Purification of stevia extract by chitosan precipitation and reversed‐phase chromatography

Summary To improve the shortness of the current purification technology of steviol glycosides (SG) extract, a two‐step purification procedure consisting of chitosan precipitation and reversed‐phase chromatography (RPC) was investigated. The impurity‐to‐SG ratio in the SG extract obtained from non‐destructive soaking was 5:1 ~ 6:1. It was found that 80.90% of the impurities could be removed by RPC using 20% (v/v) ethanol solution as the eluent with a high SG recovery of 96.98%. When 25% ethanol was applied, the SG recovery was reduced to 71.23%. An adsorption test using D280 anionic resin suggested that the impurities were negatively charged; thus, chitosan was used to co‐precipitate the impurities. An optimal decolourisation result of ~ 70% was obtained at 0.06 g·g −1 (w/w, to solids in extract) chitosan addition, shaking at 28 °C for 1 h. Afterwards, the extract was further purified by RPC. The total removal rate of impurities was increased to 91.20%, and the SG recovery was 85.15%.