Synergistic modification of soy protein as plant-based molecular emulsifiers by enzymatic hydrolysis and heat-assisted pH shifting

This study developed a synergistic approach combining enzymatic hydrolysis and heat-assisted pH-shifting to enhance the emulsification-related functionalities of soy protein isolate (SPI), in order to design plant-based molecular emulsifiers for applications in low-viscosity food emulsions requiring finely dispersed droplets. Trypsin outperformed pepsin at enhancing the emulsifying-related properties of SPI due to specifically cleaving peptide bonds, leading to more significant exposure of hydrophobic domains and disruption of protein aggregates. The subsequent alkaline pH-shifting (pH 10) further dissociated protein aggregates and improved the functional properties of SPI hydrolysates, while acidic pH-shifting (pH 2) caused substantial protein reaggregation and much reduced functionalities. Our results demonstrated that trypsin digestion followed by heat-assisted alkaline pH-shifting tailored SPI into high-performance molecular emulsifiers, capable of creating O/W emulsions with submicron-sized oil droplets ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>D</mml:mi> <mml:mrow><mml:mn>4</mml:mn> <mml:mo>,</mml:mo> <mml:mn>3</mml:mn></mml:mrow> </mml:msub> </mml:math> =0.593 μm) which exhibited excellent storage stability ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>D</mml:mi> <mml:mrow><mml:mn>4</mml:mn> <mml:mo>,</mml:mo> <mml:mn>3</mml:mn></mml:mrow> </mml:msub> </mml:math> =0.737 μm after 30 days), remarkable thermal resistance ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>D</mml:mi> <mml:mrow><mml:mn>4</mml:mn> <mml:mo>,</mml:mo> <mml:mn>3</mml:mn></mml:mrow> </mml:msub> </mml:math> =0.635 μm after 95 °C/60 min heating), and moderate freeze-thaw stability.