Synthesis and characterization of ion-induced sodium alginate/soy protein isolate microgels for the controlled release

In this study, sodium alginate/ soy protein isolate (SPI) microgels cross-linked by various divalent cations including Cu2+, Ba2+, Ca2+, and Zn2+ were fabricated. Cryo-scanning electron microscopy observations revealed distinctive structural variations among the microgels. In the context of gastric pH conditions, the degree of shrinkage of the microgels followed the sequence of Ca2+ > Ba2+ > Cu2+ > Zn2+. Meanwhile, under intestinal pH conditions, the degree of swelling was ranked as Zn2+ > Ca2+ > Ba2+ > Cu2+. The impact of these variations was investigated through in vitro digestion studies, revealing that all microgels successfully delayed the release of β-carotene within the stomach. Within the simulated intestinal fluid, the microgel cross-linked with Zn2+ exhibited an initial burst release, while those cross-linked with Cu2+, Ba2+, or Ca2+ displayed a sustained release pattern. This research underscores the potential of sodium alginate/SPI microgels cross-linked with different divalent cations as efficient controlled-release delivery systems.

Salt reduction in myofibrillar protein gel via inhomogeneous distribution of sodium-containing encapsulated fish oil coacervate: Mucopenetration ability of sodium carboxymethyl cellulose

The potential application of fish oil microcapsules as salt reduction strategies in low-salt myofibrillar protein (MP) gel was investigated by employing soy protein isolates/carboxymethyl cellulose sodium (SPI-CMC) coacervates enriched with 25 mM sodium chloride and exploring their rheological characteristics, taste perception, and microstructure. The results revealed that the SPI-CMC coacervate phase exhibited the highest sodium content under 25 mM sodium level, albeit with uneven distribution. Notably, the hydrophilic and adhesive properties of CMC to sodium facilitated the in vitro release of sodium during oral digestion, as evidenced by the excellent wettability and mucopenetration ability of CMC. Remarkably, the fish oil microcapsules incorporating SPI-CMC as the wall material, prepared at pH 3.5 with a core-to-wall ratio of 1:1, demonstrated the highest encapsulation efficiency, which was supported by the strong hydrogen bonding. Interestingly, the presence of SPI-CMC coacervates and fish oil microcapsules enhanced the interaction between MPs and strengthened the low-salt MP gel network. Coupled with electronic tongue analysis, the incorporation of fish oil microcapsules slightly exacerbated the non-uniformity of sodium distribution. This ultimately contributed to an enhanced perception of saltiness, richness, and aftertaste in low-salt protein gels. Overall, the incorporation of fish oil microcapsules emerged as an effective salt reduction strategy in low-salt MP gel.

Ultrasound-assisted preparation of protein-polyphenol conjugates and their structural and functional characteristics

Herein, ultrasound-assisted conventional covalent binding methods (alkali treatment, free radical mediation, and an enzymatic method) were used to prepare soybean protein isolate (SPI)-(-)-epigallocatechin gallate (EGCG) conjugates to investigate the enhancement effect of the ultrasound synergistic treatment. In addition, the influence of EGCG grafting on the structure and properties of SPI was evaluated via reactive group analysis, spectral analysis, surface hydrophobicity measurements, emulsification property assessment, and α-glucosidase inhibition analysis. The obtained results revealed that the enzymatic method produced the highest polyphenol grafting content among the conventional techniques. Meanwhile, ultrasound treatment increased the amount of grafted polyphenol species during the alkali treatment and free radical mediation procedure, decreased the grafting efficiency in the enzymatic method, and maximized the grafting efficiency during the alkali treatment. In addition, reactive group and spectral analyses demonstrated that EGCG formed C-N and C-S bonds with SPI and decreased the α-helix content in the protein structure, thereby increasing the molecular flexibility of SPI. It also produced hydrogen bonds and hydrophobic interactions, as demonstrated by the results of molecular docking. Furthermore, the EGCG grafting of SPI conducted under the ultrasound-assisted conditions endowed SPI with unique functional characteristics, including good emulsification and antioxidant properties and high α-glucosidase inhibitory activity, while the ultrasound-assisted alkali treatment resulted in the optimal functional properties. The results of this study provide new insights into the effective preparation of SPI-EGCG complexes with multiple functionalities, thereby expanding the scope of high-value SPI utilization.

Fabrication of a novel antioxidant emulsifier through tuning the molecular interaction between soy protein isolates and young apple polyphenols

Soy protein isolates (SPI) exhibit weaker emulsifying properties than those of animal proteins, thereby limiting their wide applicability. In this study, a novel plant-based antioxidant emulsifier was developed using SPI and young apple polyphenols (YAP), and its underlying interaction mechanisms were discovered using multispectral technology and molecular docking. YAP physically bound to SPI through hydrogen bonds and hydrophobic interactions, which significantly enhanced the free radicals scavenging, reducing, and metal ion chelating abilities of SPI by introducing free hydroxyl groups. Moreover, SPI modified by YAP exerted better emulsifying performance owing to a looser protein structure, reflected by a higher random coil and a lower α-helix content. In addition, YAP may bridge adjacent SPI molecules, promoting the adsorption and anchoring of SPI at the oil-water interface. SPI-YAP complexes are promising antioxidant emulsifiers that can be used to nano-deliver functional oils and nutrients, thereby broadening SPI and YAP applications in the food industry.

