Brown rice is whole grain rice with the hull removed.It contains a variety of bio-functional components preserved in the germ and bran layers that are removed from white rice by polishing or milling[1]. Due to the specific amino acid composition, high biological value and low sensitivity,brown rice protein has been considered as one high-quality vegetable protein. In comparison to soy protein and casein,the brown rice protein has a better amino acid pattern[2].However, the extensive disulfide bonding and aggregation make the solubility of brown rice protein much poor. It is an economical and popular practice to improve the solubility of brown rice protein by seed germination. The solubility and emulsification properties can be increased due to the enzymatic hydrolysis of rice endosperm protein[3]. During the germination of brown rice, the activation of endogenous protease results in the decreased endosperm protein and the increased soluble protein of germinated brown rice (GBR)[4].This might be the reason why solubility of germinated brown rice protein (GBRP) was enhanced. Furthermore, this kind of GBRP is preferred for the increased contents of total protein,soluble protein and essential amino acids, and the improved protein digestibility and amino acid bioavailability[5].Therefore, it can improve the property and content of brown rice protein by means of germination.
Although germination can relatively increase the solubility of GBRP, application of GBRP as an emulsifying agent in food industry is limited due to its high hydrophobicity and low solubility. The emulsifying capacity of plant proteins, such as rice and pea protein, is limited mainly because of the change in its molecular conformation,state of aggregation, functional properties during certain processing and storage, such as heat, pH, ion etc.[6]. Physical,chemical and genetic treatments can be used to improve the functional properties of proteins[7]. Among them, Maillard reaction is highly effective in protein modification by linking protein to polysaccharides with covalent bonds[8-9]. Previous studies have shown that Maillard reaction products have better solubility[6], thermal stability[10], colloidal stability[11],freeze-thaw stability[12], lonic strength stability[12] than the native proteins.
Although rice proteins with high ratio of lysine are liable to undergo Maillard reaction, reports on rice protein modification through Maillard reaction have been very few[13].Initial results[13] showed that the rice proteins exhibited the improved solubility and emulsifying activity, but their physical and chemical stability is unknown yet. Therefore,the purpose of this study was to investigate the emulsifying property of GBRP-dextran conjugate (GBRP-Dex Con) in oil in water (O/W) emulsions. As oil is dispersed in water in the form of small spheres (r ＜ 100 nm), O/W emulsions belong to an unstable thermodynamic system[14]. In order to improve the properties of the O/W emulsion, a special method is used to produce new emulsifiers by covalently linking proteins and polysaccharides through Maillard reaction[10,12].
The sacha inchi oil contains 93% unsaturated fatty acids and is rich in alpha linolenic acid, which has high nutritional value. In the present study, we used sacha inchi oil as the core material to investigate the embedding effect of different emulsifiers. We selected GBRP and dextran as the sources of protein and polysaccharide to prepare conjugation respectively. Thus, the objective of this study was to fabricate GBRP-Dex Con, characterize their molecular properties, investigate their solubility, thermal stability, antioxidant activity, and determine their effects on the physicochemical stability of sacha inchi oil emulsion.Although further research will be needed to elucidate precise mechanism in details, this study will extend our knowledge of the physicochemical changes due to Maillard reaction of hydrophobic plant proteins.
Brown rice Oryza sativa L. Daohuaxiang No. 2 (a popular rice cultivar for consumption in the North China)was purchased from Beidahuang Agriculture Co. Ltd.(Heilongjiang, China); sacha inchi oil was obtained from Xishuangbanna Yinqi Biological Resources Development Co.Ltd. (Yunan, China); dextran (Dex, average molecular weight of 20 kDa) was purchased from J & K Scientific Ltd. (Beijing,China); all the other chemicals were of analytical grade and commercially available.
Differential scanning calorimetry (DSC) system(Q2000, TA instruments, New Castle, DE, USA); Fourier transform infrared (FTIR) spectrometer (WQF520A, Beifen-Ruili, Beijing, China); D-8 advance diffractometer (Bruker AXS, Karlsruhe, Germany); high shear blender (T25, IKA,Beijing, China); two-stage high-pressure valve homogenizer(Homelab, Fabriano, Italy); dynamic laser light scattering instrument (S3500, Microtrac, North largo, FL, USA);stability analyzer (LUMiSizer 611, L.U.M. GmbH, Berlin,Germany).
