Fabrication and characterization of soy protein isolation-ferulic acid antioxidant hydrogels.

BACKGROUND: Soy protein gel products are prone to direct oxidation by reactive oxygen during processing and transportation, thus reducing their functional properties and nutritional values. A covalent complex was prepared with soy protein isolate (SPI) and ferulic acid (FA) catalyzed by laccase (LC). The complex was further treated with microbial transglutaminase (TGase) to form hydrogels. The structural changes of the covalent complex (SPI-FA) and the properties and antioxidant stability of hydrogel were investigated. RESULTS: The SPI-FA complexes were demonstrated to be covalently bound by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and they had the least hydrophobic and free sulfhydryl groups at a 1.0 mg mL-1 FA concentration. The α-helix of complexes increased from 11.50% to 27.39%, and random coil dropped from 26.06% to 14.44%. The addition of FA caused SPI fluorescence quenching and redshift. The hydrogel was formed after the complex was induced with TGase, and its hardness and water holding capacity was increased by 50.61% and 26.21%, respectively. Scanning electron microscopy showed that a layered and ordered gel structure was formed. After in vitro digestion, the complex hydrogels maintained stable antioxidant activity, and the free radical scavenging rates of DPPH and ABTS reached 87.65% and 84.45%, respectively. CONCLUSION: SPI-FA covalent complexes were prepared under laccase catalysis, and complex hydrogels were formed by TGase. Hydrogels have stable antioxidant activity, which provides application prospects for the antioxidant development of food. © 2023 Society of Chemical Industry.

Fabrication of soy protein-polyphenol covalent complex nanoparticles with improved wettability to stabilize high-oil-phase curcumin emulsions.

BACKGROUND: Recent studies have shown that the wettability of protein-based emulsifiers is critical for emulsion stability. However, few studies have been conducted to investigate the effects of varying epigallocatechin gallate (EGCG) concentrations on the wettability of protein-based emulsifiers. Additionally, limited studies have examined the effectiveness of soy protein-EGCG covalent complex nanoparticles with improved wettability as emulsifiers for stabilizing high-oil-phase (≥ 30%) curcumin emulsions. RESULTS: Soy protein isolate (SPI)-EGCG complex nanoparticles (SPIEn) with improved wettability were fabricated to stabilize high-oil-phase curcumin emulsions. The results showed that EGCG forms covalent bonds with SPI, which changes its secondary structure, enhances its surface charge, and improves its wettability. Moreover, SPIEn with 2.0 g L -1 EGCG (SPIEn-2.0) exhibited a better three-phase contact angle (56.8 ± 0.3o) and zeta potential (-27 mV) than SPI. SPIEn-2.0 also facilitated the development of curcumin emulsion gels at an oil volume fraction of 0.5. Specifically, the enhanced network between droplets as a result of the packing effects and SPIEn-2.0 with inherent antioxidant function was more effective at inhibiting curcumin degradation during long-term storage and ultraviolet light exposure. CONCLUSION: The results of the present study indicate that SPIEn with 2.0 g L -1 EGCG (SPIEn-2.0) comprises the optimum conditions for fabricating emulsifiers with improved wettability. Additionally, SPIEn-0.2 can improve the physicochemical stability of high-oil-phase curcumin emulsions, suggesting a novel strategy to design and fabricate high-oil-phase emulsion for encapsulating bioactive compounds. © 2024 Society of Chemical Industry.

Self-assembled pea vicilin nanoparticles as nanocarriers for improving the antioxidant activity, environmental stability and sustained-release property of curcumin.

