Improvement of functional properties of peanut protein isolate by conjugation with dextran through Maillard reaction

Effects of whey protein isolate-dextran glycosylation conjugate and different oils on the dispersion and in vitro digestibility of β-carotene emulsions

β-carotene is a lipophilic substance with excellent antioxidant activity, but its bioactivity in the gastrointestinal tract is easily destroyed. Glycosylation can improve the emulsifying activity of Whey protein isolate(WPI). In this study, the effects of different oil phases(corn oil, coconut oil, soybean oil) and WPI-dextran(WPI-D) on the stability and digestion efficiency of emulsions loaded with β-carotene were investigated. The glycosylation of WPI with dextran was confirmed by SDS-PAGE and Atomic Force Microscope(AFM). The results of contact angle and surface tension experiments demonstrate that the interfacial properties of WPI-D particles are enhanced, allowing them to adsorb better at the oil-water interface, thereby improving the stability of the emulsion. The in vitro digestion results indicate that different oil phases and glycosylation have effects on the digestion rate of the emulsions and the bioaccessibility of β-carotene. The enhanced steric effect of WPI-D allows for the regulation of the release rate of free fatty acids (FFA). Coconut oil, rich in medium-chain fatty acids, is easily broken down and absorbed during digestion. The release rate of free fatty acids (FFA) is relatively high. This study provides a theoretical basis for controlling the release rate of bioactive substances through the regulation of oil phases and glycosylation.

Preparation, structural characterization, and functional properties of a tilapia-soybean dual proteins: Effects of different complexation modes

The limited functional properties of tilapia protein isolate (TPI), such as low solubility, emulsification, and foaming, restrict its use in the food industry. However, combining it with hydrophilic proteins can improve these properties. Different assembly methods may affect the structure and functionality of the resulting dual proteins. To study this, tilapia-soybean protein mixtures (T-SPM), complexes (T-SPC), and co-precipitates (T-SPCP) were prepared using physical mixing, pH-regulated complexation, and pH-regulated co-precipitation. The effects of these methods on the structure and functional properties of the tilapia-soybean dual proteins were then analyzed. Structural analysis revealed that TPI combined with SPI through non-covalent forces and disulfide bonds under pH-regulation, leading to structural changes. Compared to T-SPCP, T-SPC showed more hydrophilic groups, with increased free sulfhydryl groups, disulfide bonds, α-helices, and zeta potential, alongside reduced surface hydrophobicity and smaller flake structures. Functional analysis indicated that pH-regulated assembly methods significantly improved the properties of the dual proteins compared to T-SPM. T-SPC exhibited higher solubility, emulsification, and foaming capacity than T-SPCP, which had a more aggregated structure due to pH adjustment to 4.5 during co-precipitation, contributing to its better thermal stability. Thus, T-SPC, assembled by pH-regulation from 12.0 to 7.0, demonstrated superior characteristics. This study offers a theoretical foundation for developing functional dual proteins and their food industry applications.

Soybean protein isolate-oxidized fucoidan nanocomplexes: Structural and interaction characterization, quercetin delivery potential evaluation

A novel nanocomplex was prepared using soybean protein isolate (SPI) and oxidized fucoidan (OFU) to explore the structural and interaction variations and evaluate its potential for quercetin delivery. The optimized SPI to OFU mass ratio of 10:1 (SFU3) resulted in a nanocomplex particle size of 198.1 nm and increased ζ-potential. The incorporation of OFU altered the structure of SPI with the decrease in α-helix and β-sheet, and the redshift and intensity drop in fluorescence spectra. X-ray photoelectron spectroscopy (XPS) confirmed the Schiff base reaction between the two, interacting through covalent imine bonds. Moreover, OFU improved the micromorphology, antioxidant capacity, and stability of Quercetin (Que) nanocomplexes, with SFU3 showing the highest encapsulation efficiency and loading amount (94.80 %, 16.96 μg/mg). The nanocomplexes achieved an effective controlled release of Que. in vitro simulated digestion. This study will provide important insights into the development of SPI-OFU as nutrient carriers.

Leguminous proteins as beneficial baking emulsifiers: A comparative study with traditional sucrose ester

In recent years, pursuing healthier and more sustainable food ingredients has increased interest in plant-based alternatives to traditional synthetic emulsifiers. In this study, the properties of five legume proteins: soybean protein isolate (SPI), pea protein isolate (PPI), black bean protein isolate (BBPI), white Canavalia protein isolate (WCAI), and white kidney bean protein isolate (WKBPI) were compared with that of the conventional emulsifier sucrose ester (SE), and add them as emulsifiers to the cake making process. The centrifugal instability index of SPI stabilized emulsion (0.11) was close to that of SE stabilized emulsion (0.08). The foaming performance of WKBPI (85 %) and BBPI (82 %) is 4 times that of SE (20 %).In the simulated cake paste system, the gelatinization temperature of the cake paste with PPI was increased by 0.49 °C compared with that of the blank group and the gelatinization enthalpy decreased by 57.8 % compared with the blank cake paste system. As temperature increases, the viscoelastic curve of the batter with legume protein exhibits an initial decrease followed by a subsequent increase. The above changes are expected to have a positive impact on the quality characteristics of the final baked product. The findings of this study indicated that legume protein could potentially substitute the traditional emulsifier SE.

Novel technologies, effects and applications of modified plant proteins by Maillard reaction and strategies for regulation: A review

With an increase in awareness of health, environmental conservation and animal welfare, the market for plant proteins is expanding. However, the low solubility and poor functional properties of plant proteins near the isoelectric point limit their application in food processing. Glycosylation refers to the structural modification of proteins by introduction of polysaccharides to form protein-polysaccharide conjugates in the early stages of Maillard reaction. Glycosylation is a green and efficient method that has been proved to produce modified proteins with superior solubility, emulsifying and forming properties. Glycosylation and the application of protein-carbohydrate conjugates have become research hotspots in recent years. This paper presented a comprehensive review of the effects of glycosylation on the functional properties of plant proteins and the mechanisms of non-thermal physical treatments assisted glycosylation. It was demonstrated that glycosylation modified the structure of plant proteins and improved their functional properties. Non-thermal physical treatments assisted glycosylation increased the reactive sites of plant proteins and further improved their functional properties. Protein-carbohydrate conjugates could be applied in delivery systems, films, emulsifiers and other applications, which have significant research prospects in food applications.

