Protein oxidation affected the encapsulation properties of rice bran protein fibril-high internal phase pickering emulsions: Enhanced stability and bioaccessibility of ß-carotene.

Rice bran protein fibril (RBPF)-high internal phase Pickering emulsions (HIPPEs) loaded with ß-carotene (CE) were constructed to enhance stability and bioavailability of CE. Rice bran (RB) protein with varying oxidation degrees was extracted from RB with varying storage period (0-10 days) to prepare RBPF by acid-heating (90 °C, 2-12 h) to stabilize HIPPEs. The influence of protein oxidation on the encapsulation properties of RBPF-HIPPEs was studied. The results showed that CE-HIPPEs could be stably stored for 56 days at 25 °C. When RB storage time was the same, the average particle size, lipid hydroperoxide content, and malondialdehyde content of CE-HIPPEs and the CE degradation rate initially fell, and then grew as the acid-heating time prolonged, while the ζ-potential value, viscosity, viscoelasticity, free fatty acid (FFA) release rate, and bioaccessibility first rose, and subsequently fell. When acid-heating time of RBPF was the same, the average particle size, lipid hydroperoxide content, and malondialdehyde content of CE-HIPPEs initially fell, and subsequently increased with RB storage time extended, while the ζ-potential value, viscosity, viscoelasticity, FFA release rate, and bioaccessibility initially increased, and then decreased. Overall, Moderate oxidation and moderate acid-heating enhanced the stability as well as rheological properties of CE-HIPPEs, thus improving the stability and bioaccessibility of CE. This study offered a new insight into the delivery of bioactive substances by protein fibril aggregates-based HIPPEs.

Effect of Rice Bran Protein on the Foaming Properties and Foaming Characteristics of Rice Bran Protein-Sodium Caseinate and Rice Bran Protein Nanoparticles-Sodium Caseinate.

Rice bran, a byproduct of rice milling, comprises 12-14% protein. The foaming properties and associated mechanisms of the composite rice bran protein system were not well studied. In this study, a composite protein system composed of rice bran protein (RBP)-sodium caseinate (NaCas) and rice bran protein nanoparticles (RBPNs)-sodium caseinate (NaCas) was investigated. The results showed that the synergistic effect of RBP and NaCas increased the foaming stability of the composite solution up to 83.77 ± 2.75%. Moreover, the foaming capacity and foaming stability of the RBPNs-NaCas composite solution were up to 177.50 ± 3.53% and 80.28 ± 0.39%, respectively. The physicochemical properties results revealed that the particle size volume peaks of RBP-NaCas and RBPNs-NaCas were mainly concentrated at 55.7 nm and 197.1 nm, and RBPNs-NaCas showed a wider single peak particle size distribution. The ζ-potential values of RBP-NaCas and RBPNs-NaCas were changed to -35.5 ± 0.07 mV and -27.2 ± 0.28 mV after complexation. The apparent viscosity and consistency factor of RBP-NaCas decreased by 31.1% compared to RBP, while RBPNs-NaCas displayed similar parameters to the single proteins. The interfacial rheological test showed that RBP and RBPNs can significantly improve the interfacial properties of NaCas by enhancing the interfacial interaction and the interfacial viscoelastic modulus of composite proteins, which is conducive to the stability of the foam system. The outcome of the study provided a theoretical basis for RBP and RBPNs to partially replace NaCas in the processing of foamed food.

Preparation of Transglutaminase-Catalyzed Rice Bran Protein Emulsion Gels as a Curcumin Vehicle.

Protein-based emulsion gels have tunable viscoelasticity that can be applied to improve the stability of bioactive ingredients. As the by-product of rice processing, rice bran protein (RBP) has high nutritional value and good digestibility, exhibiting unique value in the development of hypoallergenic formula. In this study, the effect of transglutaminase (TGase) cross-linking on the physicochemical properties of RBP emulsion gels was investigated. To improve the stability of curcumin against environmental stress, the entrapment efficiency and stability of curcumin in the emulsion gel systems were also evaluated. The results indicated that TGase increased the viscoelastic modulus of RBP emulsion gels, resulting in a solid-like structure. Moreover, the entrapment efficiency of curcumin was increased to 93.73% after adding TGase. The thermal stability and photo-stability of curcumin were enhanced to 79.54% and 85.87%, respectively, compared with the sample without TGase addition. The FTIR results showed that TGase induced the cross-linking of protein molecules and the secondary structure change in RBP. Additionally, SEM observation confirmed that the incorporation of TGase promoted the formation of a compact network structure. This study demonstrated the potential of RBP emulsion gels in protecting curcumin and might provide an alternative strategy to stabilize functional ingredients.

