Insight into the transformation of 4′-O-methylpyridoxine and 4′-O-methylpyridoxine-5′-glucoside in Ginkgo biloba seeds undergoing the heat treatment

Overconsumption of Ginkgo biloba seeds leads to poisoning. 4'-O-methylpyridoxine (MPN) and 4'-O-methylpyridoxine-5'-glucoside (MPNG) are responsible for poisoning by intaking ginkgo seeds. It had been reported that heat treatment could increase the MPNG content but decrease the MPN content in ginkgo seeds. However, the definite mechanism for the transformation of MPN and MPNG in ginkgo seeds undergoing heat treatment has not been elucidated to this day. In this work, a Chinese ginkgo cultivar was firstly employed to investigate the effect of heat treatment on the levels of MPN and MPNG. Similar syngenetic succession between the MPN and MPNG contents was also found. Several groups of experiments were further designed to explore the inter-conversion mechanism between MPN and MPNG under heat treatment. The results showed that non-enzymatic and enzymatic glycosylation mechanisms could not explain the transformation between MPN and MPNG. Enzymatic hydrolysis mechanism could better explain the dynamic relationship between the MPN and MPNG. Therefore, inactivating the endogenous enzymatic hydrolysis before HPLC analysis is needed to accurately determine the contents of MPN and MPNG in the ginkgo seeds.