The Effects of Different Potassium and Nitrogen Levels on the Growth and Production of Steviol Glycoside of Stevia Rebaudiana Bertoni

Choo, Jia Min (2020) The Effects of Different Potassium and Nitrogen Levels on the Growth and Production of Steviol Glycoside of Stevia Rebaudiana Bertoni. Final Year Project (Bachelor), Tunku Abdul Rahman University College.

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Abstract

Stevia rebaudiana Bertoni is a native perennial shrub of Paraguay belonging to the Asteraceae (Compositae) family. Traditionally used for its therapeutic and sweetening properties, the demand of S. rebaudiana Bertoni has increased in the agricultural and food industry as a high potency sweetener. The sweet constituents are due to the presence of diterpene glycosides. These metabolites are 100 to 300 sweeter than sucrose. The increasing popularity for a plant-based, zero-calorie sweetener among consumers has driven the focus on the growth and improvement on the stevia plant and the different steviol glycosides. Currently, reports on hydroponic-grown Stevia and the effect of macronutrient manipulations are limited. The aim of this project is to study the effect of different potassium (K) and nitrogen (N) levels on the growth and production of steviol glycosides of S. rebaudiana Bertoni using hydroponic system. The project was carried out in randomized block design of a 2x4 factorial arrangement. Four concentrations of potassium and nitrogen (25%, 50%, 75% and 100%) were applied to cocopeat-filled bags with four replications. S. rebaudiana Bertoni were harvested after 45 days of transplanting. Growth parameters such as total chlorophyll content, leaves area, height and number of leaves were measured subsequently. Soxhlet extraction of stevioside and rebaudioside A was done. The leaf extracts were analyzed with HPLC using a C18 column and UV detector set at 200 nm. The mobile phase consisted of 80:20 (v/v) mixture of acetonitrile and water with 0.1% formic acid, set to a flow rate of 1.0 mL/min. From this study, it was found that 75% of K gave the highest number of leaves (167 ± 32.01), height (60 cm ± 9.95) and extraction yield (38.5%). The lowest level of K (25%) p roduced the highest concentration of rebaudioside A, which is 13315 mg/kg. In the N treatments, 75% of N gave better effect on growth parameters as the number of leaves (325 ± 63.73) and leaves area (4.4 cm 2 ± 1.55) were the highest among the four concentrations. Similarly, 25% of N was found to produce the highest concentration of rebaudioside A (34830 mg/kg ±7517.11).