Effect of heat-induced aggregation of soy protein isolate on protein-glutaminase deamidation and the emulsifying properties of deamidated products

The effect of protein-glutaminase from Chryseobacterium proteolyticum on physicochemical and functional properties of high-temperature soybean meal protein

Protein-glutaminase (EC 3.5.1.44, PG) can significantly improve the functional properties of food proteins. However, the low yield of PG has limited industrial applications. Results showed that 0.02 % tea saponin could increase the PG yield by 18.93 %. The transcription level of the PG gene was significantly enhanced, which promoted the extracellular secretion of PG through an increase in membrane permeability. On this basis, PG was used to modify high-temperature soybean meal protein (HSMP) due to its poor properties. In this study, the deamidation degree (DD) of PG-modified HSMP was optimized to 58.61 % by the response surface method. HSMP with different DD was prepared and its physicochemical and functional properties were studied. After PG treatment, the intermolecular repulsive force of HSMP increased, the particle size distribution became uniform, and the solution system was more stable. In addition, the surface morphology of HSMP gradually became loose and porous. The solubility of HSMP significantly improved, reaching 11.34 times that of untreated HSMP at pH 5.00. Meanwhile, the emulsifying and foaming capacity of HSMP significantly improved, but the foaming stability was reduced.

Influence of substrate aggregation state on the enzymatic-induced crosslinking of soy protein isolate

Transglutaminase (TGase) induced-crosslinking of soy protein isolate (SPI) was markedly influenced by the substrate aggregation state. Results showed that appropriate heating significantly accelerated the TGase crosslinking, and the 7S and 11S acidic subunits were more susceptible to the enzyme than the 11S basic proteins. The content of ε-(γ-glutamyl)-lysine isopeptide bonds increased from 4.74 to 8.61 μmol/g protein when the heating intensity was increased from 75 °C for 15 min to 95 °C for 30 min, due to sufficient unfolding of the protein structure. Rheological data indicated that the gel formed from the SPI heated at 95 °C for 30 min exhibited the best properties, with a 60 % increase in the storage modulus compared with the unheated sample. However, excessive heating (95 °C, 60-120 min) caused severe aggregation of SPI and formation of insoluble aggregates, resulting in poor crosslinking efficiency and weaker gel properties.

Molecular modification of low-dissolution soy protein isolates by anionic xanthan gum, neutral guar gum, or neutral konjac glucomannan to improve the protein dissolution and stabilize fish oil emulsion

Herein, the effects of anionic xanthan gum (XG), neutral guar gum (GG), and neutral konjac glucomannan (KGM) on the dissolution, physicochemical properties, and emulsion stabilization ability of soy protein isolate (SPI)-polysaccharide conjugates were studied. The SPI-polysaccharide conjugates had better water dissolution than the insoluble SPI. Compared with SPI, SPI-polysaccharide conjugates had lower β-sheet (39.6 %-56.4 % vs. 47.3 %) and α-helix (13.0 %-13.2 % vs. 22.6 %) percentages, and higher β-turn (23.8 %-26.5 % vs. 11.0 %) percentages. The creaming stability of SPI-polysaccharide conjugate-stabilized fish oil-loaded emulsions mainly depended on polysaccharide type: SPI-XG (Creaming index: 0) > SPI-GG (Creaming index: 8.1 %-21.2 %) > SPI-KGM (18.1 %-40.4 %). In addition, it also depended on the SPI preparation concentrations, glycation times, and glycation pH. The modification by anionic XG induced no obvious emulsion creaming even after 14-day storage, which suggested that anionic polysaccharide might be the best polysaccharide to modify SPI for emulsion stabilization. This work provided useful information to modify insoluble proteins by polysaccharides for potential application.

Enhancing the solubility and emulsion properties of rice protein by deamidation of citric acid-based natural deep eutectic solvents

The characteristics of rice protein deamidated (DRP) by choline chloride-citric acid and glucose-citric acid natural deep eutectic solvents (C-C NADES, G-C NADES) at different dilutions were investigated. Compared with the effect of citric acid deamidation on the structural and functional properties of the protein, the DRP from the NADESs led to remarkable differences in the degree of hydrolysis (DH), SDS-PAGE, morphology, surface hydrophobicity, average particle size, intrinsic fluorescence, amino acid compositions, and emulsion activity. The results of SDS-PAGE, DH, and SEM showed the NADESs reduced the occurrence of uncontrolled hydrolysis of protein during acid deamidation. DRP from C-C and G-C NADESs was found to significantly improve solubility. DRP prepared by C-C NADES showed a more than 40 % solubility over a wide pH range associated with its higher emulsifying activity (37.62-44.19 m2/g) and emulsifying stability (73.76-86.9 min), as well as a better deamidation effect while lower DH. Thus, these findings showed that acid-based NADESs had great potential as a deamidation solvent to expand the application of protein.

