A Study On Chemical Composition And Solid Extracts Properties Of Rwandan CTC Teas

The tea plant is utilized in one way or another at the domestic or industrial level as either food or health keeping material. Various bioactive compounds, mainly polyphenols, vitamins, minerals and antioxidants are found in varying proportions in the tea plant mainly tea leaves.In this manuscript, we report our research work in three core parts on the approximate analysis of Rwandan green and black tea, the production and the characteristics of solid soluble tea extracts and functionality on the mains bioactive compounds.Green tea and black tea from Rwanda were subjected to a proximate analysis of their chemical composition. Moisture content was in the range of 3-5% which deduces that the total solid content was of 95-97%. The quantity of K, Ca and P were higher compared to other essential minerals also existing in significant amounts in both Rwandan green and black tea where they were 511±8.48μg/g,161±4.24μg/g and 479±38.18μg/g respectively for the black tea and 460±7.07μg/g,185.5±20.51μg/g and 503±8.18μg/g respectively for the green tea. The theanine and other amino acids were found in the green and black, theanine as a unique amino acid to tea was found as 12.189 mg/g in black tea and 11.815 mg/g in green tea; that was the most abundant amino acid in tea. Some essential amino acids were found in non negligible amount which are threonine, valine, methionine phenylanine, isoleusine, leucine, lysine; they were in range of 0-0.3 mg/g. Flavor compounds were found in around 60 different compounds and different from green to black tea due to the change in chemical composition which takes place during the production process of black tea. The total polyphenolic content of Rwandan green and black tea was 174±2.64 mg (GAE)/g and 126±2.44 mg (GAE)/g. using different methods of polyphenols extraction, we found that Green tea extract from microwave assisted extraction (GTMAE) had higher concentration of total tea polyphenols than others;(GTMAE26%>GTD21%>BTMAE16%>BTD14%).The higher the concentration of the total tea polyphenols, the higher was free radical scavenging activity. Antioxidant activity of the teas extracts is expressed by the DPPH radical scavenging with the decreased absorbance in the order: green tea microwave assisted extraction> green tea decoction> black tea microwave assisted extraction> black tea decoction extraction. Consequently, MAE method was found to much more effective than decoction in total polyphenolics content, scavenging capacity, time and energy consumption for both CTC black and green tea. Solid soluble tea extracts were produced using spray dryer and freezer dryer as drying methods. Both methods gave a yield in range of 32-36.5% for freeze dried tea extracts and 31-38% for spray dried ones. Their solubility was in range of 94-97% in both cold and hot water. Their water activity was assessed and was of 0.435 for green tea soluble extract while for the black tea soluble extract was 0.325.In this study, we found that 0.3-0.5 g of solid soluble tea extract were needed to produce a tea liquor of same sensory characteristics as a cup of tea made up using one tea bag from the Lipton tea company.Flavor compounds in solid soluble tea extract were identified in this study, and found more than 60 compounds, phenol,2,6-bis(1,1-dimethylethyl)-4-ethyl-showed the prominent peak in both tea extracts.In this study the RP-HPLC was used to determine the major catechins and caffeine in green and black tea from Rwanda and the solid soluble extracts. The standards of EGCG, EGC, ECG, EC and caffeine were used to quantify the content of those catechins in tea products. We found that the EGCG was much higher in green tea and its solid soluble compared to black teas'. The content in EGCG of the green tea was 209.73 mg/g which is much higher that that found in black tea which was 0.916 mg/g; and was 416.04 mg/g in solid soluble green tea extract and that also was too much higher than that found in black tea solid soluble extracts. This big difference in EGCG content green tea and its products and black tea with its products is due to the oxidation of this EGCG into thearubigins and theaflavins. This oxidation takes place during the process of fermentation of the black tea processing.Caffeine content was found in higher amount in green tea,109.1 mg/g, in solid soluble green tea extract 293.9 mg/g and in solid soluble black tea extract 304 mg/g and found in fewer amounts in black tea 32.12 mg/g.