Chockchai Theerakulkait

Isolation and identification of antioxidant peptides from enzymatically hydrolyzed rice bran protein.

Khao Dawk Mali 105 rice bran protein (RBP) was fractionated into albumin (12.5%), globulin (13.9%), glutelin (70.8%) and prolamine (2.9%). The native and denatured RBP fractions were hydrolyzed with papain and trypsin for 3h at optimum conditions. The RBP fractions and their hydrolysates were evaluated for their antioxidant activity by the Oxygen Radical Absorbance Capacity (ORAC) assay. The trypsin-hydrolyzed denatured albumin exhibited the highest antioxidant activity with an ORAC value of 4.07 μmol of Trolox equivalent (TE)/mg protein. This hydrolysate was separated by using RP-HPLC and three fractions with high antioxidant activity were examined by LTQ-FTICR ESI mass spectrometry. The MW of the peptides from these fractions were 800-2100 Da. and consisted of 6-21 amino acid residues. Most of the peptides from the fractions demonstrated typical characteristics of well-known antioxidant peptides. The results suggest that trypsin-hydrolyzed denatured rice bran albumin might be useful as a natural food antioxidant.

Inhibitory effect of rice bran extracts and its phenolic compounds on polyphenol oxidase activity and browning in potato and apple puree.

Full-fatted and commercially defatted rice bran extracts (RBE and CDRBE) were evaluated for their ability to inhibit enzymatic browning in potato and apple. RBE showed more effective inhibition of polyphenol oxidase (PPO) activity and browning in potato and apple as compared to CDRBE. Five phenolic compounds in RBE and CDRBE (protocatechuic acid, vanillic acid, p-coumaric acid, ferulic acid and sinapic acid) were identified by HPLC. They were then evaluated for their important role in the inhibition using a model system which found that ferulic acid in RBE and p-coumaric acid in CDRBE were active in enzymatic browning inhibition of potato and apple. p-Coumaric acid exhibited the highest inhibitory effect on potato and apple PPO (p ⩽ 0.05). Almost all phenolic compounds showed higher inhibitory effect on potato and apple PPO than 100 ppm citric acid.

Extraction of rice bran extract and some factors affecting its inhibition of polyphenol oxidase activity and browning in potato.

Abstract The extraction conditions of rice bran extract (RBE), including extraction ratio, extraction time, and extraction temperature, were studied in relation to enzymatic browning inhibition in potato. The inhibitory effect of RBE on potato polyphenol oxidase (PPO) activity and its total phenolic compound content were highest at an extraction ratio of 1:3 (rice bran:water, w/v), extraction time of 30 min, and extraction temperature of 40°C. RBE showed the most inhibitory effect on PPO activity at pH 6.5. However, the inhibitory effect of RBE on potato PPO activity and its total phenolic compound content were decreased at the higher temperature and longer time.

Introduction of New Computer Softwares for Classification and Prediction Purposes of Bioactive Peptides: Case Study in Antioxidative Tripeptides

Antioxidative tripeptides were successfully classified according to their structure by using Sequence Principal Component Similarity (SPCS) software. During SPCS computation, hydrophobicity was the main characteristic of peptide residues in aspect of antioxidative activity to inhibit lipid peroxidation in linoleic acid model system. The prediction made by Homology Similarity Search (HSS)-BIOPEP combined software indicated that C-hordein fraction from barley protein showed the greatest potential to be antioxidative protein source followed by prolamin fraction from rice protein. Moreover, these homology segments of C-hordein were resistant against the digestion of mixed gastrointestinal enzymes in BIOPEP digestive model system.

Isolation and some characteristics of Lipoxygenase from aromatic brown rice (Oryza sativa L.) cv. Khao Dawk Mali 105.

Abstract Lipoxygenase from Khao Dawk Mali 105 aromatic brown rice was isolated by extracting brown rice liquid nitrogen powder using 0.2 M phosphate buffer pH 7, fractionating with 30–60% (NH4)2SO4, dialyzing and gel filtration on Sephadex G-200. The optimum pHs for dialyzed lipoxygenase activity were around 7.5 and 9.5. The enzyme appeared to be completely inactivated after heating 30 min at 70°C, 20 min at 80°C and 10 min at 90°C. The enzyme could be inhibited by MgCl2, ZnCl2, KCl, BHA, vitamin E, vitamin C, and BHT; however, CaCl2 acted as the enzyme activator.

Preparation and Some Functional Properties of Rice Bran Protein Concentrate at Different Degree of Hydrolysis using Bromelain and Alkaline Extraction

Abstract Rice bran protein was extracted by using defatted rice bran and water at 1:6 (w/w) and 6% of bromelain at pH 9.0, 50°C, 500 rpm for 15 and 30 mins. The degree of hydrolysis (DH) of rice bran protein extract (RBPE) was 19 and 36.5%, respectively, and their nitrogen solubility was higher than the controls. Rice bran protein concentrate (RBPC) was prepared by spray drying. Emulsion activity of RBPC produced from 19% DH RBPE was increased while emulsion stability index was not significantly different from the control. Foam capacity and rehydration ability of RBPC were greater than the control.

