A quantitative gel-filtration method for analysis of the proteinaceous fraction of Cheddar cheese

Abstract

SummaryMethods are described for the solubilization of the nitrogenous portion of cheese in a dissociating solvent system and separation of the solution into fractions on a Sephadex G-100 column under conditions where the proteins and peptides would be expected to be split into monomeric units. TheE280measurement of the fractions, expressed as a percentage of the total material eluted, followed a reproducible pattern, both with duplicate runs on the same sample and comparative runs on non-identical samples of the same type. With cheese curd, a small peak of undissociated material was obtained at the void volume of the column; this was followed by a main peak and a minor third peak, with a small quantity of material being eluted at larger volumes. A qualitatively similar pattern was obtained with 43-day-old cheese as the sample, but the main peak was smaller, the third peak was larger, and a relatively larger amount of material was eluted at greater volumes. There was only partial separation of the proteins on the column; the main peak contained β- and αs-caseins, their larger breakdown products and some para-κ-casein, and the third peak contained smaller breakdown products of the main casein fractions and para-κ-casein. Although the resolution was considerably inferior to that obtained by gel electrophoresis, the method has the advantage over this and other methods in that it gives a quantitative analysis of the sample based on molecular size. Thus, it is suggested that it may find use in analysing protein breakdown in cheese during ripening.