The synergistic effects of rice bran rancidity and dephenolization on digestive properties of rice bran protein.

Both rice bran (RB) rancidity and dephenolization could affect the structural characteristics and phenolics composition of rice bran protein (RBP), thereby affecting RBP digestibility. The synergistic effects of RB rancidity and dephenolization on RBP digestibility were investigated. Excessive RB rancidity (RB stored for 10 d) and non-dephenolization reduced RBP digestibility, while moderate RB rancidity (RB stored for 1 d) combined with dephenolization improved RBP digestibility to a maximum of 74.19%. Dephenolization reduced the antioxidant capacities of RBP digestive products. The digestibility of non-dephenolized RBP (NDRBP) was significantly (P < 0.05) related with its carbonyl content, surface hydrophobicity, and ζ-potential. The digestibility of dephenolized RBP (DRBP) was significantly related with its ß-sheet structure content, surface hydrophobicity, ζ-potential, and average particle size. Overall, moderate RB rancidity combined with dephenolization enhanced RBP digestibility by reducing the non-competitive inhibition of endogenous phenolics on protease and regulating the spatial structural characteristics of RBP.

Heat treatment improves the dispersion stability of rice bran milk through changing the settling behavior.

Poor dispersion stability of nutritious rice bran milk limits its production. In this study, the dispersion stability of rice bran milk after heating at 95 °C for 0-5 min was investigated. Visual observation revealed improved dispersion stability and changes in settling behavior with heat durations. After heating for 5 min, the serum turbidity increased from 1.86 to 2.95. The centrifugal sedimentation rate unexpectedly rose from 9.25% to 29.18%, indicating an increase in volumetric particle concentration. Fourier transform infrared spectroscopy revealed that heating induced starch gelatinization and protein denaturation in rice bran milk, leading to increased volumetric particle concentration. Rice bran protein aggregates after heating were developed and embedded in the gel-like network composed of swollen starch granules. These results suggested that rice bran milk, due to thermal-induced alteration in biomacromolecules, may behave progressively from free settling to hindered settling to compression settling, resulting in improved dispersion stability.

Effects of rice bran rancidity on the interfacial adsorption properties of rice bran protein fibril aggregates and stability of high internal phase Pickering emulsions.

The effects of rice bran rancidity-induced protein oxidation and heating time on the stability of rice bran protein fibril aggregates (RBPFA)-high internal phase Pickering emulsions (HIPPEs) were investigated. The optimal conditions for RBPFA-HIPPEs were 8 mg/mL RBPFA with an oil phase volume fraction of 75 %. Moderate oxidation (rice bran stored for 3 d) and moderate heating (8 h) enhanced the wettability, flexibility, diffusion rate, and adsorption rate of RBPFA, meanwhile, the rheological properties of RBPFA-HIPPEs increased. RBPFA-HIPPEs could be stably stored for 50 d at 25 °C. Moderate oxidized and moderate heated RBPFA-stabilized HIPPEs could remain stable after heat treatment and could be re-prepared after freeze-thaw (3 cycles). Additionally, the stability of RBPFA-HIPPEs was significantly related to the structural characteristics and interfacial properties of RBPFA. Overall, moderate oxidation and moderate heating enhanced the storage, thermal, and freeze-thaw stability of RBPFA-HIPPEs by improving the interfacial properties of RBPFA.

Effect of epigallocatechin-3-gallate modification on the structure and emulsion stability of rice bran protein in the presence of soybean protein isolate.