1.3.1 GBR preparation
Brown rice was washed 3 times with tap water to remove bran powder and dust, followed by surface-sterilization in 200 mmol/L sodium hypochlorite for 25 min. After washing 3 times with deionized water, the brown rice was steeped in deionized water at a constant temperature of (28 ± 1) ℃for 12 h. The soaking water was replaced every 4 h and drained at the end of steeping. The brown rice was then placed in a Petri dish (150 mm-in-diameter) and covered with double layers of cotton cloth. Germination was carried out at a constant temperature of (32 ± 1) ℃ for 24 h with 90%-95%relative humidity. After germination, the rice was dried for 5 h at 50 ℃ and crushed into 60 mesh.
1.3.2 Rice protein preparation
The BRP and GBRP were prepared following the method of Du Yanxue et al.[15]. Firstly, the GBR powder was dispersed in 100 mmol/L NaOH at the ratio of 1:6 (m/m) by gently mixing at 40 ℃ for 2 h, followed by centrifugation at 8 000 × g for 15 min. Secondly, the protein supernatant was adjusted to pH 5.0 using 100 mmol/L HCl and centrifuged at 8 000 × g for 15 min. Thirdly, the protein precipitate was washed 3 times with deionized water and neutralized to pH 7.0 with 100 mmol/L NaOH. Finally, the BRP and GBRP samples were prepared by freeze drying. The protein contents of the samples were determined to be 85% (dry mass) by the Kjeldahl method (N% × 5.95). After determination, the protein contents of BRP and GBRP were 79.8% and 80.7%,respectively.
1.3.3 Preparation of GBRP-Dex Con by Maillard reaction
GBRP (2.0 g) was suspended in 200 mL of deionized water, and the pH was adjusted to 12.0 with 100 mmol/L NaOH. The protein was completely dispersed by vigorous and continuous agitation for 30 min at 50 ℃. Dextran (2.0 g)was then added into the protein solution and mixed with a magnetic stirrer for 30 min at 30 ℃. The pH was readjusted to pH 11.0 with 100 mmol/L HCl. Aliquots of 15 mL were transferred to 50 mL screw-capped glass tubes and capped.The samples were heated at 95 ℃ for 1 h and placed in an ice bath immediately after Maillard reaction. The GBRPDex Con was then freezing-dried and stored at 4 ℃. Equal amounts of GBRP and dextran (2.0 g of each) were mixed as GBRP-Dex Mix for comparison.
1.3.4 Solubility measurement
10 mg of BRP, GBRP, and GBRP-Dex Con were solved in 10 mL of buffers with various pH values(50 mmol/L citrate buffer, pH 3.0 and 4.0; 50 mmol/L sodium phosphate buffer, pH 5.0, 6.0, 7.0 and 8.0; and 50 mmol/L sodium hydrogen carbonate buffer, pH 9.0 and 10.0). The samples were centrifuged for 20 min at 10 000 × g. The protein contents in the supernatant were measured by the Kjeldahl method (N% × 5.95). Solubility was calculated as a percentage of protein in the supernatant to the total protein content.
1.3.5 Structural analysis of GBRP-Dex Con 1.3.5.1 DSC analysis
The thermal transition patterns were determined by using a DSC system as described by Liu Fuguo et al.[16].The samples (5.0 mg) were put onto aluminum pans and hermetically sealed. After heating from 40 to 180 ℃ at a rate of 10 ℃/min, the denaturation temperature (Td) and entropy change (ΔH) of the samples were measured. The sealed empty aluminum pan was used as reference.
1.3.5.2 FTIR spectroscopy
A FTIR spectrometer was used to measure the spectra of GBRP and GBRP-Dex Con. The dried samples of GBRP and GBRP-Dex Con were mixed with KBr, respectively,followed by compression to form appropriate tablets. Their spectra were scanned against air background for 24 times at a resolution of 4 cm-1 in the range of 4 000-400 cm-1.
1.3.5.3 X-ray diffractometer (XRD)
X-ray powder diffraction spectra of GBRP, dextran,GBRP-Dex Mix, and GBRP-Dex Con were recorded using a D-8 advance diffractometer with the Cu Kα radiation(λ = 0.154 nm). It was operated at a voltage of 40 kV at room temperature. The samples were tested in the 2θ angle range of 10°-80° and the scanning rate was 5°/min[17].
