Effect of combined treatments of ultrasound and high hydrostatic pressure processing on the physicochemical properties, microbial quality and shelf‐life of cold brew tea
Yongcheng Song, Xiufang Bi, Min Zhou, Zhong‐Yu Zhou, Lei Chen, Xiaoqiong Wang, Yuan Ma
Abstract
Summary Effects of ultrasound combined with high hydrostatic pressure (HHP) on physicochemical properties,microorganisms and storage attributes of cold brew tea were investigated. HHP at 400 MPa/5 min/25 °C inactivated the total aerobic bacteria, yeast and mould in cold brewed tea prepared by static brewing (SB‐tea) at 13 h/4 °C, ultrasonic bath (UB‐tea) at 150 W/120 min/0 °C and ultrasonic pulveriser (UP‐tea) at 600 W/40 min/0 °C, ensuring their microbiological safety. The results showed that there was no significant difference in the concentration of tea polyphenols between hot brewed tea prepared by 7 min/100 °C and cold brewed tea under different preparation conditions, while the caffeine in cold brewed tea was significantly lower ( P < 0.05) than that in hot brewed tea. During the storage period of 8 days, compared with the untreated group, the cold brewed tea after HHP treatment had better microbiological safety. In addition, HHP treatment constantly maintained the tea polyphenols, pH, colour, antioxidant capacity and turbidity in cold brewed tea. The untreated and HHP‐treated cold brew tea were evaluated by 20 trained volunteers. Results showed that UB‐tea was more close to SB‐tea than UP‐tea in sensory profile, while HHP seem to maintain a good sensory profile as well. Therefore, this particular combined technology of ultrasonic bath and HHP displayed considerable potential for application in the cold brew tea manufacturing industry.