For improving the emulsion stability of rice bran protein (RBP), RBP was modified by different concentrations of epigallocatechin-3-gallate (EGCG) in the presence of soybean protein isolate (SPI), and RBP-EGCG-SPI conjugate was prepared by alkaline pH-shifting. The results showed that the addition of EGCG led to an increase in the bound phenol content and the flexibility of the secondary structure, a decrease in the free sulfhydryl and disulfide bond content of the RBP-EGCG-SPI conjugate. EGCG covalently bound to RBP and SPI through non-disulfide bonds. When the concentration of EGCG was 10 % (w/v), the emulsifying activity index and emulsion stability index of conjugate reached the maximum value (36.61 m2/g and 255.61 min, respectively), and the conjugate had the best emulsion stability. However, an EGCG concentration above 10 % (w/v) negatively affected the emulsion stability, with increasing particle size due to protein aggregation. Summarily, the modification of EGCG improved the emulsion stability of conjugate by regulating the spatial structure of RBP-EGCG-SPI conjugate. The work provided an important guide to further improve the emulsion stability of RBP.

Self-assembly embedding of curcumin by alkylated rice bran protein.

Lysine-rich rice bran protein (RBP) can be used as raw material for alkylation modification to improve the self-assembly performance of protein. The results of 1H NMR, degree of alkylation, and DSC analysis showed that the alkyl chain was successfully attached to the RBP. The surface hydrophobicity and absolute ζ-potential increased. The three-dimensional structure of the alkylated RBP (ARBP) become more porous and ARBP-2 was selected as the material for embedding curcumin. The XRD results revealed that curcumin induced self-aggregation of ARBP-2 and the inclusion of curcumin was attained. The maximum encapsulation efficiency of curcumin was 82.67 % and the maximum loading amount was 171.37 g/100 g RBP. The results of atomic force microscopy (AFM), particle size, and polydispersity index (PDI) analyses revealed that the particles in the system were aggregated after curcumin was added. Curcumin was well protected by encapsulation in the self-assembled particles. Thus, this study provides a new strategy for the embedding and delivery of curcumin.

Effect of protein oxidation on the emulsion carrier prepared by rice bran protein for improving stability and bioavailability of ß-carotene.

The emulsion carriers which prepared by rice bran protein (RBP) with different oxidation extents were utilized to deliver ß-carotene (BC). The effects of RBP oxidation extent on stability and bioaccessibility of BC in rice bran protein emulsion (RBPE) were investigated by measuring the droplet size, microstructure, digestive stability, cellular antioxidant, and delivery property of BC-RBPE. The results showed that BC-RBPE prepared by moderately oxidized RBP (extracted from rice bran with a storage time of 5 d) presented excellent digestive stability and delivery property during gastrointestinal digestion. The particle size of initial BC-RBPE, BC-RBPE after gastric digestion, and BC-RBPE after intestinal digestion were 509.73, 2149.33, and 997.82 nm, respectively. Compared with free BC suspension, the BC retention after gastric digestion and the BC bioavailability of BC-RBPE prepared by moderately oxidized RBP increased by 23.50% and 27.54%, respectively. In addition, the BC cellular antioxidant activity and BC cellular uptake of BC-RBPE prepared by moderately oxidized RBP were significantly higher than that of free BC-suspension, which increased by 29.63% and 13.84%, respectively. In summary, the study showed that oil-in-water emulsion prepared by moderately oxidized protein is a potential delivery system of BC, which can provide a theoretical basis for improving the utilization of protein by adjusting the extent of protein oxidation.

Ultrasonic treatment of rice bran protein-tannic acid stabilized oil-in-water emulsions: Focus on microstructure, rheological properties and emulsion stability.

Rice bran protein (RBP)-tannic acid (TA) complex was prepared and the RBP-TA emulsions were subjected to ultrasonic treatment with different powers. Ultrasonic treatment has a positive effect on improving the properties of RBP-TA emulsion. This study investigated the influence of different ultrasonic power levels on the physicochemical properties, microstructure, rheological properties, and stability of emulsions containing RBP-TA. Under the ultrasonic treatment of 400 W, the particle size, zeta potential, and adsorbed protein content of the RBP-TA emulsion were 146.86 nm, -20.7 eV, and 61.91%, respectively. At this time, the emulsion had the best emulsifying properties, apparent viscosity, energy storage modulus and loss modulus. In addition, the POV and TBARS values of RBP-TA emulsions were 6.12 and 7.60 mmol/kg, respectively. The thermal, salt ion, pH and oxidative stability of the emulsions were investigated, and it was shown that ultrasonic treatment was effective in improving the stability of RBP-TA emulsions.

