Microwave radiation is one of the main heating methods for food processing, especially affecting the color quality of colorful foods. This work presents the effect of microwave radiation on the green color loss of green tea powder (GTP) by the color description (L*, a*, b*, and Ha of green tea powder, L*:whiteness/darkness, a*: redness/greenness, and b*: yellowness/blueness; Ha derived from Hunter a and b could visually describe the color space) of the Hunter color system. First, the L*, a*, and b* were determined from the GTP samples treated with various microwave powers with the change of time to investigate the kinetic of color loss. Then, the L*, a*, and b*and temperature of GTP samples with serious thickness treated with constant microwave power (700 W) for a different time were determined to study the effect of sample thickness on the color loss. Finally, the chemicals that contributed to color change in the GTP samples treated with mild, moderate, and severe radiation were analyzed. The results showed that L*, |a*| (|a*|was the absolute value of a*), b*, and Ha decreased with the power increase in microwave radiation, and their changes conformed to the first-order kinetics. The activation energies (Ea) of different thickness GTP for change of L*, a*, b*, and Ha values could be predicted with the fitting models, and Ea for 20 mm-thick GTP were approximately 1/5, 1/8, 1/8, and 1/13 of those for 4 mm-thick GTP. The color loss was mainly caused by the Mg2+ loss of chlorophylls and the formation of derivates under mild radiation, the degradation of chlorophylls and the formation of theaflavin from catechins under moderate radiation, and the degradation of chlorophylls and their derivates accompanied by Maillard reaction between reducing sugar and amino acids under severe radiation. The results indicate that sample thickness and radiation time are two key parameters to keeping the color of GTP in food processing and microwave pasteurization.
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机译：微波辐射是食品加工的主要加热方法之一，尤其影响五颜六色食品的色泽质量。本研究通过绿茶粉的颜色描述 （L*、a*、b* 和 Ha，L*：白/暗，a*：红/绿，b*：黄/蓝;从 Hunter a 和 b 派生的 Ha 可以直观地描述 Hunter 颜色系统的色彩空间）。首先，从用各种微波功率处理的 GTP 样品中测定 L*、a* 和 b*，并随时间变化研究颜色损失的动力学。然后，测定恒定微波功率 （700 W） 处理严重厚度的 GTP 样品在不同时间的 L*、a* 和 b* 和温度，以研究样品厚度对颜色损失的影响。最后，分析了导致轻度、中度和重度辐射处理的 GTP 样品颜色变化的化学物质。结果显示 L*， |a*|（|a*|是 a*）、b* 和 Ha 的绝对值随着微波辐射功率的增加而减小，它们的变化符合一阶动力学。用拟合模型可以预测不同厚度 GTP 对 L*、a*、b* 和 Ha 值变化的活化能 （Ea），其中 20 mm 厚 GTP 的 Ea 约为 4 mm 厚 GTP 的 1/5、1/8、1/8 和 1/13。颜色损失主要由轻度辐射下叶绿素的Mg2+损失和衍生物的形成引起，中度辐射下儿茶素降解和茶黄素形成，重度辐射下叶绿素及其衍生物的降解伴有还原糖与氨基酸之间的美拉德反应。结果表明，样品厚度和辐射时间是食品加工和微波巴氏杀菌中保持 GTP 颜色的两个关键参数。
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