Phenolic profiles and bioactivities of different milling fractions of rice bran from black rice

Biomarkers of the main nutritional components in purple rice during five successive grain filling stages

Differences in main nutritional components in relation to biomarkers of metabolites in purple rice grains at different fillings stages have not been determined previously. This study measured the contents of amino acids, several nutritional indicators, and mineral elements in purple rice grains at five stages following the filling stage. The results revealed that the amino acid, ascorbic acid, total sugar, carotenoid, vitamin B9, cyanidin-3-O-glucoside, peonidin 3-glucoside and seven minerals were highest in the final stage of grain filling. Citric acid, L-isoleucine, trigonelline, and L-glutamate are key metabolites in the metabolic pathway and exhibit strong correlations with various nutritional indicators. Hence, this research preliminarily suggested that trigonelline, L-isoleucine, L-glutamate, and citric acid could be potential biomarkers of nutritional components in purple rice grains during various postfilling stages.

Structural elucidation, binding sites exploration and biological activities of bound phenolics from Radix Puerariae Thomsonii

Radix puerariae thomsonii (RPT) contains many phenolics and exhibits various health benefits. Although the free phenolics in RPT have been identified, the composition and content of bound phenolics, which account for approximately 20% of the total phenolic content, remain unknown. In this study, 12 compounds were isolated and identified from RPT-bound phenolic extracts, of which 2 were novel and 6 were reported first in RPT. ORAC and PSC antioxidant activities of 12 compounds, as well as their effects on alcohol dehydrogenase (ADH), aldehyde dehydrogenase (ALDH), α-glucosidase, and α-amylase were evaluated. Genistein exhibited the highest ORAC activity, while daidzin demonstrated superior PSC activity. Five compounds, including two new compounds, exhibited the ability to activate both ADH and ALDH. All the compounds except 4-hydroxyphenylacetic acid methyl ester and 2,4,4'-trihydroxydeoxybenzoin demonstrated inhibitory effects on α-glucosidase and α-amylase. Alkaline hydrolysis and stepwise enzymatic hydrolysis revealed that bound phenolics in RPT mainly exist within starch.

Towards sustainable upcycling of side streams of purple bread wheat using dry fractionation: Enhancing bioactive compounds and reducing harmful elements

Side streams from milling result in significant food wastage. While highly nutritious, their harmful elements raise concerns. To repurpose these side streams safely, this study designed a dry fractionation technique for anthocyanin-rich purple bread wheat. Four fractions - from inner to outer layers: flour, middlings, shorts and bran - alongside whole-wheat flour were obtained and examined by microstructure, antioxidant activity, anthocyanin profiles, and essential and harmful minerals. Across the four investigated cultivars, both anthocyanin content and antioxidant capacity increased from inner to outer layers. In comparison to flour, cyanidin-3-glucoside concentrations in middlings, shorts and bran were 2-5 times, 3-9 times, and 6-19 times, respectively. Concentrations of Cr, Ni, Sr and Ba progressively increased from inner to outer layers, Pb and Se exhibited uniform distribution, while Al was more concentrated in inner layers. These findings indicate that the fractionation technique is effective in deriving valuable ingredients from underexploited side streams, especially bran.

Functional Foods from Black Rice (Oryza sativa L.): An Overview of the Influence of Drying, Storage, and Processing on Bioactive Molecules and Health-Promoting Effects

Black rice (Oryza sativa) stands out for its high content of bioactive compounds with functional properties that play an important role in health benefits. The phytochemical level is affected by industrial processing due to its instability to the hydrothermal process. Studies about the influence of industrial processing on the phytochemical profile of black-rice-based foods are still scarce. This study carried out a comprehensive review of the influence of industrial applications on the bioactive compounds in food products based on black rice and their health-promoting effects. Most industrial processes such as drying, storage, cooking, and extrusion affect phytochemical content and antioxidant capacity. Alternatively, technologies such as fermentation, UV-C irradiation, and sprouting can maintain or improve the phytochemical content in black rice products.