Covalent modification of (+)-catechin to improve the physicochemical, rheological, and oxidative stability properties of rice bran protein emulsion.

The aim of this study is the effects of (+)-catechin (CC) covalent cross-linking (CCCI) (0.05-0.25 %, w/v) on the physicochemical properties, rheological properties, and oxidative stability of rice bran protein (RBP) emulsion. Analysis of particle size, ζ-potential, circular dichroism, fluorescence spectroscopy, surface hydrophobicity, and emulsifying properties demonstrated that a concentration of 0.15 % (w/v) CCCI facilitated protein structure unfolding, resulting in reduced particle size, enhanced electrostatic repulsion, and improved emulsion stability. Moreover, the covalent complexes of RBP-0.15 %CC (w/v) exhibited increased viscosity and shear stress, reflected by the highest G' and G″ values, ultimately enhancing the oxidative stability. Furthermore, analysis using atomic force microscopy and confocal laser scanning microscopy revealed that the RBP-0.15 %CC complexes exhibited the smallest particle size (164 nm) and displayed greater homogeneity. An increase in CC concentration to 0.25 % (w/v) resulted in a higher emulsion aggregation. The emulsions stabilized by CCCI exhibited superior rheological properties and enhanced oxidation stability compared to the control. In conclusion, an appropriate amount of CC can enhance the rheology and oxidation stability of the RBP emulsion, while CCCI treatment holds potential for expanding the utility of RBP in various applications.

Structure and emulsifying properties of rice bran protein alkylated using an electrochemical reactor.

To replace the application of reducing agents for protein alkylation, electrochemical reduction techniques have been considered. In this study, a custom-made electrochemical reactor was used to alkylate rice bran protein (RBP). The structure, morphology, and emulsification properties of RBP were investigated under different voltages. When treated at 35 V, the content of the α-helix and ß-sheet of RBP decreased at first and then increased, whereas the content of the ß-turn and random coil increased steadily. The CH3 group of RBP was exposed and S-S decreased. The endogenous fluorescence spectral curve exhibited a redshift. The free sulfhydryl (-SH) content increased. The average particle size of the modified RBP decreased by 69.35 %, and its zeta potential decreased to -21.8 mV. Atomic force microscopy (AFM) revealed that the treated protein particles dispersed more evenly and their roughness (Rq) decreased. The contact angle, water holding capacity (WHC), fat holding capacity (FHC), and solubility were enhanced. The emulsification capacity increased to 65.82 m2/g and emulsification stability increased to 36.34 min. These results demonstrated that the RBP was alkylated by the electrochemical reactor and the modified RBP showed improved emulsification properties compared to the untreated RBP.

Physicochemical properties and in vitro digestion behavior of emulsion gels stabilized by rice bran protein aggregates: Effects of heating time and induction methods.

To investigate the effects of heating time and induction methods on the physicochemical properties and in vitro digestion behavior of emulsion gels, rice bran protein aggregates (RBPAs) were formed by acid-heat induction (90 °C, pH 2.0) and the emulsion gels were further prepared by adding GDL or/and laccase for single/double cross-linked induction. Heating time affected the aggregation and oil/water interfacial adsorption behavior of RBPAs. Suitable heating (1-6 h) was conducive to faster and more adsorption of aggregates at the oil/water interface. While excessive heating (7-10 h) resulted in protein precipitation, which inhibited the adsorption at the oil/water interface. The heating time at 2, 4, 5 and 6 h was thus chosen to prepare the subsequent emulsion gels. Compared with the single cross-linked emulsion gels, the double-cross-linked emulsion gels showed higher water holding capacity (WHC). After simulated gastrointestinal digestion, the single/double cross-linked emulsion gels all exhibited slow-release effect on free fatty acid (FFA). Moreover, the WHC and final FFA release rate of emulsion gels were closely related to the surface hydrophobicity, molecular flexibility, sulfhydryl, disulfide bond and interface behavior of RBPAs. Generally, these findings proved the potential of emulsion gels in designing fat alternatives, which could provide a novel technique for the fabrication of low-fat food.

