Tannin dynamics in hypocotyls and pericarps of Aegiceras corniculatum fruits during dry storage

Abstract

In this study, we investigated the changes in total phenolics, extractable condensed tannins (ECT), protein noncovalent bound condensed tannins (PNBCT) and irreversible covalent bound condensed tannins (ICBCT) in the hypocotyls and pericarps of Aegiceras corniculatum fruits during dry storage. The loss of moisture content and survival rate, as indicators of the viability and quality of plant tissues, were also monitored during the dry storage. Great amount of free condensed tannins combined with proteins in the senescent pericarps during the process of deteriorative reactions associated with dry storage, which contributed to the rapid increase of PNBCT characterized by the sigmoid model. However, there was a rapid loss of total phenolics and ECT from pericarps during the first 9 days of the dry storage, with 37.3% loss of ECT due to the transformation of PNBCT. PNBCT of the hypocotyls also fitted a sigmoid model with dry storage time, and was related to the viability of the hypocotyls. During the dry storage, most of the disappeared ECT of hypocotyls formed complexes with protein, and the total condensed tannins (TCT) did not decline during the 27 days dry storage. The distribution of the oligomers and polymers in the condensed tannins was significantly different between the fresh and dried hypocotyls of A. corniculatum. The oligermers with lower degree of polymerization (DP) appeared to have higher capacity of binding to proteins than the polymers with high DP in plant tissues during the dry storage. The changes of hydroxy pattern of tetramers in the fresh and dried hypocotyls showed that the proteins would be selective binding those flavan-3-ol oligomers with more hydroxyl in plant tissues with deteriorative reactions during dry storage. However, the hydroxy pattern of nomamers was not significantly different between the fresh and dried hypocotyls. Our results indicated that few flavan-3-ol polymers reacted with proteins in hypocotyls of A. corniculatum associated with the deteriorative reactions during the dry storage.