Effect of milling on in vitro Digestion-Induced release and bioaccessibility of active compounds in rice

To investigate the impact of milling on the active components in rice, this study examined the stability of phenols, vitamin B1 (VB1), and alpha-aminobutyric acid (α-GABA) during cooking and digestion of rice and their distribution in digestive juices and residue by adjusting the degree of milling (DOM). The findings revealed that milling exacerbated the instability of γ-GABA during cooking and VB1 during digestion. Their total losses peaked at 19.76% and 39.53% as DOM respectively reached 6.07% and 8.06%. In vitro digestion combined with release mathematical models demonstrated the impact of milling on their bioaccessibility. This effect increased the small intestinal bioaccessibility of phenols and γ-GABA, whilst reducing that of VB1. This was attributed to milling-induced pre-gastric full release of VB1, which amplifies its intestinal susceptibility and induces its re-entry into digestive residues. In conclusion, this study recommends keeping DOM below 6.07% to optimize the bioaccessibility of these active compounds.

In vitro gastrointestinal digestion and colonic fermentation of media-milled black rice particle-stabilized Pickering emulsion: Phenolic release, bioactivity and prebiotic potential

This is a pioneer study that investigated the digestive characteristics of Pickering emulsions stabilized by media-milled black rice particles during in vitro digestion and colonic fermentation. Free fatty acid release of the emulsions improved from 28.42 ± 3.13% to 33.68 ± 4.05% after media milling. The phenolics released from media-milled sample were close to those from unground sample. Media-milled sample exhibited higher DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging ability and α-glucosidase inhibition rate than unground sample. Media milling increased the generation of short-chain fatty acids (SCFAs) during colonic fermentation, especially acetic acid (23% improvement in media-milled sample over unground sample). It also inhibited the growth of harmful bacteria namely Escherichia Shigella and Streptococcus, and promoted the growth of beneficial bacteria including Bifidobacterium and Blautia. These findings revealed that media-milled black rice particle-stabilized Pickering emulsions possessed intrinsic bioactivity and prebiotic potentials in the gastrointestinal tract for the first time.

Anthocyanins-natural pigment of colored rice bran: Composition and biological activities

Rice by-products are a potential source of various bioactive substances with great processing potential, which are receiving increasing attention. Among them, rice bran is a by-product of rice milling, with high nutritional value and health benefits. Colored rice bran contains a large amount of anthocyanins responsible for color and bioactivities. And anthocyanins are often added to foods as a natural pigment, serving to enhance both the visual appeal and nutritional value. Recent advances in the composition and bioactivities of four common colored rice bran anthocyanins (black, purple, red, and purple red rice) are reviewed in this paper. Rice bran anthocyanins have been confirmed to exhibit biological potential for human health, with their main biological activities being antioxidant, anti-atherosclerosis, anti-cancer, neuroprotective, retinoprotective, immunomodulatory, anti-aging and anti-obesity effects. The structure of anthocyanins determines their biological activities. The anthocyanins composition of rice bran with different colors varied greatly, while that of rice bran with the same color is also slightly different, which is attributed to the rice varieties, growing environment and cropping conditions. However, it remains necessary to conduct further clinical studies to support the health activities of anthocyanins. The present review provides information value for the further development and comprehensive utilization of rice bran anthocyanins.

Physicochemical properties, phenolic content and in vitro digestion profile of Chinese black rice (Oryza sativa L.)

Yangxian black rice, as one of the ancient Chinese black rice varieties, is widely planted in the Yangxian area of China. This study investigated the physicochemical properties, phenolic content and in vitro digestion profile of Chinese black rice under gradient milling treatment. The chemical composition, color, pasting and thermal properties of black rice with different milling degrees were comprehensively compared. In vitro digestion analysis indicated that cooked rice flour had higher rapidly digestible starch (RDS) and lower resistant starch (RS) contents compared with the uncooked one. Besides, all cooked black rice samples exhibited high predicted glycemic index (pGI) value and whole black rice showed a lower pGI than refined rice. The microstructure and the abundance of phenolic compounds in the solid matrix during different treatments or digestion stages were observed by CLSM. Furthermore, a total of 102 phenolic constituents were absolutely quantified by targeted metabolomics techniques. Methanol extraction and moderate cooking treatment contributed to the release of phenolic compounds from the solid matrix of whole black rice. Besides, compared to the gastric digestion stage, the transition in the intestinal environment caused a decrease in the majority of the analyzed polyphenols. Identifying the phenolic constituents was favorable for a better elucidation of the chemical basis of the function and nutritional value of Chinese black rice.

