Effect of different harvesting times on quality of jatropha zeyheri indigenous tea

Abstract

Tea is globally regarded as the second most consumed in the world after water. It is associated with various health benefits such as anti-cancer, anti-inflammation, anti-obesity and reduction in cholesterol blood levels. Jatropha zeyheri indigenous tea has medicinal and nutritional properties, therefore knowledge of its chemical compositions is essential for increasing its quality. This indigenous tea is currently harvested in rural areas when the leaves are already dry, which is in contrary to what is practised in most tea industries. Therefore, the determination of harvesting time has an opportunity to contribute towards increasing the quality of J. zeyheri indigenous tea. The study investigated whether harvesting times has an effect on essential and non-essential mineral elements and phytochemicals and antioxidant activity of J. zeyheri leaves. The study materials were collected in the wild at Khureng village, Lepelle-Nkumpi Municipality, Limpopo Province, South Africa. Five treatments constituting of harvesting times (February, March, April, May and June) were arranged in a randomised complete block design, with 10 replications. Leaves were harvested, oven-dried at 60°C for 24 hrs and pulverised. A microwave digestion system (PerkinElmer, Titan MPS, United States) was used to prepare the samples prior analysis. After the preparations, mineral elements were determined using Inductively Coupled Plasma Emission Spectrometer-9000 (Shimadzu, Japan). The 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging activity assay was used to quantify the antioxidant activity of the acetone extracts of plants. The total phenol and tannin contents in each plant extract were determined using the Folin-Ciocalteu assay method. The total flavonoid contents were determined using the Aluminium Chloride colorimetric assay. The absorbance for antioxidant activity and phytochemicals were recorded using UV/visible spectrophotometer (Beckman Coulter-DU730, USA). Harvesting times had highly significant effects on Cr, Fe, K, Mg, Ni, P and S contributing 58, 65, 73, 62, 55, 67 and 69%, respectively, in total treatment variation, but were significant on Ca, Cu, Mn, Al, Co and Na contributing 62, 58, 66, 53 and 57%, respectively, in total treatment variation (TTV). However, harvesting times did not influence Zn and Si amounts in J. zeyheri leaves. Harvesting times increased majority of essential and non-essential mineral elements, except for K which was gradually decreased. Essential and non-essential mineral elements over different harvesting times exhibited positive quadratic relations. Using the optimisation equation (x = –b1/2b2) from the quadratic equation, harvesting of J. zeyheri was optimised at 2.46 months. Harvesting times had highly significant effects on the antioxidant activity, total phenol and flavonoid contents contributing 62, 88 and 60% in total treatment variation, respectively, but was not significant on total tannin contents. The negative quadratic relationship models explained 51, 90 and 95% of the observed variation in antioxidant activity, total phenol and flavonoid contents, respectively. In conclusion, findings of this study suggested that harvesting of J. zeyheri leaves be done between April-May for improved accumulation of mineral elements, whereas, for phytochemicals and antioxidant activity the results suggested that further studies be conducted from early summer until winter to find the optimum harvesting time of J. zeyheri indigenous tea.