BACKGROUND: The application of curcumin (Cur) in the food industry is usually limited by its low water solubility and poor stability. This study aimed to fabricate self-assembled nanoparticles using pea vicilin (7S) through a pH-shifting method (pH 7-pH 12-pH 7) to develop water-soluble nanocarriers of Cur. RESULTS: Intrinsic fluorescence, far-UV circular dichroism spectra and transmission electron microscopy analysis demonstrated that the structure of 7S could be unfolded at pH 12.0 and refolded when the pH shifted to 7.0. The assembled 7S-Cur exhibited a high loading ability of 81.63 µg mg-1 for Cur and homogeneous particle distribution. Cur was encapsulated in the 7S hydrophobic nucleus in an amorphous form and combined through hydrophobic interactions and hydrogen bonding, resulting in the static fluorescence quenching of 7S. Compared with free Cur, the retention rates of Cur in 7S-Cur were approximately 1.12 and 1.70 times higher under UV exposure at 365 nm or heating at 75 °C for 120 min, respectively, as well as 7S-Cur showing approximately 1.50 times higher antioxidant activity. During simulated gastrointestinal experiments, 7S-Cur exhibited a better sustained-release property than free Cur. CONCLUSION: The self-assembled 7S nanocarriers prepared using a pH-shifting method effectively improved the antioxidant activity, environmental stability and sustained-release property of Cur. Therefore, 7S isolated from pea protein could be used as potential nanocarriers for Cur. © 2023 Society of Chemical Industry.

Modulation of fried spring roll wrapper quality upon treatment of batter with maltogenic amylase, transglutaminase and bromelain.

BACKGROUND: Fried foods are favored for their unique crispiness, golden color and flavor, but they also face great challenge because of their high oil content, high calories and the existence of compounds such as acrylamide and polycyclic aromatic hydrocarbons. Long-term consumption of fried foods may adversely affect health. Therefore, it is necessary to explore fried foods with lower oil contents and a high quality to meet the demand. RESULTS: A method of enzyme treatment was explored to investigate the effects of maltogenic amylase (MA), transglutaminase (TG) and bromelain (BRO) on the physicochemical properties of the batter and the quality of fried spring roll wrapper (FSRW). The results showed that the MA-, TG- or BRO-treated batters had a significant shear-thinning behavior, especially with an increase in viscosity upon increasing TG contents. FSRW enhanced its fracturability from 419.19 g (Control) to 616.50 g (MA-6 U g-1), 623.49 g (TG-0.75 U g-1) and 644.96 g (BRO-10 U g-1). Meanwhile, in comparison with BRO and MA, TG-0.5 U g-1 endowed batter with the highest density and thermal stability. MA-15 U g-1 and TG-0.5 U g-1 displayed FSRW with uniform and dense pores, and significantly reduced its oil content by 18.05% and 25.02%, respectively. Moreover, compared to MA and TG, BRO-50 U g-1 improved the flavor of FSRW. CONCLUSION: MA, TG or BRO played a key role in affecting the physicochemical properties of the batter and the quality of FSRW. TG-0.5 U g-1 remarkly reduced the oil content of FSRW with a great potential in practical application. © 2024 Society of Chemical Industry.

Preparation of high complex concentration emulsion stabilized by soy protein/dextran sulfate composite particles.

BACKGROUND: Soy protein isolate (SPI) can be used as an emulsifier to stabilize emulsions, though SPI is unstable under low acidic conditions. Stable composite particles of SPI and dextran sulfate (DS) can be formed by the electrostatic interaction at the pH 3.5. Furthermore, the SPI/DS composite particles can be used to prepare a high complex concentration emulsion. The stabilization properties of the high complex concentration emulsion were investigated. RESULTS: Compared to uncompounded SPI, the particle size of SPI/DS composite particles was smaller at 1.52 µm, and the absolute value of the potential increased to 19.9 mV when the mass ratio of SPI to DS was 1:1 and the pH was 3.5. With the DS ratio increased, the solubility of the composite particles increased to 14.44 times of the untreated protein at pH 3.5, while the surface hydrophobicity decreased. Electrostatic interactions and hydrogen bonds were the main forces between SPI and DS, and DS was electrostatically adsorbed on the surface of SPI. The emulsion stability significantly enhanced with the increase of complex concentration (38.88 times higher than at 1% concentration), the emulsion average droplet size was the lowest (9.64 µm), and the absolute value of potential was the highest (46.67 mV) when the mass ratio of SPI to DS was 1:1 and the complex concentration of 8%. The stability of the emulsion against freezing was improved. CONCLUSION: The SPI/DS complex has high solubility and stability under low acidic conditions, and the emulsion of the SPI/DS complex has good stability. © 2023 Society of Chemical Industry.

The preparation of soy glycinin/sugar beet pectin complex network gels catalyzed by laccase under weakly acidic conditions.

