Time of harvesting and storage of soyabeans: influence on oil quality

Abstract

Soybean var. IAC-8 was harvested in five different times, two previous (R7 and R8) and two subsequent (C1 and C2) to the usual commercial harvest time (H). The seeds were air dried at normal ambient temperature before storage. Those with 15% moisture could be kept for only three months. Those with 12% moisture were kept for six months. Initial characterization of the seeds revealed the least oil content in seeds from the harvest of R8. In addition, the sample R8 had the least acidity and the oil had better storage properties regarding peroxide value. During storage a general increase in acidity has been observed in the oil from seeds from all the samples and at the two moisture levels. Peroxide value of the oil decreased after three months of storage, except for R8 oils, and were even lower in the 15% moisture seeds. Spectrophotometric absorption in the ultraviolet range indicated the formation of conjugated double bonds as the period of storage increased, independently of the harvest time and seed moisture. There was little change in the iodine values of any of the samples during the storage period. The oils from R8 were the ones that showed the least oxidative deterioration during the period studied, whereas R7 and C2 seed oils were considered to have deteriorated the most.