The Role Of Cell Wall Metabolism In Aril Breakdown Of Postharvest Longan Fruit

Longan (Dimocarpus longan Lour.) is a famous subtropical fruit species in the South of China. Since longan fruit mature during the hot and humid August/September in China, the fruit deteriorate rapidly after harvest due to percarp browing, aril breakdown and decay, the fruit have a very short postharvest life of 3-4 days at ambient temperature. This short postharvest period limits its long-distance transportation, marketing and consumption. Therefore, postharvest research becomes a key problem in the development of longan production. The materials of this experiment were fruits of longan (Dimocarpus longan Lour. cv. Fuyan), which is a major and famous cultivar in Fujian Province of China. The metabolism of cell wall and its role in aril breakdown of postharvest longan fruit, and the change of cell wall ultrastructure during aril breakdown in postharvest longan fruit were conducted. The results were as follows:1. Changes of aril breakdown index and cell wall components and their hydrolases of postharvest longan flesh in (10±l) °C were studied. The results were as follows: Aril breakdown index increased continuously after harvest, and rised dramatically 12 days after harvest, with an increase of 0.1311 in an average per day. During the period of storage, mass of cell wall material (CWM), cellulose, semicellulose and protein in cell wall decreased successively. The protopectin content kept on reducing. But soluble pectin content increased, the peak appeared on the 18th day after harvest, by 1.16 fold as compared with that at harvest day. The trend of pectin viscosity was similar with soluble pectin. The content of cellulose, semicellulose, protopectin negatively correlated with aril breakdown index, with a relative coefficient of r₁ =—0.9346, r₂=-0.9397 and r₃ = — 0.9510, respectively. The activities of polygalacturonase (PG) and pectinesterase (PE) gradually decreased, and disappeared at the 30th day of storage. The cellulase activity increased by 1.21 fold within 12 days after harvest. The activity of P-galactosidase appeared descent trend firstly, but rose suddenly at the end as a result of protein dropping quickly, and kept high activity in the whole storage period. Therefore, aril breakdown in postharvest longan fruit was...