Producing mixed-soy protein adsorption layers on alginate microgels to controlled-release β-carotene

In this study, the effects of soy protein isolate (SPI) on the morphology, encapsulation efficiency, storage stability, swelling behavior, and in vitro digestion behavior of calcium alginate (CA) microgels were investigated. CA and calcium alginate-SPI (CAS) microgels with encapsulated β-carotene were prepared by extruding a mixture of alginate and SPI using a co-extrusion technique, followed by cross-linking with Ca²⁺. All microgels exhibited homogeneous sizes and spherical shapes, and CAS microgels showed high levels of protein loading efficiency. The encapsulation efficiency and storage stability of β-carotene within CAS microgels were higher than those within CA microgels. The introduction of SPI into CAS microgels resulted in a higher degree of gel size shrinkage in gastric fluid and a lower degree of swelling in intestinal fluid compared to CA microgels. In vitro digestion was conducted to investigate the effects of the addition of SPI on the release behavior of CA and CAS microgels. Results obtained showed that CAS microgels were more resistant to simulated gastric fluid than CA microgels. Cryo-scanning electron microscopy (cryo-SEM) and confocal laser scanning microscopy (CLSM) observations indicated that the release behavior was dependent on the porosity of the CA and CAS microgels, and the porosity was influenced by the concentration of SPI. This study showed that the introduction of SPI to CA microgels can lead to the development of an effective controlled release delivery system.

Physicochemical properties of soy protein isolates-cyanidin-3-galactoside conjugates produced using free radicals induced by ultrasound

Free radicles produced by ultrasound were used to produce soy protein isolate (SPI)-cyanidin-3-galactoside conjugates. The conjugation between SPI and cyanidin-3-galactoside was confirmed by the increased ratio of bound polyphenol and the disappearance of cyanidin-3-galactoside's absorption peak in ultraviolet-visible spectrum. Conjugation with cyanidin-3-galactoside resulted in breakdown of SPI aggregate, which also led to a decrease in particle size and an increase in fluorescence intensity. Conjugation disrupted the hydrogen bonds of SPI as indicated by the lowest band intensity at 1646, 1533 and 3300-3450 cm^-1 on FTIR spectra. Conjugation also increased the electrostatic repulsion and decreased the hydrophobic interactions between SPI molecules. The SPI-cyanidin-3-galactoside conjugate had higher solubility and less aggregated structure in aqueous medium. The aqueous dispersions and solid powders of these conjugates had better thermal stability than that of SPI.

Comparative nutritional value of Jatropha curcas protein isolate and soy protein isolate in common carp

Jatropha seed cake (JSC) is an excellent source of protein but does contain some antinutritional factors (ANF) that can act as toxins and thus negatively affect the growth and health status of fish. While this can limit the use of JSC, detoxified Jatropha protein isolate (DJPI) may be a better option. An 8-week study was performed to evaluate dietary DJPI to common carp Cyprinus carpio. Five iso-nitrogenous diets (crude protein of 38%) were formulated that consisted of a C ontrol (fish meal (FM) based protein), J 50 or J 75 (50 and 75% of FM protein replaced by DJPI), and S 50 or S 75 (50 and 75% of FM protein replaced by soy protein isolate, SPI) and fed to triplicate groups of 75 carp fingerlings (75; av. wt. ± SD; 11.4 ± 0.25 g). The growth, feeding efficiencies, digestibility, plasma biochemistry, and intestinal enzymes were measured. Results showed that growth performance of fish fed the S 75- or DJPI-based diets were not significantly different from those fed the C ontrol diet, while carp fed the S 50 had significantly better growth than the J 75 diet. Fish fed the J 75 diet had significantly lower protein and lipid digestibility as well as significantly lower intestinal amylase and protease activities than all other groups. However, all plant protein-based diets led to significantly higher crude protein, crude lipid, and gross energy in the body of common carp compared to the control treatment. Plasma cholesterol and creatinine significantly decreased in the plant protein fed groups, although plasma triglyceride as well as the red blood cells count, hematocrit, albumin, globulin, total plasma protein, and lysozyme activity were higher in plant protein fed groups compared to FM fed group. White blood cells, hemoglobulin concentration, alkaline phosphatase and alanine transaminase activities, and glucose level in blood did not differ significantly among treatments. The results suggest that the DJPI is non-toxic to carp and can be used to replace FM in the diets of common carp up to 75%, but further research to potentially reduce some inherent ANF within this protein source, such as non-starch polysaccharides, may improve nutrient utilization.