Techno-functional attributes of oilseed proteins: influence of extraction and modification techniques

Plant-based protein isolates and concentrates are nowadays becoming popular due to their nutritional, functional as well as religious concerns. Among plant proteins, oilseeds, a vital source of valuable proteins, are continuously being explored for producing protein isolates/concentrates. This article delineates the overview of conventional as well as novel methods for the extraction of protein and their potential impact on its hydration, surface properties, and rheological characteristics. Moreover, proteins undergo several modifications using physical, chemical, and biological techniques to enhance their functionality by altering their microstructure and physical performance. The modified proteins hold a pronounced scope in novel food formulations. An overview of these protein modification approaches and their effects on the functional properties of proteins have also been presented in this review.

Protein-glutaminase improves water-/oil-holding capacity and beany off-flavor profiles of plant-based meat analogs

An unresolved challenge for plant-based meat analogs (PBMAs) is their lack of juiciness. Saturated fats significantly contribute to the juiciness of PBMAs, but there are concerns about the undesirable health effects related to saturated fats; thus, demand for their replacement with vegetable unsaturated oils has increased. Although many food additives are used to reduce the leakage of unsaturated oils, this solution cannot meet the clean-label requirements that have been trending in recent years. In this study, we aimed to develop better consumer-acceptable methods using protein-glutaminase (PG) to improve the juiciness of PBMA patties to meet clean-label trends. We found no significant difference between the visual surface of control and PG-treated textured vegetable proteins (TVPs). However, the microstructure of PG-treated TVP had a more rounded shape than that of the control TVP as observed under a scanning electron microscope. After grilling process, the PBMA patties composed of PG-treated TVP showed significantly higher liquid-holding capacities (a juiciness indicator) than the control patties. This suggested that PG treatment could potentially produce PBMA patties with increased juiciness. Interestingly, after the PG-treated TVP underwent the wash process, we found that PG treatment of TVP easily reduced the various beany off-flavor compounds by 58-85%. Moreover, the results of the in vitro protein digestion test showed that the amounts of free amino nitrogen released from PBMA patties composed of PG-treated TVP were 1.5- and 1.7-fold higher than those from control patties in the gastric and intestinal phases, respectively. These findings indicate that PG treatment of TVP could enhance the physical, sensory, and nutritional properties of PBMA patties and meet the clean-label requirements.

Protective effect of soy isolate protein against streptozotocin induced gestational diabetes mellitus via TLR4/MyD88/NF-κB signaling pathway

BACKGROUND

Gestational diabetes mellitus (GDM) is a serious complication of pregnancy that is characterized by high blood sugar levels that occur due to insulin resistance and dysfunction in glucose metabolism during pregnancy. It usually develops in the second or third trimester of pregnancy and affects about 7 % of all pregnancies worldwide. In this experimental study, we scrutinized the GDM protective effect of soy isolate protein against streptozotocin (STZ) induced GDM in rats and explore the underlying mechanism.

MATERIAL AND METHODS

Sprague-Dawley (SD) rats were used in this experimental study. A 55 mg/kg intraperitoneal injection of streptozotocin (STZ) was administered to induce diabetes in female rats, followed by oral administration of soy isolate protein for 18 days. Body weight, glucose levels, and insulin were measured at different time intervals (0, 9, and 18 days). Lipid profiles, antioxidant levels, inflammatory cytokines, apoptosis parameters, and mRNA expression were also assessed. Pancreatic and liver tissues were collected for histopathological examination during the experimental study.

RESULTS

Soy isolate protein significantly (P < 0.001) reduced the glucose level and enhanced the insulin level and body weight. Soy isolate protein remarkably decreased the placental weight and increased the fetal weight. Soy isolate protein significantly (P < 0.001) decreased the HbA1c, hepatic glycogen, serum C-peptide and increased the level of free fatty acid. Soy isolate protein significantly (P < 0.001) altered the level of lipid, antioxidant and inflammatory cytokines. Soy isolate protein significantly (P < 0.001) improved the level of adiponectin, visfatin and suppressed the level of leptin and ICAM-1. Soy isolate protein significantly (P < 0.001) altered the mRNA expression and also restored the alteration of histopathology.

CONCLUSION

Based on the result, soy isolate protein exhibited the GDM protective effect against the STZ induced GDM in rats via alteration of TLR4/MyD88/NF-κB signaling pathway.

