Influence of low temperature on physiology and bioactivity of postharvest Dendrobium officinale stems

Polysaccharides are the most important group of active ingredients in the orchid Dendrobium officinale. Previous studies have focused on D. officinale polysaccharides during the pre-harvest period, but little is known about the changes in the amounts and activities of polysaccharides in D. officinale stems during the postharvest period. In this study, we evaluated the physiological properties of D. officinale stems during postharvest storage for 90 days at ambient temperature (25 °C) and at low temperatures (4 °C and 0 °C). The contents of polysaccharides, mannose, and glucose first increased then decreased during all storage conditions (storage at 25 °C, 4 °C and 0 °C). The carbohydrate and starch contents decreased considerably as the storage period extended, while cellulose content showed the opposite trend. Polysaccharides from D. officinale stored at ambient temperature exhibited lower antioxidant activity in vitro than polysaccharides from D. officinale stored at low temperatures. The transcript levels of genes encoding α-amylases and β-amylases were related to the degree of starch degradation, and application of an amylase inhibitor prevented starch degradation and polysaccharide accumulation. These results suggested that the increase in polysaccharide content in D. officinale stems stored under low temperatures was related to the decrease in starch content. Our results show that low-temperature storage is a useful approach to enhance the content of polysaccharides and extend the shelf-life of D. officinale.