Comprehensive Changes in Nutrient Constituents and Antioxidant Activity during Food Processing of Isoflavone-Enriched Soybean Leaf by Mycelia of Tricholoma matsutake

Abstract

We studied the changes induced in pH, acidity, brix, reducing sugar, soluble protein, nutritional components, primary metabolites, and antioxidant activities of isoflavone-enriched soybean leaf during the different stages involved in Tricholoma matsutake mycelia fermenting. We found that total fatty acid contents increased sequentially in dried soybean leaf, sterilized soybean leaf, and fermented soybean leaf (413.8, 420.3, and 909.4 mg/100 g, respectively). Particularly, linoleic acid content was 5-fold higher in the fermented soybean leaf than in the previous stages. The total free amino acid contents were decreased with progressing processing stages (2389.71, 1860.90, and 1434.25 mg/100 g). However, glutamic acid and lysine contents were highest in fermented soybean leaves. Total mineral contents increased with progressing processing stages (40.30, 41.72, and 55.32 mg/100 g). Water-soluble vitamins, riboflavin, and niacin were about 26-fold and 2.6-fold higher, respectively, in fermented soybean leaf. Comprehensive data analysis of primary metabolites detected changes in a total of 28 metabolites, including, amino acids, organic acids, carbohydrates, and fatty acid metabolites. Antioxidant activities were measured by 2,2-diphenyl-1-picrylhydrazyl, 2,2-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid), and hydroxyl radical scavenging activities and ferric-reducing antioxidant power. Overall, the antioxidant activities increased with progressing processing stages. Thus, we show that T. matsutake mycelia fermented isoflavone-enriched soybean leaf products have excellent nutritional value.