1.3.6 Antioxidant activity assay
1.3.6.1 Determination of radical-scavenging activity
Free radical-scavenging and reducing power activity represented the antioxidant capacity of hydrogen-donating.The radical-scavenging activities of GBRP, GBRP-Dex Con and soy protein isolate (SPI) were measured according to the method of Wang Wenqiong et al.[18] with some modifications.An aliquot of 1.0 mL sample (wt, containing 0.5%, 1.0%,2.0%, 4.0%, and 8.0% protein) was mixed with 1.0 mL of 20 μmol/L 1,1-diphenyl-2-picrylhydrazyl (DPPH) in 95%ethanol, and placed at 25 ℃ for 30 min in the dark. The supernatant was then collected by centrifugation for 5 min at 750 × g, and its absorbance was measured at 517 nm. Each treatment was performed in triplicate. The DPPH radicalscavenging activity was calculated by the following equation:
Where Asample, Acontrol, and Ablank are the absorbances of sample, control (ethanol added to the samples in place of DPPH) and blank control (ethanol added to samples in place of samples).
1.3.6.2 Reducing power assay
Reducing power assay of GBRP, GBRP-Dex Con and SPI was performed by using the method of You Juan et al.[19]with a slight modification. An aliquot of 1.0 mL sample(containing 0.5%, 1.0%, 2.0%, 4.0%, and 8.0% protein) was blended with 1.0 mL of 1 g/100 mL potassium ferricyanide and 2.5 mL of 200 mmol/L phosphate buffer (pH 6.6). The solution was heated at 50 ℃ for 30 min, followed by the addition of 2.5 mL of 10 g/100 mL trichloroacetic acid. After centrifugation for 10 min at 3 000 × g, the supernatant (2.0 mL)was mixed with 1.0 mL of 1 g/100 mL ferric chloride and 5.0 mL of distilled water. The solution absorbance was then measured at 700 nm after a 10 min standing time.
1.3.7 Emulsion formation
Oil-in-water emulsions were prepared using GBRP,GBRP-Dex Con, or SPI as the emulsifier. Water phase was prepared by solving GBRP, GBRP-Dex Con, or SPI in 5 mmol/L phosphate buffer (pH 7.0) at the concentrations of 0.5%, 1.0%, 2.0%, 4.0%, and 8.0%. To ensure complete dispersion and dissolution, the protein solution was stirred at 300 r/min. Sacha inchi oil (oil phase) was then added phase into the water phase at the ratio of 8:92. After vigorous mixing with a high shear blender for 10 min at 10 000 × g,the emulsion was formed by homogeneous treatment(40 MPa) using a two-stage high-pressure valve homogenizer for three cycles. The emulsions were then stored at 4 ℃before analysis.
1.3.8 Measurement of emulsion droplet size
The average diameter of the droplets in the emulsions was tested by a dynamic laser light scattering instrument.Based on the theory of dynamic light scattering, the droplet size and droplet distribution were determined according to the correlation of particle size and scattering intensity. In order to avoid multiple scattering, samples were diluted with phosphate buffer (5 mmol/L, pH 7.0) and measured at 25 ℃.All measurements were performed in triplicate.
1.3.9 Physical stability of emulsions
The emulsion creaming stability was analyzed with a stability analyzer. According to the Lambert-Beer law, the stability of emulsion was determined by accelerating the stratification and quantitative precipitation and suspension.The parameters used for the measurement were as follows:temperature, 25 ℃; centrifugal speed, 4 000 r/min; time interval, 10 s; number of times, 255; wavelength, 865 nm;and light scattering coefficient, 1.0.
All the experiments were performed in triplicate and the results were shown as ± s. Data were subjected to statistical analysis of variance (ANOVA) using SPSS 22.0 (SPSS,Chicago, IL, USA). Means of treatments were separated at the 5% significance level using the LSD method.
Protein-glycan coupling technology via the Maillard reaction is a new branch in the field of protein solubilization and improvement. Protein may interact with polysaccharide in reversible (such as electrostatic interactions, hydrophobic bonding, hydrogen bonding, and Van Der Waals force) or irreversible binding (such as covalent bonding)[20]. In this work, a binary conjugate of GBRP and dextran were prepared as a new emulsifier. As a surface-active protein, GBRP can fix the conjugate to fat droplet surface; while dextran as a functional polysaccharide can improve the steric stability of conjugate. Thus the formation of GBRP-Dex Con is supposed to improve the emulsifying property and stability of the emulsions prepared with GBRP.
