Fate of beneficial and undesirable components in wheat germ oil during molecular distillation

Wheat germ oil (WGO) is a nutrient-rich byproduct of wheat processing, characterized by high levels of tocopherols and phytosterols. However, limited information is available regarding the simultaneous fate of beneficial compounds and hazardous contaminants during refining. In this study, molecular distillation (MD) was applied to WGO at temperatures ranging from 160 to 200 °C to investigate component migration behavior and quality changes. Key bioactive compounds including tocopherols and sterols, contaminants including malathion, 2-monochloropropanediol esters (2-MCPDE), 3-monochloropropanediol esters (3-MCPDE) and glycidyl esters (GEs), and quality indices including acid value (AV), peroxide value (PV), p-anisidine value (p-AV) and total oxidation value (TOTOX) were systematically analyzed. The results demonstrated that MD effectively reduced free fatty acids and completely removed malathion from the residue. Increasing temperature promoted the migration of bioactive compounds into the distillate; however, excessive temperatures led to significant thermal degradation, with total tocopherol loss reaching 66.33% at 200 °C. Contaminants such as 2-MCPDE, 3-MCPDE and GEs were enriched in the distillate at lower temperatures but decreased at higher temperatures due to thermal decomposition. Meanwhile, PV decreased whereas p-AV and TOTOX increased, indicating the formation of secondary oxidation products. Overall, MD enables the simultaneous removal of contaminants and selective enrichment of bioactive compounds, while temperature governs a critical trade-off between component recovery and thermal degradation. These findings provide a mechanistic basis for optimizing WGO refining to improve safety, quality, and nutritional value.