Solid-State Yeast Fermented Wheat and Oat Bran as A Route for Delivery of Antioxidants

Abstract

The purpose of our study was to evaluate the potential of solid-state yeast fermentation (SSYF) in improving the phenolic acid content and composition, and the antioxidant activity of commercial wheat bran (WB) and oat bran (OB). The ultrasound-assisted methanolic extracts were compared for their total phenolic content (TPC), phenolics composition, and in vitro antioxidant activity in order to study the effect of fermentation time on the chemical profile and activity of bioactive compounds. The comparative analysis revealed significant differences (p < 0.05) between days of fermentation (0 through 6). The highest TPCs were obtained on day 3 for WB (0.84 ± 0.05 mg of gallic acid equivalents [GAE]/g dry weight [DW]), and on day 4 for OB (0.45 ± 0.02 mg GAE/g DW). The highest relative percentage increase in the phenolics concentration of WB was also registered on day 3 (ferulic acid +56.6%, vanillic acid +259.3%, dihydroxybenzoic acids +161.2%, apigenin-glucoside +15.3%); for OB, this was observed on day 4 (avenanthramide 2f +48.5%, ferulic acid +21.2%). Enhanced antioxidant activities were significantly correlated with the highest TPCs. Our results suggest that SSYF may be a useful procedure for enrichment of antioxidants in cereal bran, considering the design of different functional foods and nutraceuticals.

Keywords: antioxidants enrichment; bioprocess; enzymes; low cost; oat bran; phenolic acids; solid-state fermentation; sustainability; wheat bran; yeast.

Figure 1

Cell viability (plate counting method) of the extracts (control and fermented (6 days)). Values are expressed as mean values ± SD, log10 CFU/g, n = 3, GraphPad Prism Version 8.0.1, Graph Pad Software, Inc. (San Diego, CA, USA).

Figure 2

Total phenolic content (Folin–Ciocalteu method) (A) illustrating WB; (B) illustrating OB of the extracts (control and fermented (6 days)). Total phenolic content of the extracts is expressed as gallic acid equivalents (GAE) in mg/g sample of waste. Values are expressed as mean values ± SD, μg/g, n = 3, and are followed by different letters (a–f), indicating significant differences (p < 0.05) between days of fermentation (One-way ANOVA - Multiple comparison test - Tukey multiple range test (p = 0.05); GraphPad Prism Version 8.0.1, Graph Pad Software, Inc., San Diego, CA, USA).

Figure 3

Antioxidant activity (DPPH free-radical-scavenging assay) (A) illustrating WB; (B) illustrating OB of the extracts (control and fermented (6 days)). The percentage inhibition (I%) was calculated as [1 − (test sample absorbance/blank sample absorbance)] × 100. Values are expressed as mean values ± SD, I%, n = 3, and are followed by different letters (a–f) indicating significant differences (p < 0.05) between days of fermentation (One-way ANOVA - Multiple comparison test -Tukey multiple range test (p = 0.05)-GraphPad Prism Version 8.0.1, Graph Pad Software, Inc., San Diego, CA, USA).

Figure 4

A schematic showing how the effect of yeast fermentation on the antioxidant activity of cereals takes place.

Figure 5

Reported linkages between dietary fiber components and phenolic acids with a loop on ferulic acid structure esterified to arabinoxylan and possible microorganisms-produced enzymes for increased bioavailability.