Effect of roasting temperatures on degradation of polyphenol contents in Oolong tea = ผลของอุณหภูมิต่อการสลายตัวของสารโพลีฟีนอลในระหว่างการคั่วชาอู่หลง


ประสิทธิ์ สุธรรมวงศ์


วิทยานิพนธ์. (2007) 109 หน้า



Antioxidants in tea are essential substances for health enhancement, however, losses occur during tea processing. This study aimed to investigate the effect of roasting temperature on the degradation of total polyphenols in Oolong tea. The bench scale tea roaster, which was scaled down from a commercial roaster, was designed, constructed and tested before performing the experiment. Roasting temperature was varied by setting the pressure of liquefied petroleum gas (LPG), which was used as energy source for roasting. The roasting temperatures of 74.5, 77.4, 81.5, 81.7, and 83.5 °C corresponded to the LPG pressures of 8, 14, 20, 26 and 32 psig, respectively. It was found that the roasting temperatures and roasting time significantly affected the moisture content and total polyphenols in tea (P≤0.05). The rate of total polyphenols degradation increased when the roasting temperature and time increased. Degradation of total polyphenols during roasting followed the first-order reaction and this degradation conformed to Arrhenius equation The activation energy of the degradation reaction of total polyphenols is 38 kJ/mol. Finally, the relationship between the moisture content and temperature of tea with polyphenol contents during roasting was determined in order to specify the end point of tea roasting. At fixed moisture content, low roasting temperature and long time could better preserve polyphenols in tea