Screening of aroma-producing yeast for improving the aroma quality of tobacco extract and optimization of its fermentation conditions

To improve the aroma quality of low-grade tobacco extract, yeast strains with excellent aroma-producing capabilities were identified through sensory evaluation. Subsequently, the fermentation conditions for these selected strains were optimized using the total aroma component content as the key optimization parameter. The volatile compounds in the fermentation broth were characterized using headspace solid-phase microextraction combined with gas chromatography-mass spectrometry (HS-SPME-GC-MS), and the alterations in the aroma of the tobacco extract following fermentation were assessed. Results indicated that seven aroma-producing strains with notable performance were initially screened, among which strain H8 achieved the highest sensory evaluation score after re-screening. Morphological examination and 26S rDNA molecular biology identification confirmed this strain as Candida tropicalis. Optimization revealed the ideal material-to-liquid ratio for the extract culture medium to be tobacco extract: waste tobacco stem: water = 3:2:30. The optimal fermentation conditions for the strain included a fermentation duration of 67 hours, an inoculation rate of 2%, and a fermentation temperature of 24°C. Under the given conditions, the content of aroma substances in the fermented extract obtained is 2.10 times that of the original extract, reaching 239.83 μg/L. Notably, the levels of aroma components such as hydroxypimoline, cantharidinone, dihydrokaurone, macrodienone, neopentyladiene, and phenylethanol were significantly elevated, thereby enhancing the richness and harmony of the extract's aroma. Therefore, the selected Candida tropicalis strain H8 demonstrated significant potential in enhancing the aroma quality of low-grade tobacco extracts.