Effects of Conjugation with Basil Seed Gum on Physicochemical, Functional, Foaming, and Emulsifying Properties of Albumin, Whey Protein Isolate and Soy Protein Isolate

Protein conjugation with the Maillard reaction has received considerable attention in the past decades in terms of improving functional properties. This study evaluated the changes in the techno-functional properties of whey protein isolate (WPI), soy protein isolate (SPI), and albumin (Alb) after conjugation with basil seed gum (BSG). The conjugates were developed via the Maillard reaction. Various analyses including FT-IR, XRD, SEM, SDS-PAGE, DSC, RVA, rheology, zeta potential, emulsion, and foaming ability were used for evaluating conjugation products. Conjugation between proteins (WPI, SPI, Alb) and BSG was validated by FT-IR spectroscopy. XRD results revealed a decrease in the peak of BSG after conjugation with proteins. SDS-PAGE demonstrated the conjugation of WPI, SPI, and Alb with BSG. DSC results showed that conjugation with BSG reduced the Tg of WPI, SPI, and Alb from 210.21, 207.21, and 210.90 °C to 190.30, 192.91, and 196.66 °C, respectively. The emulsion activity and emulsion stability of protein/BSG conjugates were increased significantly. The droplet size of emulsion samples ranged from 112.1 to 239.3 nm on day 3. Nanoemulsions stabilized by Alb/BSG conjugate had the smallest droplet sizes (112.1 and 143.3 nm after 3 and 17 days, respectively). The foaming capacity of WPI (78.57%), SPI (61.91%), and Alb (71.43%) in their mixtures with BSG increased to 107.14%, 85.71%, and 85.71%, respectively, after making conjugates with BSG. The foam stability of WPI (39.34%), SPI (61.57%), and Alb (53.37%) in their mixtures with BSG (non-conjugated condition) increased to 77.86%, 77.91%, and 72.32%, respectively, after formation of conjugates with BSG. Conjugation of BSG to proteins can improve the BSG applications as a multifunctional stabilizer in pharmaceutical and food industries.

Tailoring Structural, Emulsifying, and Interfacial Properties of Rice Bran Protein Through Limited Enzymatic Hydrolysis After High-Hydrostatic-Pressure Pretreatment

We carried out limited enzymatic hydrolysis with trypsin on rice bran protein (RBP) pretreated by high hydrostatic pressure (HHP) in this study. The effects of the degree of hydrolysis (DH) on the structural and emulsifying properties were investigated. The results indicated that the molecular structure of RBP changed after limited enzymatic hydrolysis. The rice bran protein hydrolysate (RBPH, DH8) exhibited a better molecular distribution, a smaller particle size (200.4 nm), a better emulsifying activity index (31.82 m2/g), and an improved emulsifying stability index (24.69 min). RBPH emulsions with different DH (0-12) values were prepared. The interfacial properties, such as particle size, the ζ-potential, and the interfacial tension of the emulsions, were measured. Compared to the control, the interfacial properties of the RBPH emulsions were significantly improved after limited enzymatic hydrolysis. The RBPH emulsion at DH8 showed better stability with a smaller emulsion droplet size (2.31 μm), a lower ζ-potential (-25.56 mV), and a lower interfacial tension. This study can provide a theoretical basis for the application of RBP as the plant protein-based emulsifier in the beverage industry.

Effect of ohmic heating-assisted glycation reaction on the properties of soybean protein isolate-chitosan complexes

The purpose of this study was to investigate the progress of glycation reaction reactions by conventional heating and ohmic heating (OH) treatment, and the effect of different electric field intensities on the structure, physical and chemical and functional properties of glycosylated proteins. The findings demonstrated that OH treatment was more efficacious than conventional heating in reducing the free amino group and increasing the absorbance at 420 nm. Concurrently, the α-helix and β-sheet content of soy protein isolate (SPI)-chitosan (CS) complexes exhibited a reduction to 18.01 % and 28.67 %, respectively, while the UV absorption peak demonstrated an increase in conjunction with the escalation of electric field intensity. When the electric field intensity was 6 V/cm, the emulsification activity index and emulsion stability index of SPI-CS complexes were found to be 95.52 m2/g and 55.60 min, respectively. The foaming capacity and foaming stability were found to be 148.33 % and 115.59 % respectively, while the solubility was also up to 91.37 %. Additionally, the air/water interface properties demonstrated a notable enhancement. The functional properties of the complexes were demonstrably enhanced following the application of an OH treatment. The aforementioned statement provided a theoretical foundation for the implementation of OH treatment.

Structural and functional impacts of glycosylation-induced modifications in rabbit myofibrillar proteins

Rabbit meat, recognized for its nutritional value, is gaining global attention. However, the inferior functional properties of rabbit myofibrillar proteins lead to quality degradation during the production process. Glycosylation represents an effective method for enhancing protein functionality. This study investigated the glycosylation modification of rabbit myofibrillar proteins. The results demonstrated that solubility of glucose-glycosylated products increased by 34 %, while the reduction capacity improved from 0.15 mg/mL to 1.6 mg/mL. The·OH free radical scavenging ability increased from 63.94 % to 94.21 %. β-Glucan-glycosylated products exhibited the highest thermal stability, and their DPPH free radical scavenging rate increased from 19.68 % to 76.21 %. Glycosylation also induced changes in protein conformation, characterized by a 10-30 °C increase in thermal denaturation peak temperature, gradual attenuation of endogenous fluorescence intensity, gradual enhancement of λmax redshift, and a 30-40 % decrease in surface hydrophobicity. Molecular docking simulations revealed that the primary interactions between glucose, lactose, and β-Glucan with myofibrillar proteins involve hydrogen bonds and van der Waals forces. In conclusion, glycosylation can effectively improve the functional properties of proteins, contributing to the development and production of high-quality, stable, and nutritious rabbit meat products.

Preparation, characterization and functional evaluation of soy protein isolate-peach gum conjugates prepared by wet heating Maillard reaction

This study was conducted to formulate a conjugate of soy protein isolate (SPI) and peach gum (PG) with improved functional properties, interacting at mass ratios of 1:1, 1:2, 1:3, 2:1, and 2:3 by Maillard reaction via wet heating method. Conjugation efficiency was confirmed by grafting degree (DG) and browning index (BI). Results indicated that DG increased with increasing concentration of PG, and decreased with increasing pH, whereas no remarkable change was observed with increasing reaction time. The conjugates were optimized at a ratio of 1:3. SDS-PAGE confirmed conjugate formation, Fourier transform infrared spectroscopy (FTIR) and circular dichroism (CD) verified conjugate secondary structural changes, and scanning electron microscopy (SEM) indicated significant overall structural changes. The functional properties, solubility, emulsifying stability, water holding, foaming, and antioxidant activity were significantly improved. This study revealed the wet heating method as an effective approach to improve the functional properties of soy protein.

