Rice Endosperm Protein Research Articles

Association between Potential Renal Acid Load and 10-Year Mortality in Patients on Hemodialysis.

Higher dietary acid load (DAL) has been linked to elevated incidence and progression of chronic kidney disease. However, the association between DAL and mortality in patients on maintenance hemodialysis (MHD) has not been evaluated. We retrospectively analyzed baseline laboratory data, self-administered diet history questionnaire results, and 10-year mortality rates in 44 patients (26 men, 67.9±10.4 years) on MHD who participated in a randomized, double-blind, crossover pilot trial of rice endosperm protein supplementation which was conducted in 2013. DAL was estimated from nutrition intake using potential renal acid load (PRAL), and patients were divided into tertiles using this score. During the 10-year observation period, 19 patients (43%) died. A higher PRAL score was significantly associated with higher all-cause mortality. The multivariable-adjusted hazard ratio for all-cause mortality in the highest tertile of PRAL versus the lowest tertile was 3.88 (95% confidence interval [CI], 1.10-13.61). Multiple logistic regression analysis showed a significant association between higher PRAL and lower intake of green and yellow vegetables (odds ratio, 5.40; 95% CI, 1.37-21.26) and fruits (odds ratio, 4.76; 95% CI, 1.30-16.76). Higher PRAL is positively associated with all-cause mortality, and these associations might be affected by a lower intake of fruits and vegetables in Japanese patients on MHD.

Characterization of rice endosperm-derived antidepressant-like peptide (REAP): An orally active novel tridecapeptide derived from rice protein

It is ideal to ingest bioactive substances from daily foods to stay healthy. Rice is the staple food for almost half of the human population. We found that an orally administered enzymatic digest of rice endosperm protein exhibits antidepressant-like effects in the tail suspension test (TST) using mice. A comprehensive peptide analysis of the digest using liquid chromatography-tandem mass spectrometry was performed, and a tridecapeptide QQFLPEGQSQSQK, detected in the digest, was chemosynthesized. Oral administration of the tridecapeptide exhibited antidepressant-like effects at a low dose comparable to classical antidepressant in the TST. This also exhibited anti-depressant-like effect in the forced swim test. We named it rice endosperm-derived antidepressant-like peptide (REAP). Intriguingly, intraperitoneal administration had no effect. Orally administered REAP(8−13) but not REAP(1−7) exhibited antidepressant-like activity, suggesting that the C-terminal structure is important for the antidepressant-like effect. We confirmed the presence of REAP, corresponding to rice glutelin type B4(130−142) and B5(130−142), in the digest. The effects of REAP were blocked by both dopamine D1 and D2 antagonists. These results suggest that it exerts its antidepressant-like activity through activation of the dopamine system.Taken together, oral administration of a novel tridecapeptide exhibited antidepressant-like effects via the dopamine system. This is the first report of a rice-derived peptide that exhibits antidepressant-like effects.

Rice Endoplasmic Protein-Derived Peptides, Rice-Ghretropins A and B, Stimulate Ghrelin Release in MGN3-1 Cells and Increase Plasma Acylated Ghrelin and Food Intake in Mice.

In this study, we demonstrated that novel rice-derived bioactive peptides promote the secretion of ghrelin, an endogenous orexigenic hormone secreted from the stomach. The enzymatic digest of rice endosperm protein with subtilisin, a microorganism-derived enzyme, stimulated acylated ghrelin secretion in the ghrelin-releasing cell line MGN3-1 and increased food intake after oral administration in mice. By performing a comprehensive analysis based on structure-activity relationships, we selected candidate peptides from over 30,000 peptides in the rice digest. Among them, we found that QAFEPIRSV and TNPWHSPRQGSF, corresponding to the amino acid sequence of the rice endoplasmic proteins glutelin A1 or A2(52-60) and B1 or B2(31-42), respectively, stimulated acylated ghrelin release in MGN3-1 cells. We named them rice-ghretropins A and B. Pyroglutamate formation of rice-ghretropin A, [pyr1]-rice-ghretropin A, also promoted ghrelin secretion. Furthermore, oral administration of rice-ghretropins increased food intake, plasma ghrelin concentration, and small intestinal transit in mice. In addition, the subtilisin digest of the rice protein significantly increased food intake for 4 h in 9 month-old (control: 0.61 ± 0.049 g; digest: 0.83 ± 0.059 g) and 24 month-old mice (control: 0.52 ± 0.067 g; digest: 1.01 ± 0.064 g). In summary, we found that novel bioactive peptides, namely, rice-ghretropins, from the enzymatic digest of rice endosperm stimulated acylated ghrelin secretion and increased food intake. This is the first report of rice-derived exogenous bioactive peptides that increase acylated ghrelin secretion.

