Enzymatic hydrolysis on protein and β-glucan content of Sang-yod rice bran hydrolysates and their anti-inflammatory activity on RAW 264.7 cells

Abstract

Background: Research focusing on the improvement of the utilization of rice bran is increasing due to its nutritional properties. Several biological activities of rice bran hydrolysates and its constituents have been reported. Sang-yod rice, a local rice variety in Southern of Thailand, is a pigmented rice. Furthermore, its bran has high nutritive value and health beneficial components. Accordingly, there is growing interest in transforming this by-product into a functional food ingredient.

Objective: To investigate the effect of enzymatic hydrolysis processes on the digestion of protein and β-glucan and evaluate anti-proinflammatory properties of selected hydrolysates on RAW 264.7 macrophage cells.

Method: Sang-yod rice bran hydrolysates were obtained using a single or co-enzymatic hydrolysis process and sequential hydrolysis process using amyloglucosidase and protease G6. Effects of enzyme concentration (3-5% v/w) and hydrolysis duration (30, 60, and 120 min) on soluble protein and β-glucan contents of obtained rice bran hydrolysates were evaluated. The selected rice bran hydrolysates were evaluated for their cell viability and inhibition against NO and pro-inflammatory cytokines generation on RAW 264.7 mouse macrophage cell lines.  

Results: Protein content (0.59-3.37 %) of the rice bran hydrolysates (RBHs) was increased by increasing of enzyme concentration (3-5% v/w) and hydrolysis time (60-120 min). However, the β-glucan content (0.88-4.63%) of RBHs decreased with the increase of those parameters. The RBHs derived by the sequential process using 5% v/w enzyme concentration and 60 min hydrolysis time gave high protein (3.23%) and high β-glucan (4.02%) contents. The hydrolysates with high amount of protein and/or β-glucan contents demonstrated no cytotoxicity against RAW 264.7 cells at concentration range of 100-2,000 μg/ml. Additionally, they demonstrated NO inhibition and pro-inflammatory inhibition ranges of 49.09-71.63% and 9.37-71.96% respectively. Generation of TNF-α, IL-6, and IL-1β cytokines was inhibited differently by the selected RBHs. 

Conclusion: Pre-digestion of Sang-yod rice bran with amyloglucosidase followed with co-hydrolysis of amyloglucosidase and protease G6 of the sequential hydrolysis process was the most effective process to release β-glucan and protein from of rice bran. The hydrolysate obtained from the process using enzyme concentration at 5%v/w and 60 min hydrolysis duration of each stage had the highest soluble β-glucan and protein content. Moreover, the process provided the hydrolysates with potential anti-inflammatory properties on nitric oxide inhibition and pro-inflammatory cytokines inhibition on RAW 264.7 macrophage cell line. 

Keywords: Sang-yod rice, Rice bran hydrolysate, β-glucan, Enzymatic hydrolysis, Anti-inflammatory activity