New conception of folacin assay in starch or glycogen containing food samples

Abstract

The generally accepted microbiological assay for „total folacin”︁ (with Lactobacillus casei), based on the sample treatment with sole conjugase, has been found to be completely unsatisfactory, when starch or glycogen‐containing samples were assayed. The so called „total folacin”︁ content, determined in this way, is much lower than the actual one, because a part of folacin remains bound to polysaccharides, and is not transferred into the extract and thus not detected by the microbiological assay.The authors showed that the additional sample treatment with amylolytic enzymes is entirely necessary when actual „total folacin”︁ content is to be determined in starch or glycogen containing samples. The presented analytical results of a series of food samples bring evidence for this idea. The actual total folacin content in such types of samples is up to 80 % higher than that determined by procedures used up till now.The ability of polysaccharides to bind folacin was studied in model systems. Pteroyl‐glutamic acid (PGA) was adsorbed onto glycogen, 4 types of starch, amylose and amylopectin. The complete desorption of PGA., was achieved with α‐amylase, in case of maize starch the addition of glucoamylase was necessary. PGA is bound to starch by physical sorption which has been proved by its desorption with increasing salt concentration.