Characterization of Carbohydrates and Their Metabolizing Enzymes Related to the Eating Quality of Postharvest Fresh Waxy Corn

Carbohydrates and their metabolizing enzymes related to sweetness and glutinosity were measured in the fresh waxy corn of "Zhongnuo 1" and "Jingkenuo 2000" cultivars during storage for 4 days at 20C. The contents of sugars decreased to a lesser degree in "Jingkenuo 2000" compared to those of "Zhongnuo 1," and both cultivars exhibited similar trends in starch content. The amylopectin and total starch contents both increased significantly and then gradually decreased, whereas the amylose content significantly increased. Furthermore, the activities of both uridine diphosphate glucose pyrophosphorylase (UGPase) and starch debranched enzyme exhibited a similar pattern with a single peak curve. The activities of adenosine diphosphate glucose pyrophosphorylase (AGPase) and soluble starch synthase decreased, whereas the activity of granule-bound starch synthase (GBSS) increased significantly. The activity of the starch-branching enzyme was mostly constant. Correlation analysis between carbohydrates and metabolizing enzymes indicates that UGPase, AGPase and GBSS may be important enzymes. Practical Applications Fresh waxy corn is widely eaten because of its sweetness and glutinosity, which are the eternal behaviors of related carbohydrate character. Contrary to other fruits and vegetables with high soluble sugar and water content, fresh waxy corn shows high starch content and low water content. Thus, the physiological basis for changes in eating quality may differ between fresh waxy corn and other fruits and vegetables. That means the postharvest changes in carbohydrates of common fruits and vegetables are not applicable to instruct the storage and retail of fresh waxy corn. In this study, we report the changes of related carbohydrates and associated enzyme activities and the correlations between them. The research realizes the reason for eating quality changing and controlling factors. These results can promote the quality of fresh waxy corn in the processing, storage and retail.