Rice Dreg Research Articles

Impact of deep eutectic solvent deamidation on the solubility and conformation of rice dreg protein isolate

Impact of deep eutectic solvent deamidation on the solubility and conformation of rice dreg protein isolate

Rice dreg protein as a high‐quality plant‐based protein resource: Characterization of structural, functional, and in vitro digestive properties

AbstractBackground and ObjectivesRice dregs, a by‐product of the process of making sugar from broken rice, have a protein content of up to 70%. However, rice dreg protein (RDP) has not yet been fully utilized due to its high‐temperature liquefaction denaturation during sugar production. In this study, the structural, functional, and in vitro digestive properties of rice protein (RP) extracted from broken rice and RDP derived from rice dregs were compared, with a view to providing a basis for further utilization of RDP.FindingsAlthough RDP was a heat‐denatured protein, it was found to have relatively better functional properties and a well‐balanced amino acid composition. Structural analysis results revealed that RDP showed a looser and disordered structure. However, SDS‐PAGE results showed that the subunit composition of the two proteins was similar. The in vitro simulated digestion results showed that the digests of RDP had higher antioxidant and ACE inhibitory activity, but RDP showed significantly lower digestibility than RP.ConclusionsThrough relevant modifications of RDP, RDP has the potential to be a good source of high‐quality protein in the human diet as the demand for plant‐based protein increases.Significance and NoveltyThis study can provide a basic theoretical basis for further development and utilization of RDP, which is also of great practical significance for seeking new plant protein resources and increasing the added value of broken rice.

The impact of pH shifting combined high-pressure homogenization on structural and functional properties of rice dreg protein

The composition and aggregation of rice dreg protein (RDP) have a major impact on its properties. The aim of the present study was to investigate the effects of pH shifting combined high-pressure homogenization (HPH) treatment on functional properties of RDP. The improvement of RDP functional properties with pH shifting at alkaline (pH 12) condition followed by HPH treatment (20, 40, 60, 80, 100 MPa) prior to neutralization at pH 7 was much better than that of HPH and/or pH shifting. The method carried out at under pH 12 followed by HPH 100 MPa was found to be the most efficient treatment for increasing the solubility of RDP from 0.86% to 63.50%, the emulsification from 3.13% to 7.10%, and the foaming capacity from 19.33% to 179.67%. It was revealed that pH shifting combined HPH treatment depolymerized the aggregates, reduced the particle size, spread the structure, decreased the surface hydrophobicity of RDP, and avoided any bitterness production. These results have important implications for the modification of proteins with improved functional profiles.

The role of heating time on the characteristics, functional properties and antioxidant activity of enzyme-hydrolyzed rice proteins-glucose Maillard reaction products

This study analyzed the influence of Maillard reaction on the physicochemical, functional properties and antioxidant activity of hydrolyzed rice dreg protein. Maillard reaction between glucose and rice dreg protein hydrolysates produced from various proteases, including trypsin, Neutrase 0.8L and flavourzyme were undertaken. The results of the sodium dodecyl sulfate-polyacrylamide gel electrophoresis and FTIR spectrometer verified the occurrence of Maillard reaction and the formation of MRPs. Analysis on the structure and characteristics of Maillard reaction products (MRPs) at different heating time revealed that the pH of MRPs decreased sharply in the early stage, while the browning intensity of MRPs largely improved. The grafting degree of the MRPs increased to maximum at 90 min and then declined. All amino acids content was decreased with the extended reaction time, and the degradation of lysine and arginine was rapid. The Maillard reaction and the thermal degradation were dominant before and after 90 min, respectively. The solubility of MRPs remained stable independent of the heating time while the emulsifying activity improved at extended reaction time. The MRPs obtained greater antioxidant activity after the Maillard reaction.

Characteristics of rice dreg protein isolate treated by high-pressure microfluidization with and without proteolysis

The characteristics of rice dreg protein isolate (RDPI) treated by microfluidization (0, 40, 80, 120, and 160 MPa) with or without proteolysis were investigated. Alcalase, Neutrase, and the combination of the two (Alcalcase:Neutrase = 1:1 [w/w]) were adopted for hydrolysis. The surface hydrophobicity and solubility of RDPI were increased. As pressure increased, different structures of RDPI exhibited disaggregation (<120 MPa) and reaggregation (160 MPa), and the effect on proteolysis was significant. The solubility of Neutrase and combined enzyme hydrolysates was improved after microfluidization. Additionally, the optimum choice of microfluidization (40 MPa) and Neutrase was efficient for improving the DPPH radical scavenging activity. The results indicate that both pressure level and enzyme type synergistically determine the functionality and antioxidant activities of products. This work may provide an alternative methodology for improving the utilization of RDPI in the food industry through desirable modifications.