Fig. 1 FRIR spectra and structural analysis of GBRP, dextran,GBRP-Dex Mix and GBRP-Dex Con
FTIR spectrometry is effective to identify compounds qualitatively and characterize molecular structures. As shown in Fig. 1A, two typical peaks of amide and hydrogen bonding, at 1 700-1 500 cm-1 and 3 392 cm-1, respectively,were identified in GBRP[21]. During the Maillard reaction,the carbonyl of dextran was added to the polypeptide chain of the GBRP, thus consuming functional groups and causing hydroxyl and carbonyl group vibrations. These variations corresponded to the distinctive peaks of 3 650-3 200 cm-1(-OH stretching) and 1 100-1 000 cm-1 (-OH bending),which are characteristic peaks of protein-glycan conjugate. In comparison with of GBRP, the intensity of GBRP-Dex Con peaks at 1 536 and 1 460-1 240 cm-1 was decreased owing to the alteration of NH2 groups. Our results are in agreement with many previous researches that Maillard reaction is highly efficient to conjugate protein and polypeptide[22-23].
XRD technology is widely used to analyze the crystal structure in a rapid, informative, and accurate way. After irradiation by X-ray, different materials will produce different degrees of diffraction, which is related to the crystal type,molecule conformation, material composition and molecule bonding mode[24]. The structures of GBRP, dextran, GBRPDex Mix and GBRP-Dex Con were analyzed by using the XRD technology. As shown in Fig. 1B, the diffractogram of GBRP and dextran consisted of two major peaks at approximately 10° and 20°. Similar patterns were detected in the diffractogram of GBRP-Dex Mix. However, the GBRPDex Con showed a few changes in the diffraction angles and peak intensity. The GBRP-Dex Con diffractogram consist of two major crystalline peaks at 15° and 25°, and a new peak at approximately 40°. These findings illustrated that the covalent bonding between dextran and GBRP altered the crystal morphology of dextran. In combination with the results of FTIR spectrum, it revealed that dextran was successfully conjugated with GBRP to form GBRP-Dex Con through the Maillard reaction.
Fig. 2 Protein solubility of BRP, GBRP and GBRP-Dex Con at different pHs
Solubility has significant effect on the molecular behavior and performance as a food additive[25]. BRP lacks functionality, largely due to its insolubility caused by the extensive disulfide bonding and aggregation. By germinating[4] or introducing covalent bonding between polysaccharide and protein[13], the solubility of brown rice protein can be improved. Fig. 2 shows the solubility of BRP,GBRP and GBRP-Dex Con at different pH values (3.0 to 11.0). BRP comprised nearly 80% of glutelin which contains a large number of disulfide-linked subunits and is soluble only in dilute acid or alkali conditions[3]. Therefore, the solubility of BRP was very low in the pH range from 5.0 to 8.0, but was increased along with the pH. Germination can increase the solubility of the protein. GBRP thereby showed increased solubility over the tested pH range, especially under acidic (pH ＜ 4.0) and alkaline (pH ＞ 7.0) conditions. In comparison to BRP and GBRP, the GBRP-Dex Con exhibited the highest solubility. Covalent linkage between dextran and GBRP might create a strong affinity for water molecules and then prevent the occurrence of protein-protein interactions.These results were supported by the work of Jimeez-Castano et al.[26] on BSA-dextran conjugation. Moreover, the lowest solubility of BRP, GBRP and GBRP-Dex Con was found to occur at pH 4.0 and 5.0, which is around the isoelectric point of GBRP (pI = 5.0).
Heat treatment results in irreversible changes in the protein properties and structures through thermal denaturation[27]. Previous studies have shown that the formation of binary covalent conjugates causes an improvement in the thermal stability of proteins[6,12]. DSC has been used to investigate the thermal stability of proteinpolysaccharide conjugate[28]. As shown in Table 1, the denaturation temperature (Td) of GBRP-Dex Con (122.2 ℃)was significantly higher than those of GBRP (107.5 ℃)and dextran (111.8 ℃) (P ＜ 0.05). It indicated that some changes occurred in the protein structure when conjugated with dextran, which resulted in the improvement of GBRPDex Con thermostability. Furthermore, the entropy changes(ΔH) of GBRP-Dex Con were lower than those of GBRP.The cross-linking between GBRP and dextran may change the exothermic reaction that reduces the ΔH value. These thermodynamic reactions agree with the experimental results. On the other hand, the Td and ΔH of GBRP-Dex Mix were higher than those of GBRP and dextran. It might be ascribed to the changes of steric spacers between the protein and dextran molecules, which prevented the GBRP from aggregation by reducing the hydrophobic interactions.