Effects of enzymatic hydrolysis combined with glycation on the emulsification characteristics and emulsion stability of peanut protein isolate

Peanut protein isolate (PPI) has high nutritional value, but its poor function limits its application in the food industry. In this study, peanut protein isolate was modified by enzymatic hydrolysis combined with glycation. The structure, emulsification and interface properties of peanut protein isolate hydrolysate (HPPI) and dextran (Dex) conjugate (HPPI-Dex) were studied. In addition, the physicochemical properties, rheological properties, and stability of the emulsion were also investigated. The results showed that the graft degree increased with the increase of Dex ratio. Fourier transform infrared spectroscopy (FTIR) confirmed that the glycation of HPPI and Dex occurred. The microstructure showed that the structure of HPPI-Dex was expanded, and the molecular flexibility was enhanced. When the ratio of HPPI to Dex was 1:3, the emulsifying activity and the interface pressure of glycated HPPI reached the highest value, and the emulsifying activity (61.08 m2/g) of HPPI-Dex was 5.28 times that of PPI. The HPPI-Dex stabilized emulsions had good physicochemical properties and rheological properties. In addition, HPPI-Dex stabilized emulsions had high stability under heat treatment, salt ion treatment and freeze-thaw cycle. According to confocal laser scanning microscopy (CLSM), the dispersion of HPPI-Dex stabilized emulsions was better after 28 days of storage. This study provides a theoretical basis for developing peanut protein emulsifier and further expanding the application of peanut protein in food industry.

Contribution of Continued Dermal Exposure of PFAS-Containing Sunscreens to Internal Exposure: Extrapolation from In Vitro and In Vivo Tests to Physiologically Based Toxicokinetic Models

Per- and polyfluoroalkyl substances (PFASs) are widely present in sunscreen products as either active ingredients or impurities. They may penetrate the human skin barrier and then pose potential health risks. Herein, we aimed to develop a physiologically based toxicokinetic (PBTK) model capable of predicting the body loading of PFASs after repeated, long-term dermal application of commercial sunscreens. Ten laboratory-prepared sunscreens, generally falling into two categories of water-in-oil (W/O) and oil-in-water (O/W) sunscreens, were subject to in vitro percutaneous penetration test to assess the impacts of four sunscreen ingredients on PFAS penetration. According to the results, two sunscreen formulas representing W/O and O/W types that mostly enhanced PFAS dermal absorption were then selected for a subsequent 30 day in vivo exposure experiment in mice. PBTK models were successfully established based on the time-dependent PFAS concentrations in mouse tissues (R2 = 0.885-0.947) and validated through another 30 day repeated exposure experiment in mice using two commercially available sunscreens containing PFASs (R2 = 0.809-0.835). The PBTK model results suggest that applying sunscreen of the same amount on a larger skin area is more conducive to PFAS permeation, thus enhancing the exposure risk. This emphasizes the need for caution in practical sunscreen application scenarios, particularly during the summer months.

Enhancing the emulsion properties and bioavailability of loaded astaxanthin by selecting the reaction sequence of ternary conjugate emulsifiers in nanoemulsions

This study investigated the effects of the conjugate reaction sequences of whey protein concentrate (WPC), epigallocatechin gallate (EGCG) and dextran (DEX) on the structure and emulsion properties of conjugates and the bioaccessibility of astaxanthin (AST). Two types of ternary covalent complexes were synthesised using WPC, EGCG and DEX, which were regarded as emulsifiers of AST nanoemulsions. Results indicated that the WPC-DEX-EGCG conjugate (referred to as 'con') exhibits a darker SDS-PAGE dispersion band and higher contents of α-helix (6%), β-angle (24%) and random coil (32%), resulting in a greater degree of unfolding structure and fluorescence quenching. These findings suggested WPC-DEX-EGCG con had the potential to exhibit better emulsification properties than WPC-EGCG-DEX con. AST encapsulation efficiency (76.22%) and bioavailability (31.89%) also demonstrated the superior performance of the WPC-DEX-EGCG con emulsifier in nanoemulsion delivery systems. These findings indicate that altering reaction sequences changes protein conformation, enhancing the emulsification properties and bioavailability of AST.

Enhancing Functional Properties and Protein Structure of Almond Protein Isolate Using High-Power Ultrasound Treatment

The suitability of a given protein for use in food products depends heavily on characteristics such as foaming capacity, emulsifiability, and solubility, all of which are affected by the protein structure. Notably, protein structure, and thus characteristics related to food applications, can be altered by treatment with high-power ultrasound (HUS). Almonds are a promising source of high-quality vegetable protein for food products, but their physicochemical and functional properties remain largely unexplored, limiting their current applications in foods. Here, we tested the use of HUS on almond protein isolate (API) to determine the effects of this treatment on API functional properties. Aqueous almond protein suspensions were sonicated at varying power levels (200, 400, or 600 W) for two durations (15 or 30 min). The molecular structure, protein microstructure, solubility, and emulsifying and foaming properties of the resulting samples were then measured. The results showed that HUS treatment did not break API covalent bonds, but there were notable changes in the secondary protein structure composition, with the treated proteins showing a decrease in α-helices and β-turns, and an increase in random coil structures as the result of protein unfolding. HUS treatment also increased the number of surface free sulfhydryl groups and decreased the intrinsic fluorescence intensity, indicating that the treatment also led to alterations in the tertiary protein structures. The particle size in aqueous suspensions was decreased in treated samples, indicating that HUS caused the dissociation of API aggregates. Finally, treated samples showed increased water solubility, emulsifying activity, emulsifying stability, foaming capacity, and foaming stability. This study demonstrated that HUS altered key physicochemical characteristics of API, improving critical functional properties including solubility and foaming and emulsifying capacities. This study also validated HUS as a safe and environmentally responsible tool for enhancing desirable functional characteristics of almond proteins, promoting their use in the food industry as a high-quality plant-based protein.

Preparation and functional properties of rice bran globulin-chitooligosaccharide-quercetin-resveratrol covalent complex

BACKGROUND

As the major protein (approximately 36%) in rice bran, globulin exhibits excellent foaming and emulsifying properties, endowing its useful application as a foaming and emulsifying agent in the food industry. However, the low water solubility restricts its commercial potential in industrial applications. The present study aimed to improve this protein's processing and functional properties.

