Chemical analysis of ultrasonic-assisted treatment on improving cold-brewed green tea extraction efficiency and quality formation

This study investigated the feasibility of ultrasound-assisted cold brewing (UACB) for enhancing the efficiency of cold-brewed tea production while preserving its sensory qualities (color, aroma, taste). Scanning electron microscopy (SEM) revealed that UACB promoted tea leaf hydration and disrupted the surface morphology, providing more diffusion channels for metabolites. Metabolomics and quantitative analysis confirmed that UACB achieved higher extraction efficiency than cold-brewed, with alcohols, aldehydes, flavonoids, and chlorophylls exhibiting maximum increases of 3.91, 9.89, 1.53, and 1.43 fold, respectively. After 8 min of UACB, the extraction of major taste compounds such as L-theanine (55.46 μg/mL) and EGCG (72.10 μg/mL) was comparable to that after 1 h cold brewing (56.29 and 64.90 μg/mL, respectively). The rapid leaching of these compounds drives swift formation of floral and bean-like aroma, umami-sweetness, and green color of cold-brewed tea. These findings highlight UACB as an efficient method for enhancing cold-brewed tea production efficiency and quality control.