Unravelling the postharvest quality diversities of different sweet corn varieties

Different varieties of sweet corn exhibit varying degrees of quality deterioration after harvest, especially changes in appearance, sugar composition, texture and flavor. Changes of 18 common phenolic acids, organic acids, and sugars of sweet corn varieties, 'Jingkenuo 2000', 'Jingkenuo 768' and 'Nongkenuo 336', during a shelf-life period of 10 d at 20 degrees C were identified in this study. The differences of flavor among the varieties may be due to their different flavor regulation pathways. Maintenance of sweetness of 'Nongkenuo 336' corn was associated with the lowest decreases of sucrose, lactose, stachyose, raffinose, melibiose and galactinol after harvest. In this variety, the expression of INV in the sucrose metabolism and BMY in starch degradation increased the least, while that of SS4 and SS5, involved in starch and sucrose metabolism pathways, decreased the lowest compared with the other two varieties. In 'Jingkenuo 2000', expression of MLS and IFS, genes relevant to the flavor components, malic acid and flavonoids, increased after harvest. In 'Jingkenuo 768' more rapid degradation of phenylalanine and citric acid was related to up-regulation of NAD-IDH and limited down-regulation level of CS. 'Nongkenuo 336' maintained alcohol production but lower ester aroma components through down-regulation of LOX and down-regulation of ADH5 and ADH2, which was associated with undesirable aroma. 'Nongkenuo 336' also had delayed expression of the cell wall degradation gene (egl) and decreased expression of cell wall synthesis genes (PE, CALS3 and CALS7), related to the firmness. This study contributes to the understanding of the molecular mechanisms affecting quality changes of sweet corn varieties after harvest.