The 90Sr/Ca and 137Cs/K ‘observed ratios’ (OR) in the food intake of nursing mothers and in their milk have been determined. Between 4 and 7 days after parturition, groups of mothers were put on a controlled diet for 4 days. Pooled samples of milk were then taken from each group. 90Sr, Ca, 137Cs and K were determined in the pooled samples and in all foods taken during the experimental period. 90Sr/Ca ratios were determined in 4 experiments and 137Cs/K ratios in 3. The OR for the 4th day's intake did not differ significantly from average ratios for the whole 4 days, so that a state of metabolic equilibrium appears to have been reached. The 90Sr/Ca OR was fairly constant and considerably less than unity, but the 137Cs/K OR was greater than unity and varied considerably between experiments.

Since potassium, which is metabolically analogous to caesium, showed a fairly constant ratio between intake and excretion in the milk, the physiological behaviour of 137Cs must be quite different from that of 90Sr. The maternal organism therefore provides the baby with efficient protection against 90Sr but not against 137Cs.

Twenty-five strains of lactobacilli isolated from dairy products, including Lactobacillus casei, Lactobacillus plantarum and Lactobacillus brevis species, were grown in semi-defined media and examined for their ability to ferment citrate and produce formate. Of 7 strains of L. casei, all utilized citrate to varying extents, as did 9 of 10 strains of L. plantarum and 3 of 8 strains of L. brevis. L. casei produced 19–35% of the theoretical yield of formate from the citrate utilized, L. plantarum 0–11% and L. brevis 0–28%. Of 2 strains of L. casei tested for their abilities to ferment citrate in the presence of 2% lactose, strain C 5 was unaffected by lactose whereas strain C 2 showed a 45% decrease in the citrate utilized. However, lactose used at 2% concentration greatly reduced formate production by L. casei C 5, which produced 62% of the theoretical yield of formate from citrate after 35 days in the absence of lactose and only 8% in its presence. The yield of diacetyl produced by L. casei C 5 from citrate plus lactose (both at 2% concentration) was 145 times that produced from citrate alone, and 800 times that from lactose alone.

A study was made of the utilization of citrate in milk by some lactic acid bacteria. When Streptococcus diacetilactis 1007 was grown alone or with either Streptococcus cremoris 924 or Lactobacillus casei B 142/C or with both these latter organisms, > 99% of the milk citrate was utilized within 5 days. L. casei B 142/C and L. casei/Str. cremoris utilized 57 and 14% of the citrate, respectively. When L. casei C 2 and L. casei C 5 were grown in milk in which Str. cremoris 924 had been previously grown, 94 and 64%, respectively, of the citrate was utilized after 7 days at 30°C.

Cheeses were made using a citrate-fermenting and a non-citrate-fermenting starter and citrate concentrations of the milks, wheys and curds were determined during cheese-making. With Str. cremoris 924, citrate was preferentially retained in the curd at pressing, the concentration in the curd moisture being 2·9 times that in the whey. With the mixed starter Str. cremoris 924/Str. diacetilactis 1007, the curd at pressing and from the press contained only 27 and 5%, respectively, of the citrate present in the Str. cremoris curd at these times.

Cheeses were made using Str. cremoris 924, combinations of Str. cremoris/Str. diacetilactis 1007, or with δ-gluconic acid lactone instead of starter, with and without the addition of L. casei C 5, in order to examine the ability of the latter organism to produce ‘blowing’ in the sense of distension of the Cryovac wrapping of film-wrapped cheeses. L. casei C 5 neither accelerated the decrease in cheese citrate nor produced blowing of the film-wrapping. Possible reasons for this behaviour are discussed.

A study has been made of methods using 2,4-dinitrophenylhydrazine (DNPH) or 2,6-dichlorophenolindophenol (DCP) for the determination of vitamin C (ascorbic acid+dehydroascorbic acid) in raw, UHT processed, evaporated and sterilized milk.

Interfering substances were not detected in milk that had received a heat treatment no more severe than 145°C for 4 s (UHT process), so that either reagent could be used.

With more drastic heat treatment, interfering substances were formed and only the DNPH method with column and thin layer chromatography of the DNPH derivatives was specific for vitamin C. With in-bottle sterilized milk, the values for ascorbic acid were (in mg/100 ml) 1·16 (DCP method with H2S reduction); 0·58 (DCP method with Escherichia coli reduction); 0·64 (DNPH method); 0·33 (DNPH method combined with chromatography).

