Pectin studies. Part I. Method of purification

Abstract

Comparative rests were carried out on the purification of crude pectin esmcts by (a) dialysis, (b) precipitation by alcohol, and (c) ionic exchange. The results showed that dialysis followed by precipitation gave the highest calcium pectate value and complete removal of sugars, free acids and free ash. Ionic exchange gave a pectin of considerably lower residual ash content, but the additional reduction was at the espcnse of the inorganic ions combined with the pectin and is thus of doubtful desirability, except for particular purposes.The present conception of the pectin molecule is of a long chain molecule of galacturonic acid units, esterified to a greater or less extent, and " pectin " emacted from the plant material a n be regarded as a mixture of such chains of various lengths. The definition of a " pure " pectin is thus a relative term and involves such questions as, for example (u) whether or not pectin is chemically inert during extraction ; (6) is it justifiable to speak of pectin as an entity ? (c) do pectins from different species of plants vary? (d) is the pectin from ripe fruit the same as pectin from unripe fruit from the same species, etc.? Consideration of the various studies that have been reported indicates that, in many cases, the results obtained can only be regarded as indicative of the composition of the particular sample under consideration, for the reason that the purity of the material is open to criticism. It is obvious that for a fundamental study the presence of adventitious substances, such as sugars, salt and acids, must be obviated as far as possible and that criteria must be established as to what constitutes " pure " pectin and to recognise the limitations of the interpretation of the analytical results. "Pectin I' is normally determined by hydrolysis to pectic acid, precipitating and weighing the insoluble calcium salt, the procedure employed being the classical method of Card and Haynest or one of the modifications of this method j other methods of deternlination by weighing the precipitate obtained on the addition of alcohol or acetone appear to lack the specific character of the calcium pectate method in relation to pectic substances as defined above. Further characterisation of " pectin " is afforded by the carboy1 groups (which as stated above are esterified to a greater or less extent) ; the total of such groups, when expressed as the equivalent sodium hydroxide, should be theoretically 22.8% of the pectic acid, or 20.5% of the equivalent calcium pectate. Thus reasonable criteria of the purity of a particular " pectin " are the approach of the calcium pectate value* to 10oq/O and the approach of the total carboxyl groups (i.e., the sum of the free acidic groups, those estcrified and those combined with inorganic ions, all expressed in terms of the equivalent sodium hydroxide) to 20.5% of this value. Methods of purification considered(I) Precipifafiorr.-The method normally employed for the separation of " pectin " from a crude extract is to precipitate the pectin from an aqu...

A Structured Approach to Recover Valuable Compounds from Agri-food Side Streams

“…Pectin purification from citrus and fruit extracts (peels and pomace) can be accomplished by solvent precipitation, ion exchange chromatography, and dialysis (Lampitt et al, 1947), among others technologies. Besides bioactive phenolics from apple pomace, Schieber et al (2003) purified pectin by alcohol precipitation of the pectin-containing effluent from the adsorption column where phenolics were captured.…”

Ion Exchange

“…Even though some degradation was apparent in the anion resin, the loss did not indicate the operation to be economically unsound. However, Lampitt, Money, and Judge (69) found the deionization of pectin by ion exchange to be unsatisfactory. The removal of Raney nickel in sorbitol has been achieved with ion exchangers by Porter (102).…”