soy protein isolate

Overview

Soy protein isolate (SPI) is a highly purified protein fraction derived from soybeans, composed predominantly of storage proteins that are widely used in food formulation and biomaterials research. In biomedical and food-science contexts, SPI is valued for its emulsifying, gelling, film-forming, and water-binding properties, which arise from its ability to unfold, aggregate, and interact with polysaccharides, lipids, salts, and enzymes under different processing conditions.

Although SPI is not a therapeutic protein in the conventional pharmaceutical sense, it is an important functional biomaterial and model protein for studying protein–polysaccharide interactions, gelation, emulsion stabilization, flavor binding, and texture modification. Recent studies have used SPI to build structured food matrices, including hydrogels, bigels, Pickering emulsions, edible films, and 3D-printed gels, often in combination with chitosan, alginate, xanthan gum, κ-carrageenan, soy hull polysaccharides, starch, and vegetable oils. These systems are relevant to dysphagia diets, reduced-sodium formulations, probiotic delivery, and controlled release of flavor compounds.

Focus of Latest Publications

Recent publications portray soy protein isolate as a central structuring component in a range of food hydrocolloid systems designed to tune texture, stability, and release behavior.

Several studies examined SPI-based gels and composite networks. One report on enzyme- and ion-induced high internal phase emulsion gels used SPI together with chitosan and alginate, incorporating a hydrophobically modified chitosan gel network (h-CSG) into SPI solution to create fat analogues with tunable texture and controlled flavor release. Another study investigated 3D-printed SPI gels for dysphagia diets, focusing on how xanthan gum side-chain substituents, including pyruvate and acetyl groups, altered interactions with SPI and changed the functional properties of the resulting composite gels. A separate paper described a “spiderweb-like” SPI gel formed through co-mediated Maillard reaction and fermentation, reporting that after 8 hours of heating the grafting degree stabilized and SPI particle aggregation became most evident through covalent bond aggregation.

SPI was also studied in combination with polysaccharides and salts to regulate gelation and emulsion stability. In one work, sonication and sodium chloride were used to modulate the interaction and gelation behavior of SPI/κ-carrageenan mixtures; the pretreated SPI complexed with κ-carrageenan produced a gel with the highest hardness and elasticity at pH 7.0. Another study examined SPI/sodium carboxymethyl cellulose complexes and showed that surface charge modulation affected structural and functional regulation, improving emulsion stability. Similarly, SPI and Ulva clathrata polysaccharides were analyzed under varying pH and calcium ion concentrations to understand phase behavior and gel properties, emphasizing the importance of ionic conditions in complex formation.

SPI has also been used in emulsion systems and delivery platforms. Plant-protein stabilized emulsions were evaluated as β-carotene delivery systems, with soy emulsions showing instability at pH 3.0 but improved stability at neutral pH. Another study developed a Tremella polysaccharide-assisted SPI Pickering emulsion for gelatinization of Nemipterus virgatus surimi under continuous microwave heating, using free soybean oil and a physical mixture control to assess the emulsion’s role in surimi gel formation. In a related direction, a dual-phase bigel was prepared from soy hull polysaccharide-SPI hydrogel and soy lecithin-stearic acid oleogel for probiotic encapsulation and gastrointestinal stability, highlighting SPI’s role in hybrid gel architectures.

SPI was also investigated in systems relevant to texture modification and preservation. A study on starch-protein edible films used corn starch and SPI to create fully bio-based interpenetrating network films via reactive extrusion for milk powder preservation. Another paper on dysphagia diets explored how SPI and blended vegetable oil influenced starch gel softening, with effects on texture, rheology, water distribution, microstructure, and thermal decomposition. In reduced-sodium meat analog research, freeze-thaw processing combined with transglutaminase and SPI supported the formation of high-quality myofibrillar protein gels under low-salt conditions, suggesting SPI can contribute to alternative gelation strategies when sodium chloride is limited.

SPI has also been linked to flavor chemistry. One study focused on dynamic regulation of beany off-aroma adsorption by protein concentration, using SPI-hexanal interactions to probe adsorption of hexanal, a key beany flavor compound in soymilk. This work reinforces SPI’s relevance not only as a structural ingredient but also as a modulator of volatile compound behavior. Across these studies, SPI repeatedly served as a matrix-forming protein whose interactions with aldehydes, polysaccharides, oils, and enzymes determined final product quality.