Fluorimetric and Microbiological Assays of Riboflavine in Malted Preparations

Abstract

IN a previous communication' we described fluorimetric and microbiological assays of riboflavine in barley, malted barley and malt extract. Whilst the two assay methods gave the same general picture for increases in content of this vitamin during malting and brewing, certain discrepancies were encountered between the results given by the two methods. On 4 samples of barley and malted barley, the fluorimetric method gave lower results (72 to 89 per cent. of the microbiological result), the deviation on 3 of the samples being significant. On 4 samples of malt extract the fluorimetric result did not deviate significantly from the microbiological result. On a fifth sample of malt extract the mean fluorimetric result was 231 per cent. of the mean microbiological result, a highly significant difference. Extensive investigations have been carried out in our laboratories to explain these discrepancies, and show how they may be overcome by improvements in fluorimetric and chromatographic technique.Elvidge* reported good recoveries (84 to 105 per cent.) of this vitamin from 5 more potent pharmaceutical preparations (an elixir, capsules and tablets) in which he estimated it fluorimetrically or spectrophotometrically. A detailed study of the spectrophotometric method was made in our laboratories3. Optical densities were recommended to be read at 267 or 375 mp as well as at the maximum of 444 to 445 mp recommended by Elvidge. The importance of controlling the pH was emphasised, and experiments described on the development of lumiflavine through the action of light on alkaline solutions of riboflavine. The possible interference of lumiflavine fluorescence has been one of the factors we have had to investigate in the fluorimetric work described below.MICROBIOLOGICAL ASSAYS The method as laid down by the Analytical Methods Sub-committee of the Society of Public Analysts4 was almost exactly followed. It has been described with comments in a previous paper1. Continued experience with the method has shown that Lactobacillus helveticus is not on the whole so easy to work with as, for example, Lactobacillus arabinosus, which is used for the assay of nicotinic acid and biotin. Difficulties are sometimes experienced in maintaining sub-cultures, and it would seem thaf the organism requires nutrilites whose nature is not necessarily exactly known, but which are present in some natural products. This is further indicated by the observation in recent months that there is a tendency to obtain less satisfactory linearity in the standard curve than in the curves for the assay samples.The effect of the presence of fats and fatty acids in samples and 915

Anaemia and vitamin B12 dietary deficiency

“…Supplements of vitamins A and D were given to almost all the children but the riboflavin content of the diet may have been marginal, depending on the conditions of malting of the cereals (cf. Klatzkin, Norris & Wokes, 1949 ; British Medical Association: Committee on Nutrition, 19 50).…”