Selective concentration of antimicrobial peptides to heat-treated porous silica gel using adsorption/desorption

Heat-treated porous silica gel (HT silica gel) previously developed by our group has selectively adsorbed cationic peptides at a pH of 7. Therefore, we focused on the use of antimicrobial peptides (AMPs) as bioactive peptides (BPs). First, 32 AMPs and 32 randomly designed peptides were generated using Fmoc solid synthesis, and their adsorption ratio to HT-silica gel was investigated. Thirty two AMPs showed a relatively higher adsorption ratio of 58.8% compared to that of randomly designed peptides, which was 35.3%. Desorption conditions were investigated using Amyl-1-18 antimicrobial peptides. Next, pepsin hydrolysate from rice endosperm protein (REP) powder was prepared by ourselves. The REP hydrolysate containing dry matter (7.5mg) was applied to the adsorption/desorption (AD) procedure using HT silica gel to obtain 1.6mg of AD hydrolysate. When the two hydrolysates were subjected to mass spectrometry, 305 concentrated peptides were obtained. In total, 26 peptides with high content and high enrichment ratios were listed and synthesized. When the antimicrobial activity of these 26 peptides was evaluated using Cutibacterium acnes, five peptides consisting of 12-27 amino acids were identified as novel AMPs. Two of these peptides, which were derived from rice glutelin, showed antimicrobial activity against all four microbes, including Porphyromonas gingivalis, Escherichia coli, and Streptococcus mutans. In the present study, we showed that AMPs could be easily enriched from protein hydrolysate using HT silica gel. The adsorption/desorption procedure using HT silica gel was confirmed to be a useful tool for convenient BP separation.

Rice Endosperm Protein Improves the Anti-Inflammatory Effects of High-Density Lipoprotein and Produces Lower Atherosclerotic Lesion Accelerated by the Renal Mass Reduction than Casein in a Mouse Model

Background Chronic kidney disease (CKD) impairs the anti-inflammatory effects of high-density lipoprotein (HDL) and increases cardiovascular mortality. Though the potential role of dietary interventions to manage HDL is well studied, the clinical trials aimed to increase HDL levels have failed to reduce cardiovascular risk, rendering HDL function to be explored as a more relevant clinical parameter. This study investigates the effects of rice endosperm protein (REP), a plant-based protein, on the anti-inflammatory properties of HDL and renal injury-driven atherosclerosis in comparison with casein, an animal protein. Materials and methods Ten-week-old apolipoprotein E-deficient hyperlipidemic mice underwent uninephrectomy. The mice (n = 6 each) were pair-fed a normal casein-based diet or a REP-based diet (both with 20.0% protein content) for seven weeks. Atherosclerotic lesions were detected by en face Sudan IV staining of the aorta. Results The number and sizes of the atherosclerotic lesions were significantly lower in the REP-based diet-fed group than the casein-based diet-fed group (p = 0.038). However, the REP-based diet neither elicited an ameliorative effect on kidney function or histology nor impacted the cholesterol profiles. Furthermore, HDL from the REP-based diet-fed mice significantly suppressed the inflammatory cytokine response of human umbilical vein endothelial cells than that from the casein-based diet-fed mice (MCP-1, p = 0.010; IL-6, p = 0.011; IL-1β, p = 0.028). Conclusions The REP-based diet has a higher potential to lessen the atherosclerotic lesions accelerated by renal mass reduction than a casein-based diet, which could be associated with the anti-inflammatory effects of HDL.

