酶催化糖基转移反应在改善罗汉果苦味皂苷口味中的应用

Improve the taste of bitter mogroside by enzymatic glycosylation method

罗汉果皂苷Ⅱ是罗汉果嫩果的主要皂苷成分,味道极苦,在罗汉果生产季节的末期大量滞长果（苦果）因为天气原因而产生,这些滞长果因体内的苦味皂苷尚未转化为甜味皂苷而被丢弃;另外,在罗汉果甜苷提取行业中,脱苦工艺同样会产生大量的苦味罗汉果皂苷Ⅱ。但在化学结构上,罗汉果苦味皂苷与甜味皂苷拥有完全相同的苷元部分,仅存在葡萄糖残基数目和位置的差别。该研究通过酶催化糖基转移反应将新的葡萄糖基团引入苦味的罗汉果皂苷Ⅱ中,可以延长其糖链,从而达到改善其口味的目的。该研究从原料选择、糖源选择以及反应温度等多方面考察了反应条件,最终确定的反应最佳条件为纯度在50%以上的罗汉果皂苷Ⅱ、2倍于皂苷重量的淀粉、60 U·g-1罗汉果苦味皂苷的酶、60~65℃反应24 h。经实际罗汉果苦果样品验证了方法的可行性,所获得的产品可以完全消除苦味,并且带有淡淡的甜味,经HPLC-MS确定了所获得的微甜产物为3~6个糖的皂苷混合物。该方法对于目前罗汉果生产中大量出现并被遗弃的嫩果、苦果以及脱苦工艺中产生的罗汉果皂苷Ⅱ而言,是一种潜在的实现废物利用的方法。

Mogroside Ⅱ is a bitter mogroside and the main saponin component of unripe Siraitia grosvenorii（ Luohanguo）fruit. Due to the existence of bitter mogroside,there are numerous bitter fruits（ growth arrest） which are discarded on the branches in the late harvest season. The only difference between bitter and sweet mogrosides on the molecular structure is the number of glucose groups. Therefore,it can be achieved the purpose of improving the taste of bitter mogroside by introducing new glucose residues on its chemical structure. In this paper,glycosyltransferase enzyme-catalyzed reaction was applied to extend the sugar chains of bitter mogroside Ⅱ. The optimum reaction conditions were determined to be more than 50% purity mogroside Ⅱ,2 times of starch in weight,60 U·g-1enzyme according to mogroside Ⅱ in weight,60- 65 ℃ reaction temperature,and 24 hours reaction time. Based on above reation condtions,bitter S. grosvenorii fruits were collected and used to confirm feasibility of this method. The resulted producd was no longer bitter but slightly sweet,By HPLC-MS detection,the components of the final mixture were determined to be saponins containing 3- 6 sugars. This method can improve the taste of mogroside Ⅱ,and it is a potential approach to utilize resources of abandoned mogroside Ⅱ in industrial production and bitter S. grosvenorii fruit in agriculture.