams and dried meats do not require refrigeration due to low water activity caused by high sugar or salt concentrations. Correct option is (D).
Step-by-step explanation:
The reason jams and dried meats often do not require refrigeration to prevent spoilage is due to the low water activity in these foods. By adding high concentrations of salts or sugars to jams and dried meats, the water activity of the microbial cells is drastically reduced.
This creates a hypertonic environment where water is drawn out of the cells, depriving microorganisms of the necessary moisture for growth and survival. As a result, these foods become inhospitable to most microorganisms, preventing spoilage.
This low water activity is achieved through the addition of large amounts of solutes such as salt or sugar, which create a hypertonic environment through osmotic pressure. This pressure effectively draws water out of microbial cells, preventing their growth and thus spoilage.
In jams, for instance, the high sugar concentration causes any bacteria not killed during cooking to become dehydrated, stopping multiplication in a medium that would otherwise promote bacterial growth. Similarly, in dried meats, the high salt concentration has a preserving effect by inhibiting bacterial growth through the same osmotic principle.