RESULTS

A novel covalent complex was fabricated by a combination of the Maillard reaction and alkaline oxidation using rice bran globulin (RBG), chitooligosaccharide (C), quercetin (Que) and resveratrol (Res). The Maillard reaction improved the solubility, emulsifying and foaming properties of RBG. The resultant glycosylated protein was covalently bonded with quercetin and resveratrol to form a (RBG-C)-Que-Res complex. (RBG-C)-Que-Res exhibited higher thermal stability and antioxidant ability than the native protein, binary globulin-chitooligosaccharide or ternary globulin-chitooligosaccharide-polyphenol (only containing quercetin or resveratrol) conjugates. (RBG-C)-Que-Res exerted better cytoprotection against the generation of malondialdehyde and reactive oxygen species in HepG2 cells, which was associated with increased activities of antioxidative enzymes superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH-Px) through upregulated genes SOD1, CAT, GPX1 (i.e. gene for glutathione peroxidase-1), GCLM (i.e. gene for glutamate cysteine ligase modifier subunit), SLC1A11 (i.e. gene for solute carrier family 7, member 11) and SRXN1 (i.e. gene for sulfiredoxin-1). The anti-apoptotic effect of (RBG-C)-Que-Res was confirmed by the downregulation of caspase-3 and p53 and the upregulation of B-cell lymphoma-2 gene expression.

CONCLUSION

The present study highlights the potential of (RBG-C)-Que-Res conjugates as functional ingredients in healthy foods. © 2024 Society of Chemical Industry.

Studies on the Increasing Saltiness and Antioxidant Effects of Peanut Protein Maillard Reaction Products

The salt taste-enhancing and antioxidant effect of the Maillard reaction on peanut protein hydrolysates (PPH) was explored. The multi-spectroscopic and sensory analysis results showed that the Maillard reaction products (MRPs) of hexose (glucose and galactose) had slower reaction rates than those of pentose (xylose and arabinose), but stronger umami and increasing saltiness effects. The Maillard reaction can improve the flavor of PPH, and the galactose-Maillard reaction product (Ga-MRP) has the best umami and salinity-enhancing effects. The measured molecular weight of Ga-MRP were all below 3000 Da, among which the molecular weights between 500-3000 Da accounted for 46.7%. The products produced during the Maillard reaction process resulted in a decrease in brightness and an increase in red value of Ga-MRP. The amino acid analysis results revealed that compared with PPH, the content of salty and umami amino acids in Ga-MRPs decreased, but their proportion in total free amino acids increased, and the content of bitter amino acids decreased. In addition, the Maillard reaction enhances the reducing ability, DPPH radical scavenging ability, and Fe2+ chelating ability of PPH. Therefore, the Maillard reaction product of peanut protein can be expected to be used as a substitute for salt seasoning, with excellent antioxidant properties.

Reduction of maillard browning in spray dried low-lactose milk powders due to protein polysaccharide interactions

Lactose hydrolysed concentrated milk was prepared using β-galactosidase enzyme (4.76U/mL) with a reaction period of 12 h at 4 °C. Addition of polysaccharides (5 % maltodextrin/β-cyclodextrin) to concentrated milk either before or after lactose hydrolysis did not result in significant differences (p > 0.05) in degree of hydrolysis (% DH) of lactose and residual lactose content (%). Three different inlet temperatures (165 °C, 175 °C and 185 °C) were used for the preparation of powders which were later characterised based on physico-chemical and maillard browning characteristics. Moisture content, solubility and available lysine content of the powders decreased significantly, whereas, browning parameters i.e., browning index, 5-hydroxymethylfurfural, furosine content increased significantly (p < 0.05) with an increase in inlet air temperature. The powder was finally prepared with 5 % polysaccharide and an inlet air temperature of 185 °C which reduced maillard browning. Protein-polysaccharide interactions were identified using Fourier Transform infrared spectroscopy, fluorescence spectroscopy and determination of free amino groups in the powder samples. Maltodextrin and β-cyclodextrin containing powder samples exhibited lower free amino groups and higher degree of graft value as compared to control sample which indicated protein-polysaccharide interactions. Results obtained from Fourier Transform infrared spectroscopy also confirmed strong protein-polysaccharide interactions, moreover a significant decrease in fluorescence intensity was also observed in the powder samples. These interactions between the proteins and polysaccharides reduced the maillard browning in powders.

Freeze-thaw stability of transglutaminase-induced soy protein-maltose emulsion gel: Focusing on morphology, texture properties, and rheological characteristics

In this study, soy protein isolate (SPI) and maltose (M) were employed as materials for the synthesis of a covalent compound denoted as SPI-M. The emulsion gel was prepared by transglutaminase (TGase) as catalyst, and its freeze-thaw stability was investigated. The occurrence of Maillard reaction was substantiated through SDS-PAGE. The analysis of spectroscopy showed that the structure of the modified protein was more stretched, changed in the direction of freeze-thaw stability. After three freeze-thaw cycles (FTC), it was observed that the water holding capacity of SPI-M, SPI/M mixture (SPI+M) and SPI emulsion gels exhibited reductions of 8.49 %, 16.85 %, and 20.26 %, respectively. Moreover, the soluble protein content also diminished by 13.92 %, 23.43 %, and 35.31 %, respectively. In comparison to unmodified SPI, SPI-M exhibited increase in gel hardness by 160 %, while elasticity, viscosity, chewability, and cohesion demonstrated reductions of 17.7 %, 23.3 %, 33.3 %, and 6.76 %, respectively. Concurrently, the SPI-M emulsion gel exhibited the most rapid gel formation kinetics. After FTCs, the gel elastic modulus (G') and viscosity modulus (G″) of SPI-M emulsion were the largest. DSC analysis underscored the more compact structure and heightened thermal stability of the SPI-M emulsion gel. SEM demonstrated that the SPI-M emulsion gel suffered the least damage following FTCs.

Comprehensive structural and functional characterization of a new protein-polysaccharide conjugate between grass pea protein (Lathyrus sativus) and xanthan gum produced by wet heating

The purpose of this work was to use a controlled wet-heating process to promote Maillard reaction (MR) between grass pea protein (GPPI) and xanthan gum (XG), and then analyse structural, functional and antioxidant properties of the conjugate (GPPI-XGCs). During heating, the degree of glycation of all conjugated samples was raised (up to 37.43 %) and, after heating for 24 h, the lightness of the samples decreased by 24.75 %. Circular dichroism showed changes in secondary structure with lower content of α-helix and random coil in conjugates. XRD patterns showed that MR destroyed the crystalline structure of the protein. In addition, Lys and Arg content of the produced conjugates decreased by 16.94 % and 6.17 %, respectively. Functional properties including foaming capacity and stability were increased by 45.17 % and 37.17 %, and solubility reached 98.88 %, due to the protein unfolding driven by MR. GPPI-XGCs showed significantly higher antioxidant activities with maximum ABTS-RS value of 49.57 %. This study revealed how MR can improve GPPI's properties, which can aid the food industry in producing a wide range of plant-based foods. Especially, among other characteristics, the foaming properties were significantly improved and the final product can be introduced as a promising foaming agent to be used in food formulation.

