In an attempt to profile the metabolites of three different varieties of germinated rice, specifically black (GBR), red, and white rice, a H-nuclear-magnetic-resonance-based metabolomics approach was conducted. Multivariate data analysis was applied to discriminate between the three different varieties using a partial least squares discriminant analysis (PLS-DA) model. The PLS model was used to evaluate the relationship between chemicals and biological activities of germinated rice. The PLS-DA score plot exhibited a noticeable separation between the three rice varieties into three clusters by PC1 and PC2. The PLS model indicated that α-linolenic acid, γ-oryzanol, α-tocopherol, γ-aminobutyric acid, 3-hydroxybutyric acid, fumaric acid, fatty acids, threonine, tryptophan, and vanillic acid were significantly correlated with the higher bioactivities demonstrated by GBR that was extracted in 100% ethanol. Subsequently, the proposed biosynthetic pathway analysis revealed that the increased quantities of secondary metabolites found in GBR may contribute to its nutritional value and health benefits.

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Glutamate decarboxylase (GAD) is an important enzyme in biological metabolisms acting on catalyzing the irreversible a-decarboxylation of L-glutamic acid to g-aminobutyric acid (GABA) and CO2, which was focused in this study. Three rice varieties different in color were germinated at different times and used for crude GAD extraction. Crude GADs with an optimal germination time from germinated black (GBR), red (GRR), and white (GWR) rice were evaluated for enzymatic properties, including the effect of pHs, temperatures, and concentrations of both L-glutamic acid and pyridoxal 5′-phosphate (PLP). Crude GAD with optimum enzymatic properties was selected to be partially purified using ammonium sulfate (AMS) precipitation. The obtained GAD was supplemented to soymilk and determined for GABA content. All crude GADs from germinated rice at 10 germination days presented the highest enzyme activity. For enzymatic properties, crude GADs showed the highest activity at pH in a range of 5.6-6.0 at 60˚C. The Km values of crude GADs were in the range of 7.68-8.06 mm for L-glutamic acid and 0.15-0.20 mm for PLP and were the lowest in crude GAD from GBR. GAD from GBR presented the highest enzyme activity in the fraction with 50% saturation (v/v) after AMS precipitation and it was purified for 14.61 folds. The addition of this GAD (1.0%, v/v) resulted in the increasing of GABA content in soymilk to 53.79 mg/100 mL, accounted for 1.23 times compared with control.

SummaryIn this work total anthocyanin content (TAC), total fl avonoid content (TFC), total phenolic content (TPC) and minerals found in fi ve black glutinous rice cultivars (MS, SK, PY, PC and KK) from Thailand were analyzed. The antioxidant activity of anthocyanin-rich black glutinous rice bran extracts against nitric oxide radical (NO˙), superoxide radical (O 2˙¯) and lipid peroxyl radical (LOO˙) was also determined. Potential chemopreventive property of rice bran extract was screened based on cellular bioassays for phase II detoxification enzyme induction. Quinone reductase (QR) induction in murine hepatoma cells was used as a marker for this eff ect. Rice bran extract of cultivar KK had the highest TAC, of SK the highest TFC and of PC the highest TPC. The best antioxidants against NO˙, O 2˙¯ and LOO˙ were cultivars KK, MS, and SK, respectively. Overall, TAC, TFC and TPC had a combinatorial eff ect on the antioxidant activities of all extracts; none of them dominated. Minerals may not play a role in the antioxidant activity of the extracts because most correlations between them and the antioxidant activity were unpredictable. However, rice bran contained high mass fractions of some essential minerals on dry mass basis, including Zn (103-133 μg/g), Se (11-18 μg/g) and Cu (3.8-7.1 μg/g). Chemopreventive study indicated that PC cultivar was the most potent chemopreventor with the lowest concentration of an inducer needed to double the QR activity (CD value) of 0.7 μg/mL. These fi ndings showed that black glutinous rice bran is rich in phytochemicals and some essential minerals, and has a potential chemopreventive property.

Sericin hydrolysate (SH), prepared from enzymatic hydrolysis of sericin, was investigated for its antipolyphenol oxidase (PPO) properties. SH decreased PPO activity from both purified mushroom PPO and extracts from apple and eggplant, and retarded browning in fresh-cut apple and eggplant. SH was a competitive inhibitor using catechol as a substrate. SH exhibited copper ion-chelating power and reducing power abilities. Fractionation of SH using size exclusion chromatography resulted in four fractions, designated as F1, F2, F3 and F4, with PPO inhibition of 35.75%, 3.89%, 24.52% and 14.75%, respectively. Ser and Asp were major amino acids found in F1. Amino acid sequences in F1, as investigated by LC-MS/MS using de novo sequencing, contained a high ratio of amino acids with chelating ability. Moreover, amino acids with reducing power ability and with antityrosinase ability were also identified in the sequences.Sericin hydrolysate peptides inhibit PPO A. Puangphet et al.977