Characterisation of volatile organic compounds in Chlorella pyrenoidosa cultured with different selenium concentrations using E-nose, GC–IMS, GC–MS, and machine learning algorithms

Chlorella pyrenoidosa is a promising plant-based protein source , whereas the volatile off-flavours derived from lipid oxidation substantially limit consumer acceptance. Selenium (Se) is recognised as a beneficial trace element that can improve flavour characteristics in plants by enhancing antioxidant capacity. This study investigated the effects of Se supplementation (0–2 mg/L) on the volatile profile of C. pyrenoidosa and explored the underlying mechanisms. E-nose analysis revealed significant differences in flavour profile among the treatments. GC–IMS and GC–MS identified 25 and 28 volatile organic compounds (VOCs), respectively. Fifteen key aroma compounds were screened by orthogonal partial least squares discriminant analysis (OPLS–DA), random forest (RF) modelling, and odour activity value (OAV) and relative OAV (ROAV) calculations. Notably, 0.50 mg/L Se was identified as the optimal enrichment concentration, as it improved overall flavour quality by reducing aldehyde accumulation, particularly hexanal. This improvement was attributed to Se-mediated reductions in lipid content and enhanced antioxidant capacity, as evidenced by increased glutathione peroxidase (GPx) activity, reduced reactive oxygen species (ROS) levels, and alleviated lipid peroxidation, alongside decreased lipoxygenase (LOX) and hydroperoxide lyase (HPL) activities by 60.08% and 37.31% respectively, thereby inhibiting the formation of off-flavour VOCs. Overall, this study provides the first evidence that Se modulates the flavour profile of C. pyrenoidosa and preliminarily elucidates the mechanism by which appropriate Se supplementation improves flavour quality through reshaping biochemical composition, maintaining redox homeostasis, and regulating key enzymes involved in aldehyde biosynthesis. These findings offer a theoretical foundation for developing novel functional microalgal-based foods.