Acid-induced formation of soy protein gels in the presence of NaCl

Binary Pea Protein-Psyllium Hydrogel: Insights into the Influence of pH and Ionic Strength on the Physical Stability and Mechanical Characteristics

Food hydrogels, used as delivery systems for bioactive compounds, can be formulated with various food-grade biopolymers. Their industrial utility is largely determined by their physicochemical properties. However, comprehensive data on the properties of pea protein-psyllium binary hydrogels under different pH and ionic strength conditions are limited. The aim of this research was to evaluate the impact of pH (adjusted to 7, 4.5, and 3) and ionic strength (modified by NaCl addition to 0.15 and 0.3 M) on the physical stability, color, texture, microrheological, and viscoelastic properties of these hydrogels. Color differences were most noticeable at lower pH levels. Inducing hydrogels at pH 7 (with or without NaCl) and pH 4.5 and 3 (without NaCl) resulted in complete gel structures with low stability, low elastic and storage moduli, and low complex viscosity, making them easily spreadable. Lower pH inductions (4.5 and 3) in the absence of NaCl resulted in hydrogels with shorter linear viscoelastic regions. Hydrogels induced at pH 4.5 and 3 with NaCl had high structural stability, high G' and G" moduli, complex viscosity, and high spreadability. Among the tested induction conditions, pH 3 with 0.3 M NaCl allowed for obtaining a hydrogel with the highest elastic and storage moduli values. Adjusting pH and ionic strength during hydrogel induction allows for modifying and tailoring their properties for specific industrial applications.

Legume milk-based yogurt mimetics structured using glucono-δ-lactone

The potential to produce protein-structured vegan yogurts with legumes was explored to offer an alternative to conventional polysaccharide-based varieties. Glucono-δ-lactone (GDL) was employed as a slow acidifying agent and was investigated for its ability to generate cold-set, yogurt-like gels using soy and lentil milks made using minimal processing steps. Soy (5.3 % protein) and lentil (6.1 % protein) milks were successfully gelled by GDL at concentrations of 0.5 % and 1 % w/w. Soy and lentil milks experienced similar acidification profiles and demonstrated good fits with double-exponential decay models. The physical properties of these legume gels were evaluated and compared to a commercial stirred dairy yogurt. Penetration tests were carried out on intact gels, then repeated after stirring. All intact soy samples demonstrated significantly stronger gel structures compared to the commercial yogurt, and most experienced greater amounts of brittleness. Results showed that the stirring of gels caused a notable decrease in firmness and brittleness in the soy gels, making them more similar to the control. Power-law modelling of viscosity curves demonstrated that all samples experienced non-Newtonian flow behavior (n < 0.29). Susceptibility to syneresis was measured by the degree of liquid loss following centrifugation. The optimization of protein type and GDL concentration to replicate the physical properties of dairy-based yogurts can enhance their consumer acceptance and provide a more customizable and controlled approach alternative to traditional fermentation methods.

Fermentation Characteristics, Antinutritional Factor Level and Flavor Compounds of Soybean Whey Yogurt

Soybean whey contains high levels of off-flavors and anti-nutritional factors and is generally considered unsuitable for direct application in the food industry. In this work, to reduce beany off-flavors and anti-nutritional factors, and to improve its fermentation characteristics, soybean whey was treated with electrodialysis desalination, vacuum concentration and lactic acid bacteria (LAB) fermentation. The results showed that electrodialysis desalination increased the fermentation rate and the number of viable lactic acid bacteria of soybean whey yogurt. More than 90% of the antinutritional factor level (urease and trypsin inhibitory activity) was removed due to high-temperature denaturation inactivation and LAB degradation. Concentrated desalted soybean whey yogurt (CDSWY) possessed larger values for firmness and consistency, and a denser network microstructure compared with undesalted yogurt. Over 90% of off-flavors including hexanal, 1-octen-3-ol and 1-octen-3-one were removed after electrodialysis desalination and concentration treatment. Meanwhile, the newly generated β-damascenone through carotenoid degradation and 2,3-butanedione improved the pleasant flavor and sensory quality of CDSWY, while the salty taste of CSWY lowered its sensory quality. This study provided a theoretical basis for better utilization of soybean whey to develop a plant-based yogurt like dairy yogurt.

Recent advance in modification strategies and applications of soy protein gel properties

Soy protein gel can be developed into a variety of products, ranging from traditional food (e.g., tofu) to newly developed food (e.g., soy yogurt and meat analog). So far, efforts are still needed to be made on modifying the gel properties of soy protein for improving its sensory properties as animal protein-based food substitutes. Furthermore, there is always a need to regulate its gel properties for designing novel and tailored products of soy protein gels due to the fast-growing plant protein-based product market. This review gave an emphasis on the latest modification strategies and applications of gel properties of soy protein. The modifying methods of soy protein gel properties were reviewed from an aspect of composition or processing. Compositional modification included changing protein composition and gelling conditions and using additives, whereas processing strategies can be achieved through physical, chemical, and enzymatic treatments. Several compositional modification and processing strategies have been both proven to alter the gel properties of soy protein effectively. So far, soy protein gel has been applied in the field of food and biomedicine. In the future, more mechanistic studies on the modification methods are still needed to facilitate the full application of soy protein gel.