Nonenzymatic glycation as a tunable technique to modify plant proteins: A comprehensive review on reaction process, mechanism, conjugate structure, and functionality

Plant proteins are expected to become a major protein source to replace currently used animal-derived proteins in the coming years. However, there are always challenges when using these proteins due to their low water solubility induced by the high molecular weight storage proteins. One approach to address this challenge is to modify proteins through Maillard glycation, which involves the reaction between proteins and carbohydrates. In this review, we discuss various chemical methods currently available for determining the indicators of the Maillard reaction in the early stage, including the graft degree of glycation and the available lysine or sugar, which are involved in the very beginning of the reaction. We also provide a detailed description of the most popular methods for determining graft sites and assessing different plant protein structures and functionalities upon non-enzymatic glycation. This review offers valuable insights for researchers and food scientists in order to develop plant-based protein ingredients with improved functionality.

Effect of ultrasonic assisted grafting on the structural and functional properties of mung bean protein isolate conjugated with maltodextrin through maillard reaction

Four different methods of maillard reaction including ultrasound (150 W, 10 min) assisted, classical wet heating (80 °C, 60min), moderate water bath heating (60°C, 12 to 30 h) and dry state method (60 °C, 79 % relative humidity and 48 h) were used to Mung bean protein isolate - Maltodexrtin conjugates (MPI-MD) preparation. The samples prepared under ultrasound and wet heating were chosen for further analysis according to degree of graft and UV-absorbance at 420 nm. Higher glycosylation at short time and lower browning were obtained under ultrasound treatment. Covalent attachment in conjugates confirmed by SDS-polyacrylamide gel electrophoresis. The structural analysis revealed prominent unfolding effect of ultrasound waves on the protein's molecules. The decrease of α-helix content was related to the exposure of buried amino group residues during reaction. Glycation of MPI under ultrasound caused changes in tertiary structure of protein and leads to decrease in the fluorescence intensity compared with native and wet heating treatments. FTIR spectra confirmed the conjugation of the MPI and MD and suggested that protein structure was changed and ultrasound promoted the graft reaction more than wet heating treatment. Conjugated MPI showed higher emulsification and solubility index than MPI, moreover the effect of ultrasonic waves on ameliorated functional properties was impressive than those for wet heating treatment. Overall, this study showed use of ultrasonication in maillard reaction was a suitable method for producing MPI- MD conjugates and improved the efficiency of graft reaction and functional properties of grafts.

Conjugation of soymilk protein and arabinoxylan induced by peroxidase to improve the gel properties of tofu

Arabinoxylan (AX) can form stable covalent bonds with protein to improve gel properties. We aimed to prepare a conjugate between soymilk protein (SMP) and AX by peroxidase, followed by the addition of transglutaminase (TG) to prepare tofu gels. The conjugate's properties and their effects on the mechanical properties, rheological properties, and microstructure of tofu gels were evaluated. Results revealed that the α-helix content decreased, the β-sheet content increased, and the surface hydrophobicity reduced from 1.60 × 105 to 1.27 × 105. The optimal amount of AX required to improve the properties of tofu gel was 1.0%. The tofu gel showed better hardness (118.44 g), water holding capacity (WHC) (86.17%), and higher storage modulus (G') and loss modulus (G″). Low-Field NMR (LF-NMR) showed that the water was evenly distributed. Scanning electron microscopy (SEM) revealed a denser and more regular three-dimensional gel network.

Preparation of meaty flavor additive from soybean meal through the Maillard reaction

Meaty flavor additive was prepared from soybean meal hydrolysate and xylose in the method of Maillard reaction. Under the conditions of reaction temperature 120 ℃, time 120 min and cysteine addition 10%, the Maillard products had strong flavor of meat. The content of free amino acids was 4.941 μ mol/mL in the products. There were 50 volatile flavor substances in Maillard reaction products according to GC-MS analysis. 4 mercaptans, 4 sulfur substituted furans, 3 thiophenes, 7 furans, 6 pyrazine, 3 pyrrole, 1 pyrimidine, 7 aldehydes, 4 ketones, 7 esters, 2 alcohols and 2 acids were included. The Maillard reaction products also have strong antioxidant activity. The scavenging ability of FRAP, DPPH radical, hydroxyl radical and ABTS+ radical was 1.82%, 69.8%, 68.7% and 71.6% respectively. The products of Mailard reaction have potential to be used in food additives.

Composition, functional properties, health benefits and applications of oilseed proteins: A systematic review

Common oilseeds, such as soybean, peanut, rapeseed, sunflower seed, sesame seed and chia seed, are key sources of edible vegetable oils. Their defatted meals are excellent natural sources of plant proteins that can meet consumers' demand for health and sustainable substitutes for animal proteins. Oilseed proteins and their derived peptides are also associated with many health benefits, including weight loss and reduced risks of diabetes, hypertension, metabolic syndrome and cardiovascular events. This review summarizes the current status of knowledge on the protein and amino acid composition of common oilseeds as well as the functional properties, nutrition, health benefits and food applications of oilseed protein. Currently, oilseeds are widely applied in the food industry regarding for their health benefits and good functional properties. However, most oilseed proteins are incomplete proteins and their functional properties are not promising compared to animal proteins. They are also limited in the food industry due to their off-flavor, allergenic and antinutritional factors. These properties can be improved by protein modification. Therefore, in order to make better use of oilseed proteins, methods for improving their nutrition value, bioactive activity, functional and sensory characteristics, as well as the strategies for reducing their allergenicity were also discussed in this paper. Finally, examples for the application of oilseed proteins in the food industry are presented. Limitations and future perspectives for developing oilseed proteins as food ingredients are also pointed out. This review aims to foster thinking and generate novel ideas for future research. It will also provide novel ideas and broad prospects for the application of oilseeds in the food industry.

