Rheological and Solubility Properties of Soy Protein Isolate

Abstract

Soy protein isolate (SPI) powders often have poor water solubility, particularly at pH values close to neutral, which is an attribute that is an issue for its incorporation into complex nutritional systems. Therefore, the objective of this study was to improve SPI solubility while maintaining low viscosity. Thus, the intention was to examine the solubility and rheological properties of a commercial SPI powder at pH values of 2.0, 6.9, and 9.0, and determine if heat treatment at acidic or alkaline conditions might positively influence protein solubility, once re-adjusted back to pH 6.9. Adjusting the pH of SPI dispersions from pH 6.9 to 2.0 or 9.0 led to an increase in protein solubility with a concomitant increase in viscosity at 20 °C. Meanwhile, heat treatment at 90 °C significantly improved the solubility at all pH values and resulted in a decrease in viscosity in samples heated at pH 9.0. All SPI dispersions measured under low-amplitude rheological conditions showed elastic-like behaviour (i.e., G′ > G″), indicating a weak “gel-like” structure at frequencies less than 10 Hz. In summary, the physical properties of SPI can be manipulated through heat treatment under acidic or alkaline conditions when the protein subunits are dissociated, before re-adjusting to pH 6.9.

Brewers’ Spent Grain: An Unprecedented Opportunity to Develop Sustainable Plant-Based Nutrition Ingredients Addressing Global Malnutrition Challenges

“…BSG-derived protein-rich ingredient has a protein content of 36 g/100 g, slightly higher than that of BSG (31 g/100 g). Although the fiber-rich BSG-derived ingredient contains less protein than the others, the ingredient can still be considered a relatively good protein source, providing 21 g of protein per 100 g. In comparison, the BSG protein isolate contains significantly more protein (87%) than BSG or the BSG-derived ingredients, with the reported protein content within the range of what has been determined previously for this ingredient, as well as for commercial isolates derived from pea and soy (81–89% protein). , The amino acid compositions of the BSG-derived ingredients are similar to each other and to that of BSG, with essential amino acids comprising 36–42% of the total protein content. Naturally, lysine is the limiting amino acid in each of the BSG-derived ingredients; however, the ingredients still provide a significant amount (82–91%) of the required lysine amount per gram of protein as outlined by the WHO.…”

Ultrasound-assisted limited enzymatic hydrolysis of high concentrated soy protein isolate: Alterations on the functional properties and its relation with hydrophobicity and molecular weight

“…Protein solubility is another important functional property of protein that does not only serve as an alteration in food processing but also play a significant role in other functional properties [26] , [51] . SPI was reported to inherent low protein solubility in water with lowest solubility near its isoelectric point [11] , [52] . As presented in Fig.…”

Characteristics of O/W emulsion gels stabilized by soy protein‐xanthan gum complex for plant‐based processed meat products

“…SPI‐XG complex forms via electrostatic interactions. Given that the isoelectric point of SPI is pH 4–5 (O'Flynn et al, 2021), the complex formation is not fully enhanced for T4 (i.e., at pH 6.5), and heat stability of the emulsion gels is lower compared to T2.…”