A Study of Application and Comparison of Thermal Drying and Freeze Drying of Fresh Edamame Seeds in the Analysis of Seed Composition

Edamame is a vegetable soybean (Glycine max) with high nutritional and market value. It is mainly grown in Asia and has expanded to North America and Africa. Freeze and low- and high-heat drying methods were used to dry fresh edamame seeds of 20 soybean lines and cultivars for analysis of their composition using near-infrared reflectance (NIR) technology. The results indicated that significant differences existed between years of samplings for all seed composition traits investigated. Differences between drying methods were significant for all the traits with whole-seed samples, while they were not significant in protein, raffinose and linoleic acid for flour samples. Ground flour and whole-seed samples were similar or comparable in most cases for freeze and low-heat drying methods, but differences in seed composition between sample types were observed for high-heat drying. Among the traits investigated, protein content was the most consistent for all three drying methods, with an over 91% estimate of repeatability, showing high stability during drying. Oil content also showed a repeatability estimate of over 86% for all three drying methods. Low-heat drying generated results more comparable to freeze drying, while high-heat drying exhibited larger differences in most cases. Estimates of repeatability and correlation coefficients further confirmed that, low-heat drying, similar to freeze drying, was appropriate for drying fresh edamame seeds, but high-heat drying was not. Therefore, low-heat drying is a suitable method for drying fresh edamame and rapid analysis of seed composition, and it can be used as an alternative of freeze-drying method.