The Impact of AAPH-Induced Oxidation on the Functional and Structural Properties, and Proteomics of Arachin

The aim of this study was to investigate the effect of 2,2'-azobis (2-amidinopropane) dihydrochloride (AAPH)-induced oxidation on the functional, structural properties and proteomic information of arachin. The results showed that moderate oxidation improved the water/oil holding capacity of proteins and increased the emulsifying stability, while excessive oxidation increased the carbonyl content, reduced the thiol content, altered the structure and thermal stability, and reduced most of the physicochemical properties. Through LC-QE-MS analysis, it was observed that oxidation leads to various modifications in arachin, including carbamylation, oxidation, and reduction, among others. In addition, 15 differentially expressed proteins were identified. Through gene ontology (GO) analysis, these proteins primarily affected the cellular and metabolic processes in the biological process category. Further Kyoto encyclopedia of genes and genomes (KEGG) analysis revealed that the "proteasome; protein processing in the endoplasmic reticulum (PPER)" pathway was the most significantly enriched signaling pathway during the oxidation process of arachin. In conclusion, this study demonstrated that AAPH-induced oxidation can alter the conformation and proteome of arachin, thereby affecting its corresponding functional properties. The findings of this study can potentially serve as a theoretical basis and foundational reference for the management of peanut processing and storage.

Behavior of protein-polysaccharide conjugate-stabilized food emulsions under various destabilization conditions

The sensitivity of protein-stabilized emulsions to flocculation, coalescence, and phase separation under destabilization conditions (i.e., heating, aging, pH, ionic strength, and freeze-thawing) may limit the widespread use of proteins as effective emulsifiers. Therefore, there is a great interest in modulating and improving the technological functionality of food proteins by conjugating them with polysaccharides, through the Maillard reaction. The present review article highlights the current approaches of protein-polysaccharide conjugate formation, their interfacial properties, and the behavior of protein-polysaccharide conjugate stabilized emulsions under various destabilization conditions, including long-term storage, heating and freeze-thawing treatments, acidic conditions, high ionic strength, and oxidation. Protein-polysaccharide conjugates are capable of forming a thick and cohesive macromolecular layer around oil droplets in food emulsions and stabilizing them against flocculation and coalescence under unfavorable conditions, through steric and electrostatic repulsion. The protein-polysaccharide conjugates could be therefore industrially used to design emulsion-based functional foods with high physicochemical stability.

Fabrication and characterization of succinylated and glycosylated soy protein isolate and its self-assembled nanogel

In this study, we used succinic anhydride (SA) acylation and dextran (DX) glycosylation modified soybean isolate protein (SPI) to develop self-assembled SPI-SA-DX adduct-based nanogels. Degree of modification, SDS-PAGE, and FT-IR studies showed that the amino group of the SPI was replaced by hydrophilic dextran and succinic acid carboxyl groups. Dextran chain and anhydride group attachment to the soybean protein surface enhanced hydrophilicity and spatial site blocking. Modification-induced protein structure unfolding, free sulfhydryl groups to be converted to disulfide bonds, and reduced surface hydrophobicity (H₀). H₀ was lowest at 33,750 ± 1008.29 when SA content = 10 % protein content (SPI-SA₃-DX). The nanometer gel based on SPI-SA₃-DX had the maximum turbidity and clear transparent solution without precipitation. Its particle size and polymer dispersibility index (PDI) were also the smallest, with values of (106.87 ± 4.51) nm and 0.21 ± 0.009, respectively. Transmission electron microscopy showed that nanogels had subspherical shell-core structures. Nanogels were stable under different pH, ionic strength, high temperature, and storage conditions.

Physicochemical and structural characterization of whey protein concentrate-tomato pectin conjugates

BACKGROUND

Protein-pectin conjugates, obtained through a controlled Maillard reaction in blends of precursors, are studied for their contribution to improving the emulsifying and thermal properties of proteins. The objective was to obtain a conjugate between whey protein concentrate (WPC) and non-conventional pectins extracted in acid (acid tomato pectin, ATP) and aqueous medium (water tomato pectin, WTP) from industrialized tomato residues (tomato waste, TW), characterize the conjugates and study their emulsion properties. The Maillard reaction was carried out at 60 °C and 75% relative humidity in blends with 2:1 proportions; 1:1 and 1:2 (m_protein :m_pectin ) for 3, 6 and 12 days. Conjugates were compared concerning treated and untreated WPC.

RESULTS

The WPC-ATP conjugate showed significant increases in color difference (ΔE). The electrophoresis profile of the conjugates showed diffuse bands of molecular weight between 37 and 250 kDa and a reduction in the intensity of bands characteristic of WPC (α-lactalbumin and β-lactoglobulin). Thermal analysis showed an increase in the peak temperature and a reduction in the enthalpy change in protein denaturation, associated with the formation of conjugates. The infrared spectroscopy of the conjugates, in the amide III zone (1300-1100 cm^-1 ), indicated an increase in the relative peak area associated with the unfolding and exhibition of the hydrophobic zones of the WPC fraction. The emulsions formulated with the conjugates showed a significant increase in the emulsifying stability index (ESI) (P < 0.05) concerning the treated and untreated WPC emulsions.

CONCLUSION

The formation of conjugates increased the emulsifying properties and improved the thermal stability of WPC, showing an innovative and alternative food ingredient too. © 2023 Society of Chemical Industry.

Silk Sericin Protein Materials: Characteristics and Applications in Food-Sector Industries

There is growing concern about the use of plastic in packaging for food materials, as this results in increased plastic waste materials in the environment. To counter this, alternative sources of packaging materials that are natural and based on eco-friendly materials and proteins have been widely investigated for their potential application in food packaging and other industries of the food sector. Sericin, a silk protein that is usually discarded in large quantities by the sericulture and textile industries during the degumming process of manufacturing silk from silk cocoons, can be explored for its application in food packaging and in other food sectors as a functional food and component of food items. Hence, its repurposing can result in reduced economic costs and environmental waste. Sericin extracted from silk cocoon possesses several useful amino acids, such as aspartic acid, glycine, and serine. Likewise, sericin is strongly hydrophilic, a property that confers effective biological and biocompatible characteristics, including antibacterial, antioxidant, anticancer, and anti-tyrosinase properties. When used in combination with other biomaterials, sericin has proved to be effective in the manufacture of films or coating or packaging materials. In this review, the characteristics of sericin materials and their potential application in food-sector industries are discussed in detail.

Changes in the functional properties of casein conjugates prepared by Maillard reaction with pectin or arabinogalactan

The aim of this study was to prepare conjugates of casein (CA) with pectin (CP) or arabinogalactan (AG) by the Maillard reaction (wet-heating) and to investigate the effects of CP or AG on the structural and functional properties of casein. The results indicated that the highest grafting degree of CA with CP or AG was observed at 90 °C for 1.5 h or 1 h, respectively. Secondary structure showed that grafting with CP or AG reduced the α-helix level and increased the random coil level of CA. Glycosylation treatment of CA-CP and CA-AG exhibited lower surface hydrophobicity and higher absolute ζ-potential values, further significantly improving the functional properties of CA (e.g., solubility, foaming property, emulsifying property, thermal stability, and antioxidant activity). Accordingly, our results indicated that it is feasible for CP or AG to improve the functional properties of CA by the Maillard reaction.