Rice Endosperm Protein Administration to Juvenile Mice Regulates Gut Microbiota and Suppresses the Development of High-Fat Diet-Induced Obesity and Related Disorders in Adulthood.

Obesity and related disorders, which are increasing in adults worldwide, are closely linked to childhood diet and are associated with chronic inflammation. Rice endosperm protein (REP) intake during adulthood has been reported to improve lipid metabolism and suppress the progression of diabetic kidney disease in animal models. However, the effects of REP intake during childhood on adulthood health are unclear. Therefore, we used a mouse model to experimentally investigate the preconditioning effects of REP intake during childhood on the development of obesity and related disorders in adulthood. Male C57BL/6J mice were pair-fed a normal-fat diet containing casein or REP during the juvenile period and then a high-fat diet (HFD) containing casein or REP during adulthood. Mice fed REP during the juvenile period showed better body weight, blood pressure, serum lipid profiles, lipopolysaccharide (LPS)-binding protein levels, and glucose tolerance in adulthood than those fed casein during the juvenile period. HFD-induced renal tubulo-glomerular alterations and hepatic microvesicular steatosis were less evident in REP-fed mice than in casein-fed ones. REP intake during the juvenile period improved HFD-induced dysbiosis (i.e., Escherichia genus proliferation and reduced gut microbiota diversity), thereby suppressing endotoxin-related chronic inflammation. Indeed, REP-derived peptides showed antibacterial activity against Escherichia coli, a major producer of LPS. In conclusion, REP supplementation during the juvenile period may regulate the gut microbiota and thus suppress the development of obesity and related disorders in adulthood in mice.

Limited hydrolysis of rice endosperm protein for improved techno-functional properties

Limited hydrolysis of rice endosperm protein isolate was carried out with acid and neutral endoproteases to evaluate the relationship between degree of hydrolysis and techno-functional properties. The highest studied degree of hydrolysis was 5.4% corresponding to 55.2% protein solubility. Solubility increased as a function of degree of hydrolysis with higher efficiency by acid endoprotease. Colloidal stability of the protein suspensions steadily increased with increasing degree of hydrolysis. Higher colloidal stability values were achieved by neutral endoprotease (31–89%) compared to that by acid endoprotease (20–75%). On the other hand, the absolute values of zeta potential and surface hydrophobicity decreased as a function of degree of hydrolysis leading to higher values by neutral endoprotease (−21.4 mV and 21.7 mV) than by acid endoprotease (−813.4 mV and 11.7 mV). Foaming, gel formation and water holding properties improved only until degree of hydrolysis values of 1.5% (neural endoprotease) and 1.9% (acid endoprotease).

2038-P: Rice Endosperm Protein Intake in Childhood Suppresses the Development of High-Fat Diet-Induced Metabolic Disorders and Kidney Disease during Adulthood in Mice

