Bio-based emulsifiers through enzymatic hydrolysis of a soy protein isolate

Protein-based surfactants are gaining interest in several industrial sectors, due to their low-cost and biodegradability. Their properties make them a valid bio-based alternative to petrochemical-based tensides, thus reducing environmental and health concerns. To enhance their techno-functional properties, protein structure must be modified. Compared to chemical methods, enzymatic hydrolysis offers an industrially viable and sustainable approach for this purpose. Particularly, by adjusting enzymatic hydrolysis parameters (type of enzyme, incubation time, temperature and pH), the surfactancy of proteins can be substantially altered, broadening both the application range and the conventional emulsifiers choice. In this study, a commercial soy protein isolate (SPI) was hydrolysed through a biocatalytic approach, using Alcalase® 2.4L FG and Protamex® as enzymatic preparations, at different incubation time (15, 120, 360 min). The resulting Soy Protein Hydrolysates (SPHs) were characterised by ultrafiltration with molecular weight cut-off membranes of 10, 5, and 1 kDa. Then, the emulsifying properties of the prepared SPHs were investigated by interfacial tension (IFT) studies. The two hydrolysates, that achieved the greatest IFT reduction, were tested as emulsifiers in simple peanut oil-in-water (O/W) emulsions, prepared with a sonicator device. Their stability over time was evaluated by turbidimetry, emulsion stability index, confocal microscopy images and dynamic light scattering analyses. Protein secondary structures/emulsifying capability relationship was proposed based on circular dichroism (CD) analyses. Furthermore, for potential industrial applications, more complex O/W emulsions (including rheological modifier, solubilizing agent, antioxidants, and buffers) were also formulated using a rotor-stator. Finally, the stability and rheological behavior of these complex emulsions were thoroughly examined.