Gelation of soybean proteins induced by sequential high-pressure and thermal treatments

Plant protein solubility: A challenge or insurmountable obstacle

Currently, there is an increasing focus on comprehending the solubility of plant-based proteins, driven by the rising demand for animal-free food formulations. The solubility of proteins plays a crucial role in impacting other functional properties of proteins and food processing. Consequently, understanding protein solubility in a deeper sense may allow a better usage of plant proteins. Herein, we discussed the definition of protein solubility from both thermodynamic and colloidal perspectives. A range of factors affecting solubility of plant proteins are generalized, including intrinsic factors (amino acids composition, hydrophobicity), and extrinsic factors (pH, ionic strength, extraction and drying methods). Current methods to enhance solubility are outlined, including microwave, high intensity ultrasound, hydrostatic pressure, glycation, pH-shifting, enzymatic hydrolysis, enzymatic cross-linking, complexation and modulation of amino acids. We base the discussion on diverse modified methods of nitrogen solubility index available to determine and analyze protein solubility followed by addressing how other indigenous components affect the solubility of plant proteins. Some nonproteinaceous constituents in proteins such as carbohydrates and polyphenols may exert positive or negative impact on protein solubility. Appropriate protein extraction and modification methods that meet consumer and manufacturers requirements concerning nutritious and eco-friendly foods with lower cost should be investigated and further explored.

Multi-dimensional analysis of heat-induced soybean protein hydrolysate gels subjected to ultrasound-assisted pH pretreatment

This study aimed to evaluate the gelation characteristics of soybean protein hydrolysate (SPH) extracted by enzyme-assisted aqueous extraction. Specifically, the changes in gelation behaviors for heat-induced (95 °C, 20 min) SPH dispersions treated with pH (pH 3, 5, 9; pH 7 as control) and ultrasound (U; 240 W, 30 min) were investigated. The results showed that typical gel behavior with high elastic nature in the viscoelasticity and network structures were observed during the heating process, where the disulfide bond played a dominant role in the gel network formation of all the samples. Notably, the heat-induced aggregation in the SPH gels was mainly formed by the association of the basic B polypeptide in 11S and β subunit in 7S. The most superior SPH gel was formed at pH 7 when assisted by ultrasonication during the heating process. This as-synthesized gel showed a uniform filamentous structure and exhibited the more excellent textural, rheological and thermal properties than those of the samples formed under acidic and alkaline conditions. These results are of great value in revealing the gelation mechanism of SPH.

Impacts of sonication and high hydrostatic pressure on the structural and physicochemical properties of quinoa protein isolate dispersions at acidic, neutral and alkaline pHs

Herein, 1 wt% quinoa protein isolate (QPI) was exposed to sonication using a 20 kHz ultrasonicator equipped with a 6 mm horn (14.4 W, 10 mL, up to 15 min) or high hydrostatic pressure (HHP, up to 600 MPa, 15 min) treatments at pH 5, pH 7, and pH 9. The changes to physicochemical properties were probed by SDS-PAGE, FTIR, free sulfhydryl group (SH), surface hydrophobicity (H0), particle size and solubility. As revealed by SDS-PAGE, substantial amounts of 11S globulin participated in the formations of aggregates via SS bond under HHP, particularly at pH 7 and pH 9. However, protein profiles of QPI were not significantly affected by the sonication. Free SH groups and surface hydrophobicity were increased after the sonication treatment indicating protein unfolding and exposure of the embedded SH and/or hydrophobic groups. An opposite trend was observed in HHP treated samples, implying aggregation and reassociation of structures under HHP. HHP and sonication treatments induced a decrease in ordered secondary structures (random coil and β-turn) accompanied with an increase in disordered secondary structures (α-helix and β-sheet) as probed by FTIR. Finally, the sonication treatment induced a significant improvement in the solubility (up to ∼3 folds at pH 7 and ∼2.6 folds at pH 9) and a reduction in particle sizes (up to ∼3 folds at pH 7 and ∼4.4 folds at pH 9). However, HHP treatment (600 MPa) only slightly increased the solubility (∼1.6 folds at pH 7 and ∼1.2 folds at pH 9) and decreased the particle size (∼1.3 folds at pH 7 and ∼1.2 folds at pH 9). This study provides a direct comparison of the impacts of sonication and HHP treatment on QPI, which will enable to choose the appropriate processing methods to achieve tailored properties of QPI.

