Isoflavone profile and protein molecular weight distribution of soy protein concentrates after soaking treatments

Abstract

The effects of soybean soaking at 40, 50, and 60°C, during 4, 8, 12, and 16 hr time periods, on the isoflavone profile and molecular weight distribution of proteins in their soy protein concentrate were evaluated. Results indicated that soaking treatments increased aglycone content (daidzein, genistein, and glycitein) and decreased β-glucosylated and malonyl glucosylated isoflavone contents. Soy protein concentrate obtained after soaking at 50°C for 16 hr yielded the greatest total aglycone content (5,993.6 µmol 100 g−1), which was 75% greater than the total aglycone content found in soy protein concentrate obtained from non-treated soybeans (3,636.9 µmol 100 g−1). Glycitein was the main isoflavone aglycone present in soy protein concentrates. Acidic and basic subunits of 11S globulins are released at low and intermediate soaking periods (4, 8, and 12 hr), while longer soaking time (16 hr) causes a protein rearrangement of partially cleaved proteins into more hydrophobic core. Practical applications Soy-based food products can be considered functional foods because of their isoflavone content, mainly the aglycone content (daidzein, genistein, and glycitein). The utilization of soaking treatment in soybeans may increase the isoflavone aglycone content in soy protein concentrate. Our results indicated that soaked soybeans had more isoflavone aglycone content than untreated ones. The highest isoflavone aglycone content was obtained from soaked soybeans at 50°C for 16 hr and glycitein was the predominant isoflavone aglycone found in soy protein concentrates. The obtained soy protein concentrate can be used in a wide range of products, such as bread, cakes, cereals, beverages, and meat products, and contributes to increasing the nutritional and functional value of the product, mainly due to the quantity and quality of proteins and isoflavones.