Effect of cold and hot enzyme deactivation on the structural and functional properties of rice dreg protein hydrolysates

This study explored the effect of three different enzyme deactivation treatments: 4 °C slow cold deactivation (RDPH-(4 °C)), −18 °C rapid cold deactivation (RDPH-(−18 °C)) and 100 °C water bath (RDPH-(100 °C)), compared to that without enzyme deactivation (RDPH-(control)) on the structural and functional properties of rice dreg protein hydrolysates (RDPHs). The RDPHs from the different enzyme deactivation methods led to significant differences in the degree of hydrolysis, surface hydrophobicity, average particle size, intrinsic fluorescence and emulsion stability. FTIR analysis revealed that the strength of RDPH-(100 °C) spectrum peaks decreased significantly. All samples showed high solubility (>85%) and potent antioxidant capacity: DPPH (~90%), ABTS (~99%), and reducing power (0.86–1.03). Among the hydrolysates evaluated, the RDPH-(100 °C) led to the lowest reducing power and hydroxyl radical scavenging activity. Results reported here will be instrumental for the development of rice protein-based products and in the optimization and scale up of manufacturing process.

Extraction of antioxidant peptides from rice dreg protein hydrolysate via an angling method

Selective enrichment of the highly active antioxidant peptides is required as the lack of an efficient method leads to long screening processes, hampering the research of antioxidant peptides. A simple synthetic metal–organic framework MIL-53 (Cr) was initially applied to extract specific antioxidant peptides from rice dreg protein hydrolysate. The highest active fraction was further purified by reversed-phase high-performance liquid chromatography. The antioxidant peptides with the highest antioxidant activities were identified as Gly-Asp-Met-Asn-Pro and Leu-Leu-Leu-Arg-Trp by LC–MS. These two peptides were synthesized and also exhibited good scavenging activity on the DPPH free radical, superoxide anion free radical and hydroxyl radical, and good chelating ability on Fe2+. The results confirmed that the angling method was effective for antioxidant peptide enrichment from protein hydrolysates.

Lysinoalanine formation and conformational characteristics of rice dreg protein isolates by multi-frequency countercurrent S-type sonochemical action

The influences of multi-frequency countercurrent S-type ultrasound (MFSU), with various frequency modes, on lysinoalanine (LAL) formation and conformational characteristics of rice dreg protein isolates (RDPI) were investigated. The ultrasonic operating mode with dual-frequency combination (20/40 kHz) indicated lower LAL content and higher protein dissolution rate of RDPI compared with that of other ultrasound operating modes. Under the dual-frequency ultrasound mode of 20/40 kHz, acoustic power density of 60 W/L, time of 20 min, and temperature of 35 °C, the relative reduction rate of LAL of RDPI reached the highest with its value of 26.95%, and the protein dissolution rate was 71.87%. The changes in chemical interactions between protein molecules indicated that hydrophobic interactions and disulfide bonds played a considerable role in the formation of LAL of RDPI, especially the reduction of g-g-g and g-g-t disulfide bond. Alterations in microstructure showed that ultrasonication loosened the protein structure and created more uniform protein fragments of RDPI. In conclusion, using MFSU in treating RDPI was an efficacious avenue for minimizing LAL content and modifying the conformational characteristics of RDPI.

Effect of dual-frequency ultrasound on the formation of lysinoalanine and structural characterization of rice dreg protein isolates.