The role of the extension region on the structural and physicochemical characteristics of the α-subunit of β-conglycinin: implications of pH value and ionic strength

BACKGROUND

To clarify the role of the extension region on the structure-functional relationship of the α-subunit of β-conglycinin, α-subunit and its segment of the core region (αc-subunit) were expressed via an Escherichia coli system. Their physicochemical properties were compared under acid, neutral or alkaline conditions (pH 4.0, 7.0, and 8.0) and high or low ionic strength (μ = 0.05 and 0.5), respectively.

RESULTS

The results showed that the extension region contributed to increasing thermal stability, especially at low ionic strength under acidic and neutral conditions. The extension region stabilized the α-subunit with high solubility, low turbidity, and small particle size under neutral and alkaline conditions, whereas these impacts were suppressed at a high ionic strength and acidic conditions. Surface hydrophobicity of the α-subunit decreased under acidic and alkaline conditions without being interfered with by ionic strength.

CONCLUSION

It can be concluded that the extension region played different roles under different pH and ionic strength conditions. These factors should be specified carefully and speculated individually to explore the more detailed and profound nature of β-conglycinin at the submolecular level. The results could benefit a better understanding of the relationship between domain structure and functions of soybean protein. © 2022 Society of Chemical Industry.

Soy protein isolates: A review of their composition, aggregation, and gelation

Considering that a series of complex issues such as environmental problems, sustainable development, animal welfare, and human health are on a global scale, the development of vegetable protein-based meat substitutes provides a potential solution to the disparity between meat consumption demand and supply. The research and development of vegetable protein-based meat substitutes have become a major commercial activity, and the market is expanding to meet the growing consumer demand. Soy protein isolates (SPI) are often used as a raw material for vegetable meat substitutes because of their potential to form fiber structures. Although significant initial success has been achieved, it is still a challenge to explain how the composition and aggregation of SPI influence gel properties and the mechanism(s) involved. This article reviews the latest research about SPI. The relationship between the composition, aggregation, and gelation properties of SPI is based on a through literature search. It focused on the application of SPI in heat- and cold-induced gels, given the diversified market demands. The research on cold gel has helped expand the market. The methods to improve the properties of SPI gels, including physical, chemical, and biological properties, are reviewed to provide insights on its role in the properties of SPI gels. To achieve environmentally friendly and efficient ways for the food industry to use SPI gel properties, the research prospects and development trends of the gel properties of SPI are summarized. New developments and practical applications in the production technology, such as for ultrasound, microwave and high pressure, are reviewed. The potential and challenges for practical applications of cold plasma technology for SPI gel properties are also discussed. There is a need to transfer the laboratory technology to actual food production efficiently and safely.

A Relation between Exopolysaccharide from Lactic Acid Bacteria and Properties of Fermentation Induced Soybean Protein Gels

Exopolysaccharide (EPS) producing lactic acid bacteria (LAB) is considered to be an effective texture improver. The effect of LAB strains (different EPS production capacity) on physicochemical properties (texture profile, water distribution, rheological properties, and microstructure), protein conformation, and chemical forces of soybean protein gel was investigated. Correlations between EPS yield and gel properties were established. Large masses of EPS were isolated from L. casei fermentation gel (L. casei-G, 677.01 ± 19.82 mg/kg). Gel with the highest hardness (319.74 ± 9.98 g) and water holding capacity (WHC, 87.74 ± 2.00%) was also formed with L. casei. The conversion of β-sheet to α-helix, the increased hydrophobic interaction and ionic bond helped to form an ordered gel network. The yield was positively correlated with hardness, WHC, A₂₂, viscoelasticity, and viscosity, but negatively correlated with A₂₃ (p < 0.05). The macromolecular properties of EPS (especially the yield) and its incompatibility with proteins could be explained as the main reason for improving gel properties. In conclusion, the EPS producing LAB, especially L. casei used in our study, is the best ordinary coagulate replacement in soybean-based products.

Differences in the physicochemical, digestion and microstructural characteristics of soy protein gel acidified with lactic acid bacteria, glucono-δ-lactone and organic acid

This study evaluated the differences in the physicochemical, digestion and microstructure of soy protein gels acidified with Lactobacillus casei (L. casei), glucono-δ-lactone (GDL) and citric acid. The maximum acidification rate was as follows: citric acid > GDL > L. casei. The gelation points of L. casei-induced gel (LC gel) and GDL-induced gel (GDL gel) occurred at 74 min and 55 min; however, gelation point of citric acid-induced gel (CA gel) was not detected because acidification was too fast. LC gel showed the high gel hardness (20.40 ± 2.23 g) and water holding capacity (84.58 ± 0.59%). At the end of intestinal digestion, the average particle size of the LC gel was the largest, but there was no significant difference between GDL gel and CA gel. The microstructure of the GDL gel was found to be the densest. Acidification rate was the "key step" of acid-induced gels, while both the proteolytic and exopolysaccharide (EPS) production capacity were involved in LC gel.

