Abstract
This study examined the effects of high-pressure homogenization (HPH) and ultrasonication pre-treatment on the structural and physicochemical properties of proteins extracted from defatted Nannochloropsis Oceania biomass (DNOB). HPH treatment was found to enhance the solubility of protein extracted from DNOB compared to ultrasound, where samples pretreated with three passes (3P) of HPH exhibited lower solubility than two passes (2P). The morphology of extracted samples was visualized by scanning electron microscopy, which HPH pre-treatment, especially with more passes, were able to breakdown DNOB into fragments. Alternatively, more holes were displayed on the surface of the extracts pretreated with ultrasound especially when higher amplitude applied. The particle size of extracts from HPH3P (129.5 µm) significant dropped from HPH2P (314.25 µm), where samples pretreated with ultrasound at 20 % amplitude (US20) also decreased in particle size compared to 40 % amplitude (US40), from 115.25 µm to 78.22 µm. Protein flexibility of DNOB extracts were 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, where samples treated with HPH3P contained the highest percentage of β-sheets (72 %) than control, HPH2P, ultrasonication at 20 and 40 % amplitude (52-62 %). The high percentage of β-sheets found in HPH3P sample also contributed to its outstanding emulsifying properties which stood out among all, especially at concentrations over 1 mg/ml. Results obtained from this study helped to direct the application of DNOB extracts as functional food ingredient for future food innovation.