Preparation of Ultrafiltered Rice Bran Extract and Some Factors Affecting its Browning Inhibition in Potato Puree

Abstract Rice bran extract (RBE) was fractionated by using ultrafiltration techniques. The obtained retentate (R) inhibited the browning of potato puree to a similar extent as RBE and more than its permeate. The R that was incubated at pH 4.0, 5.0, and 6.0 inhibited the browning of potato puree more than R that was incubated at pH 7.0 or 8.0. Potato puree that was treated with heated R at 80°C for 10 min had a browning value similar to that of puree treated with unheated R and lower than those treated with heated R at 40 or 60°C for 10 min.

Preparation, aroma characteristics and volatile compounds of flavorings from enzymatic hydrolyzed rice bran protein concentrate: Flavorings from enzymatic hydrolyzed rice bran protein

BACKGROUND Rice bran is a by-product obtained from the rice milling industry. The aims of this research were to add value to rice bran by preparation of enzymatic hydrolyzed rice bran protein concentrate (HRPC) as a flavoring agent and the flavoring which was produced by HRPC has not been investigated. Different drying methods (freeze-drying and spray-drying) and fructose additions were studied for improvement of rice bran protein sensorial aroma characteristics. RESULTS The most abundant amino acids in liquid HRPC (LH) were glutamic acid, arginine, aspartic acid and leucine. The intensity of desirable aromas, such as cereal-like, nut-like, milk-powder-like, sweet, and cocoa-like aroma, were higher in spray-dried HRPC powder (SHP) than in LH and freeze-dried HRPC. Volatile compounds, such as aldehydes, pyrazines and ketones, were significantly increased in HRPC powders in which fructose was added before spray-drying (SHP-F). Higher amounts of 2-methylbutanal, 3-methylbutanal, phenylacetaldehyde, 2,5-dimethylpyrazine, vanillin, 2-acetylpyrrole and maltol were detected in SHP-F. Moreover, these compounds had high odor active values, which accounted for the cocoa-like, sweet, nut-like, and milk-powder-like characteristics of SHP-F. CONCLUSIONS These findings could lead to the creation of desirable aroma characteristics of rice bran protein concentrate by different preparation methods.

Sensory aroma characteristics of alcalase hydrolyzed rice bran protein concentrate as affected by spray drying and sugar addition

The sensory aroma characteristics of alcalase hydrolyzed rice bran protein concentrate as affected by spray drying and sugar addition were investigated. Rice bran protein concentrate (RBPC) was hydrolyzed by alcalase. Sucrose, glucose or fructose was added to the liquid rice bran protein hydrolysate (LRBPH) and subsequently spray dried. The sensory aroma intensities of the hydrolysates were evaluated. Results showed that after spray drying, the rice bran protein concentrate powder (RBPC-P) had higher sweet and cocoa-like aroma intensities than RBPC (p ≤ 0.05) and hydrolyzed rice bran protein powder (HRBPP) had higher milk powder-like aroma intensities than LRBPH (p ≤ 0.05). The sweet, cocoa-like and milk powder-like aroma intensities in hydrolyzed rice bran protein powder with fructose addition (HRBPP-F) were significantly higher (p ≤ 0.05) than those of hydrolyzed rice bran protein powder with sucrose or glucose addition (HRBPP-S or HRBPP-G). HRBPP-F had the highest overall aroma liking score. These results also indicate that spray drying and sugar addition could improve the sensory aroma characteristics of alcalase hydrolyzed RBPC.

Isolation and Identification of Tyrosinase Inhibitory and Copper-Chelating Peptides from Hydrolyzed Rice Bran-Derived Albumin

Rice-bran albumin (RBAlb), which shows higher tyrosinase-inhibitory activity than other protein fractions, was hydrolyzed with papain to improve the bioactivity. The obtained RBAlb hydrolysate (RBAlbH) was separated into 11 peptide fractions by RP-HPLC. Tyrosinase inhibition and copper chelation activities decreased with increasing retention times of the peptide fractions. RBAlbH fraction 1, which exhibited the greatest activity, contained 13 peptides whose sequences were determined by using LC-MS/MS. Most of the peptide sequences contained features of previously reported tyrosinase-inhibitory and metal-chelating peptides, especially peptide SSEYYGGEGSSSEQGYYGEG. RBAlbH fraction 1 showed more effective tyrosinase inhibition (IC50 = 1.31 mg/mL) than citric acid (IC50 = 9.38 mg/mL), but it was less effective than ascorbic acid (IC50 = 0.03 mg/mL, P ≤ 0.05). It showed copper-chelating activity (IC50 = 0.62 mg/mL) stronger than that of EDTA (IC50 = 1.06 mg/mL, P ≤ 0.05). These results suggest that RBAlbH has potential as a natural tyrosinase inhibitor and copper chelator for application in the food and cosmetic industries.