The Extraction of Pectin from the Fruit Rind of the Lime ( Citrus medica acida )

Abstract

INTRODUCTION. THE extraction of pectin from plant tissues has recently been somewhat extensively investigated. In their work on the pectic substances contained in turnips, strawberries, rhubarb stem and apples, Schryver and Haynies [1916] employed a hot dilute solution of ammonium oxalate to extract pectinogen from the washed and dried material. Subsequently, Farnell [1923], working in conjunction with Schryver, showed that oxalic acid could be substituted for the salt, and indeed, is preferable in so far that it remains in solution when the extracted pectinogen is precipitated by alcohol, whereas ammonium oxalate is strongly adsorbed by the alcohol-gel. Farnell also demonstrated that solutions of ammonium sulphate and of carbonic acid are capable of extracting appreciable amounts of pectinogen from dried turnip, but that water alone is without effect. He suggested that pectinogen is loosely combined with calcium in plant tissues, and is liberated therefrom by any reagent which precipitates the metal. Carre [1922] has, however, shown that dilute hydrochloric acid is an effective extractor of pectinogen, a result which is not concordant with this generalisation. In examining the factors which influence the extraction of pectinogen from the fibre of sugar cane, Farnell (private communication) has employed hydrochloric acid in preference to other reagents, and has demonstrated that the quantity of pectinogen extracted depends (a) on the degree of subdivision of the material, (b) on the length of time of extraction, and (c) on temperature. Maximum extraction was obtained in one to two hours; more prolonged treatment led to diminishing yield. Similarly, greater extraction was obtained at 980 than at 300, but, when the material was extracted with acid in the autoclave at 1200, hydrolysis caused a marked reduction in the amount of pectinogen brought into solution. This last result was not observed, however, when acetic acid and when water were employed. Finally, lime water, of strong alkaline reaction, extracted no pectinogen from the fibre. Evidently the hydrogen ion concentration of the extracting agent is a factor of major importance in deciding the ultimate products of the reaction. 19 13ioh. xvi In order further to test this conclusion, and the more clearly to explain the results of other investigations, the writer has carried out a preliminary study of the behaviour of the pectic substance contained in the white inner rind of the fruit of the lime toward…