## 4 Discussion
Focusing on the peptide fraction size of the HRBE, the lower IC\({}_{50}\) value of the \(>\)50 kDa fraction (compared to other fractions) indicates the growth inhibitory activity of rice bran peptides. Interestingly, this \(>\)50 kDa HRBE fraction showed higher efficacy on SW-620 cells over the crude extract, which is implied by the lower IC\({}_{50}\) value of this fraction (4908 \(\upmu\)g/mL) than that of the crude extract (5492.31 \(\upmu\)g/mL) at 72 h. The apoptotic morphology of SW-620 cells was also observed after being treated with the \(>\)50 kDa fraction, characterized by membrane blebbing and chromatin condensation. Rice bran is a rich source of dietary fibers and proteins such as albumin, globulin, glutenlin and prolamin with high nutritional value, minerals, unsaturated fat and vitamins, where the highest phytate content was found in albumin and the lowest in prolamin [4; 5; 6]. Since albumin is a water-soluble protein, the aqueous extraction of albumin always results in globulin contamination because of the minerals present in the rice grain that dissolve in a water solvent. Albumins were separated into three to four subfractions using gel filtration chromatography and had a molecular weight of 100 kDa or less when analyzed by size-exclusion HPLC [35]. Rice bioactive compounds such as tooo (tocopherols and tocotrienols), phytosterosols and \(>\)-oryzanols have been reported to have antioxidative properties including free radical scavenging activity and the inhibition of lipid peroxidation. These substances are valuable for health promotion being able to help reduce free radicals and cholesterol in the body. Moreover, the hydrolysis of protein with proteases produces many potential peptide sequences that provide numerous functional and antioxidative properties [11; 36]. In addition, rice protein hydrolysates obtained from pepsin and trypsin hydrolysis exhibit much greater antioxidative activities than those before digestion. Previous research indicated that when peptides \(<\)5 kDa in size were separated from the hydrolysate bran protein by treating heat-stabilized defatted rice bran with the Alcalase enzyme, followed by treatment with simulated gastric and intestinal juices, resistant peptides were obtained. These hydrolyzed peptides have a high potential anticancer effect on colon cancer cells [25]. The optimal hydrolysis condition was 2 h after using an Alcalase-yielding protein content of 30.3% [9], which is comparable to the extraction yields in this study. According to a previous study, Alcalase is an alkaline endo-peptidase that gives higher oil and protein yields. Its activity in hydrolyzing glutenlin, as the main protein accounting for 60-80% of the total protein in rice, was higher than neutral protease. In addition to purified and isolated anticancer pentapeptide, Glu-Gln-Arg-Pro-Arg was obtained from rice bran, and the peptide with a molecular mass of 685.378 Da caused the growth inhibition of 84% against colon cancer cells (Caco-2 and HCT-116), 80% against breast cancer cells (MCF-7, MDA-MB-231) and 84% against liver cancer cells (HepG-2) at a dose of 600-700 \(\upmu\)g/mL [21]. There are reported anticancer effects of the rice bran bioactive components that can induce apoptosis, inhibit cell proliferation and alter cell cycle progression in malignant cells. Rice bran bioactive components can also protect tissue damage through the scavenging of free radicals and the blocking of chronic inflammatory responses. Rice bran phytochemicals have also been shown to activate anticancer immune responses as well as affect the colonic tumor microenvironment in favor of enhanced colorectal cancer chemoprevention. Rice bran extracts and pure extracts alone can inhibit cancer cell growth without any side effects in response to the components of rice bran in normal cells.