Pea protein composition, functionality, modification, and food applications: A review

The demand for proteins continues to increase due to their nutritional benefits, the growing world population, and rising protein deficiency. Plant-based proteins represent a sustainable source to supplement costly animal proteins. Pea (Pisum sativum L.) is one of the most produced plant legume crops in the world and contributes to 26% of the total pulse production. The average protein content of pea is about 20%-25%. The commercial utilization of pea proteins is limited, partially due to its less desirable functionalities and beany off-flavor. Protein modification may change these properties and broaden the application of pea proteins in the food industry. Functional properties such as protein solubility, water and oil holding capacity, emulsifying/foaming capacity and stability, and gelation can be altered and improved by enzymatic, chemical, and physical modifications. These modifications work by affecting protein chemical structures, hydrophobicity/hydrophilicity balance, and interactions with other food constituents. Modifiers, reaction conditions, and degree of modifications are critical variables for protein modifications and can be controlled to achieve desirable functional attributes that may meet applications in meat analogs, baking products, dressings, beverages, dairy mimics, encapsulation, and emulsions. Understanding pea protein characteristics will allow us to design better functional ingredients for food applications.

Effect of basil seed gum and κ-carrageenan on the rheological, textural, and structural properties of whipped cream

BACKGROUND

Basil seed gum (BSG) is a novel polysaccharide that has been found wide application in the food industry. It can be used in whipped cream due to its thickening and emulsifying properties. The effect of BSG and κ-carrageenan on the structure-rheology relationships of whipped cream was evaluated.

RESULTS

The viscosity of cream containing BSG was higher than that of carrageenan. Basil seed gum resulted in a strong capacity to improve the viscosity of the cream. Rheological results showed the low-frequency dependence of the elastic modulus was improved by BSG, which had a strong effect on the rigidity of the emulsion. The fracture strain of the creams containing BSG or κ-carrageenan was between the normal cream and acidified caseinate stabilized emulsion foam. It was found that the protein segments of BSG could be adsorbed at the oil-water interface, resulting in the formation of a pseudo-gel network, which creates a stronger molecular protein network in the whipped cream. Microstructure study revealed that whipped cream containing κ-carrageenan exhibited some flocculation, which could be caused by non-adsorbed polysaccharides or proteins. In contrast, cream containing BSGshowed more voids, which have considerably decreased by fat content and enhance the foam structure.

CONCLUSION

As a result, synergistic interactions between proteins and polysaccharides (BSG and κ-carrageenan) could promote the development of a cross-linked network. Indeed, due to its high levels of hydrophilicity, BSG absorbs water, acts as a thickening agent, and competes against caseinate at the interfaces and is incorporated into whipped cream to provide a more desirable physical structure for the product. © 2021 Society of Chemical Industry.

Comparison of Thermal and High-Pressure Gelation of Potato Protein Isolates

Potato protein isolate (PPI), a commercial by-product of the starch industry, is a promising novel protein for food applications with limited information regarding its techno-functionality. This research focused on the formation of both thermal and high-pressure gels at acidic and neutral pH levels. Our results reveal that physical gels are formed after 30 min by heat at pH 7 and pH 3, while pressure (300-500 MPa) allows the formation of physical gels only at pH 3, and only when the system crosses 30 °C by adiabatic heating during pressurization. Texture profile analysis (TPA) revealed that gel hardness increased with both gelation temperature and pressure, while water-holding capacity was lower for the pressure-induced gels. The proteins released in the water-holding test suggested only partial involvement of patatin in the gel formation. Vitamin C as a model for a thermally liable compound verified the expected better conservation of such compounds in a pressure-induced gel compared to a thermal one of similar textural properties, presenting a possible advantage for pressure-induced gelation.

Structural and functional modification of food proteins by high power ultrasound and its application in meat processing

In the field of agricultural and food processing, high power ultrasound (HPUS) is recognized as a green, physical and non-thermal technology in improving the safety and quality of foods. The functional properties of food proteins are responsible for texture, yield and organoleptic of food products which are the theoretical basis for food processing optimizing. HPUS treatment could provide the possibility for creating novel functional properties of new foods with desirable properties due to the modification of protein structure. In this article, an overview of the previous studies and recent progress of the relationship between structure modification and functional properties of food proteins using the HPUS technique were presented. The research results revealed that HPUS could significantly affect the conformation and structure of protein due to the cavitation effect resulting in the improvement of solubility, interfacial, viscosity, gelation and flavor binding properties of proteins. During meat processing, HPUS can modify the structure and thereby improve the functional properties of myofibrillar protein (MP), leading to the quality enhancement, low fat and/or salt products development and the shelf life extending. In view of this review, the recent findings of applications of HPUS in the production of meat products based on the modification of MP including curing, freezing/thawing and thermal processing have been summarized. Finally, the future considerations were presented in order to facilitate the progress of HPUS in meat industry and provided the suggestions based on the advanced protein modification by HPUS for the commercial utilization of HPUS in producing the innovative meat products.

