Chemical qualities and phenolic compounds of Assam tea after soil drench application of selenium and aluminium

Tea is considered native to south China and is currently cultivated in many countries, including Thailand, which has been growing increasingly large amounts of Assam tea in the Northern provinces. Although Assam tea contains greater phenolic contents, the flavor is claimed to have an astringent taste due to tannin content. The aims of this study were to improve the chemical qualities, phenolics, and catechins contents on Assam tea grown in a controlled environment of hydroponic subjected with Se and Al. Our results showed that Se and Al enhanced the chemical qualities and phenolics of Assam tea. This characteristic gives an added value to Assam tea, which might stimulate its production for exporting both fresh and dried tea leaf products manufactured in Thailand while simultaneously minimizing importing of tea from abroad. Assam tea has been grown increasingly in the Northern provinces of Thailand. Although Assam tea contains a greater phenolic content, its flavor is claimed to have an astringent taste due to tannin content. The aim of this study was to investigate the effect of two beneficial elements; selenium (Se) and aluminium (Al), on the improvement of chemical qualities and phenolics contents of Assam tea. Soil drench application of sodium selenite and aluminium sulphate at concentrations of 0, 50, and 500 ppm were applied to pots with 3-year-old Assam tea plants. Tea leaves were harvested at 30, 60, 90 and 120 days after the Se and Al treatments. Our results revealed that Se and Al promoted the ascorbic acid, chlorophylls, carotenoids, total phenolics and proline contents of tea leaves. The highest chemical quality and the highest phenolic content were found in tea leaves receiving 50 ppm of Se. The highest catechins derivatives, namely, (+)-gallocatechin (GC), (-)-epigallocatechingallate (EGCG), (+)-gallocatechingallate (GCG), (-)-epicatechingallate (ECG) and (+)-catechingallate (CG) in tea plants treated with Al were greater than in tea plants treated with Se. The total phenolic content increased with the increment in total chlorophyll, catechins and its derivatives.