Introduction: Obesity is associated with lifestyle diseases such as type 2 diabetes and organ complications including kidney disease. Childhood diet has a great influence on the development of obesity and its related disorders. Rice endosperm protein (REP) has been reported to improve lipid metabolism and suppress the progression of diabetic kidney disease in animal models. Therefore, we aimed to clarify the effects of REP intake during childhood on the development of high-fat-diet (HFD)-induced obesity and its related disorders during adulthood in mice. Methods: Four-week-old male C57BL/6J mice were pair-fed a normal-fat diet containing casein or REP for 6 weeks (childhood), and subsequently, an HFD containing casein or REP for 12 weeks (adulthood). Mice were then tested for oral glucose tolerance and subjected to the analyses of growth status, biochemical parameters, kidney histology, and fecal gut microbiota by 16S rRNA gene sequencing. Antibacterial activity of REP-derived peptides against gut microbiota was evaluated in vitro. Results: Mice fed REP in childhood showed less increase in body weight, total fat mass, blood pressure, serum total cholesterol, triglyceride, and lipopolysaccharide (LPS)-binding protein, and better glucose tolerance than those fed casein in childhood followed by HFD with casein or REP. Furthermore, HFD-induced glomerular hypertrophy, mesangial expansion, and vacuolar formation in proximal tubules were suppressed in mice fed REP than those fed casein in childhood. The intake of REP in childhood ameliorated dysbiosis caused by HFD. Additionally, REP-derived peptides showed antibacterial activity against E. coli, a major producer of LPS. Conclusion: These results indicate that the intake of REP during childhood can inhibit the progression of HFD-induced metabolic disorders and kidney disease in adulthood, probably through the effects of REP on gut microbiota. Disclosure Y. Higuchi: None. M. Hosojima: Research Support; Self; Astellas Pharma Inc., Biotech Japan Corporation, Daiichi Sankyo Co.,Ltd., Eli Lilly Japan K.K., Forica Foods Co.,Ltd., Kameda Seika Co.,Ltd., Kyowa Hakko Kirin Co., Ltd., Mitsubishi Tanabe Pharma Corporation, MSD K.K., Novo Nordisc Pharma Ltd., Sato Foods Industries Co.,Ltd., Taisho Toyama Pharmaceutical.Co.,Ltd., Takeda Pharmaceutical Co.,Ltd. H. Kabasawa: Research Support; Self; Astellas Pharma Inc., Biotec Japan Corporation, Daiichi Sankyo Company, Limited, Forica Foods CO.,LTD., KAMEDA SEIKA CO., LTD., Kyowa Hakko Kirin Co., Ltd., Mitsubishi Tanabe Pharma Corporation, MSD K.K, Novo Nordisc Pharma Ltd, Sato Foods Industries CO.,LTD., Taisho Toyama Pharmaceutical.CO.,LTD., Takeda Pharmaceutical Company Limited. S. Kuwahara: None. R. Kaseda: None. H. Arao: None. T. Tanaka: None. I. Narita: None. A. Saito: None.

Characterisation of the physicochemical properties of intact and hydrolysed rice protein ingredients

The physicochemical properties of rice protein ingredients, including three rice protein concentrates (RPC 1, RPC 2 and RPC 3), two rice endosperm protein hydrolysates (RPH 1 and RPH 2) and two rice bran protein hydrolysates (RBPH 1 and RBPH 2), were investigated and compared to those of selected dairy protein ingredients, i.e., skim milk powder (SMP), whey protein isolate (WPI) and whey protein hydrolysate (WPH). RPC samples had low solubility in water (2–35%) in the pH range 2–8, while RPH samples were highly soluble and RBPH samples had intermediate (>60%) solubility. RPHs had the highest foaming capacity, and foams generated using these ingredients displayed the slowest drainage rate and a relatively high stability of foam volume. Increases in viscosity during heating to 95 °C, and on subsequent cooling to 35 °C, of RBPH 1 solution were associated with gelatinisation and retrogradation, respectively, of its starch component. Severe heat treatment (140 °C × 30 min) did not affect the colloidal stability of RPH solutions, but resulted in extensive thickening and particulation of RBPH solutions and coagulation of SMP and WPI solutions. These results demonstrate the excellent physicochemical properties of RPHs and highlight their potential as functional and value-added ingredients in a range of food products.