Microstructure and chemorheological behavior of whipped cream as affected by rice bran protein addition

The effect of rice bran protein (RBP) isolate addition on the rheological and structural properties of commercial whipped cream with 25% and 35% fat was investigated. Results showed that increasing the fat content from 25% to 35% leads to an increase in the elastic modulus. Furthermore, by increasing the amount of RBP from 1% to 3% in both creams, significant increase occurred in the complex modulus. As the fat content increased from 25% to 35%, the slope of flow behavior was increased, which revealed more thinning behavior and pseudoplasticity index of cream. The cream containing 35% fat and 3% RBP had also shown the low index (n = 0.298) which confirmed the firmer structure of the cream. The maximum consistency index (k) obtained was 9.41 for the cream with 35% fat and 3% RBP, which approved its strong foam structure. In general, according to our results it is obvious that whipped cream with the highest amount of fat and the lowest value of protein can lead to maximum stability of the whipping cream. Among the samples, the lowest stiffness was observed in cream of 35% fat, containing 3% rice bran protein. However, cream containing 35% fat and 1% RBP had convenient overrun and good stability. The microstructural results showed that the cream structure has relatively large globular aggregates in network and develops large pores, which permit to retain sufficient water/air. By increasing the fat content of cream from 25% to 35%, the voids and spaces in the cream were significantly decreased and the pores become less which improve the foam structure. Therefore, it can be concluded the cream with more fat has the more overrun and stability. In general, it is possible to improve the foam structure of cream by substituting fat by RBP.

Process optimization of ultrasound-assisted treatment for soya bean protein isolate/polyacrylamide composite film

In this paper, composite films composed of soya bean protein isolate (SPI) and polyacrylamide (PAM) were prepared under variations of ultrasonic power, treatment time and heating temperature. The effects of the major processing parameters related to ultrasonic-assisted treatment were evaluated and optimized through the single-factor analysis and Box-Behnken design (BBD), respectively, when the tensile strength of composite films was considered as the response value. The single-factor analysis was carried out to study the effects of ultrasonic power, treatment time and heating temperature on the viscosity and cohesion of the slurry and the tensile strength of SPI/PAM composite films, which also provided a reasonable data range of each factor for further optimization. Experiment results indicated that these three factors play a significant role in the tensile strength of films. Then BBD was applied to optimize the treatment conditions of these three factors, using the tensile strength of films as the response value. According to the interactive second-order polynomial model of three factors and the three-dimensional response surface, the maximum tensile strength of films was obtained under the optimal condition. To verify the reliability of the model, the experiment with the optimal condition was conducted, and results demonstrated that the observed tensile strength was in agreement with the predicated one. Also, the morphology and water solubility of the films showed that the film can be coated on the yarns evenly and removed clearly.

The genetic architecture of water-soluble protein content and its genetic relationship to total protein content in soybean

Water-soluble protein content (WSPC) is a critical factor in both soybean protein quality and functionality. However, the underlying genetic determinants are unclear. Here, we used 219 soybean accessions and 152 recombinant inbred lines genotyped with high-density markers and phenotyped in multi-environments to dissect the genetic architectures of WSPC and protein content (PC) using single- and multi-locus genome-wide association studies. In the result, a total of 32 significant loci, including 10 novel loci, significantly associated with WSPC and PC across multi-environments were identified, which were subsequently validated by linkage mapping. Among these loci, only four exhibited pleiotropic effects for PC and WSPC, explaining the low correlation coefficient between the two traits. The largest-effect WSPC-specific loci, GqWSPC8, was stably identified across all six environments and tagged to a linkage disequilibrium block comprising two promising candidate genes AAP8 and 2 S albumin, which might contribute to the high level of WSPC in some soybean varieties. In addition, two genes, Glyma.13G123500 and Glyma.13G194400 with relatively high expression levels at seed development stage compared with other tissues were regarded as promising candidates associated with the PC and WSPC, respectively. Our results provide new insights into the genetic basis of WSPC affecting soybean protein quality and yield.

Physical, Chemical and Biochemical Modifications of Protein-Based Films and Coatings: An Extensive Review

Protein-based films and coatings are an interesting alternative to traditional petroleum-based materials. However, their mechanical and barrier properties need to be enhanced in order to match those of the latter. Physical, chemical, and biochemical methods can be used for this purpose. The aim of this article is to provide an overview of the effects of various treatments on whey, soy, and wheat gluten protein-based films and coatings. These three protein sources have been chosen since they are among the most abundantly used and are well described in the literature. Similar behavior might be expected for other protein sources. Most of the modifications are still not fully understood at a fundamental level, but all the methods discussed change the properties of the proteins and resulting products. Mastering these modifications is an important step towards the industrial implementation of protein-based films.

