六堡茶茶汤中胶体颗粒及沉淀性状研究

黑茶主要由微生物发酵形成,六堡茶是典型的黑茶之一,发酵对茶汤胶体性质与茶乳酪的成分组成是否有影响,尚未明确。本文通过动态光散射、扫描电子显微镜和高效液相色谱等方法比较了六堡茶毛茶以及发酵后的成品茶茶汤的胶体颗粒性质。结果表明,六堡茶毛茶和成品茶的茶汤均存在丁达尔现象,即存在胶体体系。两种茶汤在冷却过程的浊度变化率逐渐减少,接近常温时,成品茶茶汤浊度增加率小于毛茶；两种茶汤中均存在球形或椭球形的胶体颗粒,且胶粒粒径与Zeta电位具有温度响应。室温下成品茶茶汤的胶体颗粒平均粒径(2131 nm)显著低于毛茶(3045.8 nm),成品茶Zeta电位绝对值(-24.8 mV)高于毛茶(-19.2 mV)。两种茶汤成分差异导致二者沉淀差异,成品茶固形物相对沉淀率(2.22%)少于毛茶(2.79%),成品茶沉淀主要成分为茶红素、茶褐素和多糖,占沉淀94.11%,毛茶则为多酚、蛋白质和多糖,占沉淀75.76%,两种茶汤沉淀中酯型儿茶素总量均高于非酯型儿茶素总量,其酯型儿茶素、蛋白质、多糖和黄酮较易参与沉淀形成。因此,发酵使成品六堡茶的茶汤的胶体颗粒的稳定性增加,使其形成的茶乳酪与发酵前存在明显的差异。本研究为黑茶饮料等食品的开发提供了理论基础。

Properties of colloidal particles and sedimentation in Liupao tea infusion

Dark tea is mainly formed through microbial fermentation, and Liupao tea is one of the typical dark teas. However, it is not clear whether fermentation affects the composition and colloidal properties of tea cream. In this study, we compared the properties of colloidal particles in raw tea and fermented tea infusion using dynamic light scattering, scanning electron microscopy, and high-performance liquid chromatography. The results demonstrated the presence of Tyndall effect and colloidal system in both raw tea and Liupao tea infusions. The rate of turbidity change of Liupao tea and raw tea showed a gradual decrease during the cooling process. As the temperature approached room temperature, the rate of turbidity change of Liupao tea exhibited a smaller increase compared to raw tea. Furthermore, both infusions of Liupao tea and raw tea contained spherical or ellipsoidal colloidal particles, and the particle size and zeta potential of these colloidal particles showed temperature-dependent responses. At room temperature, the average particle size of colloidal particles in Liupao tea infusion (2131 nm) was significantly smaller than that in raw tea infusion (3045.8 nm), and the zeta potential of Liupao tea (-24.8 mV) was higher than that of raw tea (-19.2 mV). The difference in composition between the two tea infusions resulted in variations in sedimentation. The relative sedimentation rate of solid particles in Liupao tea (2.22%) was lower than that in raw tea (2.79%). The main components contributing to sedimentation in Liupao tea were thearubigins, theabrownins, and polysaccharides, accounting for 94.11% of the sedimentation. In contrast, polyphenols, proteins, and polysaccharides accounted for 75.76% of the sedimentation in raw tea. The sedimentation of both tea infusions showed a higher total amount of ester-type catechins compared to non-ester-type catechins. Ester-type catechins, proteins, polysaccharides, and flavonoids were more readily involved in the formation of sedimentation. Therefore, fermentation increases the stability of colloidal particles in the Liupao tea infusion, resulting in significant differences in the tea cream compared to before fermentation. This finding provides a theoretical basis for the development of dark tea beverages and other food products.