Effects of maturity on the nutrients, bioactive substances and taste of two cultivars of lotus seeds (Nelumbo nucifera Gaertn.)

• VC decreased, soluble protein, soluble sugar increased during maturation. • Phenolics decreased during maturation, correlated with the downregulation of NnPAL . • Flavonoids reached peak at S1 in CS and S3 in TK, correlated with F3H, ANR, UGT88B1. • Upregulation of BGL18, GBE1, SSI was positively correlated with starch accumulation. • Neferine peaked at S4 in CS and S3 in TK, corresponded to lotus seeds’ bitterness. The dynamic changes in nutrients and bioactive substances in Cun San lotus seeds (CS) and Tai Kong lotus seeds (TK) were investigated at different stages of maturity. The color of lotus seeds deepened with maturity. CS displayed longitudinal growth and TK exhibited transverse growth. CS and TK showed a decrease in VC content and an increase in soluble protein and soluble sugar content during the maturation process. Total phenolics and DPPH scavenging rate decreased, with NnPAL4 downregulation correlating with phenolics. The flavonoid content was highest in CS at milk ripening (S1) and TK at full ripening (S3), which was positively correlated with the expression patterns of NnF3H, NnANR and NnUGT88B1. As the maturity increased, the starch content increased, and the starch content of CS in S1-S3 was higher than that of TK. The expression levels of NnBGL18, NnGBE1 and NnSSI were upregulated and were positively correlated with starch accumulation. CS had a higher content of chlorogenic acid in phenolic compounds and catechins in flavonoids than TK, with gastrodin being the highest content of non-flavonoid compounds. The content of Neferine in CS at S4 and TK at S3 was the highest, corresponding to the most obvious bitterness in CS and TK.This study provided a theoretical basis for improving the quality of lotus seeds and post harvest deep processing.