科學高手救命

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首先將香口膠樣本切/剪碎, 放到研砵中加水研磨, 目的是使樣本中的蔗糖溶出.

過濾, 然後到最不尋常的一步: 加鹽酸 (氫氯酸) 到濾液中, 隔水座熱一小時左右. 由於蔗糖不是還原糖, 而本立德溶液沒法測出非還原糖, 故需要加酸加熱, 將蔗糖水解成葡萄糖及果糖 (均是還原糖), 方可繼續測試.

取出你的pH 試紙, 加入碳酸鈉水溶液, 使pH 值提升至7以上 (鹼性). 使用本立德溶液測試還原糖時, 必須有鹼性的環境.

加入本立德溶液, 隔水座熱15分鐘. 原先含有蔗糖 -- 現在變成了還原糖 -- 的溶液, 將會出現磚紅色沉澱物.

無糖香口膠中的代糖, 一般份量很小, 即使有還原性質亦不可能製造與上面一樣的結果.

結論: 製造磚紅色沉澱物的樣本是含糖, 沒有的是無糖.


2010-09-29 00:04:13 補充：
you should've told me! typing english is easier than chinese.

cut the gum samples into small pieces, grind them in water with mortar and pestle. this is to dissolve sample's sugar.

2010-09-29 00:04:29 補充：
filter the mixture and add hydrochloric acid to the filtrate. heat in hot water bath for 1 hour.

2010-09-29 00:04:37 補充：
common sugar is sucrose, which is not reducing sugar and cannot be detected by Benedict's solution. the procedures above hydrolyzes sucrose into glucose and fructose, which are reducing sugars and can be detected in such way.

2010-09-29 00:04:46 補充：
raise the pH of reaction mixture with sodium carbonate solution and pH paper. alkaline medium in essential for benedict's solution to function.

add benedict's solution and heat in hot water bath for 15 min. samples originally containing sucrose would produce red precipitate.

2010-09-29 00:04:58 補充：
sugar-free gums do not contain much reductant, and cannot produce results as above.

thus sample producing red precipitate is sugar-containing; without ppt. is sugar-free.

To determine sugar content, you can prepare a set of standard solutions of sucrose,

2010-09-29 00:05:07 補充：
consists of a series of concentrations of sucrose. Carry same procedures to these solutions, and determine mass of red. ppt. of every samples and standards. With standards, you can make calibration curve, relating amount of sugar and mass of ppt.