The effects of ionizing radiation on the alkaline phosphatase activity of milk have been studied under different environmental conditions. Twenty-five megarads were required to inactivate the enzyme completely. A combination of heat treatment and irradiation given either before or after heating showed that inactivation of the enzyme was greater when heating occurred after irradiation, this effect of the different forms of energy possibly indicating different mechanisms of heat inactivation. Varying the dose rate over the range 12–250 krad/min did not affect the amount of enzyme inactivated. After irradiation, activity declined during storage at 30°C but not at 5°C. Irradiation did not change the value of Km yet the Vmax fell, indicating that there are fewer active sites present after irradiation but that affinity of the remaining sites for the substrate remains unchanged.

The effect of preservative tablets added to milk on its composition and density is discussed. A comparison between the S.N.F. content of 10-day composite samples of milk from individual herds after making due allowance for added preservative, and the weighted mean S.N.F. calculated on a daily basis, showed that the 10-day composite sample could be used successfully for estimating S.N.F. hydrometrically. A comparison of the weights of S.N.F. supplied when estimated by gravimetric and hydrometric methods was made for ten herds supplying a commercial plant over a period of 260 days. The mean difference was –0·14% of the gravimetrically estimated weight, S.D. 0·4, and the range was ±0·6%. The result is discussed and is considered of sufficient accuracy to justify, on a technical basis, using the hydrometric method of estimating S.N.F. for determining and, if necessary, paying for the S.N.F. supplied.

A simple system was developed, consisting of a solution of β-glycerophosphate, β-lactoglobulin and magnesium ions, in which alkaline phosphatase isolated from milk became strongly reactivated following heat treatment for 45 sec in boiling water. From 10 to 30% of the original enzyme activity reappeared after incubation at 37°C. Variations in the components of the system, and factors affecting it, were studied. Salts of Hg, Zn and Cd inhibited reactivation at low concentrations.

Milk which, after the same heat treatment, became reactivated to a much smaller extent (about 1%), was found to contain a dialysable, heat labile inhibitor whose presence is thought to be largely responsible for the low level of reactivation, though other factors, e.g. the suboptimal concentration of phosphate esters must be considered as contributory causes.

Milk contains also a non-dialysable, heat stable activator of the reactivation process, capable of replacing β-lactoglobulin in the simple system and active at very low concentration, e.g. 0·2% (v/v).

The considerable falls in viscosity of sodium caseinate solutions under the action of rennet are shown to be due to changes in volume and shape (or either alone) of loosely coiled long chain molecules, resulting from the discharge of ionization (‘Third-type electro-viscous effects’). This reduction may be as well effected by small amounts of NaCl or by the separated decomposition products of the rennin-caseinate reaction. Even at the highest practicable caseinate concentrations (9–10% by weight) the solutions are truly fluid over the range of shear-rate of the Ostwald viscometers used

The initial rate of fall of viscosity is found to be proportional to the maximum (initial) specific viscosity, leading to an equation Xk1 = 1/τ where X the proportional viscosity loss, varies with the source of caseinate but is constant for all normal rennets; k1, the first-order reaction constant, varies with the rennet but is independent of the source of casein over a wide range; and τ, which has the dimensions of time, varies with both caseinate and rennet.

The parameter k1 may be found either from the exponential viscosity fall or calculated from the asymptotic initial slope and has been shown to serve as a useful index of rennet activity. This method of rennet testing does not depend on the keeping qualities of rennins, rennets, milks or caseinates. Details of the preparation of caseinates and of the methods for practical testing of commercial rennets are given.

A rapid spectroturbidimetric method for the determination of the fat content of homogenized ice-cream mixes using a simple filter absorptiometer has been devised. Turbidities are measured at two different wavelengths to allow for changes in the degree of homogenization. The standard deviation of the differences from the values obtained by the Werner-Schmid method was found to be 2·5% of the mean fat content value. The method also enables the mean fat globule diameter to be determined.

Spray-dried whole milk powders have been prepared containing 0·01% of four flavones, propyl and dodecyl gallates, butylhydroxyanisole (BHA) and nordihydroguaiaretic acid (NDGA). The powders were stored at 20 and 37°C and examined at intervals of 25 days for taste of the reconstituted milk, peroxide value of the fat and oxygen absorption of the powder. Three of the four flavones, 7,8-dimethoxy-3,2',5'-trihydroxyflavone, 6-ethyl-3,7,2',5'-tetrahydroxyflavone and 6-dodecyl-3,7,2',5'-tetrahydroxyflavone improved the keeping quality of the powder, the last-named compound being the most effective, but 3,7,8,2'5'-pentahydroxyflavone was without antioxidative properties in this system. These results are briefly discussed with respect to substitution within the flavone molecule.

Dodecyl gallate was a very effective antioxidant for spray-dried whole milk powder and propyl gallate and NDGA, whilst affording good protection, were less so; BHA did little to improve keeping quality.

The best antioxidant of the flavones investigated, 6-dodecyl-3,7,2',5'-tetrahydroxyflavone, appeared to be almost as effective as propyl gallate and NDGA in these milk powders.

When the teats of dry cows were dipped in a culture containing 3–25 × 106 mastitis organisms/ml only 25% of 71 quarters acquired an intramammary infection. Small numbers of organisms applied to teats caused negligible infection. The degree of contamination also determined the survival of the organisms on the exterior of teats, which was much greater at the teat apex than on the body of the teat.

There was no evidence that swabbing the teat apex increased the chance of intramammary infection. Washing the udder of infected cows with a disinfectant increased the chance of recovering the organisms from the teat skin.

A within-cow comparison was made of methods of control of udder infection in dry cows whose teats were deliberately contaminated with cultures of mastitis organisms. Very nearly complete protection against infection with staphylococci and streptococci was obtained by infusion of antibiotics through the teat canal. Disinfection alone, i.e. dipping the teats in 2% chlorhexidine, gave good protection against staphylococci but no protection against Streptococcus uberis.