Effects of Nitrogen Fertilizer Rates and Seasons on Polyphenols and Catechins of Non-aerated Green Tea Processed from Seedling Tea (Camellia sinensis)

Abstract

Seasonal biochemical profiling was performed on non-aerated green tea processed from high nitrogenous fertilizer rates (0-800 kg N/ha/year) trial on seedling tea to determine the effects of fertilizer rates and seasons on total polyphenols, catechins and caffeine levels. Increasing fertilizer rates significantly, (p less than 0.05) increased total polyphenols and catechins levels up to 400 kg N/ha/ year rate. There was no increase in the polyphenolic compounds beyond this rate. Although some non-aerated green tea producing countries apply very high rates, of up to 800 kg N/ha/year, to improve quality, in Kenyan seedling tea, there were no green tea quality benefits from applying higher rates beyond 400 kg N/ha/year. Polyphenols levels ranged from 21.19-21.85% while catechins ranged catechin form 16.01-17.31% between 0-800 kg N/ha/year application rates. There were seasonal biochemical variations. Polyphenols levels ranged from 22.91-23.37% during October-December, 21.17-21.18% in January-March, 16.47-16.48% in April-June and 20.38- 20.52% in July–September. Catechins values were 17.32-16.05%, 17.66-17.23%, 14.91-15.73% and 17.39-17.59%, while caffeine values were 3.02-3.20%, 3.43-3.25%, 3.88-3.94%, and 2.70- 2.78% in the respective seasons. Total polyphenols were higher during the cold and wet (October- December) and hot and wet (April-June) seasons and low in cold and dry (July September) and hot and dry (January-March) seasons. Irrespective of the temperatures, wet months produced higher levels of the parameters evaluated.