Little knowledge of solar terms: Why is the first frost apple sweet?

The first frost is the last solar term in autumn. Every year around Gregorian calendar1October 23, the sun reaches 2 10 degrees of the yellow meridian, which is the solar term for the transition from autumn to winter. There is a lot of heat dissipation on the ground in autumn night, and the temperature drops below 10 degrees. In order to resist the cold, apples will convert starch into sugar, so that the cell fluid in apples is not easy to be destroyed, nor is it easy to be destroyed by frost. This is a way for plants to protect themselves and adapt to environmental changes. After the first frost, the starch in fruits and vegetables is hydrolyzed into maltase by amylase in plants, and then turned into glucose by maltose. Glucose is soluble in water and tastes sweet, so apples and vegetables taste sweet.