A comparative study of the impacts of preparation techniques on the rheological and textural characteristics of emulsion gels (emulgels)

A subtype of soft solid-like substances are emulsion gels (emulgels; EGs). These composite material's structures either consist of a network of aggregated emulsion droplets or a polymeric gel matrix that contains emulsion droplets. The product's rheological signature can be used to determine how effective it is for a specific application. The interactions between these structured system's separate components and production process, however, have a substantial impact on their rheological imprint. Therefore, rational comprehension of interdependent elements, their structural configurations, and the resulting characteristics of a system are essential for accelerating our progress techniques as well as for fine-tuning the technological and functional characteristics of the finished product. This article presents a comprehensive overview of the mechanisms and procedures of producing EGs (i.e., cold-set and heat-set) in order to determine the ensuing rheological features for various commercial applications, such as food systems. It also describes the influence of these methods on the rheological and textural characteristics of the EGs. Diverse preparation methods are the cause of the rheological-property correlations between different EGs. In many ways, EGs can be produced using various matrix polymers, processing techniques, and purposes. This may lead to various EG matrix structures and interactions between them, which in turn may affect the composition of EGs and ultimately their textural and rheological characteristics.

Fabrication mechanism and functional properties of ovalbumin fibrils prepared by acidic heat treatment

BACKGROUND

Ovalbumin (OVA), accounting for 50% of proteins in egg white, is a kind of high-quality protein with excellent nutritional and processing functions. Acid heat treatment will induce the deformation and filtration of OVA, endowing it with improved functionality. However, the molecular kinetic process during the fibrillation of OVA and the application of the fabricated OVA fibrils (OVAFs) have not been thoroughly studied and revealed.

RESULTS

In this study, the fabrication mechanism and the application OVAFs as an interfacial stabilizer and polyphenol protector were investigated. Acidic (pH 3.0) heat treatment was used to induce the fibrillation of OVA, and thioflavin T fluorescence intensity, molecular weight distribution, and the tertiary and secondary structures of OVAF samples were recorded to determine the fibrillation efficiency and the molecular mechanism. The results showed that, in the initial stage of fibrillation, OVA first hydrolyzed to oligopeptides, accompanied by the exposure of hydrophobic domains. Then, oligopeptides were connected by disulfide bonds to form primary fibril monomers. Hydrophobic interaction and hydrogen bonding may participate in the further polymerization of the fibrils. The fabricated OVAFs were characterized by a β-sheet-rich structure and possessed improved emulsifying, foaming, and polyphenol protection ability.

CONCLUSION

The research work was meaningful for exploring the application of globular water-soluble OVA in an emerging nutritious food with novel texture and sensory properties. © 2023 Society of Chemical Industry.

Advances in preparation and application of food-grade emulsion gels

Emulsion gel is a semi-solid or solid material with a three-dimensional net structure produced from emulsion through physical, enzymatic, chemical methods or their combination. Emulsion gels are widely used in food, pharmaceutical and cosmetic industries as carriers of bioactive substances and fat substitutes due to their unique properties. The modification of raw materials, and the application of different processing methods and associated process parameters profoundly affect the ease or difficult of gel formation, microstructure, hardness of the resulting emulsion gels. This paper reviews the important research undertaken in the last decade focusing on classification of emulsion gels, their preparation methods, the influence of processing method and associated process parameters on structure-function of emulsion gels. It also highlights current status of emulsion gels in food, pharmaceutical and medical industries and provides future outlook on research directions requiring to provide theoretical support for innovative applications of emulsion gels, particularly in food industry.

Effect of Protein-Glutaminase on Calcium Sulphate-Induced Gels of SPI with Different Thermal Treatments

The effects of protein-glutaminase (PG) on calcium sulphate (CaSO₄)-induced gels of soy protein isolate (SPI) with different heat treatment levels were investigated. The time-dependent degree of deamidation showed that the mild denaturation of the protein favored the deamidation. The particle size distribution showed that the heat treatment increased the SPI particle size, and the particle size distribution of the SPI shifted to the right or increased the proportion of the large particle size component as the degree of deamidation increased for each sample. Rheological analysis showed that the deamidation substantially pushed up the gel temperature and decreased the value of G'. The gel strength and water-holding capacity showed that the higher the amount of enzyme added, the more significant the decrease in gel strength, while the gel water-holding capacity increased. In summary, the deamidation of PG and heat treatment can affect the gel properties of SPI synergistically.

