Regulation of Sugar Metabolism in Apricots by Hexokinase and Fructokinase during Drying Process
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Abstract:
Using apricot fruits at the green ripe stage, variations in the sugar content and activities of hexokinase, fructokinase, and sucrose-metabolizing enzymes during natural drying and hot air drying processes were analyzed to understand the mechanisms of action of key enzymes in the regulation of sugar metabolism. The results showed that the fructose, glucose, and sucrose content changed from 33.52, 47.25, and 45.22% of the total soluble sugars in apricots before drying to about 9.70, 28.24, and 54.16% after drying, respectively. The content of fructose and glucose had significantly negative correlations with sucrose content. Therefore, the accumulation of sucrose in apricots during drying was mainly due to the conversion from hexose. The activities of sucrose cleavage enzymes [neutral invertase (NI), sucrose synthase (SSc), and acid invertase (AI)] were decreased during the drying process and were correlated positively with the content of fructose and glucose; NI and AI were the dominant cleavage enzymes. Sucrose synthesis enzymes [sucrose phosphate synthase (SPS) and sucrose synthase (SSs)] played a supplementary role in sucrose metabolism, and their activities were effectively enhanced by hot-air treatment at temperatures of 40~50 ℃, so that the sucrose content and the sucrose percentage of total soluble sugar were increased. Fructokinase and hexokinase activities were increased slightly during the early stage of the drying process, and high fructokinase and hexokinase activity could increase hexose consumption in the fruits, providing the basis for the accumulation of sucrose.
