Involvement of fungi in the increase of free fatty acids in stored soybeans

Abstract

Application of the fungicide Captan to whole soybean seeds stored at 85% relative humidity did not prevent either the development of the natural fungal population underneath the seed coat or the increase of free fatty acids. At 65 and 75% relative humidity the increase in free fatty acids and fungi development during storage were lower than at 85% relative humidity, but even at these lower levels no differences were observed between Captan-treated and nontreated seeds. In split soybeans, where fungi developed profusely on the unprotected damaged site of the seed, treatment with Captan or thiourea resulted in free fatty acid values significantly lower than those of the untreated controls. The fungi most frequently isolated from stored soybeans were Aspergillus candidus, A. ruber, A. versicolor, and Penicillium cyclopium, all of which showed lipolytic activity. Inoculation of intact soybean seeds with these fungi did not cause an increase in free fatty acids as compared with noninoculated controls, probably because the intact seed coat prevented the penetration of the inoculated fungus. The similar increase in free fatty acids in both the inoculated and the noninoculated controls was probably caused by the internal mycoflora in both treatments. Since fungicide treatments prevented the increase of free fatty acid levels in all cases where the fungicide could reach those sites at which fungi developed, it was concluded that fungi play an important role in the increase of free fatty acids in stored soybeans.