BACKGROUND: Traditional soy protein gel products such as tofu, formed from calcium sulfate or magnesium chloride, have poor textural properties and water retention capacity. Soy glycinin (SG) is the main component affecting the gelation of soy protein and can be cross-linked with polysaccharides, such as sugar beet pectin (SBP), and can be modified by changing system factors (e.g., pH) to improve the gel's properties. Soy glycinin/sugar beet pectin (SG/SBP) complex double network gels were prepared under weakly acidic conditions using laccase cross-linking and heat treatment. The structural changes in SG and the properties of complex gels were investigated. RESULTS: Soy glycinin exposed more hydrophobic groups and free sulfhydryl groups at pH 5.0. Under the action of laccase cross-linking, SBP could promote the unfolding of SG tertiary structures. The SG/SBP complex gels contained 46.77% ß-fold content and had good gelling properties in terms of hardness 290.86 g, adhesiveness 26.87, and springiness 96.70 mm at pH 5.0. The T22 relaxation time had the highest peak, and magnetic resonance imaging (MRI) showed that the gel had even water distribution. Scanning electron microscopy (SEM) and confocal scanning laser microscopy (CLSM) indicated that the SG/SBP complex network structure was uniform, and the pore walls were thicker and contained filamentous structures. CONCLUSION: Soy glycinin/ sugar beet pectin complex network gels have good water-holding, rheological, and textural properties at pH 5.0. The properties of soy protein gels can be improved by binding to polysaccharides, with laccase cross-linked, and adjusting the pH of the solution. © 2022 Society of Chemical Industry.

Encapsulation of curcumin in soluble soybean polysaccharide-coated gliadin nanoparticles: interaction, stability, antioxidant capacity, and bioaccessibility.

BACKGROUND: Gliadin nanoparticles are used as a delivery system for active substances because of their amphiphilicity and bioavailability. However, they are susceptible to destabilization by external agents. In this study, gliadin nanoparticles stabilized by soluble soybean polysaccharide (SSPS) were prepared by antisolvent precipitation. Formed stable complex nanoparticles were applied to protect and deliver curcumin (Cur). RESULTS: Gliadin/SSPS nanoparticles with the smallest particle size (196.66 nm, polydispersity index < 0.2) were fabricated when the mass ratio of gliadin to SSPS was 1:1 at pH 5.0. SSPS-stabilized gliadin nanoparticles had excellent stability at pH 3.0-8.0, 0.02-0.1 mol L-1 NaCl and at 90 °C heat. Gliadin/SSPS nanoparticles were used to encapsulate the Cur. The encapsulation efficiency of the Cur-loaded gliadin/SSPS nanoparticles was 84.59%. Fourier transform infrared spectroscopy and fluorescence spectrophotometry showed that the main forces were hydrogen bonds, electrostatic interactions and hydrophobic interactions between gliadin and SSPS. The X-ray diffraction patterns exhibited that the crystalline form of Cur converted to an amorphous substance. The retention rates of Cur-loaded gliadin/SSPS nanoparticles reached 79.03%, 73.43% and 87.92% after ultraviolet irradiation for 4 h, heating at 90 °C and storage at 25 °C for 15 days, respectively. Additionally, simulated digestion demonstrated that the bioavailability of gliadin/SSPS-Cur nanoparticles was four times higher than that of free Cur. CONCLUSION: This study showed that SSPS improved the stability of gliadin nanoparticles. Gliadin/SSPS nanoparticles have the function of loading and delivering Cur. © 2022 Society of Chemical Industry.

Study on preparation of acylated soy protein and stability of emulsion.

