DNS法测定茶叶中掺杂蔗糖含量

Study on the DNS method for measuring the content of doped sucrose in tea

建立了茶叶中蔗糖的测定方法,茶叶经热水浸泡后,亚铁氰化钾和乙酸锌沉淀除蛋白质等干扰物,盐酸水解,经3,5-二硝基水杨酸(DNS)显色,分光光度计比色测定。结果表明,取5 g左右茶叶,加入50 mL的去离子水,置于45℃水浴锅中,振荡浸提1 h,取茶汤,3000 r/min离心3 min,过滤茶汤,定容至100 mL,DNS法分别测总糖和还原糖,能实现茶叶中蔗糖的定量检测。在5 g茶叶中,分别添加10和50 mg蔗糖,回收率分别为117.60%和91.22%,取5份相同茶叶样品测得相对标准偏差为2.47%,方法检出限为2 mg/g。在20份茶叶样品检测中,可以明显区分人工添加蔗糖与正常茶叶样品。该方法灵敏度和重现性好,操作要求不高,有实际应用价值。

A method for the determination of sucrose in tea was established.The tea was soaked in hot water,potassium ferrocyanide and zinc acetate were precipitated to remove interferences such as protein,hydrolyzed by hydrochioric acid,developed by 3,5-dinitrosalicylic acid(DNS),and compared with spectrophotometer color determination.The results show that,take about 5 g of tea leaves,add 50 mL of tertiary water,place in a 45℃water bath,shake and extract for 1 hour,take the tea soup,centrifuge at 3000 r/min for 3 minutes,filter the tea soup,dilute the volume to 100 mL,measure the total sugar and reducing sugar by DNS method,and calculate the sucrose content by the minusing.In 5 g of tea,when 10 mg and 50 mg of sucrose were added,the recoveries were 117.60%and 91.22%,respectively.The relative standard deviation of 5 samples of the same tea was 2.47%,and the detection limit of the method was less than 2 mg/g.In the test of 20 tea samples,the artificially added sucrose can be clearly distinguished from normal tea samples.The method has good sensitivity and reproducibility,low operation requirements,and practical application value.