Dynamics of Water-soluble Pectin during Unrefined Tea Processing: Content and Molecular Weight Distribution

Abstract

We examined the dynamics of water-soluble pectin (WSP), specifically the content and molecular weight distribution, in tea leaves and tea infusions in relation to steaming time during unrefined tea processing. It was revealed that the fraction of higher-molecular weight (MW) WSP in tea leaves was infused at the beginning of unrefined tea processing at all steaming times, and lower-MW WSP was not infused during any processing steps.Moreover, by increasing steaming time, the increase of higher-MW WSP content in tea leaves was reflected by the increase in WSP content of corresponding size in the tea infusions.Keywords: water-soluble pectin, molecular weight, unrefined tea processing, steaming time IntroductionWater-soluble pectin (WSP) is contained in tea leaves at less than 1.5% (dry weight) (Takayanagi et al., 1987a;Matsuo et al., 2012;Hirono and Uesugi, 2014). It has been shown that the WSP content in both tea leaves and tea infusions alters significantly with steaming time, in contrast to catechins, caffeine and amino acids, the main components of tea (Takayanagi et al., 1987a, b;Matsuo et al., 2012).We recently clarified that when tea leaves were steamed, pectin fractions with a molecular weight (MW) of 1,100 × 10 3 were degraded from water-insoluble pectin and eluted as WSP, resulting in increased WSP content of the steamed tea leaves. Additionally, the longer the steaming time, the greater the degradation of WSP (Hirono and Uesugi, 2014).Green teas are popular beverages that are composed of the infusions of refined tea leaves. Unrefined teas, which possess the fundamental quality of teas and are the base of refined teas, are typically manufactured using drying and rolling processes after the initial steaming process. Therefore, it was necessary to reveal the transition of WSP during the unrefined tea manufacturing processes and the leachability of WSP in tea infusions in order to clarify the properties of WSP in unrefined teas. In this paper, we investigated the dynamics of WSP in both tea leaves and tea infusions, in terms of content and molecular weight distribution, in relation to the duration of unrefined tea steam processing. 60 or 120 seconds using a SD-500 steaming machine (Terada Seisakusho Co., Ltd., Shimada, Japan), and then manufactured into unrefined teas. After the initial steaming process, unrefined tea processing proceeded sequentially from primary drying, tea rolling, secondary drying, to the final rolling; which were all conducted using tea manufacturing machines specified for 2 kg of production (Kawasaki Kiko Co., Ltd., Kakegawa, Japan). For analysis, a small amount of tea leaves from each step in the process was removed and dried to about 5% moisture content using a circulation dryer at 40℃. Manufacturing of each unrefined tea according to steaming H. Hirono 298 time was performed in triplicate. Materials and Methods Preparation of tea leaves Determination of WSP content in tea leaves Dried tea leaveswere powdered using a ZM200 cyclone sample mill (Retsch GmbH, Haan, Germany). Preparation ...

Dynamics of Water-soluble Pectin in the Roasting Process during Green Tea Manufacturing

“…Unroasted and roasted tea leaves were powdered using a ZM200 cyclone sample mill (Retsch GmbH, Haan, Germany). Preparation of Alcohol-Insoluble Substances (AIS), WSP and HSP extraction from AIS, and determination of WSP and HSP contents by the colorimetric method were conducted using the 3,5-dimethylphenol method as described previously (Hirono and Uesugi, 2014;Hirono 2016). The extraction method is briefly described as follows: AIS was prepared by washing powdered tea leaves using 70% ethanol until the remaining free sugars were below 20 μg/mL of D-glucose.…”

“…During unrefined tea manufacturing processes, it has been observed that the water-soluble pectin (WSP) content in tea leaves increases during the steaming process, which is in the initial stages of tea processing, via non-enzymatic β-elimination degradation, and steaming time proportionally influences the increase of WSP content in tea leaves and pectin content in tea infusions (Takayanagi et al, 1987a;Takayanagi et al, 1987b;Matsuo et al, 2012;Hirono and Uesugi, 2014;Hirono, 2016). During green tea manufacturing, pectin might be degraded by heating during the roasting process in refined tea manufacturing as is degraded during the steaming process in unrefined tea manufacturing.…”