Effects of Different Processing Methods on the Flavor Characteristics of Rapeseed Protein Isolate

This study aimed to investigate the differential effects of cold pressing, microwave, and roasting pretreatments on the extraction efficiency, structural characteristics, and flavor quality of rapeseed protein. Defatted rapeseed meal was used to prepare rapeseed protein isolate (RPI) via salt extraction. The yield, color, and amino acid composition of RPI were systematically analyzed. The protein subunit composition was characterized using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The overall flavor profile and volatile compounds were comprehensively evaluated by the combined use of an electronic nose, an electronic tongue, and headspace solid-phase microextraction followed by gas chromatography-mass spectrometry (HS-SPME-GC-MS). The results showed that cold pressing resulted in the highest extraction yield (35.90%) and total amino acid content, along with the lightest color. However, the resulting sample exhibited the poorest flavor quality, with its volatile composition dominated by aldehydes (1450.8 μg/kg) from lipid oxidation and isothiocyanates from glucosinolate degradation, presenting strong green and pungent notes. The roasting process generated abundant pyrazines (357.9 μg/kg) and furans (414.0 μg/kg) via the Maillard reaction, contributing to a rich roasted nutty aroma. However, it caused severe protein aggregation, significantly reduced the extraction yield (18.05%) and lysine retention rate (24.8%), and resulted in the darkest color. The microwave process surpassed roasting in terms of extraction yield (19.35%) and nutrient retention. Its unique advantage lies in efficiently inactivating endogenous enzymes while simultaneously producing the highest levels of pyrazines (639.5 μg/kg). Microwave treatment resulted in the most prominent nutty aroma and the most balanced aroma profile but also generated a pronounced bitter taste. This study provides a theoretical basis for the high-value utilization of rapeseed protein.