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

Abstract

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.

Keywords

Cold-pressed rapeseed oil / Alkali-refined / Off-flavor / Odor activity value / Aroma recombination

Ethical statements

Ethical clearance for the involvement of human subjects in this study was obtained from the Research Ethics Committee of China Agricultural University, under reference number CAUHR-20240703.

Author contributions

The authors confirm contributions to the paper as follows: study conception and design: Wu J, Zhou Y, Shi H, Liu C, Xu X; data collection: Yu P, Lao F; analysis and interpretation of results: Yu P, Lao F, Wu J; draft manuscript preparation: Wang J. All authors reviewed the results and approved the final version of the manuscript.

Data availability

The datasets generated during and/or analyzed during the current study are available from the corresponding author upon reasonable request.

Acknowledgments

Thanks for the financial support from Arawana Charity Foundation. Thanks to all the R&D personnel of Wilmar (Shanghai) Biotechnology Research and Development Center Co., Ltd, for their technical guidance on this project. The author extends special thanks to distinguished engineers Ms. Jing Wang, Ms. Yunfei Zhou, and Mr. Chuan Zhou for their invaluable assistance and significant contributions to the experimental design of the vegetable oil off-flavor identification project over the past four years.

Conflict of interest

The authors declare that they have no conflict of interest.

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