1. The amide, tyrosine, tryptophan, cyst(e)ine, methionine, arginine, histidine and lysine contents of protein preparations from senescent leaves of Trifolium 8ubterraneum, expressed as percentages of the protein N occurring in these for'ms, were found to be 5-39-5-71, 2-80-2-90, 1-65-1-85 (best 1-80), 1-42-1-47, 1-02-1-13, 13-5, 4-26 and 5-72, respectively.2. From comparison of these values with those previously found for non-senescent material (arginine, histidine and lysine values were not available) and from other considerations, it has been concluded tentatively thatthe onset of senescence was accompanied by an increase in the cyst(e)ine and possibly in the tyrosine content, and a decrease in the methionine content of the whole protein in the tissues.We wish to thank Mr D. S. Riceman for providing the leaf material used in this work.
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
Summary The total nitrogen content of malt extract may range from 0ṁ2 to 1ṁ2 per cent. but is usually well above 0ṁ64 per cent. which corresponds to the B.P. 1948 minimum content of 4 per cent. (total nitrogen x 6ṁ25). Lower diastatic values are usually associated with lower total nitrogen contents, the tendency being observed with malted barley as well as with malt extract. Of the total nitrogen of malt extract only 12 to 44 per cent. is true protein nitrogen. The greater part represents breakdown products of protein, largely formed during malting and brewing. The “less soluble” nitrogen of malt extract may range from 1ṁ8 to 10 per cent. of the total nitrogen, and should be reduced to as low a level as possible in malted preparations. In baby foods prepared from malt extract, wheat flour and soya flour sufficient aneurine and nicotinic acid may be derived from the raw materials if care is taken to use malt extract of high vitamin B content. Fortification with riboflavine may be necessary. If the diet is adequately supplemented by vitamins A, C and D the growth-promoting effect on babies may provide a measure of the protein value of the diet. We are indebted to Dr. F. W. Norris for microbiological assays, to Dr. R. G. Booth and to Mr. J. G. Heathcote for checking at the Cereals Research Station some of our protein analyses, to Miss Hazel Williams for fluorimetric estimations of aneurine, to Miss Janet Horsford for technical assistance, and to Dr. H. Chick and her colleagues for advice and generous comments on our work.
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