Abstract: Granular shape is a preferable appearance for green tea manufactured by a machine. Uncovering the correlation between the physical characteristics of granular green tea and its appearance quality factors is great significance for the mechanical processing and quality control of green tea. Therefore, in this study, 8 kinds of granular green tea and 1 type of curly green tea were chosen for sensory evaluation, and representative samples were selected for analysis of their color and shape features by computer vision technology, and their physical properties such as bulk density, hundred-grain mass, elasticity and plasticity by graduated cylinder and texture analyzer, respectively. The correlation of the physical parameters with the appearance quality factors were explored by multiple stepwise regression analysis (MSRA). The results showed that ‘Gouqing’ tea had a good appearance quality and uniformity, and its appearance quality score was above 85. Accordingly, it could be considered as a typical representative of granular green tea. As the maturity of the raw material increased, the color parameters red channel value, green channel value, blue channel value, lightness value and saturation value decreased, while Hue value increased, and the color changed from yellow green to dark green. The circular degree and shape index of ‘Gouqing’ tea increased whereas the bulk density decreased. Furthermore, the hundred-grain mass increased up to 33.1 g. Meanwhile, the plasticity was weakened, and thus its ratio to elasticity increased up to 1.5. However, there were different correlations of each physical property with the appearance quality of granular green tea. The results of MSRA showed that the effects of blue channel value, hue value, elasticity, plasticity and circularity on the appearance quality of granular green tea were more obvious than those of the other factors. Hue value and elasticity had negative effects on the shape and color. Blue channel value and circular degree were associated with the uniformity. Therefore, scrutinizing the appearance quality factors of granular green tea and evaluating the dominant factors responsible for individual quality attributes will be helpful to reveal the contribution of each physical property to the appearance quality of granular green tea.

Key words: green tea; granular green tea; appearance quality; physical properties; shape quality; uniformity; color quality