Emulsifying properties of acid-hydrolyzed insoluble protein fraction from Chlorella protothecoides: Formation and storage stability of emulsions

Abstract

Microalgae are promising alternative protein sources due to their high protein content. However, the techno-functional properties of microalgae proteins are limited by their high content of insoluble proteins. Recently though, it has been reported that hydrolysis with 0.5 M HCl improved their solubility and interfacial activity, which could enhance their ability to act as emulsifying agents. In this study, we, therefore, investigated the use of an insoluble microalgae protein fraction from Chlorella protothecoides as oil-in-water emulsifiers after hydrolysis at 65 °C and 85 °C for 4 h. Mean particle diameter, microscopic images, and ζ-potential of emulsions stabilized by untreated insoluble microalgae protein fraction and their hydrolysates at different protein concentrations (1%–5%) were recorded during storage for 14 days. Results showed that emulsions prepared by untreated and hydrolyzed protein fractions all exhibited droplet flocculation, but effective droplet size decreased with increasing protein concentrations and storage time. Moreover, emulsions droplets were stable against coalescence at protein concentrations ≥3%. Overall, hydrolysates showed higher interfacial activities compared to untreated microalgae proteins. Results were attributed to the presence of protein aggregates causing droplet flocculation, and mixed protein aggregate - hydrolyzed peptide interfaces preventing coalescence. Results indicated a potential application of hydrolysates of insoluble microalgae protein fraction in emulsion-based foods, especially concentrated emulsions, such as mayonnaise, dips or salad dressings.