Characteristics of antioxidant capacity and metabolomics analysis of flavonoids in the bran layer of green glutinous rice (Oryza sativa L. var. Glutinosa Matsum)

Green glutinous rice is a unique genetic germplasm that has yet to be adequately studied. This study investigated antioxidant capacity and flavonoid metabolites in the bran layer of green glutinous rice (LvH) compared to purple (HeiH), red (HongH) and white (GJG) varieties. The results showed that LvH bran had significantly higher content of total flavonoids and anthocyanin than that of HongH (1.91-fold and 4.34-fold) and GJG (2.45-fold and 13.30-fold). LvH bran also showed significantly higher levels of vitamin B1 and vitamin E than that of HeiH (1.94-fold and 1.15-fold) and HongH (1.22-fold and 1.13-fold), indicating that green glutinous rice bran was rich in bioactive components. LvH bran showed significantly lower IC50 values for scavenging DPPH and ATBS radicals than GJG and even significantly lower IC50 value for scavenging DPPH radicals than HongH, highlighting its potential as an effective source of antioxidants. LvH bran had significantly different downstream metabolite synthesis in the flavonoid pathway compared to HeiH, HongH, and GJG, with 40, 26, and 22 different metabolites, 23, 20, and 33 up-regulated differentially expressed metabolites (DEMs), and 73, 50, and 13 down-regulated DEMs, respectively. Of the 139 flavonoid metabolites identified in colored rice bran, 26 metabolites showed significant positive correlation with both ABTS and DPPH radical scavenging capacity. Typically, quercetin derivatives showed potential for evaluating the antioxidant capacity of colored rice bran. These findings offer valuable insights into the antioxidant properties of green glutinous rice bran and provide references for better understanding of flavonoid metabolites in different colored rice bran.

Effects of degree of milling on nutritional quality, functional characteristics and volatile compounds of brown rice tea

This study investigated the effects of rice preparation using different degrees of milling (DOM) from 0% to 13% on the nutritional composition, functional properties, major volatile compounds and safety of brown rice tea (BRT). We found that 2% DOM reduced 52.33% of acrylamide and 31.88% of fluorescent AGEs. When DOM was increased from 0% to 13%, the total phenolic content (TPC) of brown rice tea decreased by 48.12%, and the total flavonoid content (TFC) and condensed tannin content (CTC) also decreased significantly, with the smallest decrease at 2% DOM. In addition, the inhibitory activities of α-amylase, α-glucosidase and pancreatic lipase as well as the antioxidant activity also decreased gradually. Analysis by electronic nose and gas chromatography-mass spectrometry (GC-MS) showed that alkanes, furans, aldehydes, pyrazines and alcohols were the major volatiles in BRT, with 2% DOM having the greatest retention of aroma compounds. An orthogonal partial least squares discriminant analysis (OPLS-DA) and VIP score (VIP > 1 and p < 0.05) analysis were used to screen 25 flavor substances that contributed to the differences in BRT aroma of different DOMs. These results suggest that 2% milled BRT can improve safety and palatability while maximizing the retention of flavor compounds and nutrients. The findings of this study contribute to an enhanced understanding of the dynamics of changes and preservation of aroma compounds and nutrients present during the processing of BRT.

