Pectic acid, calcium salt

After boiling, the goods are washed with water, and then treated with a dilute solution of hydrochloric acid (1 -5 to 2 per cent). This liberates the fatty acids from the lime soaps and pectic acid from the pectates, with the formation of calcium chloride. The goods are then rinsed to remove the calcium chloride and returned to the kier where they are boiled again with sodium carbonate and rosin or a high-titre soap. The free fatty and pectic acids are now converted into their soluble sodium salts which can be washed away with water. 

The cellular tissue of many fruits contains cellulose associated with other substances of the nature of carbohydrates. Apples, pears, and other fruits contain a substance called pecto-cellulose, which is probably a chemical compound of cellulose and pectin, as it gives cellulose and pectic acid on hydrolysis with an alkali. Pectin, which is a complex carbohydrate present in certain fruits, is converted into pectic acid when heated with a solution of an alkali. The formation of jellies from fruits is brought about as the result of the hydrolysis of the pectin which they contain. The hydrolysis converts pectin into pectic acid, which forms calcium pectate with the calcium salts always... 

The edible salts of calcium and magnesium do not precipitate pectins until the degree of esterification of the pectin molecule has been reduced below 8.2% methoxyl content on the basis of 100% calcium pectate (10, 17). In 1935 a patent (16) was granted on the use of soluble salts of alkaline earth metals, such as calcium chloride, to precipitate pectic substances which had received a partial de-esterification treatment. Olsen and Stuewer obtained a patent (IS) on a digestion-extraction procedure, termed pickling and carried out at less than 50 C. below pH 1 for a period sufficient to produce pectin precipitable by calcium salts at pH 4. The metal-free pectinic acids can be isolated from either the aluminum or calcium salts by treatment with acidified alcohol in accordance with methods well known for years. 

A series of O-acetyl derivatives of pectic acid has been prepared to study the intramolecular binding of Ca + ions to pectic acids. The electrostatic free enthalpy of dissociation of these polyacids and the rate of exchange of the counter-ion from Ca + to K+ were determined by potentiometric titration measurements. The binding of Ca + ions was characterized by the production of single ion affinity coefficients determined in solutions of the calcium salts of 0-acetyl pectic acids and by the circular dichroism measurements of calcium and potassium salts of the pectate derivatives. The intramolecular binding of Ca + ions to isolated pectate macromolecules is purely of electrostatic character in contrast to the intermolecular chelate binding of Ca + ions which takes place when the pectate macromolecules aggregate. 

A typical pectin, such as that found in beetroot, yields (i) a polysaccharide, araban, and (ii) a complex acid, pectic acid, which is present as a calcium magnesium salt in the original pectin, and causes the gel formation. 

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