GB582147A - An improved process for the treatment of plant flesh, and the recovery of pectic products therefrom - Google Patents

Abstract

Pectic products are recovered from the flesh of sisal, sanseviera, phormium tenax, and like vegetable matter which has been separated from fibre, by subjecting it to a pretreatment of leaching with water for some hours at a temperature of 10 DEG C. or for 15 minutes at 80-100 DEG C., preferably with agitation, and then, if necessary, washing with water, separating the flesh and subsequently treating for the extraction of the pectic substances. Sodium hypochlorite can be added to the leaching or washing water to bleach the flesh. The flesh so treated may also be subjected to the action of an acid having a soluble calcium salt, e.g., hydrochloric acid, or hydrochloric acid may be added to the leaching or washing water, to facilitate the extraction of the pectic products. This treatment is carried out for 1/4 -5 hours at room temperature. The flesh, after washing is treated with an aqueous solution of an alkali-metal or ammonium salt having an alkaline reaction and having an anion which gives an insoluble calcium salt and an alkali-metal or ammonium salt of pectic acid which is colloidally soluble in the solution. Sodium carbonate, trisodium phosphate, or sodium metasilicate are examples of salts which may be used, and the extraction may be carried out at normal or elevated temperatures. The alkali -metal pectate sol thus produced is treated by (a) adding alcohol, acetone, or other water-miscible organic solvent or a concentrated solution of sodium chloride, sodium sulphate, or other electrolyte which will not react with the pectate, collecting the gelatinous precipitate, drying, and grinding, sodium hypochlorite solution being added before or during precipitation to improve the whiteness of the precipitate; (b) adding an acid such as hydrochloric acid having a dissociation constant greater than 10-4 to produce a flocculent p precipitate of pectic acid which is dried and ground, and which, if sodium metasilicate were used in the extraction, may contain silicic acid; or (c) adding a dilute solution of a water-soluble metallic salt, e.g., zinc chloride, nickel chloride, silver nitrate or calcium chloride to the alkali-metal pectate sol which has been brought to a pH value of between 6 and 8 by careful addition of an acid such as hydrochloric, nitric, or acetic acid, and from which carbon dioxide, if present, has been removed by boiling or passage of a current of air, and which has been diluted to contain not more than 0.25 per cent, to produce flocculent precipitates insoluble in water, which are dried and ground. If ammonium pectate is required, it can be produced by dissolving the pectic acid in ammonia, or by treatment of the flesh with ammonium phosphate. Alternatively, the flesh is treated with a solution of an alkali-metal salt having an anion which forms a water-soluble complex with calcium, e.g., hexametaphosphate, pyrophosphate or the like whereby pectin, which is separated by salting-out, is produced provided the pH value of the solution is below 7, or the alkali-metal pectate results if the solution is rendered alkaline with sodium hydroxide or the like. Pectin can also be produced by treating the pretreated flesh with any warm or hot aqueous electrolyte, particularly ammonium oxalate, of a pH value of 5 or less, filtering, and salting-out, adding alcohol or the like, or precipitating with aluminium hydroxide. If the flesh has been pretreated with hydrochloric acid, either at the leaching or washing stage, the pectic substances can be extracted by means of alkaline solutions which do not contain anions capable of forming insoluble calcium salts or soluble calcium complexes, e.g., ammonia or alkali-metal hydroxides.