Modification of rice protein with glutaminase for improved structural and sensory properties

SummaryRice protein is highly nutritive and hypoallergenic but certain physicochemical properties restrict its applications in beverages. This study aimed to tackle this issue by modifying rice endosperm protein with glutaminase via deamidation. Glutaminase treatment facilitated an increase in deamidation degree and mean particle size of rice protein and a continuing decrease in turbidity with time. Favourable changes induced in sensory properties included: improved suspendability (increased by 81.25%), lumpiness (decreased by 84.78%), grittiness (decreased by 72.34%) and overall taste liking (improved by 12.24%). Visual observations of rice protein dispersions and turbidity measurements further confirmed the improved suspendability in water. Fourier transform infrared spectroscopy analysis revealed that the action of glutaminase did not remarkably change the protein structure, but slightly reduced α‐helical conformation whilst increased β‐sheet and β‐turn structures. Glutaminase could be useful for deamidation modification of products with high content of glutamine residues (like rice protein), through inducing the breakdown of some intermolecular and intramolecular bonds including hydrophobic interactions and hydrogen bonding without serious cleavage of the peptide bonds, allowing protein rearrangements to more flexible or extended forms. As a result of protein unfolding with more hydrophobic clusters exposed, certain physicochemical properties of rice protein were improved.

Peptides from rice endosperm protein restrain periodontal bone loss in mouse model of periodontitis

ObjectiveFood-derived peptides have been reported to exhibit antibacterial activity against periodontal pathogenic bacteria. However, no effect has been shown on inflammation and bone resorption in periodontal pathology. The overall objective of the current study was to investigate how rice peptides influence biological defense mechanisms against periodontitis-induced inflammatory bone loss, and identify their novel functions as a potential anti-inflammatory drug. DesignThe expression of inflammatory and osteoclast-related molecules was examined in mouse macrophage-derived RAW 264.7 cell cultures using qPCR. Subsequently, the effect of these peptides on inflammatory bone loss in mouse periodontitis was examined using a mouse model of tooth ligation. Briefly, periodontal bone loss was induced for 7 days in mice by ligating the maxillary second molar and leaving the contralateral tooth un-ligated (baseline control). The mice were microinjected daily with the peptide in the gingiva until the day before euthanization. One week after the ligation, TRAP-positive multinucleated cells (MNCs) were enumerated from five random coronal sections of the ligated sites in each mouse. ResultsRice peptides REP9 and REP11 significantly inhibited transcription activity of inflammatory and osteoclast-related molecules. Local treatment with the rice peptides, in mice subjected to ligature-induced periodontitis, inhibited inflammatory bone loss, explaining the decreased numbers of osteoclasts in bone tissue sections. ConclusionTherefore, these data suggested that the rice peptides possess a protective effect against periodontitis.

A Randomized, Double-Blind, Crossover Pilot Trial of Rice Endosperm Protein Supplementation in Maintenance Hemodialysis Patients

In maintenance hemodialysis (MHD) patients, low protein intake is associated with protein-energy wasting, a risk factor that affects outcome. However, increased protein intake may lead to hyperphosphatemia and hyperkalemia, which are also mortality risk factors. Here, we evaluated the safety and effects of purified rice endosperm protein (REP), which contains less phosphorus and potassium than soy and casein proteins, as a supplemental protein source for MHD patients. This randomized, double-blind, placebo-controlled, crossover pilot study of REP supplementation (5 g/day × 4 weeks) was carried out in 50 Japanese adult MHD patients (1 dropped out); the primary outcome was the change in the urea kinetic-based normalized protein catabolic rate (nPCR), an indicator of protein intake in MHD patients. Intention-to-treat analyses of 24 patients in the REP-first group and 25 in the placebo-first group showed that REP supplementation increased nPCR significantly by 0.07 g/kg/day (95% confidence interval, 0.03–0.11), whereas changes in serum phosphorus and potassium concentrations were not different from the placebo. REP supplementation did not show a significant effect on other nutritional or metabolic parameters and no specific complications. In conclusion, purified REP with efficient bioavailability may be safe and useful for dietary supplementation in MHD patients.