A novel strategy for preparation of rice bran protein oleogels based on high internal phase emulsion template.

BACKGROUND: Oleogels have been extensively explored as fat substitutes with no trans fatty acids and low saturated fatty acids in recent years as a result of increased health problems found to be related to the intake of trans and saturated fatty acids. RESULTS: Herein, high internal phase emulsion (HIPE) stabilized by rice bran protein (RBP) was prepared and further utilized as a template for preparation of RBP oleogels. RBP HIPE with the strongest rheological properties was obtained at pH 5.0 as a result of appropriate structural deformation, surface charge and a high three-phase contact angle at this pH. However, RBP oleogels prepared at pH 9.0 exhibited the highest yield stress after drying process. At this pH, RBP showed higher resistance to deformation caused by water evaporation. This highlighted the importance of structural stability of protein network on rheological properties of the resultant oleogels. Furthermore, with an increase in drying temperature, RBP oleogels exhibited higher yield stress and gel strength because water was better removed as a result of an enhanced capability to overcome the capillary pressure of emulsion. CONCLUSION: The present study further revealed the structure-activity relationship between protein, HIPE and oleogel, and also provided theoretical support for the development of protein-based oleogel. © 2023 Society of Chemical Industry.

The effect of alkaline extraction and drying techniques on the physicochemical, structural properties and functionality of rice bran protein concentrates.

Rice bran protein concentrates (RBPC) were extracted using mild alkaline solvents (pH: 8, 9, 10). The physicochemical, thermal, functional, and structural aspects of freeze-drying (FD) and spray-drying (SD) were compared. FD and SD of RBPC had porous and grooved surfaces, with FD having non-collapsed plates and SD being spherical. Alkaline extraction increases FD's protein concentration and browning, whereas SD inhibits browning. According to amino acid profiling, RBPC-FD9's extraction optimizes and preserves amino acids. A tremendous particle size difference was prominent in FD, thermally stable at a minimal maximum of 92 °C. Increased pH extraction gives FD greater exposal surface hydrophobicity and positively relates to denaturation enthalpy. Mild pH extraction and drying significantly impacted solubility, improved emulsion properties, and foaming properties of RBPC as observed in acidic, neutral, and alkaline environments. RBPC-FD9 and RBPC-SD10 extracts exhibit outstanding foaming and emulsion activity in all pH conditions, respectively. Appropriate drying selection, RBPC-FD or SD potentially employed as foaming/emulsifier agent or meat analog.

Rice bran protein-based delivery systems as green carriers for bioactive compounds.

Natural protein-based delivery systems have received special interest over the last few years. Different carriers are already developed in the food industry to protect, encapsulate and deliver bioactive compounds. Rice bran protein (RBP) is currently used as a carrier in encapsulating bioactives due to its excellent functional properties, great natural value, low price, good biodegradability, and biocompatibility. Recently, RBP-based carriers including emulsions, microparticles, nanoparticles, nanoemulsions, liposomes, and core-shell structures have been studied extensively in the literature. This study reviews the important characteristics of RBP in developing bioactive delivery systems. The recent progress in various modification approaches for improving RBP properties as carriers along with different types of RBP-based bioactive delivery systems is discussed. In the final part, the bioavailability and release profiles of bioactives from RBP-based carriers and the recent developments are described.

Effect of salt treatment on the stabilization of Pickering emulsions prepared with rice bran protein.

In this study, salt addition (NaCl and CaCl2) was utilized to improve the stability of emulsions formed by rice bran protein (RBP). The result showed that salt addition improved the adsorption of protein on the oil-water interface and enhanced the physical stability of emulsions. Compared to NaCl condition, emulsions with CaCl2 (especially 200 mM) addition exhibited more significant storage stability, as microscopy images showed emulsion structure unchanged and droplet size increasing slightly from 12.02 µm to 16.04 µm in 7 days. It was attributed to the strengthened particle complexation with CaCl2 and the increased hydrophobic interactions, which is explained by the improved particle size (260.93 nm), surface hydrophobicity (1890.10) and fluorescence intensity, thus inducing dense and hardly destroyed interfacial layers. Rheological behavior analyses suggested that salt-induced emulsions had higher viscoelasticity and maintained a stable gel-like structure. The result of study explored the mechanism of salt treated protein particles, developed a further understanding of Pickering emulsion, and was beneficial to the application of RBP.

