Effects of High-pressure Homogenization and Ultrasound on the composition, structure, and physicochemical properties of proteins extracted from Nannochloropsis Oceania

Nannochloropsis Oceania, often in livestock feed, boasts a nutrient-rich profile with high polyunsaturated fatty acids, antioxidants, minerals, etc. Its protein content competes with traditional sources, providing an alternative for human consumption amid global animal-sourced protein shortages. Despite extensive study of protein extraction methods, the impacts of physical pre-treatments on protein functionalities, particularly high-pressure homogenization and ultrasonication, remains underexplored. Investigating the composition, structure, and emulsifying properties will apprise the integration of Nannochloropsis Oceania extracts as alternative functional food ingredients.

This study explored the impacts of high-pressure homogenization (HPH) and ultrasonication pre-treatments on the structural and physicochemical properties of proteins extracted from defatted Nannochloropsis Ocean biomass (DNOB). HPH was found to enhance the solubility of proteins extracted from DNOB compared to ultrasound, where samples pre-treated with three passes (3P) of HPH exhibited lower solubility than two passes (2P). Scanning electron microscopy images indicated that HPH pre-treatment with more passes induced breaking down of DNOB into small debris. Alternatively, more holes were displayed on the surface of the cell debris pre-treated with ultrasound, especially when higher amplitude was applied. The particle size of DNOB extracts from HPH3P (129.5 µm) was significantly lower than HPH2P (314.25 µm), whereas samples pre-treated with ultrasound at 40% amplitude (US40) decreased in particle size compared to 20% amplitude (US20), from 78.22 µm to 115.25 µm. Protein flexibility was enhanced by both HPH2P and HPH3P but decreased for ultrasound samples. β-sheets were found to be the most abundant protein secondary structure for all samples, with HPH3P contained the highest percentage (72%) compared to control, HPH2P, US20, and US40 (52-62%), contributing to the outstanding emulsifying properties of extracts at concentrations above 1 mg/ml. Results obtained from this study help to direct the application of DNOB extracts as a functional protein ingredient for future food innovation.