Comparative study of phenolic compounds, vitamin E, and fatty acids compositional profiles in black seed-coated soybeans (Glycine Max (L.) Merrill) depending on pickling period in brewed vinegar

BACKGROUND: Pickled soybeans or vinegar beans have long been used as a folk remedy and also a supplemental nutritional source in Korea. In general the pickling process in vinegar improves the digestibility of soybeans as well as increases the availability of various (non-)nutrients in soybeans. However, detailed information about the changes in functional substances such as (poly)phenolic compounds, vitamin E, and fatty acids (FAs) in soybeans during the pickling process is quite limited. Therefore, this study aims to investigate the changes in the selected phenolic compounds, vitamin E, and FAs in soybeans as a function of the pickling time. RESULTS: The sum of the total phenolics in both the pickled soybeans and the pickling solutions increased by as much as 47% after pickling. Naringenin, vanillin, and catechin were the major phenolics observed in the pickled soybeans and pickling solutions. The total vitamin E content in the pickled soybeans decreased by 23% after pickling, although no vitamin E molecules were found in the pickling solution. γ–Tocopherol was abundant in the untreated soybeans, but decreased by ~29% after pickling. Both the total and major FA contents varied by less than 1% during the pickling period. In this study, a 10–20 day pickling period may be considered suitable in terms of retention of functional substances in the pickled soybeans, such as selected phenolics, vitamin E, and FAs. CONCLUSIONS: Our findings provide basic information and insight into the production of functional compounds in soybeans upon immersing in brewed vinegar, and also may be helpful toward improving the health-functionality of soybean-based foods in the food industry. [Figure: see text] ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s13065-017-0298-9) contains supplementary material, which is available to authorized users.