BACKGROUND: Protein can be used as an emulsifier to improve emulsion stability at the interface of water-in-oil emulsion. However, natural soybean protein isolate (SPI) does not meet the high demands as an emulsifier in the food industry. The effect of acylation modification by ethylenediaminetetraacetic dianhydride (EDTAD; 0-300 g kg-1 ) on the physicochemical properties of SPI was studied. RESULTS: The results of the Fourier transform infrared spectra analyses showed that carboxyl groups were introduced into the SPI structure by the EDTAD treatment. The carboxyl concentration of SPI was increased by 30-74.07% with an increase in EDTAD addition from 50 to 300 g kg-1 . When 150 g kg-1 EDTAD was added, the surface hydrophobicity, the emulsifying activity, and the absolute value of the zeta potential were increased by 213%, 120%, and 68% respectively, and the particle size decreased to 247 nm. The droplet size of emulsion decreased to 10 µm when pH was 6. At the same concentration of SPI and pH, the absolute value of zeta potential of the emulsion was biggest. A comparison of the emulsions during storage showed the improvement of emulsion stability was related to the increase in the zeta potential and the decrease in the average particle size. The experimental group showed no destabilization on day 21, and no obvious aggregation phenomenon was observed. CONCLUSION: Acylation modification by EDTAD changed the emulsifying properties of SPI and enhanced the stability of the SPI emulsion. © 2021 Society of Chemical Industry.

Heterologous signal peptides-directing secretion of Streptomyces mobaraensis transglutaminase by Bacillus subtilis.

Microbial transglutaminase (MTG) from Streptomyces mobaraensis has been widely used for crosslinking proteins in order to acquire products with improved properties. To improve the yield and enable a facile and efficient purification process, recombinant vectors, harboring various heterologous signal peptide-encoding fragments fused to the mtg gene, were constructed in Escherichia coli and then expressed in Bacillus subtilis. Signal peptides of both WapA and AmyQ (SP wapA and SP amyQ ) were able to direct the secretion of pre-pro-MTG into the medium. A constitutive promoter (P hpaII ) was used for the expression of SP wapA -mtg, while an inducible promoter (P lac ) was used for SP amyQ -mtg. After purification from the supernatant of the culture by immobilized metal affinity chromatography and proteolysis by trypsin, 63.0 ± 0.6 mg/L mature MTG was released, demonstrated to have 29.6 ± 0.9 U/mg enzymatic activity and shown to crosslink soy protein properly. This is the first report on secretion of S. mobaraensis MTG from B. subtilis, with similar enzymatic activities and yields to that produced from Escherichia coli, but enabling a much easier purification process.

Improvement of the activity and thermostability of microbial transglutaminase by multiple-site mutagenesis.

Microbial transglutaminase (MTG) is an enzyme widely used in the food industry. Mutiple-site mutagenesis of Streptomyces mobaraensis transglutaminase was performed in Escherichia coli. According to enzymatic assay and thermostability study, among three penta-site MTG mutants (DM01-03), DM01 exhibited the highest enzymatic activity of 55.7 ± 1.4 U/mg and longest half-life at 50 °C (418.2 min) and 60 °C (24.8 min).

Cell regeneration and cyclic catalysis of engineered Kluyveromyces marxianus of a D-psicose-3-epimerase gene from Agrobacterium tumefaciens for D-allulose production.

D-Allulose as a low-energy and special bioactive monosaccharide sugar is essential for human health. In this study, the D-psicose-3-epimerase gene (DPEase) of Agrobacterium tumefaciens was transferred into thermotolerant Kluyveromyces marxianus to decrease the production cost of D-allulose and reduce the number of manufacturing procedures. The cell regeneration of K. marxianus and cyclic catalysis via whole-cell reaction were investigated to achieve the sustainable application of K. marxianus and the consumption of residual D-fructose. Results showed that DPEase, encoding a 33 kDa protein, could be effectively expressed in thermotolerant K. marxianus. The engineered K. marxianus produced 190 g L-1 D-allulose with 750 g L-1 D-fructose as a substrate at 55 °C within 12 h. Approximately 100 g of residual D-fructose was converted into 34 g of ethanol, and 15 g of the engineered K. marxianus cells was regenerated after fermentation at 37 °C for 21 h. The purity of D-allulose of more than 90% could be obtained without isolating it from D-allulose and D-fructose mixture through residual D-fructose consumption. This study provided a valuable pathway to regenerate engineered K. marxianus cells and achieve cyclic catalysis for D-allulose production.

Formation of macromolecules in wheat gluten/starch mixtures during twin-screw extrusion: effect of different additives.

