Whole-cell biocatalyzed organic solvent-free conversion of dill oil to cis-(-)-dihydrocarvone rich aromatic hydrosol: Chemical and aroma profiling

Biotechnologically produced flavours and fragrances are labeled as 'natural' and in great demand. In the current study, Fusarium equiseti was utilized as the whole-cell biocatalyst for the selective transformation of S-(+)-carvone in the dill oil to cis-(-)-dihydrocarvone [cis-(-)-DHC]. In an optimized condition (pH 5-6, dill oil 1.0 g/L and incubation period 24 h) F. equiseti produced S-(+)-carvone metabolites, dominated by cis-(-)-DHC (92-96% through gas chromatography-mass spectrometry or GC-MS) in nearly quantitative conversion (similar to 99%). In the next step, distillation of the whole culture isolated the product in the form of cis-(-)-DHC rich (0.33 g/L) hydrosol; thus eliminating the use of organic solvent for the extraction and reducing the solvent soluble off-odour in the product. Detailed sensory analysis demonstrated the uniqueness of hydrosol aroma in reference to the dill oil and characterized it as sweet, minty, fresh, spicy and herbal. Headspace-GC-MS analysis supported by the odour activity value and sensory profile showed cis-(-)-DHC as the key odorant in the produced hydrosol. The developed bioconversion technique was novel in terms of its high selectivity towards cis-(-)-DHC and organic solvent-free downstream processing, producing a unique aromatic hydrosol.

Automated summary

In this study, Fusarium equiseti was used as a biocatalyst to selectively transform S-(+)-carvone in dill oil to cis-(-)-dihydrocarvone [cis-(-)-DHC]. The optimized conditions resulted in nearly quantitative conversion of S-(+)-carvone to cis-(-)-DHC. Distillation of the culture isolated the product as a high concentration hydrosol of cis-(-)-DHC. Sensory analysis confirmed the unique aroma of the hydrosol, with cis-(-)-DHC identified as the key odorant.