Soybean lipophilic protein: Influence of extraction pH and drying technique on physicochemical and functional...

In this study, the effects of varying alkaline extraction pH levels (8, 9, and 10) and two drying techniques (freeze drying, FD; spray drying, SD) on the composition, structure, and functional properties of soybean lipophilic protein (LP) were systematically investigated. The results indicate that protein extraction yield increased with pH; however, excessively high pH values led to the co-precipitation of non-protein substances. Sample FD 9 exhibited the highest protein content (76.56 %). Compared to FD, SD yielded higher essential amino acid content and improved lipid retention; however, the high-temperature processing involved in SD reduced the levels of unsaturated fatty acids. Structural characterization using SDS-PAGE and mass spectrometry identified the major components of LP and their relative abundance. Secondary structure analysis revealed that SD-treated samples contained a higher proportion of β-sheet structures. Fluorescence spectroscopy and surface hydrophobicity measurements both peaked at pH 9. Functional evaluations demonstrated that SD samples exhibited superior solubility and gelation properties compared to FD. pH 9 was identified as the optimal condition in several other aspects: SD 9 showed the lowest surface tension and the highest foaming capacity (325.76 %), albeit with relatively poor foam stability. In contrast, FD 9 displayed the best foam stability (57.66 %) and excellent water- and oil-holding capacities. Notably, SD 10 achieved the highest emulsifying activity (42.13 m²/g). These findings provide a scientific basis for selecting extraction conditions that yield LP with desirable functional properties for practical food production applications, thereby facilitating the broader utilization of LP in the food industry.