BACKGROUND: Wheat gluten comprises a good quality and inexpensive vegetable protein with an ideal amino acid composition. To expand the potential application of wheat gluten in the food industry, the effect of different additives on the physicochemical and structural properties of wheat gluten/starch mixtures during twin-screw extrusion was investigated. RESULTS: Macromolecules were observed to form in wheat gluten/starch mixtures during twin-screw extrusion, which may be attributed to the formation of new disulfide bonds and non-covalent interactions, as well as Maillard reaction products. Additionally, the water retention capacity and in vitro protein digestibility of all extruded wheat gluten/starch products significantly increased, whereas the nitrogen solubility index and free sulfhydryl group (SH) content decreased, during twin-screw extrusion. Secondary structural analysis showed that α-helices disappeared with the concomitant increase of antiparallel ß-sheets, demonstrating the occurrence of protein aggregation. Microstructures suggested that the irregular wheat gluten granular structure was disrupted, with additive addition favoring transformation into a more layered or fibrous structure during twin-screw extrusion. CONCLUSION: The findings of the present study demonstrate that extrusion might affect the texture and quality of extruded wheat gluten-based foods and suggest that this process might serve as a basis for the high-value application of wheat gluten products. © 2017 Society of Chemical Industry.

Enzymatic lipophilization of epicatechin with free fatty acids and its effect on antioxidative capacity in crude camellia seed oil.

BACKGROUND: Crude camellia seed oil is rich in free fatty acids, which must be removed to produce an oil of acceptable quality. In the present study, we reduced the free fatty acid content of crude camellia seed oil by lipophilization of epicatechin with these free fatty acids in the presence of Candida antarctica lipase B (Novozym 435), and this may enhance the oxidative stability of the oil at the same time. RESULTS: The acid value of crude camellia seed oil reduced from 3.7 to 2.5 mgKOH g-1 after lipophilization. Gas chomatography-mass spectrometry analysis revealed that epicatechin oleate and epicatechin palmitate were synthesized in the lipophilized oil. The peroxide, p-anisidine, and total oxidation values during heating of the lipophilized oil were much lower than that of the crude oil and commercially available camellia seed oil, suggesting that lipophilized epicatechin derivatives could help enhance the oxidative stability of edible oil. CONCLUSION: The enzymatic process to lipophilize epicatechin with the free fatty acids in crude camellia seed oil described in the present study could decrease the acid value to meet the quality standards for commercial camellia seed oil and, at the same time, obtain a new edible camellia seed oil product with good oxidative stability. © 2016 Society of Chemical Industry.

Effects of microwave pretreatment and transglutaminase crosslinking on the gelation properties of soybean protein isolate and wheat gluten mixtures.

BACKGROUND: The integration of soybean protein isolate (SPI) with wheat gluten (WG) crosslinked via microbial transglutaminase (MTGase) may enhance the formation of ϵ-(γ-glutamyl)lysine covalent bonds, because SPI is rich in lysine and WG contains more glutamine. Microwave pretreatment may accelerate enzymatic reactions. In this study, we aimed to elucidate the effects of microwave pretreatment on the gelation properties of SPI and WG crosslinked with MTGase. RESULTS: Interestingly, the gel strength, water-holding capacity (WHC) and storage modulus (G') values of MTGase-induced SPI/WG gels were dramatically improved with increasing microwave power. Moreover, the MTGase crosslinking reaction promoted the formation of disulfide bonds, markedly reducing the free SH group and soluble protein content of gels. Fourier transform infrared spectroscopic analysis of SPI/WG gels showed that microwave pretreatment increased the proportion of α-helices and ß-turns and decreased the proportion of ß-sheets. Results from scanning electron microscopy indicated that the MTGase-induced SPI/WG gels had denser and more homogeneous microstructures after microwave pretreatment. CONCLUSION: The effect of microwave pretreatment is useful in advancing gelation characters of MTGase-induced SPI/WG gels and provides the possibility for expanding the application of food protein. © 2015 Society of Chemical Industry.

Metabolic control analysis of L-lactate synthesis pathway in Rhizopus oryzae As 3.2686.