Effect of citric acid on physicochemical properties and protein structure of low-salt restructured tilapia (Oreochromis mossambicus) meat products

BACKGROUND

The growing consumer demand for healthy products has encouraged the development of low-salt meat products. In this study, to develop low-salt restructured tilapia (Oreochromis mossambicus) meat products, citric acid was used to improve the properties of restructured tilapia products.

RESULTS

In comparison with control restructured fish products (RP) and surimi products (SP), 0.2% citric acid-treated restructured fish products (RPC) and surimi products (SPC) showed a significant decrease in expressible water and water activity and a remarkable increase in whiteness, dry matter, hardness, chewiness, gumminess, and acceptability. Mechanistic studies suggested that citric acid significantly changed the content of total protein and myofibrillar proteins and promoted degradation of heavy myosin chains. Fourier-transform infrared and Raman spectra revealed the citric acid-mediated alteration in the peak intensities of amide I and amide II bands, which changed the secondary structures of RPC and SPC.

CONCLUSION

It is feasible to prepare low-salt restructured tilapia meat products using citric acid, which offers a means of using muscle by-products and exploiting new functional products with an added commercial value. © 2020 Society of Chemical Industry.

Improving the technology of chilled semi-finished products from Japanese mackerel with an extended shelf life

Abstract One of the actual areas of processing the aquatic biological resources is the production of chilled fish semi-finished products, the most prepared for heat treatment. Such products have a very limited shelf life, because fish raw materials have high enzymatic activity. This research work aimed to improve the technology of chilled fish semi-finished products from Japanese mackerel with an extended shelf life. To achieve this goal, Japanese mackerel was injected with multicomponent salting media, containing food additives that slow down microbial contamination, have a bacteriostatic effect and assist in improving the organoleptic characteristics of the finished product. New receptions of salting multicomponent compositions provide faster salting and ripening of raw materials compared to the control sample. Salt concentration in fish, amine nitrogen and peroxide value were determined by titration methods. The total number of mesophilic aerobic and facultative anaerobic microorganisms (КMAFAnM) in fish semi-finished products was determined by identifying the number of grown colonies of microorganisms on nutrient media from agar. The treatment of Japanese mackerel with developed salting media, including moisture-retaining components, organic acids and flavoring additives with anti-bactericidal properties, improves the organoleptic characteristics of the finished product, promotes more salting and maturation of fish, as well as reducing the number of microorganisms (KMAFAnM). The increase in amine nitrogen content ranged from 1.4 g/kg (at the beginning of the salting) to 1.55 g/kg in the control and up to 3.05 g/kg in the test samples by the end of the salting. Salt concentration in Japanese mackerel treated with control salting media amounted to 1.19%, new developed salting media - from 2.84% to 3.17%. The total abundance of microorganisms in Japanese mackerel was 2.0 x 102 CFU/g, after salting it decreased to 0.1 to 3.0 x 101 CFU/g depending on the formulation of media for salting. According to the research results, the rational duration of the salting of Japanese mackerel, with new media for salting was 4 to 5 h at a temperature of 6 °С to 8 °С. Along with the salting media developed by us, the use of modern packaging materials in the technology provided chilled culinary semi – finished products from Japanese mackerel with longer shelf life of up to 20 days at a temperature of 0 °С to 5 °C, and humidity 95% to 98%.

Addition of Salt Ions before Spraying Improves Heat- and Cold-Induced Gel Properties of Soy Protein Isolate (SPI)

Spray drying is used in the food industry to convert liquids into dry powders. The effect of the addition of salt ions before spray drying to improve the heat- and cold-induced gel properties of soy protein isolate (SPI) was investigated. Certain concentrations of Na+ (0.005–0.01 M), Mg2+ (0.005 M), and Ca2+ (0.005 M) significantly increased the hardness, springiness, cohesiveness, chewiness, gumminess, resilience, and water holding capacity of the heat- and cold-induced gels. This effect arises predominantly due to the functional groups buried in the protein matrix that are partially exposed to improve the interactions between the protein molecules. The main interactions that promoted gel formation and maintained the three-dimensional structure of the heat- and cold-induced gels were hydrophobic and disulfide interactions. Analysis using scanning electron microscopy showed that the heat- and cold-induced gels were uniform, had smooth surfaces, and had smaller pores with added Na+ (0.01 M), Mg2+ (0.005 M), and Ca2+ (0.005 M). The results indicate that we might broaden the applications of SPI by simulating the industrial gel manufacturing process for products such as fish balls and chiba tofu. Overall, adding salt ions before spray drying could offer great potential for the development of SPI with enhanced functionality suitable for comminuted meat products.