Metabolites Associated with the Main Nutrients in Two Varieties of Purple Rice Processed to Polished Rice

Under the same nitrogen fertilizer and cultivation conditions, the nutrients of rice are strongly affected during the processing of brown rice to polished rice, especially in special rice varieties. In this study, twenty-two amino acids in brown and polished rice of two purple rice varieties were quantified using targeted metabolomics, and the relationships among the main nutrients, mineral elements and metabolites were analysed. The results showed that the amino acid levels in YZN1_H (polished rice of Yangzinuo No. 1) and YZN2_H (polished rice of Yangzinuo No. 2) decreased to different degrees compared with those in YZN1_B (brown rice of Yangzinuo No. 1) and YZN2_B (brown rice of Yangzinuo No. 2). Citric acid is closely associated with amino acids. The total sugar (TS), ATP, and soluble dietary fiber (SDF) levels in YZN1_B decreased by 9.37%, 53.85%, and 75.71%, respectively, compared with those in YZN1_H. The TS, ATP, and SDF levels in YZN2_B decreased significantly by 6.92%, 21.03%, and 76.78%, respectively, compared with those in YZN2_H. Citric acid was significantly negatively correlated with ATP and SDF but significantly positively correlated with carotenoids. The Se content in YZN1_H was significantly higher than that in YZN1_B by 87.02%. The Se content in YZN2_H was significantly higher than that in YZN2_B by 72.02%. Citric acid was significantly positively correlated with Fe, Mn, Ca, and Mg. Citric acid was identified as a candidate key metabolite that affects changes in the main nutrients in purple rice during processing.

Extraction Optimization, UHPLC-Triple-TOF-MS/MS Analysis and Antioxidant Activity of Ceramides from Sea Red Rice Bran

As a new type of salt-tolerant rice, sea red rice contains more minerals, proteins, and lipid compounds, and, in particular, its by-product rice bran may be used to replace other commercial rice brans as the main source of ceramides (Cers). However, the extraction rate of Cers is generally low, and it is crucial to seek an efficient extraction method. This study optimized the ultrasonic-assisted extraction of Cers from sea red rice bran using response surface methodology (RSM) and obtained a Cers yield of 12.54% under optimal conditions involving an extraction temperature of 46 °C, an extraction time of 46 min, and a material–to-liquid ratio of 5 g/mL. The Cers content in sea red rice bran was preliminarily analyzed using thin-layer chromatography, and the Cers content was determined via UHPLC-Triple-TOF-MS/MS after purification and separation using silica column chromatography. Forty-six different types of Cers were identified in sea red rice bran, of which Cer 18:0/24:0 (2OH), Cer 18:0/26:0, Cer 18:0/26:0 (2OH), and Cer 18:0/24:0 accounted for 23.66%, 17.54%, 14.91%, and 11.96%. Most of the Cers structures were mainly composed of sphingadienine. A biological activity assay indicated that Cers extracted from sea red rice bran had significant antioxidant and anti-aging properties. These findings indicate that the extracted Cers show great potential for applications in the cosmetic and pharmaceutical industries.

Quantification of Amino Acids, Phenolic Compounds Profiling from Nine Rice Varieties and Their Antioxidant Potential

In recent years, the health benefits of the pigmented rice varieties have been reported due to the richness of their bioactive compounds. Therefore, this study evaluated the antioxidant, total flavonoid, total phenolic, anthocyanin content, amino acid and individual phenolic compound quantification of nine Korean-grown rice varieties using spectrophotometric, HPLC-FLD-MS/MS and UHPLC Q-TOF-MS/MS methods. Our research found that the free fractions of DM29 (red rice) had the highest free radical scavenging ability of ABTS and DPPH. In contrast, the highest ferric reducing antioxidant power was observed in the 01708 brown rice variety. The majority of phenolic compounds such as quercetin, ferulic acid, p-coumaric acid, ascorbic acid, caffeic acid and genistein were found in the DM29 sample. The phenolic content of rice varies depending on its color, with DM29 red rice having the highest TPC, TFC and TAC levels. At the same time, the presence of the majority of amino acids was quantified in the 01708 and GR (Gangwon) brown rice varieties. According to this study, colored rice varieties are high in amino acids, phenolic compounds and antioxidants. This research would be beneficial in furthering our understanding of the nutritional value of different colors of rice and their high potential as a natural antioxidant.