Process Optimization and Flavor Quality Analysis of <italic>Eurotium cristatum</italic> Fermented <italic>Penthorum chinense</italic> Pursh Leaf Tea

In the present work, Eurotium cristatum fermentation was applicated in Penthorum chinense Pursh (PCP) leaf tea production, to reduce the bitterness, astringent tastes and pronounced herbaceous flavor of PCP leaves. Based on the results of single-factor experiments and response surface methodology (RSM) according to sensory evaluation, the optimal fermentation conditions were determined as follows: water contents 27%, incubation amount 21%, with 16 days of incubation time. The E. cristatum fermented PCP leaf tea produced in the optimal condition had orange-yellow infusion appearance with abundant E. cristatum colonization, tasting smooth and mellow with harmonious aroma, which achieved the sensory score at 91.60, while the total polyphenols and total flavonoids contents were reduced by 16.95% and 18.70%, respectively. Compared with the unfermented samples, the ratio of bitter and sweet amino acids of fermented PCP leaf tea decreased by 7.16%. The results of HS-SPME-GC-MS showed that the undesirable volatile components (VOCs), including hexanal, trans-2-hexenal, (E,E)-2,4-heptadienal, and 6-methyl-5-hepten-2-one representing grassy, pungent, and irritating odors, remarkably decreased, and the VOCs associated with floral, fruity, and fungal aromas, including acetophenone, linalool, and 2-butanone were newly generated and increased in PCP leave tea after fermentation. In summary, the optimal E. cristatum fermentation was confirmed to significantly improve the sensory quality of PCP leaf tea, especially eliminating the undesirable flavors and tastes, which could be a promising technology applicated in PCP tea process.