With 5 Figures) SYNOPSIS Pait I. The application of Jansen's thiochrome lest to the estimation of vitamin B l m milk. Introduction Experimental The thiochrome test Study of factors influencing the action of takaphosphatase (takadiastase) on milk in the chemical estimation of vitamin Bj Effect of pH. Period of incubation Method of incubation Peptic digestion Tryptic digestion Comparison of the effect of takaphosphatase, pepsm and trypsin preparations on the assay of vitamin B, in milk. The effect of crystalline pepsm. Part II. The different forms of vitamin B 2 m milk. Fractionation of the vitamin Bj of milk Introduction Ultra-filtration through Cellophane. Ultra filtration through collodion membranes The extraction of vitamin B 1 from milk by trichloroacetic acid Examination of the protein residue obtained in the ultiafiltration of milk through Cellophane. Vitamin B t firmly bound to protein. Tiichloioacetic acid experiments. Fuller's earth adsorbates. Form in which cocarboxylase is piesent in full lactation milk. Part I I I Effect of stage of lactation and of season on tlic vitamin B r and 1 tboflavm content of milk.

With 1 Figure) THE experiments to be described here form a continuation of our work(1,2) on the effect of various commercial heat treatments on the nutritive value of milk. In the present series of experiments we have turned our attention to dried and evaporated milks. Thanks to the kindness of Messrs Aplin and Barrett, Ltd. we have been able to obtain from their Frome factory two types of dried milk and one of evaporated, all prepared simultaneously from one bulk of raw milk. THE PREPARATION OF THE MILKSThe processing was carried out on 1 October 1937 and was as follows: 1500 gal. of mixed milk from Somerset herds of predominantly Shorthorn type were placed immediately after receipt at the dairy in a large storage tank. After thorough mixing a sample was withdrawn for analysis. Batches were then drawn off and submitted to the following processes:(1) Raw milk. 17 gal. were withdrawn and of this 10 pints were put immediately into sterile thermos flasks and brought to the Institute at Reading the same evening. The remainder was cooled to 35° F., 50 pints were put into sterile thermos flasks and the rest into a churn. This milk was dispatched to Reading by rail and was received in the laboratory at 10 a.m. the following morning. There was some clotting in both batches, especially in the uncooled one.(2) Spray-dried milk. 500 gal. of raw milk were passed over an open tinned copper forewarmer and then flash-heated in an internal tubular heater to 160° F. and held at this temperature for 1-4 min. Some of the tin was missing from the forewarmer and the milk was probably exposed in it to naked copper for about 20 sec. during which time the temperature was raised from 45 to 110° F. The milk was then concentrated at 110° F. in a Kestner climbing film evaporator. This process was completed in 10 min. when the milk reached a concentration of 45% total solids. Within 30 min. of concentration the milk was fed into a Kestner spray-drier with an inlet temperature of 320-329° F. and an outlet temperature of 203° F. For the bulk of the milk the time of passage through the drier was about 30 sec, variations were from about 5 sec. to about 15 min. (this latter figure applies to mill? which unavoidably adhered to the sides of the drier). The milk powder was then put into 1 and 3f lb. tins and sealed at once in an atmosphere of 75% N 2 and 25% C0 2 .(3) Roller-dried milk. 50 gal. of raw milk were flash-heated to 160° F. as in the case of the spray-dried mill?-The milk was then fed at this temperature on to Hatmaker rollers running at 45 lb. steam pressure and 13 rev./min. After milling it was put into tins and sealed as already described.

Experiments were carried out to study the effects on the quality and nutritive value of bread of the addition to white flour of roller-dried skim milk and roller-dried whey. Both samples were typical commercial products.Additions of 2% of the dried milk could be made without any marked effect on loaf quality or on flavour. The addition of 4% or more definitely lowered the quality of the bread, the volume being smaller and the crumb more rubbery. As the content of milk was increased above 2% the flavour of the bread became increasingly distinctive and departed from the normal neutral flavour of water bread.Up to 5% of dried whey could be added to the flour without any marked deterioration in the crumb of the bread, although with one flour this quantity decreased the volume by 16%. At this level, however, the whey imparted a distinct cheesy flavour to the bread.Attention is drawn to the fact that the effects produced by the addition of dried milk or whey to bread can only be considered in relation to the particular sample used, since other workers have found that modifications in the method of manufacture considerably alter the value of the product as far as its use in bread is concerned. For this reason improved types of dried milk or whey might well lead to their greater use by the baking industry.

THE development of a technique for the satisfactory milking of small laboratory animals [Cox & Mueller, 1937; Temple & Kon, 1937] and the recent progress in the chemical and physical estimation of various vitamins have made it possible to measure several of these factors in the milk of rats and of guinea-pigs. We have examined the milks of both species for vitamin A and carotene, vitamin B1, riboflavin and vitamin C. We have also studied the effect of changes in the diet on the levels of these factors in rat's milk. EXPERIMENTAL (1) The guinea-pig Guinea-pigs were generally milked about the 4th day of lactation, some being used several times at intervals. For milking in the morning the doe was separated from her young on the previous evening at 5 p.m. Their food consisted of a dry mash, the composition of which is given in Table I. In addition they were allowed unlimited hay and water and about 1 oz. of fresh cabbage daily. Table I. Composition of the guinea-pig diet Bran 27 Crushed oats 27 Lucerne meal 13 Linseed cake 13 Flaked maize 13 Fish meal 7 Approximately 1% cod liver oil was mixed in immediately before feeding. Twenty milkings yielded 99-6 ml. of milk, i.e. an average of 5 ml. The best yield from one guinea-pig was 12 ml. (a) Vitamin A and carotene. 15-5 ml. of milk were diluted with 2 vol. of water and the fat was extracted by the method of Gillam et at. [1938]. The yield was 1L27 g. or 8-2 %. Our usual technique [Gillam et al. 1937] showed a content of 4 yellow and 42 blue Moore [1930] units per g. fat, equivalent to 0*143 mg. carotene and 1F08 mg. vitamin A per 100 g. of fat [Bartlett et al. 1938]. (b) Vitamin B1 was estimated fluorimetrically [Henry et al. 1938; Houston & Kon, 1939; Houston et at. 1939, 1], both the form which reacts in the Jansen [1936] technique ("free" vitamin B1) and the total aneurin being measured. In February 1938 a figure of 18-4 i.u./100 ml. was obtained for the "free" form in the pooled milk* of 2 guinea-pigs. In October of the same year the readings were 15-4 i.u./100 ml. as "free" aneurin and 22-4 i.u./100 ml. after incubation with pepsin and takaphosphatase (takadiastase of Parke Davis and Co.). These figures are not greatly different from those for cow's milk (Table VII). Read in part before the Biochemical Society, 11 March 1938 [Houston et al. 1938].

1. Cheshire, Cheddar and Stilton cheeses were made on one occasion from winter, and on another from summer, milk.2. The distribution of vitamin A and carotenoids, vitamin B1, riboflavin and vitamin C between milk, whey and curd was measured during cheese-making.3. The fate of these vitamins during ripening was determined.4. Some 80% of vitamin A and carotene, 15% of vitamin B1 and 25% of riboflavin originally present in milk were recovered in the green cheese and persisted throughout ripening.5. Vitamin C disappeared progressively during cheese-making and was absent from the cheeses.6. Vitamin B1 and especially riboflavin were recovered in cheese in larger proportions than would be expected from the partition of water between curd and whey, indicating that they were partly present in milk in combination with the coagulable solids.