Abstract

The present study proposes microwave-assisted extraction as a sustainable technique for the biosynthesis of bioactive compounds from rice fermented with Aspergillus flavus (koji). First, fermentation conditions (i.e., pH from 3–12, five temperatures from 20–40 °C, and four culture-fermentation media viz. wheat, wheat bran, malt and rice) were optimized for producing microbial bioactive compounds. Microwave extraction was performed at 2450 MHz and 500 W for 20, 30, and 40 s with seven solvents (distilled water, ethyl acetate, hexane, ethanol, chloroform, diethyl ether, and methanol). The obtained results revealed that ethyl acetate is the most appropriate solvent for extraction. Effects of this ethyl acetate extract were compared with a commercial synthetic antioxidant. Antioxidant properties were enhanced by preventing the oxidation of the linoleic acid (C18H32O2) with an inhibition rate (antioxidant efficacy) of 73.13%. Notably, the ferrous ion binding ability was marginally lower when compared to the disodium salt of ethylenediaminetetraacetic acid (EDTA). Additionally, the obtained total content of phenolic compounds in the ethyl acetate extract of fermented rice (koji) by Aspergillus flavus was 232.11 mg based on gallic acid/mL. Antioxidant compounds in the ethyl acetate extract of fermented rice showed stability under neutral conditions, as well as at high temperatures reaching 185 °C during 2 h, but were unstable under acidic and alkaline conditions. The results demonstrate the efficacy of novel microwave-assisted extraction technique for accelerating antioxidant production during rice fermentation.

Highlights

  • Lipid oxidation may cause damage to food quality and human health, due to reactive oxygen and nitrogen species (RONS), which are present in food matrices and the human body [1]

  • To create spore suspensions required for the inoculation of rice, A. flavus was incubated for 5 days on malt extract agar (MEA), suspended spores were collected from the supernatant without centrifugation

  • The fermentation of A. flavus on rice medium, with 15 days of incubation at 30 ◦ C at pH 7 was chosen as the optimal procedure for the production of antioxidant compounds

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Summary

Introduction

Lipid oxidation may cause damage to food quality and human health, due to reactive oxygen and nitrogen species (RONS), which are present in food matrices and the human body [1]. It is necessary to consume foods containing antioxidants to help the human body reduce the damage of oxidation and delay the occurrence of several diseases For this reason, industrial antioxidants such as butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA), propyl gallate (PG), and tertiary butylhydroquinone (TBHQ) have been used in diets, even though some side effects related to human health, associated with their decomposition, have been reported [7]. Industrial antioxidants such as butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA), propyl gallate (PG), and tertiary butylhydroquinone (TBHQ) have been used in diets, even though some side effects related to human health, associated with their decomposition, have been reported [7] Some natural antioxidants, such as tocopherol and herbal extracts, have been used on a limited basis due to their high costs, intense flavors, and colors

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