Utilization of ultrasound and glycation to improve functional properties and encapsulated efficiency of proteins in anthocyanins

The purpose of this study is to explore the optimal conditions for the preparation of bovine serum albumin (BSA)/casein (CA)-dextran (DEX) conjugates by ultrasonic pretreatment combined with glycation (U-G treatment). When BSA and CA were treated with ultrasound (40% amplitude, 10 min), the grafting degree increased 10.57% and 6.05%, respectively. Structural analysis revealed that ultrasonic pretreatment changed the secondary structure, further affected functional properties of proteins. After U-G treatment, the solubility and thermal stability of BSA and CA was significantly increased, and the foaming and emulsifying capacity of proteins were also changed. Moreover, ultrasonic pretreatment and glycation exhibited a greater impact on BSA characterized with highly helical structure. Complexes fabricated by U-G-BSA/CA and carboxymethyl cellulose (CMC) exhibited protection on anthocyanins (ACNs), delaying the thermal degradation of ACNs. In conclusion, the protein conjugates treated by ultrasonic pretreatment combined with glycation have excellent functionality and are potential carrier materials.

Functional Proteins from Biovalorization of Peanut Meal: Advances in Process Technology and Applications

Environmental costs associated with meat production have necessitated researchers and food manufacturers to explore alternative sources of high-quality protein, especially from plant origin. Proteins from peanuts and peanut-by products are high-quality, matching industrial standards and nutritional requirements. This review contributes to recent developments in the production of proteins from peanut and peanut meal. Conventional processing techniques such as hot-pressing kernels, use of solvents in oil removal, and employing harsh acids and alkalis denature the protein and damage its functional properties, limiting its use in food formulations. Controlled hydrolysis (degree of hydrolysis between 1 and 10%) using neutral and alkaline proteases can extract proteins and improve peanut proteins' functional properties, including solubility, emulsification, and foaming activity. Peanut proteins can potentially be incorporated into meat analogues, bread, soups, confectionery, frozen desserts, and cakes. Recently, pretreatment techniques (microwave, ultrasound, high pressure, and atmospheric cold plasma) have been explored to enhance protein extraction and improve protein functionalities. However, most of the literature on physicochemical pretreatment techniques has been limited to the lab scale and has not been analysed at the pilot scale. Peanut-derived peptides also exhibit antioxidant, anti-hypertensive, and anti-thrombotic properties. There exists a potential to incorporate these peptides into high-fat foods to retard oxidation. These peptides can also be consumed as dietary supplements for regulating blood pressure. Further research is required to analyse the sensory attributes and shelf lives of these novel products. In addition, animal models or clinical trials need to be conducted to validate these results on a larger scale.

Effects of Sequential Enzymolysis and Glycosylation on the Structural Properties and Antioxidant Activity of Soybean Protein Isolate

The effects of limited hydrolysis following glycosylation with dextran on the structural properties and antioxidant activity of the soybean protein isolate (SPI) were investigated. Three SPI hydrolysate (SPIH) fractions, F30 (>30 kDa), F30-10 (10-30 kDa), and F10 (<10 kDa), were confirmed using gel permeation chromatography. The results demonstrated that the glycosylation of F30 was faster than that of F30-10 or F10. The enzymolysis caused the unfolding of the SPI to expose the internal hydrophobic cores, which was further promoted by the grafting of dextran, making the obtained conjugates have a loose spatial structure, strong molecular flexibility, and enhanced thermal stability. The grafting of dextran significantly enhanced the DPPH radical or •OH scavenging activity and the ferrous reducing power of the SPI or SPIH fractions with different change profiles due to their different molecular structures. The limited enzymolysis following glycosylation was proven to be a promising way to obtain SPI-based food ingredients with enhanced functionalities.

Development of high-internal-phase emulsions stabilized by soy protein isolate-dextran complex for the delivery of quercetin

BACKGROUND

Protein-polysaccharide complexes have been widely used to stabilize high-internal-phase emulsion (HIPEs). However, it is still unknown whether soy protein isolate-dextran (SPI-Dex) complexes can stabilize HIPEs or what is the effect of Dex concentration on the HIPEs. Furthermore, the non-covalent interaction mechanism between SPI and Dex is also unclear. Therefore, we fabricated SPI-Dex complexes and used them to stabilize HIPEs-loaded quercetin and explore the interaction mechanism between SPI and Dex, as well as the effect of Dex concentration on the particle size, ζ-potential, microstructure, rheology, quercetin encapsulation efficiency, and gastrointestinal fate of the HIPEs.

RESULTS

Spectral analysis (fourier transform infrared spectroscopy, ultraviolet spectroscopy, and fluorescence spectroscopy) results identified the formation of SPI-Dex complexes, and indicated that the addition of Dex changed the spatial structure of SPI, whereas thermodynamic analysis (ΔH > 0, ΔS > 0) showed that hydrophobic interactions were the main driving forces in the formation of SPI-Dex complexes. Compared with HIPEs stabilized by SPI, the SPI-Dex complex-stabilized HIPEs had smaller particles (3000.33 ± 201.22 nm), as well as higher ζ-potential (-21.73 ± 1.10 mV), apparent viscosities, modulus, and quercetin encapsulation efficiency (98.19 ± 0.14%). In addition, in vitro digestion revealed that SPI-Dex complex-stabilized HIPEs significantly reduced the release of free fatty acid and improved quercetin bioaccessibility.

CONCLUSION

HIPEs stabilized by SPI-Dex complexes delayed the release of free fat acid and improved the bioaccessibility of quercetin, and may be help in designing delivery systems for bioactive substances with specific properties. © 2022 Society of Chemical Industry.

Structural and emulsifying properties of soybean protein isolate glycated with glucose based on pH treatment

BACKGROUNDS

In the present study, a glycosylated soybean protein with glucose was prepared after pH treatment under different conditions (5.0, 6.0 7.0, 8.0, 9.0) and the conformation and emulsifying properties of soybean protein isolate (SPI) and soybean protein isolate-glucose (SPI-G) were investigated.

