Changes in isoflavone profiles and antioxidant activities in isoflavone extracts from soybeans and soyfoods under riboflavin photosensitization

Abstract

Isoflavone extracts from soybeans and soyfoods were treated with riboflavin photosensitization and changes in antioxidant activities of isoflavone extracts under riboflavin sensitization were determined using 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS), and ferric reducing antioxidant power (FRAP) assays. Extracts rich in malonyl derivatives, β-glucosides, and aglycones were prepared from raw, ovendried, and almond-incubated soybeans, and the fermented soyfoods cheongukjang and natto. As the period of visible light irradiation increased to 120 min, the total isoflavone content determined using HPLC decreased in all samples. Aglycones in almond-incubated extracts decreased by 77.5% after 120 min, and β-glucosides in oven-dried extracts decreased by 52.0%. The radical scavenging activity based on DPPH and ABTS assays significantly (p<0.05) decreased in most extracts, compared with controls. The reducing power in aglycone-and β-glucoside-rich extracts increased, whereas the reducing power in extracts with high malonyl forms was not significantly (p>0.05) increased after riboflavin sensitization.

Riboflavin Phototransformation on the Changes of Antioxidant Capacities in Phenolic Compounds

“…Radical cation scavenging activity of the samples was determined by the ABTS method according to a previous report (Seol and others ). Briefly, a mixture of 7 mM aqueous ABTS solution and 2.45 mM potassium persulfate was diluted with ethanol to an absorbance of 0.700 ± 0.050 at 734 nm.…”

“…The FRAP assay was performed according to a previous report (Seol and others ). The stock solutions were 300 mM acetate buffer (pH 3.6), 10 mM 2, 4, 6‐tripyridyl‐s‐triazine (TPTZ) solution in 40 mM HCl, and 20 mM FeCl 3 solution.…”

“…RF phototransformation can modify isoflavone aglycone chemical structure, such as daidzein and genistein in model systems (Park and others ; Soel and others ) and change the profiles of isoflavones in real food systems including soymilks and soyfoods (Lee and others ; Seol and others ). RF photosensitization induced the formation of 7,3′,4′ trihydroxyisoflavone (or 3′‐hydroxydaidzein) and 2 dimmers of daidzein from daidzein (Park and others ) and hydroxygenistein from genistein (Soel and others ).…”

“…RF photosensitized genistein derivatives have a higher free radical scavenging ability than the original form, which may be due to genistein derivatives with an additional hydroxyl group. Seol and others () report that RF photosensitized aglycone‐rich isoflavones in the extracts from soyfoods had enhanced ferric reducing antioxidant power (FRAP), whereas radical scavenging abilities determined by 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) and the 2,2′ azino bis(3‐ethylbenzothiazoline‐6‐sulphonic acid) (ABTS) assays decreased in the extracts of soyfoods (Seol and others ). RF phototransformation may be a possible way to modify phenolic compounds without using hazardous solvents and high‐energy input.…”

Comparison of nutritional components (isoflavone, protein, oil, and fatty acid) and antioxidant properties at the growth stage of different parts of soybean [Glycine max (L.) Merrill]

“…Numerous methods with distinctive mechanisms can be used to evaluate antioxidant capacity. In particular, radical-scavenging methods have been extensively used to screen antioxidants from crops, fruits, vegetables, and natural plants owing to their good reproducibility and easy quality control (8,11,(19)(20)(21). Based on the above background, previous studies have evaluated the variations in phytochemical contents and antioxidant capacities at different growth stages of natural materials (4,22).…”