應用Pectinesterase之脫甲基作用測定果膠中甲氧基含量之新法

A New Method for Estimation of the Methoxyl Content of Pectin by Demthylation of Pectinesterase

因pectinesterase（PE）對果膠中甲脂基（-COOCH3）水解之特殊性甚高，故以酵素作用法可迅速地測出柑桔果膠中之甲氧基（-OCH3）量。皂化法與酵素法之測定值甚為符合，惟前者需時3小時而後者僅費8~10min則可。酵素作用法如下：以B.T.B.（bromothymol blue）為指示劑，酵素液及試料果膠液均予先中和至pH7.0。對於作用液加入0.6~0.8%之食體，在40℃恒溫下連續攪拌令其作用，並不斷加入0.05N苛性鈉以保持作用液之pH為7.5。至已無作用達2min以上時，補充0.05N苛性鈉溶液少許藉以調節作用液呈Ph8.2之深藍色為止。試料液中之甲氧基量可由酵素作用而產生之酸量中和所需之0.05N苛性鈉a ml換算如下式：OCH3 mg=a×1.55 mg。

Since the action of pectinesterase (PE) is highly specific, the methoxyl content of pectin solution can be determined by the enzymatic method of present paper. The estimated value by this enzymatic method for citrus pectin solution is very coincide with that of the saponification method. Although the saponification method would need three hours but we expended only 8-40 minutes with the enzymatic method. The procedure is described as follows: Use bromothymol blue as indicator, neutralize each of the emzyme solution and the sample pectin solution to pH 70. Add about 0.6~0.8% of sodium chloride into the digest, keep at 40℃ and continuously stirred. Then a 0.05 N NaOH solution is successively added in order to maintain the pH of the digest at 7.5. After the action is ceased f or more than two minutes, adjust the digest to the deep blue colour of pH 8.2 by adding few drops of 0.05 N NaOH solution. The amount of methoxyl in the sample pectin solution may be calculated from total amount of 0.05N NaOH solution, a ml, as follow; OCH3 mg=a×1.55 mg.