Protease-induced soy protein isolate (SPI) characteristics and structure evolution on the oil–water interface of emulsion

Effect of xanthan gum (XG) and carrageenan (CG) ratio on casein (CA)-XG-CG ternary complex: Used to improve the stability of liquid diabetes formula food for special medical purposes

Poor storage stability limits the application of liquid diabetes formula food for special medical purposes (L-D-FSMP) in maintaining blood sugar stability in diabetic patients. This work aims to improve the stability of L-D-FSMP by adjusting the ratio of xanthan gum (XG) and carrageenan (CG) in casein (CA)-XG-CG ternary complex. The centrifugal sedimentation rate results showed that the compound ratio of XG and CG had a greater impact on L-D-FSMP storage stability. Transmission electron microscopy (TEM) results showed that the combination of CA, XG and CG occurred. Fourier transform infrared spectroscopy (FTIR) results showed that CA, XG and CG were mainly combined through hydrogen bonds and ionic bonds to form a CA-XG-CG ternary complex. When the ratio of XG and CG was 1:1, the number of disulfide bonds was the largest. The results of three-phase contact angle and emulsifying ability confirmed that when the ratio of XG and CG was 1:1, CA-XG-CG had the strongest emulsifying ability. The particle size distribution and zeta-potential results showed that when the ratio of XG and CG was 1:1, L-D-FSMP had the narrowest particle size distribution range and the strongest stability. These results may provide valuable information for the production of stable L-D-FSMP.

High moisture extrusion of soybean protein isolate: Effect of β-glucan on physicochemical properties of extrudates

This study is focused on exploring the effect of twin-screw high-moisture extrusion technology on the physico-chemical properties of β-glucan-soybean protein isolate (SPI-BG) extrudates. Different proportions (0 %, 1 %, 2 %, 3 %, 4 %, 5 %) of oat β-glucan (BG) were added with soybean protein isolate (SPI) to prepare SPI-BG extrudates. Results showed that the addition of a high quantity of β-glucan (BG) decreased the elastic properties of soy protein isolate (SPI) extrudates and then increased. The strengthening of S1-S2-S3 interactions (hydrogen bonds, hydrophobic interactions, and disulfide bonds) was primarily responsible for this trend. Fourier transform infrared (FTIR) spectral analysis was conducted which revealed that BG did not significant affect random coil content of SPI. However, it was observed that α-helix content was increased significantly and the β-sheet content was decreased. An observation was noted in the value of enthalpy (ΔH) change that increased from 115.80 J/g to 159.68 J/g.

Ultrasound viscous reduction effects on the proteolysis of soy protein isolate at a limited degree of hydrolysis: Changes in the functional characteristics and protein structure

High-concentration soy protein isolate was subjected to ultrasonication for viscosity reduction to assist the process of limited enzymatic hydrolysis. Ultrasonication (20 kHz, 10 min, 160 W/L) effectively reduced the viscosity of soy protein isolate at a comparatively high concentration of 14 % (w/v) and promoted the limited enzymatic hydrolysis (controlled degree of hydrolysis of 12 %) with a higher peptide yield than that of the conventional method. The correlations between substrate viscosity and peptide yield, as well as the viscosities of the resulting hydrolysates, were studied. The findings revealed positive correlations between the viscosities of the substrate and hydrolysate, underscoring the potential impact of altering substrate viscosity on the final product. Furthermore, the utilization of ultrasonic viscosity reduction-assisted proteolysis has shown its capability to improve the functional and physicochemical properties, as well as the protein structure of the hydrolysate, while maintaining the same level of hydrolysis. It is worth noting that there were significant alterations in particle size (decrease), β-sheet content (increase), β-turn content (increase), and random coil content (increase). Interestingly, ultrasonication unexpectedly impeded the degradation of molecular mass in proteins during proteolysis, while increasing the hydrophobic properties of the hydrolysate. These findings aligned with the observed reduction in bitterness and improvement in emulsifying properties and water-holding capacity.

The influence of protein oxidation on structure, pepsin diffusion, and in vitro gastric digestion of SPI emulsion

The stability behaviors of oxidized SPI emulsions under in vitro gastric conditions and the effects of pepsin diffusion on the proteolysis of emulsions were investigated using a static gastric model and the fluorescence recovery after photobleaching method. Results showed that protein oxidation increased the particle size of droplets and decreased the viscoelasticity of the interfacial layer. Compared to the control group (82.81 m²/s), the pepsin diffusivity decreased to 68.52 m²/s (7LA + LOX group) due to the space hindrance of oil droplets. After gastric digestion, protein hydrolysates were re-absorbed on the oil-water interface and formed a thick layer, thereby decreasing the size of oil droplets and reducing the contents of free amino acids in gastric digesta. The protein oxidation may affect the adsorption of interfacial proteins and alter the distribution of droplets, decreasing pepsin diffusion and ultimately impairing the emulsion gastric digestion. And this should be considered in the design of emulsion as the controllable delivery system.

Conformational evolution of soybean protein-polysaccharide at oil-water interface in simulated gastric environment in vitro

The conformation and characteristics of soybean hull polysaccharide (SHP)/soy bean protein isolate (SPI) complex at oil-water interface in simulated gastric environment in vitro were discussed. Isothermal titration calorimetry (ITC) thermodynamic results illustrated that SPI formed a complex with SHP. ζ-potential and microstructure showed a flocculation phenomenon after SPI/SHP emulsion droplet treatment (especially at 60 min), which indicated that the inter droplet steric hindrance and repulsion were reduced after the emulsion was treated. Additionally, at 60 min, in FT-IR spectrum fitting results, the contents of β-sheet and β-turn structure were the lowest, which might be that the polar group residues exposed in the SPI/SHP complex at the interface interacted with Na⁺ by ion-dipole interaction or protonated with H⁺. The blue shift of maximum absorption intensity also indicated that the tryptophan residues moved to the hydrophobic environment, which made the treated droplets flocculate without obvious aggregation.

Improving probiotic survival using water-in-oil-in-water (W1/O/W2) emulsions: Role of fish oil in inner phase and sodium alginate in outer phase

Aqueous probiotic suspensions were dispersed in an oil phase consisting of fish oil and medium chain triglycerides to form W₁/O emulsions. These emulsions were then homogenized with an aqueous solution containing soybean protein isolate and sodium alginate to form W₁/O/W₂ emulsions. Fish oil was used to promote the growth of the probiotics and increase their ability to adhere to the intestinal mucosa. Sodium alginate increased the viscosity, stability, and probiotic encapsulation efficiency of the double emulsions, which was mainly attributed to its interactions with adsorbed soy proteins. The encapsulation efficiency of the probiotics in the double emulsions was relatively high (>96%). In vitro simulated digestion experiments showed that the double emulsions significantly increased the number of viable probiotics remaining after passing through the entire gastrointestinal tract. This study suggests that encapsulation of probiotics in double emulsions may increase their viability under gastrointestinal conditions, thereby enhancing their efficacy in functional foods.