Effects of high-pressure homogenization and ultrasound on the composition, structure, and physicochemical properties of proteins extracted from Nannochloropsis Oceania

Graphical abstract

Highlights

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  HPH 2 passes pre-treatment enhanced protein solubility but not for 3 passes.

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  HPH caused the DNOB to be fragmented while ultrasound induced holes on the surface.

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  Protein flexibility was enhanced by HPH treatment but decreased by ultrasound.

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  Highest percentage of β-sheets was found in sample that underwent 3 passes of HPH.

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  Emulsifying properties of samples underwent 3 passes of HPH stood out among all.

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 HPH _3P (129.5 µm) significant dropped from HPH _2P (314.25 µm), where samples pretreated with ultrasound at 20 % amplitude (US ₂₀) also decreased in particle size compared to 40 % amplitude (US ₄₀), from 115.25 µm to 78.22 µm. Protein flexibility of DNOB extracts were enhanced by both HPH _2P and HPH _3P but decreased for ultrasound samples. β-sheets were found to be the most abundant protein secondary structure for all samples, where samples treated with HPH _3P contained the highest percentage of β-sheets (72 %) than control, HPH _2P, ultrasonication at 20 and 40 % amplitude (52–62 %). The high percentage of β-sheets found in HPH _3P 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.