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.

Key Publications

• Jun Tailoring texture for dysphagia diets: Unraveling the synergistic role of protein and blended vegetable oil in softening starch gels. (Carbohydrate polymers, 2026, PMID 42002333): "This study investigated how interactions between starch, soy protein isolate, and blended vegetable oil regulate the gel network formation, focusing on texture, rheology, water distribution, microstructure, and thermal decomposition behavior."
• Jun Enzyme- and ion-induced high internal phase emulsion gels based on soy protein isolate, chitosan, and alginate as fat analogues: Tunable texture and controlled flavor release. (International journal of biological macromolecules, 2026, PMID 42086137): "hydrophobically modified chitosan gel network (h-CSG) was incorporated into a soy protein isolate (SPI) solution"
• Jun Tailoring 3D-printed soy protein gels for dysphagia diets: Influence of xanthan gum's substituents and underlying mechanism. (International journal of biological macromolecules, 2026, PMID 42134693): "In this study, the effects of xanthan gum (XG) side-chain substituents (pyruvate and acetyl groups) on the interaction with soy protein isolate (SPI) and the functional properties of SPI-XG composite gels were systematically investigated."
• Jun Formation mechanism of "spiderweb-like" soy protein gel co-mediated by Maillard reaction and fermentation. (Food research international (Ottawa, Ont.), 2026, PMID 41895959): "Results showed that after 8 h of heating, the grafting degree stabilized, and soy protein isolate (SPI) particle aggregation was most evident by covalent bond aggregation."
• May Dual-phase bigels from soy hull polysaccharide-soy protein isolate hydrogel and soy lecithin-stearic acid oleogel: A novel strategy for probiotic encapsulation and gastrointestinal stability. (Food chemistry, 2026, PMID 41861735): "In this study, hydrogel was prepared using soy hull polysaccharides (SHP) and soy protein isolate (SPI) as matrices."
• May Impact of sonication and sodium chloride on the interaction and gelation behavior of soy protein isolate/κ-carrageenan mixtures. (Food chemistry, 2026, PMID 41865524): "When the pretreated-SPI was complexed with κ-Car, the obtained gel exhibited the highest hardness (69.3 g) and elasticity (93.4%) at pH 7.0."
• May Structural and functional regulation of soy protein isolate/sodium carboxymethyl cellulose complexes via surface charge modulation for enhanced emulsion stability. (Food chemistry, 2026, PMID 41865512): "This study investigates the interaction between soy protein isolate (SPI) and sodium carboxymethyl cellulose (CMC) at different pH levels and their emulsifying performance."
• May Plant-protein stabilized emulsions as β-carotene delivery systems: colloidal stability and behaviour during in vitro digestion conditions. (Food & function, 2026, PMID 42052689): "Conversely, soy and pea emulsions were unstable at pH 3.0 (droplets >6 μm) but stabilized at neutral pH, where wheat emulsions destabilized (droplets >7 μm)."
• May Exploring the physical phase behavior of Ulva polysaccharide and soybean isolate protein complexes: the effects of pH and ionic strength on gel properties. (Carbohydrate polymers, 2026, PMID 41831984): "This manuscript examined the interactions between soy protein isolate (SPI) and Ulva clathrata polysaccharides (UCP) under varying pH and calcium ion concentrations, elucidating the underlying mechanisms."
• May Freeze-thaw gelation of myofibrillar proteins and soy protein isolate mediated by transglutaminase under low-salt conditions: A potential alternative to thermal processing. (International journal of biological macromolecules, 2026, PMID 41962713): "This study demonstrates that freeze-thaw processing combined with transglutaminase (TGase) and soy protein isolate (SPI) facilitates the formation of high-quality myofibrillar protein (MP)-based gels under reduced-sodium conditions (0.3 mol·L-1 NaCl)."