RESULTS

The degree of grafting (37.11%) and browning (39.2%) of SPI-G conjugates were obtained at pH 9.0 (P < 0.05). The results of analysis of polyacrylamide gel electrophoresis, Fourier transform infrared spectroscopy and Endogenous fluorescence spectroscopy showed that the Maillard reaction between the SPI and glucose occurred and the natural rigid structure of test proteins was stretched and became looser, and thus the tertiary conformation was unfolding. Furthermore, the particle size of the all of samples was reduced under different pH conditions, indicating that pH treatment can increase the flexibility of SPI molecules. The proteins exhibited the best surface hydrophobicity, thermal stability and emulsifying activity (EA) of modified products when subjected to a pH treatment of 9.0, whereas they afforded the best emulsion stability (ES) at pH 8.0. There was a good correlation between the molecular flexibility and emulsifying properties of SPI-G [0.963 (F:EA) and 0.879 (F:ES)] (P < 0.05).

CONCLUSION

The present study shows that the structural and emulsification characteristics of natural SPI and SPI-G conjugates have been significantly enhanced via pH treatment and these results provide a theoretical guidance for the application of glycosylated SPI in the food industry. © 2022 Society of Chemical Industry.

Effects of Different Amounts of Corn Silk Polysaccharide on the Structure and Function of Peanut Protein Isolate Glycosylation Products

Covalent complexes of peanut protein isolate (PPI) and corn silk polysaccharide (CSP) (PPI-CSP) were prepared using an ultrasonic-assisted moist heat method to improve the functional properties of peanut protein isolate. The properties of the complexes were affected by the level of corn silk polysaccharide. By increasing the polysaccharide addition, the grafting degree first increased, and then tended to be flat (the highest was 38.85%); the foaming, foam stability, and solubility were also significantly improved. In a neutral buffer, the solubility of the sample with a protein/polysaccharide ratio of 2:1 was 73.69%, which was 1.61 times higher than that of PPI. As compared with PPI, the complexes had higher thermal stability and lower surface hydrophobicity. High addition of CSP could made the secondary structure of PPI change from ordered α-helix to disordered β-sheet, β-turn, and random coil structure, and the complex conformation become more flexible and loose. The results of multiple light scattering showed that the composite solution exhibited high stability, which could be beneficial to industrial processing, storage, and transportation. Therefore, the functional properties of peanut protein isolate glycosylation products could be regulated by controlling the amount of polysaccharide added.

The Effect of Glycosylated Soy Protein Isolate on the Stability of Lutein and Their Interaction Characteristics

Lutein is a natural fat-soluble carotenoid with various physiological functions. However, its poor water solubility and stability restrict its application in functional foods. The present study sought to analyze the stability and interaction mechanism of the complex glycosylated soy protein isolate (SPI) prepared using SPI and inulin-type fructans and lutein. The results showed that glycosylation reduced the fluorescence intensity and surface hydrophobicity of SPI but improved the emulsification process and solubility. Fluorescence intensity and ultraviolet–visible (UV–Vis) absorption spectroscopy results showed that the fluorescence quenching of the glycosylated soybean protein isolate by lutein was static. Through thermodynamic parameter analysis, it was found that lutein and glycosylated SPI were bound spontaneously through hydrophobic interaction, and the binding stoichiometry was 1:1. The X-ray diffraction analysis results showed that lutein existed in the glycosylated soybean protein isolate in an amorphous form. The Fourier transform infrared spectroscopy analysis results revealed that lutein had no effect on the secondary structure of glycosylated soy protein isolate. Meanwhile, the combination of lutein and glycosylated SPI improved the water solubility of lutein and the stability of light and heat.

Recent Advances for the Developing of Instant Flavor Peanut Powder: Generation and Challenges

Instant flavor peanut powder is a nutritional additive that can be added to foods to impart nutritional value and functional properties. Sensory acceptability is the premise of its development. Flavor is the most critical factor in sensory evaluation. The heat treatment involved in peanut processing is the main way to produce flavor substances and involves chemical reactions: Maillard reaction, caramelization reaction, and lipid oxidation reaction. Peanut is rich in protein, fat, amino acids, fatty acids, and unsaturated fatty acids, which participate in these reactions as volatile precursors. N-heterocyclic compounds, such as the pyrazine, are considered to be the key odorants of the “baking aroma”. However, heat treatment also affects the functional properties of peanut protein (especially solubility) and changes the nutritional value of the final product. In contrast, functional properties affect the behavior of proteins during processing and storage. Peanut protein modification is the current research hotspot in the field of deep processing of plant protein, which is an effective method to solve the protein denaturation caused by heat treatment. The review briefly describes the characterization and mechanism of peanut flavor during heat treatment combined with solubilization modification technology, proposing the possibility of using peanut meal as material to produce IFPP.

Synergistic effect of preheating and different power output high-intensity ultrasound on the physicochemical, structural, and gelling properties of myofibrillar protein from chicken wooden breast

The effects of preheating to 50 ℃ and the subsequent application of high-intensity ultrasound (HIU, 20 kHz) at 200, 400, 600, and 800 W on the physicochemical, structural, and gelling properties of wooden breast myofibrillar protein (WBMP) were studied. Results suggested that the WBMP structure expanded to the balanced state at 600 W, and rheological properties exhibit that 600 W HIU (P < 0.05) significantly improved the storage modulus (G') of WBMP. Notably, the WBMP gel (600 W) had the best hardness (65.428 ± 0.33 g), springiness (0.582 ± 0.01), and water-holding capacity (86.11 ± 0.83%). Raman spectra and low-field NMR indicated that 600 W HIU increased the β-fold content (37.94 ± 0.04%) and enlarged the immobilized-water proportion (93.87 ± 0.46%). Scanning electron micrographs confirmed that the gel was uniform and dense at 600 W. Therefore, preheating to 50 ℃ followed by HIU (600 W) helped form a superior WBMP gel.

Inhibition of Maillard reaction during alkaline thermal hydrolysis of sludge

The Maillard reaction (MR) occurs during the alkaline thermal hydrolysis (ATH) of sludge, which affects the quantity and quality of recovered protein. In this paper, four different sulfites were added to investigate their inhibitory effects on melanoidin production. The results showed that sulfites inhibited melanoidin production during ATH of sludge and the inhibitory rate increased with their concentration. At a concentration of 5.71 g/L, the inhibitory rates of NaHSO₃ on melanoidin were 63.27%. Furthermore, the 3D-EEM (Three-Dimension Excitation-Emission-Matrix) fluorescence spectroscopy and protein testing data showed that the inhibition of melanoidin production was accompanied by an increased protein concentration, and protein increased with increasing sulfites concentration. A 2.5-fold increase in protein concentration with Na₂S₂O₄ significantly enhanced the quantity of protein recovered. Therefore, the addition of sulfite during ATH of sludge reduces the amount of non-biodegradable melanoidin, which in turn benefits protein recovery.