Table 1 Denaturation temperatures (Td) and entropy changes (ΔH) of GBRP, dextran, and their physical mixture and conjugate
Note: Different superscript letters in the same column indicate significant differences (P ＜ 0.05). The same as in Table 2.
Samples Td/℃ ΔH/(J/g)
Fig. 3 DPPH radical scavenging effect (A) and reducing power (B) of GBRP, GBRP-Dex Con and SPI at different concentrations
The antioxidant activities of proteins could be improved by Maillard reaction due to the generation of heterocyclic compounds, amino reductones and high molecular melanoidins[18]. Therefore, the effects of mass concentrations of GBRP, GBRP-Dex Con and SPI on the DPPH inhibition and reducing power were also determined. SPI was chosen as a contrast because SPI was not only vegetable protein,but also a common emulsifier. As shown in Fig. 3A, the DPPH inhibitions of all tested samples were increased with the increasing mass concentrations, and those of GBRPDex Con were dramatically enhanced. It indicated that the DPPH radical-scavenging activity of GBRP-Dex Con can be increased via Maillard reaction. SPI as a reference showed disadvantages for application. The reducing power of GBRP,GBRP-Dex Con and SPI are depicted in Fig. 3B. GBRPDex Con in different mass concentrations exhibited higher reducing powers than GBRP and SPI. Eichner[29] reported that the intermediate reductone compounds produced by the Maillard reaction can break the radical chain by donating a hydrogen atom. Similarly, through the Maillard reaction,GBRP-Dex Con gained better antioxidant activity as reported in the xylose-soybean peptide conjugates and silver carp protein hydrolysate-glucose conjugates[19].
Droplet size and distribution is one of the key indexes to measure the emulsifying property of emulsifier, and it is also an important factor affecting the physical and chemical properties and the sensory characteristics of the emulsion[30].During the preparation of emulsion, the emulsifier molecule with surface activity is adsorbed to the oil/water interface,small droplets are then formed due to the reduction of interfacial tension. Therefore, the structure and solubility of an emulsifier have effects on the droplet size. The droplet sizes of sacha inchi oil emulsified by different concentrations of GBRP, GBRP-Dex Mix, GBRP-Dex Con, and SPI were compared (Table 2). Treatment with GBRP and GBRP-Dex Mix resulted in larger droplets than those of GBRP-Dex Con and SPI. For the GBRP, this phenomenon could be attributed to a result of droplet flocculation owing to their relatively low charge, which means that electrostatic repulsion is not strong enough to overcome any hydrophobic attraction or Van Der Waals[15]. For the GBRP-Dex Mix, the free dextran molecules in the continuous phase may generate droplet flocculation through a depletion mechanism[31]. The droplet diameters of emulsion stabilized by GBRP-Dex Con were much lower,with the minimum of 0.483 μm for 2% concentration. It indicated the advantages of conjugates in generating small droplets throughout homogenization and inhibition of droplet aggregation. The covalent bonding of GBRP and dextran increased the interfacial coating thickness between the droplets and thereby enhanced the steric repulsion. These results are in good agreement with those from a previous study of Liu Fuguo et al.[16].
Table 2 Droplet size of sacha inchi oil emulsions prepared with different emulsifiers at different concentrations
Concentration/% Droplet size in diameter/μm GBRP GBRP-Dex MixGBRP-Dex Con SPI 0.5 3.75 ± 0.07a 4.16 ± 0.01a 1.77 ± 0.01a 2.00 ± 0.01a 1 2.59 ± 0.03b 2.39 ± 0.00b 0.65 ± 0.00b 0.96 ± 0.00b 2 1.08 ± 0.01c 1.55 ± 0.02c 0.48 ± 0.00c 0.59 ± 0.00c 4 1.23 ± 0.00b 1.79 ± 0.02c 0.58 ± 0.00d 2.97 ± 0.00d 8 1.78 ± 0.04d 2.06 ± 0.01a 0.52 ± 0.01e 3.72 ± 0.01d
The effect of emulsifier concentration on the particle size of sacha inchi oil emulsion was found to be remarkable(P ＜ 0.05). The droplet sizes of sacha inchi oil showed a “down-up trend” along with the increase of emulsifier concentration, and reached minima at the concentration of 2%.Because the low concentration of emulsifier was not enough to cover all of the O/W interface, large mechanical stress might cause mutual coalescence of droplets to form large particles in the process of homogenization[32]. It might explain for the “up trend”. Moreover, at high concentrations, free emulsifier could be adsorbed onto the surface of saturated droplets and resulted in larger droplets. This mutual attraction gets stronger along with higher concentrations, and eventually lead to the increase of droplet size[33].
