RD - Commission on Dietetic Registration (CDR) Practice Test

Which food is preserved by lowering water activity through solute addition?

1. Canned corn

2. Sun-dried tomatoes

3. Frozen peas

4. Grape jelly

The correct answer is: Grape jelly

The preservation of food through lowering water activity primarily involves the addition of solutes, which reduce the availability of water for microbial growth and spoilage. In the case of grape jelly, the process of jelly-making typically includes the addition of a significant amount of sugar, which acts as a solute. This high concentration of sugar creates an environment that inhibits the growth of bacteria, yeast, and molds by binding to water molecules, effectively lowering the water activity in the product. While canned corn and frozen peas involve preservation methods like canning and freezing, which do not primarily rely on solute addition to lower water activity, sun-dried tomatoes do involve reducing the moisture content but mainly through dehydration rather than solute addition. The unique combination of high sugar levels and the preservation process in grape jelly decisively demonstrates the effective lowering of water activity through the intentional inclusion of solutes, making it the correct choice in this scenario.