Cationic peptides from peptic hydrolysates of rice endosperm protein exhibit antimicrobial, LPS-neutralizing, and angiogenic activities

In this study, we hydrolyzed rice endosperm protein (REP) with pepsin and generated 20 fractions containing multifunctional cationic peptides with varying isoelectric point (pI) values using ampholyte-free isoelectric focusing (autofocusing). Subsequently, we determined antimicrobial activities of each fraction against the pathogens Prophyromonas gingivalis, Propionibacterium acnes, Streptocossus mutans, and Candida albicans. Fractions 18, 19, and 20 had pI values greater than 12 and exhibited antimicrobial activity against P. gingivalis, P. acnes, and C. albicans, but not against S. mutans. In further experiments, we purified and identified cationic peptides from fractions 18, 19, and 20 using reversed-phase high-performance liquid chromatography and matrix-assisted laser/desorption ionization–time-of-flight mass spectroscopy. We also chemically synthesized five identified peptides (RSVSKSR, RRVIEPR, ERFQPMFRRPG, RVRQNIDNPNRADTYNPRAG, and VVRRVIEPRGLL) with pI values greater than 10.5 and evaluated antimicrobial, lipopolysaccharide (LPS)-neutralizing, and angiogenic activities. Among these synthetic peptides, only VVRRVIEPRGLL exhibited antimicrobial activity against P. gingivalis, with an IC50 value of 87μM. However, all five cationic peptides exhibited LPS-neutralizing and angiogenic activities with little or no hemolytic activity against mammalian red blood cells at functional concentrations. These present data show dual or multiple functions of the five identified cationic peptides with little or no hemolytic activity. Therefore, fractions containing cationic peptides from REP hydrolysates have the potential to be used as dietary supplements and functional ingredients in food products.

Obtaining and purification of a highly soluble hydrolyzed rice endosperm protein

Abstract Rice endosperm proteins are quite insoluble and have low commercial value mainly due to their poor functional properties. In this study the influence of enzymatic hydrolysis and tangential flow ultrafiltration were evaluated in obtaining a hydrolyzed rice endosperm protein of high solubility and reduced sodium content. Initially, enzymatic hydrolysis kinetics was evaluated to select the enzyme/substrate ratio and hydrolysis time appropriate to the process. The rice endosperm proteins were extracted by the alkaline method and hydrolyzed with Alcalase® until reaching degree of hydrolysis of 9.40% when 40% of the protein became solubilized. The molar masses of the soluble peptides were evaluated via LC-MS QTOF MS/MS. The hydrolyzed soluble fraction was recovered by centrifugation, pre-treated by microfiltration and then concentrated by tangential flow ultrafiltration using a 1 kDa membrane. The sample was subjected to two diafiltrations with reduced solvent volume, after it was dried and analyzed with respect to their protein, mineral, sodium and potassium contents, solubility and foaming properties. The hydrolyzed protein showed 71.28% of protein; ultrafiltration removed 70% of the total mineral content. Even so, the sample still showed 1.97% of sodium, demonstrating the need to carry out more diafiltrations. The hydrolysate has solubility higher than 88.5% in the pH 3 to 7, reaching 99.8% at pH 6. The sample had high foaming capacity, but low foam stability. Thus, enzymatic hydrolysis associated with ultrafiltration can be a suitable alternative for obtaining a soluble fraction with low sodium content, improving the quality of rice endosperm protein.

Rice endosperm protein slows progression of fatty liver and diabetic nephropathy in Zucker diabetic fatty rats.

