Effect of acetic acid treatment on isoflavones and carbohydrates in pickled soybean

• Isoflavones after pickling for 30 days were increased by a maximum of 93%.
• Malonyl glucosides were decreased max 41%, but glucosides were increased max 160%.
• Aglucones were found to maximum 154.6 μg·g− 1 in the pickled soybean.
• Total carbohydrates in pickled soybean were 50–65% less than that of raw soybean.
• Oligosaccharides in pickled soybean were decreased by > 50% within the first 24 h.

Acetic acid treatment improves the physical, chemical, and physiological properties of soybeans. This study investigated the changes in isoflavone and carbohydrate profiles in four soybean cultivars subjected to different acetic acid treatment durations. The sum of total isoflavone content of the pickled soybeans and the pickling solution was increased by 30–93% after acetic acid treatment for 30 days. In the comparison to four isoflavone groups of the untreated soybean, malonyl glucosides were decreased by 17–41%, whereas glucosides were increased by 54–160% in the pickled soybeans. In particular, aglucones were found in the pickled soybeans, but not in the untreated soybeans. Following acetic acid treatment, the total carbohydrate content in the pickled soybeans was 50–65% less than that of untreated soybeans. In particular, oligosaccharides and sucrose in the pickled soybeans decreased significantly (> 50%) within the first 24 h. This study provides important information on the changes in isoflavone and certain carbohydrates profiles during soybean pickling, and may be useful to produce functional soybean-based foods containing more bioactive compounds.