The droplet size distributions of emulsions prepared by GBRP, GBRP-Dex Mix, GBRP-Dex Con and SPI are shown in Fig. 4. The droplet sizes of GBRP, GBRP-Dex Mix, and GBRP-Dex Con were mainly within the range of 0.1-10 μm,while 10-100 μm for SPI. When different concentrations of GBRP-Dex Con were used as the emulsifier, the droplet size distribution of emulsion showed a single peak, suggesting that it had a uniform distribution. In contrast, those of GBRP,GBRP-Dex Mix and SPI were found to have multiple peaks,corresponding to their poor homogeneity. Therefore, the emulsions prepared by GBRP-Dex Con are superior to those of GBRP, GBRP-Dex Mix and SPI.
Fig. 4 Droplet size distribution of emulsions prepared with GBRP (A),GBRP-Dex Mix (B), GBRP-Dex Con (C) and SPI (D)
Mutual exclusion (as steric repulsion or electrostatic repulsion) of emulsifier molecules and formation of hydration layer between droplets usually prevent droplets from flocculation or coalescence, thereby keeping the emulsion stability[31]. Therefore, the effect of emulsifier type and concentration on the physical stability of sacha inchi oil emulsions was also determined. Under analytical centrifugation, the space-and temporal-related transmission profiles of GBRP, GBRP-Dex Mix, GBRP-Dex Con, SPI were measured. The less changes of the transmission was, the more stable of the emulsions was. As shown in Fig. 5A, the changes of light transmittance of each sample were gradually reduced with the increased of emulsifier concentration.It indicated that the floating capacity of emulsions was weakened, and the stability was improved. This might be a result of viscosity increased along with the increase in the emulsifier concentration. Accordingly, the collision probability between droplets decreased, which finally improved the stability of emulsion.
Fig. 5 LUMiSizer scanning images of emulsions prepared with different emulsifiers (A), slope (B) and instability index (C) of emulsions prepared with different emulsifiers
To further compare the physical stability differences of emulsions, instability index and slope were calculated by plotting the integrated transmission profiles versus time[16].Low values of instability index and slope represent greater stability. As shown in Fig. 5B and Fig. 5C, the emulsions prepared by GBRP and GBRP-Dex Mix had high instability index and slope values. It indicated that these two emulsifiers went through rapid creaming. The poor physical stability of emulsions stabilized by GBRP and GBRP-Dex Mix might be attributed to their large droplet sizes. For the emulsions stabilized by GBRP-Dex Con with concentrations greater than or equal to 2%, no phase separation or creaming was detected at the bottom of the test tubes after centrifugation.Moreover, the instability index and slope values were the lowest. As results, the emulsion stabilized by GBRP-Dex Con had the best physical stability. The minimum droplet sizes(Table 2) or the increase of steric repulsion between droplets with the covalent bonding of dextran and GBRP may give the answer[34]. When the GBRP-Dex Con concentration increased from 2% to 8%, the instability index and slope values further decreased. These results were in accordance with that of the previous studies of polyphenol-protein-polysaccharide conjugates and soy protein-polysaccharide conjugates[12,35].Although SPI show better stabilizing effect than GBRP and GBRP-Dex Mix, its physical stability is worse than GBRPDex Con. Therefore, GBRP-Dex Con with greater stability represents as an excellent emulsifier with application potentials in food industry.
In this work, a new GBRP-Dex Con was developed by Maillard reaction. The formation of conjugates was confirmed by FTIR spectroscopy and XRD analysis. Further experimental results demonstrated that the physicochemical properties of GBRP were remarkably improved by conjugation with dextran, including solubility, antioxidant activity, and thermal stability. In addition, the GBRP-Dex Con was found to emulsify sacha inchi oil into tiny droplets down to 0.483 μm homogeneously and stably. Consequently,a protein-polysaccharide conjugate (GBRP-Dex Con) is developed as a new emulsifier with great significance for utilization in functional food products. Further investigations on the in vitro digestion and oxidative stability (rancimat) of the GBRP-Dex Con stabilized emulsions will be carried out.
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发芽糙米蛋白-葡聚糖共价接枝复合物的开发及其物理化学性能、乳液稳定性的评价