In our experience the DNPH method combined with chromatography of the derivatives is highly specific for vitamin C and should be used to check the results obtained by other and simpler methods.

The association of lipase with casein micelles and soluble casein complexes was investigated by gel-filtration on Sephadex G-200 and Sepharose 2B columns which were equilibrated with synthetic milk serum. Gel-filtration indicated that the molecular weight of casein micelles in milk is > 108 whereas the casein in colloidal phosphate-free milk is present as soluble complexes of molecular weight ca. 2×106 containing αs-, β- and κ-casein. The soluble complexes appear to be stabilized in the micelle by colloidal calcium phosphate linkages. On addition of pancreatic lipase to milk, activity was impaired due to binding of the enzyme both to micellar and to soluble casein complexes. The enzyme dissociated from the latter during gel-filtration on Sepharose 2B columns. The binding of lipase to casein was not dependent on the presence of colloidal phosphate and consequently complete micellar structure is not essential for association of lipase with casein. Binding of the lipase to phosvitin did not result in a loss of enzyme activity. Lipases in milk appear to be involved in the equilibrium between micellar and soluble casein. The activity of lipases in milk is apparently influenced by this equilibrium. Some problems encountered in the use of gel-filtration to study the interactions of lipases with caseins are described.

A laboratory technique using glass and stainless steel slides has been developed to study the build-up of milk film on hard surfaces and its removal with detergent-disinfectant mixtures. Soiling and cleansing treatments were of similar duration to those used in practice but were repeated 6 or 7 times a day for 4 days to simulate 12 or 14 days' milking and washing procedures in the farm dairy; no mechanical assistance was used with the cleaning solutions. Soiling was followed immediately by a pre-rinse, wash and final rinse, allowing a short period for drying before further re-soiling. The technique eventually developed involved treatments repeated 18 times, using solutions at 15·5 °C. The weight of milk film and its content of fat, mineral and ‘protein’ were determined.

Under the conditions of the experiments the following were observed.

(1) The deposit left by all treatments consisted mainly of fat with a smaller proportion of protein and still less of mineral matter.

(2) Glass accumulated slightly less deposit than did stainless steel with an aquablast finish.

(3) Removal of milk film was more complete when sodium hypochlorite was added to certain detergent solutions than when the materials were used separately.

(4) With the treatments studied, the use of the detergent solution from a previous treatment as a pre-rinse did not result in a reduction in the residual film.

(5) A final rinse with 0·1% phosphoric acid virtually eliminated the mineral matter from the residual film.

(6) The substitution of a warm (46°C) for a cold (15·5°C) pre-rinse resulted in a reduction of 40% in residual film and the further use of a warm final rinse effected a reduction of 64%.

(7) The addition of 0·05% wetting agent (Lissapol NDB, I.C.I. Ltd.) to the prerinse effected only marginal improvement in the treatments studied.

(8) Omission of the pre-rinse and corresponding lengthening of the detergent treatment had no consistent effect.

The contribution of certain components of leucocytes and milk to the viscosity and precipitate which develop in the Whiteside mastitis test was studied to obtain information on the mechanism of the reaction. The viscosity obtained in the Whiteside test reaction was considerably less than that in the California mastitis test reaction and the Whiteside test was found to be more dependent on precipitation than increased viscosity.

Leucocyte nuclei were mainly responsible for the formation of the precipitate in the Whiteside reaction and CaCl2 dispersed the precipitate formed by the leucocyte nuclei into small clumps. Leucocyte protein and fibrinogen increased the amount of precipitate formed by the leucocyte nuclei. Fat globules also increased the amount of precipitate, probably by being trapped in the precipitate.

The addition of non-gelable or gelable nuclei resulted in the formation of similar amounts of precipitate in the modified Whiteside reaction. Furthermore, storage of milk for 5 days did not decrease the amount of precipitate formed, indicating that the DNA-protein complex of the leucocyte nuclei need not be present in the native form to contribute to the precipitate in this reaction.

(1) The rate of release of fatty acids from milk by porcine pancreatic lipase was studied as a model system for the development of lipase taint. The rate was low initially but then increased logarithmically and later declined. Addition of milk which had been subjected to the action of lipase and then boiled to inactivate the enzyme enhanced fatty acid release. An extract containing monoglycerides from lipolysed milk had a similar action whereas an extract of free fatty acids had an effect mainly in the early stages, increasing the initial rate. Addition of Ca2+, which accelerated lipolysis of fresh milk, enhanced the action of fatty acids and depressed that of monoglycerides.

