Identification of the key odorants causing soapy and metallic off-flavors in alkali-refined rapeseed oil via molecular sensory science

This is the authors' abstract. We don't add key points for this paper.

Alkali refining may sometimes induce soapy and metallic off-flavors in cold-pressed rapeseed oil, yet the molecular mechanisms remain unclear. A comparative flavor sensomics study was performed on crude cold-pressed, thermally treated control, water-degummed, and alkali-refined rapeseed oils. Quantitative descriptive analysis (QDA) showed that alkali refining increased soapy and metallic sensory attributes. Aroma extract dilution analysis (AEDA) detected 46 odor-active compounds across processing stages. The metallic off-flavors were primarily associated with elevated levels of trans-4,5-epoxy-(E)-2-decenal, (Z)-1,5-octadien-3-one, and 1-octen-3-one. The soapy attribute was linked to the accumulation of medium-chain saturated aldehydes, particularly nonanal and decanal. Omission experiments confirmed that these aldehydes collectively contributed to the soapy off-flavors, despite their low individual odor activity values (OAVs). Collectively, aldehydes and ketones were identified as the primary sources of off-flavor, marking the alkali neutralization step as the critical control point for flavor quality. These findings can offer theoretical guidance for process optimization of cold-pressed rapeseed oil refining.