The relationship between the metabolic flux and the activities of the pyruvate branching enzymes of Rhizopus oryzae As 3.2686 during L-lactate fermentation was investigated using the perturbation method of aeration. The control coefficients for five enzymes, pyruvate dehydrogenase (PDH), pyruvate carboxylase (PC), pyruvate decarboxylase (PDC), lactate dehydrogenase (LDH), and alcohol dehydrogenase (ADH), were calculated. Our results indicated significant correlations between PDH and PC, PDC and LDH, PDC and ADH, LDH and ADH, and PDC and PC. It also appeared that PDH, PC, and LDH strongly controlled the L-lactate flux; PDH and ADH strongly controlled the ethanol flux; while PDH and PC strongly controlled the acetyl coenzyme A flux and the oxaloacetate flux. Further, the flux control coefficient curves indicated that the control of the system gradually transferred from PDC to PC during the steady state. Therefore, PC was the key rate-limiting enzyme that controls the flux distribution.

Cloning, expression, and characterization of a novel xylose reductase from Rhizopus oryzae.

Rhizopus oryzae is valuable as a producer of organic acids via lignocellulose catalysis. R. oryzae metabolizes xylose, which is one component of lignocellulose hydrolysate. In this study, a novel NADPH-dependent xylose reductase gene from R. oryzae AS 3.819 (Roxr) was cloned and expressed in Pichia pastoris GS115. Homology alignment suggested that the 320-residue protein contained domains and active sites belonging to the aldo/keto reductase family. SDS-PAGE demonstrated that the recombinant xylose reductase has a molecular weight of approximately 37 kDa. The optimal catalytic pH and temperature of the purified recombinant protein were 5.8 and 50 °C, respectively. The recombinant protein was stable from pH 4.4 to 6.5 and at temperatures below 42 °C. The recombinant enzyme has bias for D-xylose and L-arabinose as substrates and NADPH as its coenzyme. Real-time quantitative reverse transcription PCR tests suggested that native Roxr expression is regulated by a carbon catabolite repression mechanism. Site-directed mutagenesis at two possible key sites involved in coenzyme binding, Thr(226) → Glu(226) and Val(274) → Asn(274), were performed, respectively. The coenzyme specificity constants of the resulted RoXR(T226E) and RoXR(V274N) for NADH increased 18.2-fold and 2.4-fold, which suggested possibility to improve the NADH preference of this enzyme through genetic modification.

Effect of sodium metabisulfite-mediated self-assembly on the quality of silver carp myofibrillar protein-EGCG composite gels.

Myofibrillar protein (MP) gels are susceptible to oxidation, which can be prevented by complexing with hydrophilic polyphenols, but may cause gel deterioration. Sodium metabisulfite (Na2S2O5) has been used to induce self-assembly of MP and analyze the impact of self-assembly on the quality of composite gels containing high amounts of (-)-epigallocatechin gallate (EGCG). Hydrophobic forces were confirmed as the main driver of self-assembly. Self-assembly reduced the size of the MP-EGCG complex to approximately 670 nm and increased the gel's hydrophobic force by approximately 3.6-fold. The maximum hardness of the Na2S2O5-treated MP-EGCG composite gel was 52.43 g/kg, which was approximately 49% greater than pure MP gel. After oxidative treatment, the Na2S2O5-treated MP-EGCG composite gel had considerably lower carbonyl and dityrosine levels (2.47-µmol/g protein and 450 a.u.) than the control (8.37-µmol/g protein and 964 a.u.). Therefore, Na2S2O5 shows potential as a cost-effective additive for alleviating MP limitations in the food industry.

Comparisons in phytochemical components and in vitro digestion properties of corresponding peels, flesh and seeds separated from two blueberry cultivars.

Highbush blueberries (HB) and rabbiteye blueberries (RB) were separated into peels, flesh, and seeds to assess the compositions of nutriment, anthocyanins, soluble sugars and fatty acids, and the in vitro digesting abilities. Total phenolics contents (TPC) of 51-56 mg GAE/g DW were found in blueberry peels. Compared with HB peels, RB peels showed much higher TPC, but only contained 35 phenolics and lacked peonidin-3-O-rutinoside. Glucose, fructose, and sucrose were all present in HB and RB, but RB flesh had a higher acid-sugar ratio. Unsaturated fatty acid concentrations in HB and RB seeds were comparable (26.65 and 26.43 mg/g, respectively). However, HB seeds have 35 fatty acids, but RB seeds lacked cis-4,7,10,13,16,19-docosahexaenoic acid and cis-10-pentadecenoic acid. The in vitro digestion test showed that the whole fruit/peels/flesh of RB had a higher recovery and bioavailability index of phenolics and anthocyanins. Therefore, the reuse of blueberry pomace needs to be emphasized. Supplementary Information: The online version contains supplementary material available at 10.1007/s10068-023-01326-w.

