Compounds transformation in Wuyi rock tea under two baking processes

【: Objective】This study aimed at comparing the effects of two baking processes，fast baking and slow baking， on their sensory characteristics and chemical transformation. Wuyi rock tea were compared，through which to provide a reference for optimizing corresponding producing process and standardized production.【Method】Wuyi Rougui raw tea was baked by fast baking and slow baking，with raw tea as control. The changes of catechin，caffeine and free amino acid contents，the composition of flavonoids and its glycosides，ester compounds，amino acid derivatives，organic acid， nucleosides and corresponding derivatives of the samples by two baking processes were investigated by sensory evaluation，targeted quantification and non-targeted metabolomics methods.【Result】According to sensory evaluation，the sensory irritation of fast baking tea was obviously stronger than that of slow baking tea. The results of component quantitative analysis showed that both baking processes resulted in gallic acid（fast baking，0.82 mg/g，slow baking，1.01 mg/g；following data in the same order），epicatechin gallate（2.60 mg/g，2.40 mg/g）and total free amino acids（2.78 mg/g，5.35 mg/g）significantly different from that of raw tea（P<0.05，the same below）. There were significant differences between these two baking processes included caffeine（11.69 mg/g，13.29 mg/g），gallic acid，epicatechin（1.90 mg/g，1.30 mg/g） and total free amino acids. KEGG metabolic pathway enrichment analysis of 6897 characteristic peaks with extremely significant（P<0.01）differences enriched 107 metabolic pathways，the identified differential metabolites caused by the baking process involved flavonoids and their glycosides，ester compounds，amino acid derivatives，organic acids，nucleosides and their derivatives. And the least partial square discriminant model mainly applied flavonoids and corresponding glycosides such as colorless anthocyanin，dihydromyricetin，geranithin，kaempferol-3-rhamnoside，disaccharide-7-MelO-rhamnoside，quercetin-3-rhamnoside-7-rhamnoside，colorless sphingosin and their glycosides to distinguished two baking techniques from each other.【Conclusion】The two baking processes lead differences mainly in caffeine，gallic acid， flavonoids and corresponding glycosides，free amino acids，resulting in distinct taste characteristics between these two teas. Differences in the composition of flavonoids and their glycosides appear to be the primary contributing factor.