The effect of dual-frequency ultrasound treatment with different working modes on the lysinoalanine (LAL) formation and structural characterization of rice dreg protein isolates (RDPI) was studied during alkaline exaction processing. Ultrasonic notably decreased the LAL amount of RDPI and enhanced the protein dissolution rate. The LAL content of RDPI, especially sequential dual frequency 20/40kHz, decreased by 12.02% (P<0.05), compared to non-sonicated samples. Herein, the protein dissolution rate was higher. The changes in sulfhydryl groups was positively correlated with the LAL formation. The amino acids (AA) such as threonine (Thr), lysine (Lys), and arginine (Arg) were reduced, resulting in a decrease in LAL content following sonication. Besides, ultrasonication altered protein secondary structure by reducing random coil and β-sheet contents, while α-helix and β-turn contents increased. Alterations in the surface hydrophobicity, particle size, particle size distribution, and microstructure indicated more irregular fragment with microparticles of RDPI by sonochemical treatment. Thus, ultrasound treatment may be a new and efficacious process for controlling the LAL generation in prepared-protein food(s) during alkali extraction.

Solubility, structural properties, and immunomodulatory activities of rice dreg protein modified with sodium alginate under microwave heating.

This research aims to investigate the solubility, structural properties, and immunomodulatory of rice dreg protein (RDP) modified with sodium alginate. The modification was done by wet heating assisted with microwave treatment. The solubility, emulsifying properties at pH 2–12, amino acid composition, molecular weight distribution, circular dichroism (CD) spectroscopy, and FTIR spectra of modified RDP were analyzed and discussed. Results showed that Maillard reaction could significantly enhance the solubility and emulsifying capacity of RDP. Further, an animal model for cyclophosphamide‐induced immunodeficiency was designed to evaluate the immunomodulatory effect of modified RDP. It is therefore suggested that modified RDP could improve the immunomodulatory effect of immunosuppressed mice, and the immunomodulation was concentration dependent, being generally enhanced by increased concentrations. This research revealed that glycosylation modification of RDP through Maillard reaction by wet heating assisted with microwave treatment may be successfully applied to improve the physicochemical properties and bioactive benefits of the final product.

Facilitating Production of Rice Dreg Peptides via Lactic Acid Bacterial Fermentation on Anti-Hypertension Efficacy

Facilitating Production of Rice Dreg Peptides via Lactic Acid Bacterial Fermentation on Anti-Hypertension Efficacy

Effects of ultrasound-assisted α-amylase degradation treatment with multiple modes on the extraction of rice protein

The effects of ultrasound-assisted α-amylase degradation (UAD) treatment with multiple modes on the extraction of rice protein (RP) from rice dreg powder were studied. The results showed that UAD treatment increased protein extraction rate significantly (p<0.05) compared to that of α-amylase degradation treatment and control. Among all the ultrasound mode treatments researched in this paper, sequential frequency ultrasound treatment presented higher protein extraction rate compared to that of simultaneous or single frequency ultrasound treatment. The highest protein extraction rate was obtained under 20/35kHz of sequential frequency UAD treatment with the protein extraction rate of 89.58% and protein purity of 92.99%. The test and analysis of fourier transform infrared spectroscopy, ultraviolet–visible spectroscopy, starch content, non-protein nitrogen content, SH and SS content, surface hydrophobicity, amino acids content and proteins characteristics were studied to reveal the mechanism of UAD on the protein extraction effect. After treated with UAD, the starch-protein agglomerates disintegrated completely, moreover, protein advanced structure was changed to some extent and the disulfide bond was partially broken, but the main chain structure (peptide chain), specificity of protein and amino acid composition were not obviously changed. Consequently, the structure modified RP extracted by UAD treatment presented higher solubility, emulsifying activity and foaming capacity, which was beneficial for the application of RP. In conclusion, UAD treatment is an effective method for maximizing extraction rate, purity and modifying properties of extracted protein.

Physical and Oxidative Stabilities of O/W Emulsions Formed with Rice Dreg Protein Hydrolysate: Effect of Xanthan Gum Rheology