High pressure effects on the structural functionality of condensed globular-protein matrices

High pressure technology is the outcome of consumer demand for better quality control of processed foods. There is great potential to apply HPP to condensed systems of globular proteins for the generation of industry-relevant biomaterials with advanced techno- and biofunctionality. To this end, research demonstrates that application of high hydrostatic pressure generates a coherent structure and preserves the native conformation in condensed globular proteins, which is an entirely unexpected but interesting outcome on both scientific and technological grounds. In microbiological challenge tests, high pressure at conventional commercial conditions, demonstrated to effectively reduce the concentration of typical Gram negative or Gram positive foodborne pathogens, and proteolytic enzymes in high-solid protein samples. This may have industrial significance in relation to the formulation and stabilisation of "functional food" products as well as in protein ingredients and concentrates by replacing spray dried powders with condensed HPP-treated pastes that maintain structure and bioactivity. Fundamental concepts and structural functionality of condensed matrices of globular proteins are the primary interest in this mini-review, which may lead to opportunities for industrial exploitation, but earlier work on low-solid systems is also summarised presently to put recent developments in context of this rapidly growing field.

Functional properties and structure changes of soybean protein isolate after subcritical water treatment

Subcritical water is an emerging method in food industry. In this study, soybean protein isolate (SPI) was treated by subcritical water (SBW) at various temperatures (0, 120, 160, 200 °C) for 20 min. The changes in the appearances, physicochemical properties and structural changes were investigated. After SBW treatment, the color of SPI solution modified turned to be yellow. The mean particle size and turbidity of SPI had similar behaviors. The mean particle size was decreased from 263.7 nm to 116.8 nm at 120 °C and then reached the maximum at 160 °C (1446.1 nm) due to the aggregation of protein. Then it was decreased to 722.9 nm at 200 °C caused by the protein degradation. SBW treatment could significantly enhance the solubility, emulsifying and foaming properties of SPI. With increasing temperature, the crystalline structure of protein was gradually collapsed. The degradation of the protein advanced structure occurred, especially at 200 °C revealed by ultra-high resolution mass spectrometry. Better functional properties exhibited in hydrolysis products indicating that SBW treatment could be used as a good method to modify the properties of soy proteins isolate for specific purposes under appropriate treatment condition.

Rapid heating of Alaska pollock and chicken breast myofibrillar protein gels as affecting water-holding properties

The gelation response of salted muscle minces to rapid versus slow heating rates is thought to differ between homeotherm and poikilotherm species. This study investigated water-holding (WH) properties of pastes prepared from refined myofibrils, at equal pH, of chicken breast versus Alaska pollock both during [cook loss (CL)] and following [expressible water (EW)] their cooking by rapid [microwave (MW)] versus slow [water bath (WB)] heating and whether such properties were related to gel matrix structure parameters and water mobility. Results did not confirm the industrial experience that pastes of meat from homeotherms benefit from slower cooking. Gels of equally high WH ability (low CL or EW) were made by rapid heating when the holding time did not exceed 5 min prior to cooling, which was sufficient for completion of gelation. Reduced CL and EW correlated with larger and smaller amplitudes of T21 and T22 water pools, respectively, measured by time-domain nuclear magnetic resonance (TD-NMR).

Structural rearrangement of ethanol-denatured soy proteins by high hydrostatic pressure treatment

The effects of high hydrostatic pressure (HHP) treatment (100-500 MPa) on solubility and structural properties of ethanol (EtOH)-denatured soy β-conglycinin and glycinin were investigated using differential scanning calorimetry, Fourier transform infrared and ultraviolet spectroscopy. HHP treatment above 200 MPa, especially at neutral and alkaline pH as well as low ionic strength, significantly improved the solubility of denatured soy proteins. Structural rearrangements of denatured β-conglycinin subjected to high pressure were confirmed, as evidenced by the increase in enthalpy value (ΔH) and the formation of the ordered supramolecular structure with stronger intramolecular hydrogen bond. HHP treatment (200-400 MPa) caused an increase in surface hydrophobicity (F(max)) of β-conglycinin, partially attributable to the exposure of the Tyr and Phe residues, whereas higher pressure (500 MPa) induced the decrease in F(max) due to hydrophobic rearrangements. The Trp residues in β-conglycinin gradually transferred into a hydrophobic environment, which might further support the finding of structural rearrangements. In contrast, increasing pressure induced the progressive unfolding of denatured glycinin, accompanied by the movement of the Tyr and Phe residues to the molecular surface of protein. These results suggested that EtOH-denatured β-conglycinin and glycinin were involved in different pathways of structural changes during HHP treatment.