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Introduction
Rice bran (RB) is a byproduct of the rice-milling process and contains various active compounds that have beneficial effects on human health. It is well known that the major active compounds of RB are phenolic compounds, which exhibit antioxidant activity (Min et al., 2011). Our previous studies showed that the Driselase-treated fraction of RB, which is the filtrate of defatted RB treated with plant cell wall-degrading enzymes, lowers blood pressure (BP) and improves lipid profiles because of the total phenolic compounds and ferulic acid present in this fraction (Ardiansyah et al., 2006). Phenolic compounds are key factors in antioxidant activities because of their ability to scavenge free radicals, disrupt radical chain reactions and chelate ion-metals (Shahidi and Naczk, 2004).
The Indonesian Agency for Agricultural Research and Development, through the Indonesian Center for Rice Research, has released over 200 rice varieties, including Inpari 6, Inpari 30, and Inpara 1 in 2008, 2012 and 2008, respectively; Inpari 6, Inpari 30 and Inpara 1 contain 18, 22 and 28 per cent amylose, respectively (Mejaya et al., 2004). Three types of RB consumed daily were analyzed in this study, among which Inpari 30 is the most widely consumed in Indonesia. Further, the rice type Inpari 30 is predicted to replace the Ciherang type, another commonly consumed type of rice.
Solid-state fermentation (SSF) is used to increase the content of functional ingredients and nutraceuticals obtained from plants and animals (Schmidt et al., 2014). SSF is a simple technique for producing bioactive compounds at a low cost by using agro-industrial residue, which reduces the environmental impact and waste (Olievera et al., 2011; Schmidt and Furlong, 2012). SSF has been used to enhance yields, productivities and product characteristics of bioactive compounds such as enzymes and organic acids (Razak et al., 2015). SSF of RB with Rhizopus oryzae increased its phenolic content by more than 100 per cent, and fermented RB inhibited 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals with an EC50 value of 250 mg/g DPPH (Razak et al., 2015).
Rhizopus sp. are among the most suitable microorganisms for use in the fermentation process and Rhizopus oligosporus is one of the main fungi isolated from the Tempe fermentation processing plant in Indonesia (Rahayu et al.,...