We previously reported that rice endosperm protein (REP) has renoprotective effects in Goto-Kakizaki rats, a non-obese diabetic model. However, whether these effects occur in obese diabetes remains unclear. This study aimed to clarify the effects of REP on obese diabetes, especially on fatty liver and diabetic nephropathy, using the obese diabetic model Zucker diabetic fatty (ZDF) rats. In total, 7-week-old male ZDF rats were fed diets containing 20 % REP or casein (C) for 8 weeks. Changes in fasting blood glucose levels and urinary markers were monitored during the experimental period. Hepatic lipids and metabolites were measured and renal glomeruli were observed morphologically. HbA1c levels were significantly lower in rats fed REP, compared with C (P<0·05). Compared with C in the liver, REP prevented lipid accumulation (total lipid, TAG and total cholesterol, P<0·01). Liver metabolome analysis indicated that levels of metabolites associated with glycolysis, the pentose phosphate pathway and carnitine metabolism were significantly greater in the REP group than in the C group (P<0·05), suggesting activation of both glucose catabolism and fatty acid oxidation. The metabolite increases promoted by REP may contribute to suppression of liver lipid accumulation. Urinary excretion of albumin and N-acetyl-β-d-glucosaminidase was significantly reduced in rats fed REP for 8 weeks (P<0·01). In addition, there was a distinct suppression of mesangial matrix expansion and glomerular hypertrophy in response to REP (P<0·01). Thus, REP had preventive effects on obese diabetes, fatty liver and diabetic nephropathy.

Physical and flow properties of rice protein powders

In this study, the physical and flow properties of a range of rice protein powders, including three rice protein concentrates (RPC 1, RPC 2 and RPC 3), two rice endosperm protein hydrolysates (RPH 1 and RPH 2) and two rice bran protein hydrolysates (RBPH 1 and RBPH 2) were determined and compared with those of selected dairy protein powders, i.e., skim milk powder, whey protein isolate and whey protein hydrolysate. The physical properties analysed included particle size distribution, particle shape and surface characteristics. Differential scanning calorimetry analysis demonstrated that RBPH samples had lower thermal stability compared to RPC and RPH samples. Analysis of the moisture sorption properties showed a higher hygroscopicity at high relative humidity values of hydrolysed protein powders compared to their intact counterparts. All protein ingredients analysed displayed good flowability (i.e., easy-flowing or free-flowing behaviour), while the bulk density of intact rice protein ingredients was higher than that of their hydrolysed counterparts. The results obtained in this study enable enhanced control of the behaviour of rice protein powders during storage, handling and processing.

Beneficial effects of rice endosperm protein intake in Japanese men with risk factors for metabolic syndrome: a randomized, crossover clinical trial

Rice protein is proved to have hypocholesterolemic and anti-atherosclerotic effects, and a few experimental studies showed its renoprotective effects, using animal diabetic models. However, no clinical studies have investigated its benefits for human health. We aimed to clarify how the intake of rice endosperm protein affects markers correlating to lipid dysfunction in human. We recruited 18 male volunteers, 26–64 years of age, with risk factors for metabolic syndrome and allocated randomly into two groups. Half of them were administered test food containing rice endosperm protein and other half were administered control food containing sodium caseinate for 4 weeks. The dose of supplemental protein was 10 g/day. After medical examinations, the study foods were switched and the intervention was continued for another 4 weeks. Lipid metabolism markers were evaluated as primary outcome measures. Cross-over analysis was performed for 18 subjects using physical and clinical values measured before and after each intervention period. The serum high-density lipoprotein cholesterol (HDL-C) level was increased at 0.08 mmol/L [interquartile range (IQR) from −0.05 to 0.19 mmol/L] during the period when rice endosperm protein was administered (the rice endosperm protein period), whereas it was decreased at −0.04 mmol/L [IQR from −0.13 to 0.05 mmol/L] during the period when casein was administered (the casein period). Treatment effect was significant with P = 0.047. Changes in total cholesterol, low-density lipoprotein cholesterol and triglycerides were not different between treatments. Among the secondary outcome measures, decrease in serum uric acid (UA) during the rice endosperm protein period [−24 μmol/L (IQR from −39 to −6 μmol/L)] was greater than that during the casein period [0 (IQR from −6 to 13 μmol/L)] with a significant treatment effect (P = 0.030). Supplemental intake of rice endosperm protein may elevate serum HDL-C level and lower serum UA level in male subjects with risk factors for metabolic syndrome. Clinical Trials Registry: UMI08923 .

Rice protein hydrolysates stimulate GLP-1 secretion, reduce GLP-1 degradation, and lower the glycemic response in rats.

