The Role of Phenolic Substances in the Adhesion between the Pellicle and Kernel of Japanese Chestnut under Experimental Conditions.

Abstract

The adhesion process between the pellicle and kernel under heat (62°C) and hypobaric (4 mm Hg) conditions was analyzed in the immature Japanese chestnut, which is easy to peel. The adhesion process under the experimental conditon was similar to that occurring in nature. The peeling time of the nuts heated for 10 hr was about 5 times longer than that of the nuts subjected to hypobaric treatments. Monophenolic substances in the water extracts from pellicle, composed mainly of (+)-catechin and gallic acid identified by GC and GC-MS, diffused to the outer cells of the kernel and the interface between the pellicle and kernel during the first 2 hr of both treatments. There the low molecular weight phenolic substances, including (+)-catechin, polymerized as noted by the shift of their peaks after 2-5 hr of heating. With continued heating, the content of phenolic substances in the alcohol insoluble solids (AIS) fraction of the pellicle increased rapidly and the pellicle tightly adhered to the kernel. Therefore, we postulate that the polyphenolic substances are the adhesive between pellicle and kernel. However, under hypobaric conditions, cell breakdown and migration of the phenolic substances in the tissues occurred during the initial 0-2 hr and ceased. Thus, little or no polyphenolic substances accumulated between the pellicle and kernel to cause their adhesion after 10 hr of treatment.