Effect of sodium trimetaphosphate on the physicochemical properties of modified soy protein isolates and its lutein-loaded emulsion.

Due to people's pursuit of healthy and green life, soy protein isolate (SPI) is occupying a larger and larger market share. However, the low solubility of SPI affects its development in the field of food and medicine. This paper aimed to investigate the effects of sodium trimetaphosphate (STMP) on the functional properties and structures of phosphorylated SPI and its lutein-loaded emulsion. After modification by STMP, the phosphorus content of phosphorylated SPI reached 1.2-3.61 mg/g. Infrared spectrum and X-ray photoelectron spectrum analysis confirmed that PO4 3- had phosphorylation with -OH in serine of SPI molecule. X-ray diffraction analysis showed that phosphorylation destroyed the crystal structure of protein molecules. Zeta potential value of phosphorylated SPI decreased significantly. When STMP addition was 100 g/kg, particle size of protein solution decreased to 203 nm, and solubility increased to 73.5%. Furthermore, emulsifying activity and emulsifying stability increased by 0.51 times and 8 times, respectively. At the same protein concentration (1%-3% [w/w]), lutein-loaded emulsion prepared by phosphorylated SPI had higher absolute potential and smaller particle size. The phosphorylated protein emulsion at 2% concentration had the best emulsion stability after storage for 17 days. PRACTICAL APPLICATION: Phosphorylation significantly improved the emulsifying properties and solubility of SPI. Phosphorylated SPI significantly improved the stability of lutein-loaded emulsion. It provides theoretical basis for the application of phosphorylated SPI as emulsifier in delivery system and broadens the development of lutein in food and medicine field.

Infrared radiation blanching-inhibited browning and extended shelf life of pecan kernels.

To evaluate infrared radiation (IR) blanching in comparison to conventional hot water (HW) blanching in inhibiting the browning and extending the shelf life of pecan kernels, the technology of IR blanching at 500-700 W for 90-45 s or HW blanching at 90°C for 60 s, and subsequently drying with hot air at 60, 70, and 80°C, respectively, was used, and then the activities of lipoxidase (LOX) and polyphenol oxidase (PPO), antioxidant capacities, color change, microscopic structure, and the shelf life of kernels were analyzed. Results showed that IR blanching not only significantly decreased the subsequent drying time but also effectively inactivated the activities of LOX and PPO, showing a lower residual activity of 15.74%-40.41% and 16.75%-56.25%, respectively. A higher retention of total phenolics was observed in kernels subjected to IR blanching, from 25.03 ± 0.04 to 29.50 ± 0.96 mg GAE/g compared with HW blanching (14.43 ± 0.07 mg GAE/g). Meanwhile, IR-blanched samples showed lower peroxide values, p-anisidine values, total color difference values, browning index, quinones contents, and lipofuscin-like pigments levels but had higher 2,2-diphenyl-1-picrylhydrazyl inhibition rate and better storage stabilities than HW-blanched samples. The technology of IR blanching at 600 W for 60 s followed by drying with hot air at 70°C for 40 min is suitable for producing pecan kernels with better qualities and a longer shelf life, through inactivating the endogenous enzymatic reactions and inhibiting the formation of lipofuscin-like pigments. PRACTICAL APPLICATION: Blanching is an essential pretreatment of food processing. Conventional blanching is achieved by hot water, which has some disadvantages of low-intensity enzyme inactivation, loss of water-soluble substances, etc. In this study, the potential of using infrared blanching, prior to drying, was studied to find solutions to improve the nutritional value, and the shelf life of pecan kernels. The results showed that infrared blanching at 600 W for 60 s followed by drying with hot air at 70°C for 40 min could inhibit the color degradation, improve the oxidation resistance, and prolong the shelf life of kernels.