Characterisation of water-soluble Nannochloropsis oceanica protein fractions: physical and functional properties

Abstract

This study presents a comprehensive physical and functional characterisation of water-soluble protein fractions extracted from defatted Nannochloropsis oceanica biomass, including electrostatic surface charge, water-absorption and oil-absorption capacities, foaming, emulsion formation and stability, and thermal behaviour, including denaturation and gelation, benchmarked against two widely used commercial proteins such as milk protein (MP) and soybean protein (SP). The water-soluble N. oceanica protein fractions (NP) showed comparable or superior surface charge density, water-absorption capacity, and oil-absorption capacity relative to MP and SP. NP achieved the highest emulsion activity index (131 m² g⁻¹), the greatest emulsion stability index (121 days), and the most negative zeta potential (−59.3 mV). It also produced the smallest emulsion droplet size among the tested proteins. Its denaturation temperature was 71 °C, indicating good thermal stability. NP formed heat-induced gels at 95 °C with a minimum concentration of 10% (w/w), although the resulting gels were not as firm as those formed by SP. These results indicate that NP possesses emulsifying, thermal, and gelling properties suitable for a range of food applications. Given its sustainable origin and multi-functional performance, NP holds promise as a novel protein ingredient in future foods.