Two Novel Angiotensin I-Converting Enzyme (ACE) Inhibitory Peptides from Rice (Oryza sativa L.) Bran Protein.

To realize the high-value utilization of rice byproducts, the rice bran protein hydrolysate was separated and purified by ultrafiltration and reversed-phase high-performance liquid chromatography (RP-HPLC), then the sequences of peptides were identified by liquid chromatography with tandem mass spectrometry (LC-MS/MS), and their molecular docking analysis and activities in vitro and in the cell were carried out. Two novel peptides FDGSPVGY (840.3654 Da) and VFDGVLRPGQ (1086.582 Da) were obtained with IC50 values of 0.079 mg/mL (94.05 µM) and 0.093 mg/mL (85.59 µM) on angiotensin I-converting enzyme (ACE) inhibitory activity in vitro, respectively. Molecular docking results showed that two peptides interacted with ACE receptor protein through hydrogen bonding, hydrophobic interactions, etc. Through the EA.hy926 cells, it was found that FDGSPVGY and VFDGVLRPGQ could promote the release of nitric oxide (NO) and reduce the content of ET-1 to achieve the effect of antihypertension. In conclusion, the peptides from rice bran protein exhibited significant antihypertension activity and may be expected to realize the high-value utilization of rice byproducts.

Fabrication of bilayer emulsion by ultrasonic emulsification: Effects of chitosan on the interfacial stability of emulsion.

In this study, the stable system of bilayer emulsion was fabricated by ultrasonic emulsification. The effect of chitosan (CS) addition (0.05 %-0.4 %, w/v) at pH 5.0 on the stability of rice bran protein hydrolysate-ferulic acid (RBPH-FA) monolayer emulsion was investigated. It was found that the addition of CS (0.3 %) could form a stable bilayer emulsion. The droplet size was 3.38 µm and the absolute ζ-potential value was 31.52 mV. The bilayer emulsion had better storage stability, oxidation stability and environmental stabilities than the monolayer emulsion. The results of in vitro simulations revealed the bilayer emulsion was able to deliver the ß-carotene to the small intestine digestive stage stably and the bioaccessibility was increased from 22.34 % to 61.36 % compared with the monolayer emulsion. The research confirmed that the bilayer emulsion prepared by ultrasonic emulsification can be used for the delivery of hydrophobic functional component ß-carotene.

Covalent binding of ultrasound-treated japonica rice bran protein to catechin: Structural and functional properties of the complex.

Due to the existence of many disulfide bonds in japonica rice bran protein (JRBP) molecules, their solubility is poor, which seriously affects other functional properties. To improve the functional characteristics of JRBP molecules, they were processed by ultrasound technology, and JRBP-catechin (CC) covalent complex was prepared. The structural and functional properties of indica and japonica rice bran proteins and their complexes were compared; furthermore, the changes in the structural and functional properties of JRBP-CC under different ultrasound conditions were investigated. The results showed that compared with indica rice bran protein (IRBP), the secondary structure of JRBP-CC was very different, the water holding capacity (WHC) was higher, and the emulsification performance was better. Different ultrasound conditions had different effects on the functional properties of JRBP-CC. When the ultrasound power was 200 W, the λmax redshift of the JRBP-CC complex was the most significant, the particle size was the smallest, the absolute value of the zeta potential was the largest, and the hydrophobicity and microstructure of the JRBP-CC complex were the best. Concurrently, the maximum WHC and oil holding capacity (OHC) of JRBP-CC under these conditions were 7.54 g/g and 6.87 g/g, respectively. Moreover, the emulsifying activity index (EAI) and emulsifying stability index (ESI) were 210 m2/g and 47.8 min, respectively, and the scavenging activities of 1,1-diphenyl-2-picrylhydrazyl (DPPH) and ABTS+ were 71.96 % and 80.07 %, respectively.