Chagyo Kenkyu Hokoku (Tea Research Journal)
Online ISSN : 1883-941X
Print ISSN : 0366-6190
ISSN-L : 0366-6190
Current issue
Displaying 1-5 of 5 articles from this issue
President's Message
Original Articles
  • Atsushi Takahashi, Kenta Nakajima
    2020 Volume 2020 Issue 129 Pages 3-10
    Published: June 30, 2020
    Released on J-STAGE: July 01, 2022
    JOURNAL FREE ACCESS

    Bark split frost injury caused by subfreezing temperatures in early winter results in enormous damage to young tea plants. To determine the specific conditions that lead to this, we investigated the effects of subfreezing temperatures and soil moisture on the occurrence of bark split through laboratory experiments and field observations. In artificial subfreezing temperature treatments, bark splits occurred more often when the temperature was lower, the number of treatments was greater, and the soil moisture content was higher. Winter temperatures and soil moisture environment of a tea field that had serious bark split frost injury were consistent with the laboratory results. These results show that the degree and frequency of subfreezing temperature and high soil moisture content are key factors in predicting bark split frost injury in tea plants.

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  • Akinori Kozaki, Akihiro Yamamoto, Yuichi Saeki
    2020 Volume 2020 Issue 129 Pages 11-18
    Published: June 30, 2020
    Released on J-STAGE: July 01, 2022
    JOURNAL FREE ACCESS

    A total of 119 sencha products, which is a kind of green tea, were classified into three grades namely: High, Medium, and Low, at a tea quality competition done at Kansai area in 2015. We collected 10 samples from each grade (High, Medium, Low) based on the ranking of the examination results. The tea leaves were used for extraction and determination of amino acids, catechins, theogallin, gallic acid, and caffeine. The contents of theanine, glutamic acid and arginine were significantly higher in High grades than the other grades. The contents of epicatechin gallate was significantly higher in High grades, and epigallocatechin gallate tended to increase from lower grade to higher grade. In addition, the theogallin content was significantly higher in High and Medium grades than those in Low grade. These compounds were also considered to be important compounds for the quality of tea by the principal component analysis.

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  • Akinori Kozaki, Akihiro Yamamoto, Yuichi Saeki
    2020 Volume 2020 Issue 129 Pages 19-26
    Published: June 30, 2020
    Released on J-STAGE: July 01, 2022
    JOURNAL FREE ACCESS

    We analyzed the inorganic elements of the three grades of green tea (High, Medium, Low) at the Kansai green tea competition in 2015 to clarify the relationship between the sencha evaluation in the competition and the inorganic components. The content of nitrogen was significantly higher in High and Medium grades than that in Low grade. In the trace elements, zinc content was also significantly higher in High and Medium grades than that in Low grade. In addition, the contents of nitrogen and zinc were highly involved in the components of appearance, aroma, liquid color, and taste, which are the evaluation items of the green tea competition. Also, the contents of nitrogen and zinc were considered to be important components for the sencha evaluation by the principal component analysis. A positive correlation (r = 0.793) was observed between the content of nitrogen and zinc for the High- and Low-grade tea leaves. These results suggested that the sencha evaluation might be associated not only with the contents of theanine and nitrogen but also with content of the trace element, zinc in green tea leaves.

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Short Communication
  • Ayuko Kameyama
    2020 Volume 2020 Issue 129 Pages 27-31
    Published: June 30, 2020
    Released on J-STAGE: July 01, 2022
    JOURNAL FREE ACCESS

    In this study tea yields were estimated using vegetation indices such as the normalized difference vegetation index (NDVI). These calculations were made from the aerial image data of tea fields taken by a multirotor unmanned aerial vehicle (UAV,drone) equipped with a multispectral camera. There was a high correlation between NDVI and the yield of tea during the growing period of first flush (R2=0.61-0.97). Another vegetation index, green NDVI, showed a varying correlation depending on observation conditions such as the test day and location of the field (R2=0.002-0.91), while normalized difference red edge index (NDRE) showed a high correlation (R2=0.65-0.99). The root mean squared error of the tea yield obtained using both NDVI and NDRE was as small as 40kg/10a or less. These results suggest that the vegetation indices NDVI and NDRE obtained by the aerial image data can be used to estimate the tea yield. Since regression lines between yield and vegetation index were different for each survey, the correction under different observation conditions with additional explanatory variables such as the accumulated temperature is a subject for future research.

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