We examined the change in the content of pectic substances in tea leaves during the steaming of green tea. In four cultivars of tea leaves, water-soluble pectin (WSP) content increased with steaming time, whereas the dilute hydrochloric acid soluble pectin (HSP) content remained almost constant. A β-elimination reaction proceeds throughout the steaming process, so it was postulated that some water-insoluble forms of pectin in HSP convert to a water-soluble form via β-elimination degradation with increasing steaming time. When tea leaves were steamed, pectin fractions with a molecular weight of 1,100 × 10 3 were degraded from water-insoluble HSP and eluted as WSP.Additionally, as steaming time increased, the fraction of smaller molecular weight pectin increased.Keywords: pectic substances, green tea, steaming process IntroductionIt has been elucidated that the bitter or astringent taste of catechins and the umami taste of amino acids such as theanine are important factors in the taste of green tea (Nakagawa et al., 1981).The taste of green tea changes depending not only on the conditions used to brew the tea, but also on how the tea leaves are processed.When raw tea leaves are processed differently, the tea products differ in quality. As an example, fukamushi tea steamed for a longer time tastes less astringent than asamushi tea steamed for a shorter time. The amounts of several components, such as catechins and amino acids, have typically been considered to be indices of the quality of the tea. However, the amounts of these components do not change during the course of tea processing (Takayanagi and Anan, 1986). In contrast, the amount of water-soluble pectin (WSP) increases during the steaming process with increased steaming time (Takayanagi et al., 1987). It was therefore assumed that the increase in WSP masked the astringent taste of catechins, as fukamushi tea tastes less astringent (Horie and Kohata, 1999 et al., 1960). In this paper, we examined the change in the content of pectic substances in tea leaves during the steaming process by varying cultivars, harvesting time, and maturity of the tea leaves. Additionally, we investigated the extent of b-elimination degradation and the molecular weight distribution of WSP during the steaming process. from the first crop season were also plucked by their degree of maturity: younger, optimum, and over-matured. On average, the interval between these three levels of maturity was 2 days. About 100 g of plucked tea leaves (raw leaves) were immediately frozen and the rest were steamed. About 100 g of tea leaves were steamed for 30, 60, 120, and 300 s for the 'Yabukita' cultivar, and for 60 and 300 s for the other three cultivars. The steamed leaves were then frozen. All frozen tea leaves were lyophilized and powdered using a cyclone sample mill. was stirred and heated in a boiling water bath for 10 min. After cooling to room temperature, the optical density was measured at 548 nm in a spectrophotometer. Materials and Methods Preparation of tea leaves Preparation of al...
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 ...
We examined changes in water-soluble pectin (WSP) and dilute hydrochloric acid soluble pectin (HSP) contents of tea leaves, and pectin content of tea infusions in the roasting process during refined tea manufacturing by crop season. In all crop seasons, WSP content in tea leaves increased with roasting temperature. HSP content was almost constant or increased with roasting temperature by crop season. Changes in pectin content of tea infusions by roasting temperature were proportional to or lagged slightly behind WSP content changes of tea leaves in all crop seasons. In all crop seasons, the molecular weight (MW) distribution of both WSP in tea leaves and pectin in tea infusions was biased toward the lower-MW range with increasing roasting temperature. In parallel, major peaks in the MW distribution of pectin in tea infusions shifted to the lower-MW range in all crop seasons. It was postulated that β-elimination degradation was involved in WSP production from water-insoluble forms of pectin in HSP and the degradation of WSP itself during the roasting process.
The effect of irradiation by black light fluorescent lamp on the coloration and hardness of detached strawberry fruits was studied. Only the coloring of fruits (var. Toyonoka) that had started to pigment was accelerated by lamp irradiation. Maintaining the irradiation distance and ambient temperature after treatment was very important to obtain the maximum effect, and the action of lamps was restricted to the irradiated parts. The accelerating effect of a lamp on coloration was observed in all 3 of other varieties examined, and in some varieties, the level of anthocyanin concentration in fruits was greater than that in ripening stage. However, the lamp did not affect the hardness of fruits.
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