Rice has historically been consumed in Asia as a major source of carbohydrates, however, little is known regarding the functional roles of rice proteins as dietary factors. In the present study, we investigated whether peptides derived from rice proteins could stimulate GLP-1 secretion, which results in reducing glycemia via the incretin effect in normal rats. Hydrolysates were prepared from the protein fraction of rice endosperm or rice bran, and the effects of these hydrolysates on GLP-1 secretion were examined in a murine enteroendocrine cell line GLUTag. Plasma was collected after oral administration of the rice protein hydrolysates, under anesthesia, or during glucose tolerance tests in rats. In anesthetized rats, plasma dipeptidyl peptidase-IV (DPP-IV) activity was measured after ileal administration of the rice protein hydrolysates. GLP-1 secretion from GLUTag cells was potently stimulated by the rice protein hydrolysates, especially by the peptic digest of rice endosperm protein (REPH) and that of rice bran protein (RBPH). Oral administration of REPH or RBPH elevated plasma GLP-1 concentrations, which resulted in the reduction of glycemia under the intraperitoneal glucose tolerance test. In addition, the plasma DPP-IV activity was attenuated after ileal administration of REPH or RBPH, which resulted in a higher ratio of intact (active) GLP-1 to total GLP-1 in the plasma. These results demonstrate that rice proteins exert potent stimulatory effects on GLP-1 secretion, which could contribute to the reduction of postprandial glycemia. The inhibitory effect of these peptides on the plasma DPP-IV activity may potentiate the incretin effect of GLP-1.

Nutritional quality of rice bran protein in comparison to animal and vegetable protein

Rice bran protein (RBP) was prepared by alkali extraction and isoelectric precipitation from defatted rice bran. The protein quality of RPB was evaluated and compared to two vegetable proteins [soy protein (ISP) and rice endosperm protein (REP)] and two animal proteins [whey protein (WPI) and casein]. RPB contained 74.93% of protein and its pepsin digestibility and KOH solubility were 89.8% and 91.5%, respectively.In Sprague-Dawley rats, RBP showed protein efficiency ratio, net protein ratio, net protein utilisation, and biological value of 2.39, 3.77, 70.7, and 72.6, which were comparable to the qualities of animal proteins. The true digestibility of RBP (94.8%) was significantly higher than that of REP (90.8%), ISP (91.7%) and WPI (92.8%) and the same as that of casein. Protein digestibility corrected amino acid score (PDCAAS) of RBP was 0.90. These results suggest that rice bran protein appears to be a promising protein source with good biological values and digestibility.

Rice Dreg Protein as an Alternative to Soy Protein Isolate: Comparison of Nutritional Properties

Rice dreg protein could be a valuable source of plant-based proteins, as an alternative to soy proteins in some food products. Here, nutritional properties of rice dreg protein were compared with those of soy protein isolate. The protein content of rice dreg protein was approximately 62.6 g/100 g sample, with large amounts of fat, carbohydrate, and ash. The denaturation temperatures of rice protein isolate from rice dreg protein were 47.4 and 97.2°C, respectively. This indicated that these proteins could be denatured during rice syrup processing to form aggregates, but were relatively more stable than rice endosperm protein and soy protein isolate. The main amino acids in rice dreg protein and rice protein isolate were Glu, Pro, Arg, Asp, and Leu, with Lys as the lowest content. Most of essential amino acids and nutritional parameters of rice protein isolate and rice dreg protein met the suggested nutritional requirements for a child according to FAO/WHO, and were relatively higher than those of soy protein isolate. In addition, rice protein isolate showed better digestibility than soy protein isolate during four hours sequential pepsin and pancreatin digestions. The final digestibility value was 96.66% for rice protein isolate compared to 91.41% for soy protein isolate. Thus rice dreg protein could potentially replace soy proteins as a good source of value-added protein for human nutrition in response to the increasing demand for plant proteins.