The shortening of shelf-life of food emulsions is frequently due to poor creaming and lipid oxidation stability. The lipid oxidation of O/W emulsions can be inhibited by rice dreg protein hydrolysate (RDPH); however, emulsions were stabilized by Tween-20. Polysaccharides can control the rheology and network structure of the aqueous continuous phase by increasing viscosity and yield stress, hence retarding phase separation and gravity-induced creaming, especially for xanthan gum. The objective of this research was to evaluate whether emulsions formed with 2 wt% RDPH and stabilized by xanthan gum (0–0.5 wt%) could produce 20 % (v/v) soybean oil-in-water emulsions that had good physical and oxidative stability. The degree of flocculation of droplets as a function of xanthan gum concentration was assessed by the microstructure, rheology, and the creaming index of emulsions. Addition of xanthan gum prior to homogenization had no significant effect on the mean droplet diameter in all emulsions studied. Increase in xanthan gum concentration led to the increase in creaming stability of emulsions, due to an increase in viscosity of the continuous phase and/or the formation of a droplet network with a yield stress, as well as the enhanced steric and electrostatic repulsion between the droplets. Lipid oxidation of the emulsions was significantly inhibited at xanthan gum concentrations of 0.12 wt% or above with RDPH, which could due to the fact that xanthan gum increases the viscosity of the aqueous phase and hindered the diffusion of oxidants to the oil droplet surface area, synergistic effect between RDPH and xanthan gum to suppress oil peroxidation, and metal ion chelation capability of xanthan gum. Thus, stable protein hydrolyzates-type emulsions could be obtained with increasing concentration of xanthan gum.

Effect of Ultrasound on Alkali Extraction Protein from Rice Dreg Flour

AbstractIn this study, Counter‐current ultrasound‐assisted alkali was employed to extract rice dreg protein (RDP) from rice dreg flour (RDF). The results indicated that extraction yield of RDP reached a maximum value at 0.08 mol/L alkali concentrate. It was only 43.20% in absence of ultrasound, whereas it reached up to 88.44% under ultrasonic condition. Amino acid composition, scanning electron microscopy, atomic force microscopy and fourier transform infrared spectra were used to determine amino acid composition, morphology, aggregates and microstructure of RDP. Ultrasound treatment could result in improving of hydrophobic amino acids content and changing of RDF and RDP microstructure, showing enhancement in the porosity of RDF particle, variation of RDP particle size. Thus, the acceleration of protein extraction was related to the changes of RDF and RDP microstructure caused by ultrasound. Counter‐current ultrasound‐assisted alkali extraction, as a modified method, was proved to be helpful in industrial manufacture of RDP from RDF.Practical ApplicationsLow‐frequency high‐intensity ultrasound has been used in many aspects in laboratory, such as extraction of components, pretreatment. Counter‐current ultrasound‐assisted extraction was proved to be helpful in industrial manufacture of protein because it can dramatically improve extraction rate of rice dreg protein, and Counter‐current ultrasound method can achieve continuous production of industrialization.

Protective effects of rice dreg protein hydrolysates against hydrogen peroxide-induced oxidative stress in HepG-2 cells.

In this paper, the effects of rice dreg protein hydrolysates (RDPHs) obtained by various proteases on hydrogen peroxide-induced oxidative stress in HepG-2 cells were investigated. Cell cytotoxicity was evaluated through the aspects of cell viability, ROS level, antioxidant enzyme activity, and production of malondialdehyde (MDA). Cell apoptosis was assessed by flow cytometry. Molecular weight distribution was analyzed by gel permeation chromatography, and amino acid composition was measured using an automatic amino acid analyzer. The survival of cells and the activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) were significantly increased through the pre-incubation of HepG-2 cells with RDPHs before H2O2 exposure. Additionally, these pretreatments also resulted in a reduction in ROS and MDA levels. As a result, apoptosis and loss of mitochondrial membrane potential of the HepG-2 cells were alleviated. Furthermore, the protective effects of protein hydrolysates obtained by various proteases were noticeably distinct, in which RDPHs prepared by alkaline protease showed higher antioxidant activities. The difference in the protective effects might be attributed to the specific peptide or amino acid composition. Therefore, enzymatic hydrolysis with different enzymes studied here could attenuate H2O2-induced cell damage, and the type of protease greatly influenced the anti-oxidative activity. Particularly, optimum use of Alcalase could produce peptides with higher antioxidant activity.

