Calcium Addition, pH, and High Hydrostatic Pressure Effects on Soybean Protein Isolates—Part 1: Colloidal Stability Improvement

Effect of High-Hydrostatic-Pressure Treatment on the Physicochemical Properties of Kafirin

The kafirin derived from Jin Nuo 3 sorghum underwent a high-hydrostatic-pressure (HHP) treatment of 100, 300, and 600 MPa for 10 min to investigate alterations in its physicochemical attributes. The findings exhibited a reduction in protein solubility, declining from 83% to 62%, consequent to the application of the HHP treatment. However, this treatment did not lead to subunit-specific aggregation. The absorption intensity of UV light diminished, and the peak fluorescence absorption wavelength exhibited a shift from 342 nm to 344 nm, indicating an increased polarity within the amino acid microenvironment. In an aqueous solution, the specific surface area expanded from 294.2 m2/kg to 304.5 m2/kg, while the average particle-size value in a 70% ethanol solution rose to 26.3 nm. Conversely, the zeta-potential value decreased from 3.4 mV to 1.3 mV, suggesting a propensity for aggregation in ethanol solutions. A notable rise in the intermolecular β-sheet content to 21.06% was observed, along with a shift in the peak denaturation temperature from 76.33 °C to 86.33 °C. Additionally, the content of disulfide bonds increased to 14.5 μmol/g. Collectively, the application of the HHP treatment not only enhanced the thermal stability but also induced a more ordered secondary structure within the kafirin.

Application of emerging technologies to obtain legume protein isolates with improved techno-functional properties and health effects

Current demand of consumers for healthy and sustainable food products has led the industry to search for different sources of plant protein isolates and concentrates. Legumes represent an excellent nonanimal protein source with high-protein content. Legume species are distributed in a wide range of ecological conditions, including regions with drought conditions, making them a sustainable crop in a context of global warming. However, their use as human food is limited by the presence of antinutritional factors, such as protease inhibitors, lectins, phytates, and alkaloids, which have adverse nutritional effects. Antitechnological factors, such as fiber, tannins, and lipids, can affect the purity and protein extraction yield. Although most are removed or reduced during alkaline solubilization and isoelectric precipitation processes, some remain in the resulting protein isolates. Selection of appropriate legume genotypes and different emerging and sustainable facilitating technologies, such as high-power ultrasound, pulsed electric fields, high hydrostatic pressure, microwave, and supercritical fluids, can be applied to increase the removal of unwanted compounds. Some technologies can be used to increase protein yield. The technologies can also modify protein structure to improve digestibility, reduce allergenicity, and tune technological properties. This review summarizes recent findings regarding the use of emerging technologies to obtain high-purity protein isolates and the effects on techno-functional properties and health.

Optimization of High Hydrostatic Pressure Treatments on Soybean Protein Isolate to Improve Its Functionality and Evaluation of Its Application in Yogurt

This work aimed to improve the functional properties of soybean protein isolate (SPI) by high hydrostatic pressure (HHP) and develop SPI incorporated yogurt. Response surface methodology (RSM) was used to optimize the HHP treatment parameters, including pressure, holding time, and the ratio of SPI/water. Water holding capacity, emulsifying activity index, solubility, and hardness of SPI gels were evaluated as response variables. The optimized HPP treatment conditions were 281 MPa of pressure, 18.92 min of holding time, and 1:8.33 of SPI/water ratio. Water and oil holding capacity, emulsifying activity, and stability of SPI at different pH were improved. Additionally, relative lipoxygenase (LOX) activity of HHP treated SPI (HHP-SPI) was decreased 67.55 ± 5.73%, but sulphydryl group content of HHP-SPI was increased 12.77%, respectively. When incorporating 8% of SPI and HHP-SPI into yogurt, the water holding capacity and rheological properties of yogurt were improved in comparison with yogurt made of milk powders. Moreover, HHP-SPI incorporated yogurt appeared better color and flavor.

Modeling counterion partition in composite gels of BSA with gelatin following high pressure treatment

We examine the morphology of hydrogels made of bovine serum albumin and gelatin following high pressure processing at 300 MPa for 15 min at 10 and 80 °C. Emphasis is on the distribution of added calcium counterions between the polymeric phases seen in changes in the structural properties of the composite gel. Protocol includes thermal and HPP treatments, dynamic oscillation rheology, ESEM, and modeling from the "synthetic polymer approach" to rationalize results. Pressurization at 10 °C produced continuous gelatin networks with dispersed BSA inclusions whereas pressurization at 80 °C yielded an inverse dispersion of BSA as the continuous phase supporting liquid gelatin inclusions. Lewis and Nielsen equations were adapted to predict the counterion distribution between the polymeric phases that profoundly affected the structural properties of the pressurized gels. The concept of counterion partition (p_c) is introduced to the literature to follow the phase behavior of the composites in the presence of added calcium counterions.

Binding of aromatic compounds with soy protein isolate in an aqueous model: Effect of pH

Interactions of the flavoring compounds hexyl acetate (HxAc), heptyl acetate (HpAc), linalyl formate (LiFo), linalyl acetate (LiAc), geraniol, linalool, limonene, and myrcene with soy protein isolate (SPI) were estimated in pH 3.0, 6.0, and 9.0 aqueous solutions using headspace solid-phase microextraction gas chromatography-mass spectrometry (SPME-GC-MS). The binding capacity of HxAc, HpAc, LiFo, LiAc, geraniol, and linalool increased in the pH of the medium from 3 to 9. For limonene and myrcene, an unexpected increase in headspace concentration or a "salting-out" effect was observed. Between pH 3 and 9, better accessibility to the primary hydrophobic sites as a result of a modification to the protein's flexibility was observed. PRACTICAL APPLICATIONS: SPME method is a technology of dynamic adsorption for flavors. The lowest level of lead be practicably detected in food as low as the practiced concentration of flavors (0.01-0.1 mM) in our study. At low concentrations of flavors, it is close to the actual flavor's concentration of food. In the previous studies, the technology, such as equilibrium dialysis, headspace-gas phase which need higher concentration of flavors (>0.2 mM). The interaction between flavors and protein has a different binding law at high and low concentrations. As we produced the acid fruit soy protein milk beverage, the off-flavors present in the beverage were due to the change in the interaction between denature SPI and flavors. The present work is aimed at paving the way for further research to elucidate flavor imbalances in acid fruit soy protein milk beverage.