The influence of processing and storage on hydrogen cyanide and tannin contents of para-rubber seed and its products

Abstract

Para-rubber seed and its products, including the autoclaved and fermented oil meals, were assayed for HCN content at post-harvest intervals from 1 week to 9 months of storage at room temperature. The tannin content of all these products was also estimated after 3 months of storage. Rubber seed and its kernels contained 638 and 749 mg HCN/kg, respectively, 1 week after harvest; these values gradually diminished to 25.3 and 26.7 mg/kg, respectively, after 9 months storage. The rate of reduction in HCN levels was fast for the first 2 months of storage and slower later. The HCN levels in other rubber seed products also declined during storage. Thus, storage at room temperature for a minimum period of 2 months appeared to be an effective method of reducing the HCN content of rubber seed and its products to safe levels. The tannin levels in rubber seed and its products were low (0.42–0.53%) and within the safety levels for incorporation in livestock feeds. Moreover, the tannins were confined to the shell portion of the rubber seeds. Thus decortication appeared to be a satisfactory method for eliminating the tannins in rubber seeds, but increased the HCN levels slightly. Oil extraction and autoclaving failed to reduce the HCN and tannin levels, but fermentation successfully reduced both HCN and tannin levels in the rubber seed and its products.