Fermentation technology and quality of sauce prepared from rice dreg protein

Fermented sauce, from rice dreg protein (RDP) instead of soybean, has unique advantages. In the present paper, the fermentation technology of RDP sauce was studied. Amino nitrogen, reducing sugar, soluble protein and colour indicators, as well as the quality of three kinds of RDP sauce fermented under different conditions, were analysed. The results suggest that an optimized fermentation technology is the addition of 2.4 times salty solution into koji, to obtain a 13% salt concentration in the sauce mash, and then fermentation at ~35°C. RDP sauce that had an addition of 0.01% Zygosaccharomyces rouxii in the fermentation stage gave a good quality RDP sauce. The RDP sauce content of amino nitrogen and reducing sugar, with 0.01% Z. rouxii, was 0.98 and 4.57 g/100 mL respectively, and the corresponding sensory quality was better than in the samples produced without Z. rouxii. It was concluded that RDP can be utilized to produce a high-quality sauce. Copyright © 2015 The Institute of Brewing & Distilling

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.

Comparison of functional and structural properties of native and industrial process-modified proteins from long-grain indica rice

Rice proteins, as a cheap plant protein source from the by-products of rice dreg processing, could potentially replace commonly used proteins such as soy and whey proteins in selected food products. In this study, the functional properties, surface hydrophobicity (H0), sulfhydryl and disulfide bond contents, thermal properties, as well as secondary structures of native rice endosperm protein (REP) and processed rice dreg protein (RDP) extracted from long-grain indica rice, were compared. RDP was found to have a higher solubility associated with its relatively higher emulsifying and foaming properties than REP, as well as its water/oil holding capacity, although it was a denatured protein. The emulsifying properties were dependent on the solubility and H0, while solubility was also related to the disulfide bond contents. Distinct differences in H0, thermal properties, and disulfide bond contents between REP and RDP could be due to the conformational changes, as the industrial processing steps in the production of rice syrups caused an increase in β-turns at the expense of β-sheets and random coils of REP, leading to the unfolding of β-sheets into higher-ordered supramolecular structures for RDP, which could be responsible for its better functional properties.

Enhancing the oxidative stability of food emulsions with rice dreg protein hydrolysate

Rice dreg protein hydrolysates (RDPH) can potentially be used as natural antioxidants for a variety of emulsion-type food systems. They contained 89.9% protein, 934.2mg/g total amino acids with 517.7mg/g total hydrophilic amino acids, and 78% peptides smaller than 5kDa. Here, the physical and oxidative stabilities of corn oil-in-water emulsions (10wt.% lipid) containing RDPH (0–20mg/mL) and stabilized by Tween-20 were investigated as a function of RDPH concentration and pH. The results showed that emulsions with RDPH and Tween-20 emulsions did not experience coalescence (when RDPH concentration<20mg/mL), and were more stable than emulsions prepared by either emulsifier alone (RDPH or Tween-20). RDPH and Tween-20 could not prevent coalescence, because when RDPH=20mg/mL, competitive adsorption existed at the interface between high concentrations RDPH and Tween-20. The negatively charged emulsion stabilized with 5mg/mL RDPH and Tween-20 was found to be more stable at pH 5. RDPH was able to inhibit lipid oxidation, reducing the formation of lipid hydroperoxides and TBARS with increasing RDPH concentrations. Similarly the increase in pH also reduced oxidation, possibly by scavenging free radicals and chelating pro-oxidant metals. The antioxidant properties of RDPH at the interface of emulsion droplets would render them suitable as natural antioxidants in some food products.

Physicochemical properties and emulsion stabilization of rice dreg glutelin conjugated with κ‐carrageenan through Maillard reaction

Rice dreg is an underutilized source of cereal protein with good potential for application in the food industry. Glutelin represents about 850 g kg(-1) of total storage protein in rice dreg. The objective of this study was to characterize the physicochemical properties and emulsion stabilization of the Maillard type conjugate formed with rice dreg glutelin (RDG) and κ-carrageenan (1:2 weight ratio) dry-heated at 60 °C and 79% relative humidity for 24 h. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Fourier transform-infrared analysis provided evidence on the formation of the Maillard type conjugation. Amino acid analysis suggested that the major locus during the Maillard reaction were lysine and arginine. Circular dichroism spectra showed decreasing amounts of α-helix and β-strand in the products with increment in the amount of turns and random coil. Conjugation with κ-carrageenan could significantly improve solubility of RDG (P < 0.05). Measurements of mean droplet size and creaming stability in oil-in-water emulsions showed that the conjugate was more effective at stabilizing emulsions at low pH or in the presence of high ionic strength. The Maillard reaction can be successfully used as a coupling method for RDG and κ-carrageenan to form the conjugate with improved solubility and emulsion stabilization.