Antioxidant activity of fractionated pigmented Thai Hawm Gra Dang Ngah 59 rice bran hydrolysates: Pretreatment-assisted enzymatic extraction

Abstract

Background: Hawm Gra Dang Ngah 59 rice (HGDN 59) is a pure line grown in the Takbai district, Narathiwat, located in the southern border province of Thailand. The previously reported HGDN 59 rice bran’s potential as a component rich in nutrients-especially high-quality protein, has not been exploited. There is also insufficient research data on biological activity and tested methods of exposing and releasing bioactive hydrolysates from HGDN 59 rice bran hydrolysates (HGDN 59-RBH). 

Objectives: This study aimed to determine the antioxidative activity of three different pretreatments following ultrafiltration fractionation of HGDN 59-RBH. 

Methods: HGDN 59 rice bran was defatted and pretreated with acid, alpha amylase, and water prior to digestion with consecutive pepsin and trypsin. HGDN 59-RBH was further fractionated by ultrafiltration into three molecular weight (MW) fractions: < 3 kDa, 3-5 kDa, and > 5 kDa. The whole RBH and three MW fractions were assessed to determine protein yield, protein recovery, total phenolic content, and the following antioxidative assays: 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical scavenging activity, 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity, ferrous ion chelating activity, and ferric ion reducing antioxidation power (FRAP).

Results: The highest protein content was obtained using pretreatment with acid, yielding 17.93± 0.08 g protein/100 g hydrolysates with 23.21 g/100 g protein recovery in defatted rice bran (DRB). The > 5 kDa fraction from the acid pretreatment-assisted enzymatic extraction of HGDN 59-RBH showed the highest phenolic content and scavenging activity against ABTS radical (2,2'-azino-bis (3-ethylbenzthiazoline-6-sulphonic acid)) (EC50 0.669 mg/mL) and DPPH radical (2,2-diphenyl-1-picrylhydrazyl) (EC50 0.065 mg/mL) (P<0.05). 

Conclusions: The findings reveal that subjecting HGDN 59-RBH to acid treatment before enzymatic breakdown is a successful approach to extracting peptides with potent antioxidant properties. Consequently, the resulting hydrolysates, rich in antioxidants, hold promise as valuable additions to food and nutraceutical formulations, enhancing their functional attributes.

Keywords: Thai Hawm Gra Dang Ngah 59 rice bran, fractionated rice bran hydrolysates, pretreatment-assisted enzymatic extraction, antioxidant activity