Abstract: The effect of chitosan flocculation on clarifying water extract from Stevia rebaudiana Bertoni leaves, prepared by twice repeated water extraction at a solid/liquid ratio of 1:10 (g/mL) followed by pooling and then rotary evaporation concentration of two extracts, was studied. Clarification rate and stevioside loss rate were investigated with respect to different factors. Using orthogonal array design method, the optimal process conditions for chitosan flocculation were determined as follows: ratio between 1% acetic acid solution of chitosan and dried Stevia rebaudiana Bertoni leaves 2:1 (mL/g), 1-fold concentration of pooled extracts from Stevia rebaudiana Bertoni leaves, pH 6.0, flocculation temperature 45 ℃, and flocculation time 4 h. Under these conditions, a clarification rate of 86.63% and a stevioside loss rate of 6.89% were achieved. Chitosan flocculation without the need for special equipment had similar effectiveness to that of membrane separation in clarifying water extract from Stevia rebaudiana Bertoni leaves. Compared with the conventional chemical flocculation, chitosan flocculation could more effectively retain effective ingredients in the water extract and had the advantages of effective flocculation, ready biodegradation, environmental safety and non-secondary contamination.

Key words: Stevia rebaudiana Bertoni, stevioside, chitosan, flocculation, clarification