Physicochemical, structural, functional and flavor adsorption properties of white shrimp (Penaeus vannamei) proteins as affected by processing methods

Proteins contribute to the flavor release and texture of foods besides their nutritional attributes. However, processing affects the protein structural conformation and, thus, their functional properties. White shrimp proteins (WSP) are well known for their nutritional and functional properties and limited attention has been paid to the flavor adsorption properties of WSP. This study investigated the effects of processing methods such as microwave drying, hot air drying, roasting, and boiling on the structural (secondary and tertiary) changes and physicochemical, functional, and flavor adsorption properties of white shrimp proteins (WSP). Structural changes of WSPs were evaluated by Fourier Transform Infrared (FTIR) spectroscopy, fluorescence spectroscopy, and sulfhydryl bond content. Results revealed that the processing triggered structural changes that affected the functional properties of WSP. The highest surface hydrophobicity (H₀) of WSP in boiling (58.27 ± 1.68) and microwave drying (39.83 ± 0.83) caused increased emulsifying properties and decreased water solubility. The increased content of α-helix and random coils leads to cross-linking and protein aggregation in hot air drying (21.62 ± 0.37 %) and roasting (24.30 ± 0.24 %), which leads to low H₀ and high foaming properties. Processing has increased the flavor adsorption ability of WSP. Among all the processing methods, boiling has shown the highest flavor adsorption potential, followed by microwave drying. The findings broaden the scope of techno-functional properties of WSP in the food industry by thermal treatment modification.

Effect of Ionic Strength on Heat-Induced Gelation Behavior of Soy Protein Isolates with Ultrasound Treatment

This study investigated the effect of ultrasound on gel properties of soy protein isolates (SPIs) at different salt concentrations. The results showed that ultrasound could significantly improve the gel hardness and the water holding capacity (WHC) of the salt-containing gel (p < 0.05). The gel presents a uniform and compact three-dimensional network structure. The combination of 200 mM NaCl with 20 min of ultrasound could significantly increase the gel hardness (four times) and the WHC (p < 0.05) compared with the SPI gel without treatment. With the increase in NaCl concentration, the ζ potential and surface hydrophobicity increased, and the solubility decreased. Ultrasound could improve the protein solubility, compensate for the loss of solubility caused by the addition of NaCl, and further increase the surface hydrophobicity. Ultrasound combined with NaCl allowed proteins to form aggregates of different sizes. In addition, the combined treatment increased the hydrophobic interactions and disulfide bond interactions in the gel. Overall, ultrasound could improve the thermal gel properties of SPI gels with salt addition.

Improved Light and In Vitro Digestive Stability of Lutein-Loaded Nanoparticles Based on Soy Protein Hydrolysates via Pepsin

In order to improve the water solubility and stability of lutein, soy protein isolates (SPI) and their hydrolysates via pepsin (PSPI) and alcalase (ASPI) were used as nanocarriers for lutein to fabricate the lutein-loaded nanoparticles (LNPS) of SPI, PSPI, and ASPI. The encapsulation properties, light, and in vitro digestive stability of lutein in nanoparticles, and protein-lutein interactions were investigated. Compared with SPI-LNPS and ASPI-LNPS, PSPI-LNPS was characterized by uniform morphology (approximately 115 nm) with a lower polydispersity index (approximately 0.11) and higher lutein loading capacity (17.96 μg/mg protein). In addition, PSPI-LNPS presented the higher lutein retention rate after light exposure (85.05%) and simulated digestion (77.73%) than the unencapsulated lutein and SPI-LNPS. Fluorescence spectroscopy revealed that PSPI had stronger hydrophobic interaction with lutein than SPI, which positively correlated with their beneficial effects on the light and digestive stability of lutein. This study demonstrated that PSPI possessed significant potential for lutein delivery.

Gel-type emulsified muscle products: Mechanisms, affecting factors, and applications

The gel-type emulsified muscle products improve fatty acid composition, maintain the oxidative stability, and achieve a better sensory acceptability. This review emphasizes the stabilization mechanisms of these emulsified muscle products. In particular, factors associated with the stability of the emulsified muscle systems are outlined, including the processing conditions (pH and heating), lipids, and emulsifiers. Besides, some novel systems are further introduced, including the Pickering emulsions and organogels, due to their great potential in stabilizing emulsified gels. Moreover, the promising prospects of emulsion muscle products such as improved gel properties, oxidative stability, freeze-thaw stability, fat replacement, and nutraceutical encapsulation were elaborated. This review comprehensively illustrates the considerations on developing gel-type emulsified products and provides inspiration for the rational design of emulsified muscle formulations with both oxidatively stable and organoleptically acceptable performance.

