Analysis of Sweetness Components by Harvest Times and Extract Methods in Stevia

The leaves of Stevia rebaudiana Bertoni have attracted much attention as a source of natural sweeteners. This study was conducted to investigate the natural sweeteners contents and analyze antioxidant materials and activity according to harvest times and extraction methods in stevia. Stevia leaves were extracted using 5 extraction methods to identify the extraction with high extraction efficiency. Extraction yield was high in the order of hot water extraction (HWE), reflux extraction (RE), high temperature and pressure extraction (HTPE), ultrasonic extraction (UE) and vacuum extraction (VE). The contents of rebaudioside A and stevioside in stevia leaves had the highest in HTPE. Also, the total phenolic and flavonoid contents had the highest in HTPE and VE. Using the HTPE method, the result analyzed that the contents of rebaudioside A and stevioside of stevia leaves harvested between April and October exhibited the tendency to increase gradually between July and October. HTPE is considered to be an appropriate method for extracting stevia leaves. Also, it was confirmed that the stevia leaves of July, September and October, except for the high temperature period of August, had superior in quality and quantity.