(2) In the early stages of lipolysis there was a preferential release of short-chain fatty acids and a high proportion of these passed into the aqueous phase. These effects were more pronounced at low temperature and at acid to neutral pH. At alkaline pH a greater proportion of the short-chain acids was present in the aqueous phase but the total release of these acids was less.

(3) Fresh milks differed in their response to ‘aeration’ and storage at 4°C. In those in which taint was induced there was a considerable release of fatty acids in response to aeration, and a further release and also a redistribution between the aqueous and fat phases during storage. No relationship was apparent between the amount of fatty acids released and the initial fatty acid content.

(4) The findings are discussed in relation to the development of lipase taint in commercial milks.

The amounts of total lipid and fatty acids consumed, leaving the stomach and excreted in the faeces were examined in 4 sheep fitted with rumen and re-entrant duodenal cannulas. Diets of high (HM1) and low (CM1) roughage content were given at 0·9 times maintenance and the low-roughage diet was also given at 1·7 and 2·3 times maintenance. With all the rations more fatty acid left the abomasum than was consumed in the food, the difference being greater on ration CM1 than on ration HM1 and increasing irregularly with the amount of the low-roughage ration fed. Of the fatty acid entering the duodenum in the chyme, 72–89% was digested in the intestine. About 80% of the increase in fatty acids in the stomach was stearic acid and most of the remainder was palmitic acid. Almost all the polyunsaturated C18 acids ingested in the food were hydrogenated in the stomach, and the amounts of oleic acid were also greatly reduced, although more oleic acid entered the duodenum in the chyme with ration CM1 than with ration HM1. The possible origins of the increase in fatty acids in the stomach are discussed.

Absorbance measurements at the 1·93 μm water band on methanol extracts from butter, cheese and dried milk enabled moisture contents to be determined with coefficients of variation of 1·0, 1·1 and 2·0%, respectively. Butter, cheese and cheese curd analyses could be completed within a few minutes, but a 2-h standing period was required for dried milk to overcome difficulties associated with lactose precipitation.

A gas-liquid chromatographic method is described for the simultaneous estimation of the carbohydrates attached to the glycopeptides released by the action of rennin on whole milk. The method can also be used for κ-casein. Certain of the findings may be applicable to other glycoproteins or glycopeptides. In particular: (a) the conditions for methanolysis of the carbohydrates from the glycopeptides must be chosen carefully to avoid decomposition of N-acetyl neuraminic acid; (b) it is not possible to obtain a satisfactory calibration for N-acetyl neuraminic acid using the free acid as a standard.

Bovine serum lipoproteins were fractionated by precipitation with dextran sulphate followed by ultracentrifugation and were examined by paper electrophoresis and by disk electophoresis in acrylamide gels. Gels containing concentration gradients of both sucrose and acrylamide gave better resolution of lipoproteins than did gels of uniform composition or gels with a concentration gradient of sucrose and a uniform concentration of acrylamide.

The densities of the lipoprotein classes isolated (listed in order of increasing mobility on electrophoresis in acrylamide gels) were as follows:

I, d < 1·019; II, 1·039 <d<1·050;

III, 1·019 <d<1·039; IVa and IVb, d > 1·050.

Lipoproteins of classes I, II and III were precipitated by dextran sulphate. On paper electrophoresis, lipoproteins of class II had β mobility and lipoproteins of classes IVa and IVb had α mobility. Lipoproteins of class I remained at the origin.

The lipoprotein classes of bovine sera resembled those of sheep and goat sera in that class IV predominated. In contrast, the sera of several non-ruminant species showed a predominance of lipoprotein classes of low electrophoretic mobility.

An examination of the spectra of some volatile carbonyl semicarbazones indicated that only compounds containing vicinal carbonyl groups formed semicarbazones which absorbed at 270 nm. This observation was used for the quantitative estimation of diacetyl. The presence of both acetaldehyde and acetoin did not interfere with the estimation of diacetyl by this method.

A simple in-line filter is described which can be fitted into the milk tube of a. milking machine in order to detect clinical mastitis. It consists of a stainless steel mesh, on which the clots are retained, and it is fitted obliquely into a short length of clear plastics tube. The filter has been developed as an alternative to the fore-milk cup. Tests made over 9 months in a 60-cow herd show good agreement between the fore-milk cup and the in-line filter recordings. For general service production the filters are made by moulding.