L-Glutamine-, peptidyl- and protein-glutaminases: structural features and applications in the food industry

L-Glutaminases are enzymes that catalyze the cleavage of the gamma-amido bond of L-glutamine residues, producing ammonia and L-glutamate. These enzymes have several applications in food and pharmaceutical industries. However, the L-glutaminases that hydrolyze free L-glutamine (L-glutamine glutaminases, EC 3.5.1.2) have different structures and properties with respect to the L-glutaminases that hydrolyze the same amino acid covalently bound in peptides (peptidyl glutaminases, EC 3.5.1.43) and proteins (protein-glutamine glutaminase, EC 3.5.1.44). In the food industry, L-glutamine glutaminases are applied to enhance the flavor of foods, whereas protein glutaminases are useful to improve the functional properties of proteins. This review will focus on structural backgrounds and differences between these enzymes, the methodology available to measure the activity as well as strengths and limitations. Production methods, applications, and challenges in the food industry will be also discussed. This review will provide useful information to search and identify the suitable L-glutaminase that best fits to the intended application.

The characteristics of protein-glutaminase from an isolated Chryseobacterium cucumeris strain and its deamidation application

Protein-glutaminase (PG), a deamidation enzyme commercially derived from Chryseobacterium proteolyticum, is used to improve the solubility and other functional properties of food proteins. In this study, a new PG-producing strain, Chryseobacterium cucumeris ZYF120413-7, was isolated from soil, and it had a high PG yield and a short culture time. It gave the maximum PG activity with 0.557 U/ml on Cbz-Gln-Gly after 12 h of culture, indicating that it was more suitable for PG production. The enzyme activity recovery and purification fold were 32.95% and 161.95-fold, respectively, with a specific activity of 27.37 U/mg. The PG was a pre-pro-protein with a 16 amino acids putative signal peptide, a pro-PG of 118 amino acids, and a mature PG of 185 amino acids. The amino acid sequence identity of PG from strain ZYF120413-7 was 74 and 45%, respectively, to that of PG from C. proteolyticum 9670T and BH-PG. The optimum reaction pH and temperature of PG was 6 and 60°C, respectively. Enzyme activity was inhibited by Cu2+. The optimum PG substrate was Cbz-Gln-Gly, and the Km and Vmax values were 1.68 mM and 1.41 μM mg protein−1 min−1, respectively. Degree of deamidation (DD) of soy protein isolate (SPI) treated by purified PG was 40.75% within the first 2 h and 52.35% after 18 h. These results demonstrated that the PG from C. cucumeris ZYF120413-7 was a promising protein-deamidating enzyme for improving the functionality of food proteins.

Recent advances in modified food proteins by high intensity ultrasound for enhancing functionality: Potential mechanisms, combination with other methods, equipment innovations and future directions

High intensity ultrasound (HIU) is an efficient and green technology that has recently received enormous research attention for modification of food proteins. However, there are still several knowledge gaps in the possible mechanisms, synergistic effects of HIU with other strategies and improvement of HIU equipment that contribute to its application in the food industry. This review focuses on the recent research progress on the effects and potential mechanisms of HIU on the structure (including secondary and tertiary structure) and functionality (including solubility, emulsibility, foamability, and gelability) of proteins. Furthermore, the combination methods and innovations of HIU equipment for proteins modification in recent years are also detailed. Meanwhile, the possible future trends of food proteins modification by HIU are also considered and proposed.

Plant Protein-Based Delivery Systems: An Emerging Approach for Increasing the Efficacy of Lipophilic Bioactive Compounds

The development of plant protein-based delivery systems to protect and control lipophilic bioactive compound delivery (such as vitamins, polyphenols, carotenoids, polyunsaturated fatty acids) has increased interest in food, nutraceutical, and pharmaceutical fields. The quite significant ascension of plant proteins from legumes, oil/edible seeds, nuts, tuber, and cereals is motivated by their eco-friendly, sustainable, and healthy profile compared with other sources. However, many challenges need to be overcome before their widespread use as raw material for carriers. Thus, modification approaches have been used to improve their techno-functionality and address their limitations, aiming to produce a new generation of plant-based carriers (hydrogels, emulsions, self-assembled structures, films). This paper addresses the advantages and challenges of using plant proteins and the effects of modification methods on their nutritional quality, bioactivity, and techno-functionalities. Furthermore, we review the recent progress in designing plant protein-based delivery systems, their main applications as carriers for lipophilic bioactive compounds, and the contribution of protein-bioactive compound interactions to the dynamics and structure of delivery systems. Expressive advances have been made in the plant protein area; however, new extraction/purification technologies and protein sources need to be found Their functional properties must also be deeply studied for the rational development of effective delivery platforms.