The effect of ‘hold’ and ‘H.T.S.T.’ heat treatment on cream was a 97–100% reduction in the tributyrinolytic flora. There was no significant difference between the two methods in this respect. The tributyrin-splitting organisms have been tested for their ‘true’ lipolytic effect upon triolein; of 967 organisms tested 55 % attacked triolein. In raw cream the most numerous lipolytic organisms were of the Micrococci and Pseudomonads groups, whereas in heated cream the former were by far the predominant lipolytic organisms.

The result of storing cream at 8–11° C. for 24 hr. was an 8- to 13-fold increase in tributy-rinolytic organisms, mostly of Gram-negative rods many of which attacked triolein. The effect of heat treatment nullified this increase and the lipolytic flora of heated cream was much the same whether or not the cream was stored before heating.

The triolein media incorporated two new indicator dye combinations which were successful but a third, nile blue, was found to be strongly inhibitory to the majority of triolein-splitting organisms.

A Gram-positive, aroma bacterium, the so-called ‘malt coccus’, has been isolated from malty-flavoured starters. It coagulates milk most readily at 35–37° C. The ‘malt coccus’ differs from the aroma bacteria mainly in that it forms acetaldehyde from pyruvic acid, evidently through carboxylase. Acetaldehyde is the chief factor in the formation of malty flavour. The ‘malt coccus’ sours milk feebly. If starter is heavily contaminated with the ‘malt coccus’, the acidity (SH°) is reduced but the aroma reaction (V.-P.) increases. The malty flavour persists in the starter during transfers and becomes more marked with rising temperature. The ‘malt coccus’ retains its aroma-forming ability for long periods in the laboratory.

1. Some account has been given of the cattle kept on the Government Farm at Samaru, Zaria, and of their management in the wet and dry seasons.

2. Figures extending over four seasons have been presented to show thatthe butterfat content of the milk produced on this farm is consistently higher in the morning than in the evening during the wet season, and that the reverseis true during the dry season.

3. The relative quantity of milk produced in the evening during the dry season is slightly less than during the wet season, but this difference is quiteinadequate to explain the change in the percentages of butterfat.

4. Some evidence is offered that this change in butterfat content is directly due to the marked climatic differences between the two seasons, and that it cannot be controlled by altering the diet of the cattle.

We have dealt in a previous communication (1) with the effects-of commercial pasteurization on the nutritive value of milk. We present here the results of an enquiry into the nutritional effects of the more drastic heat treatment to which milk is subjected during commercial sterilization. There is no legal definition of either sterilized milk or of the process of sterilization, but in commerce it is customary to apply the term to milk which has been heated to at least 212° F. for varying lengths of time.

Samples of caseins having different Ca contents as used in cheese processing were analysed by techniques using differential scanning calorimetry and thermally stimulated currents (TSC) before and after treatment with Na poly-phosphate, a food additive used in the manufacture of processed cheese. These techniques revealed structural changes induced by the salt, and the different types of water molecules associated with the protein are evident. This characterization is in agreement with results obtained by other techniques, particularly X-ray diffraction of proteins. Transmission electron microscopy of the same samples confirmed that the changes observed by TSC were associated with an unravelling of the protein.

Mature lactating Friesland ewes had a mean lactation yield of 293 ± 26 kg during a lactation period of 35 ± 2 weeks giving an average daily milk yield of 1·2 kg/d. Ewes were injected intravenously after normal milking with either saline (sham) or oxytocin and then remilked to determine the volume of residual (alveolar) milk. After a long milking interval of 16 h oxytocin treatment gave a significantly greater total daily milk yield than the sham treatment (oxytocin minus saline, morning milking, 0·199±0·038 kg, mean ±s.e.m., P < 0·01). Oxytocin had a small significant reverse effect after a short milking interval of 8 h (afternoon milking, –0·065±0·022 kg, P <0·05). The average increase in total daily yield over four stages of lactation was 0·133±0·029 kg (P < 0·01), or 11% of the average daily milk yield. The galactopoietic effect of oxytocin was associated with the efficient removal of residual (alveolar) milk. Residual milk accounted for 7·4 and 27·2% of the total daily milk yield in ewes treated with saline or oxytocin respectively. Residual milk expressed as a proportion of daily total milk yield remained steady in ewes studied between April and July, but declined in September when yields were less than 1 kg/d.

The reproducibility of Scott Blair's method for measuring curd firmness has been tested and measurements of the “firmness” of cheese curds immediately prior to cutting have been made and related to an expert's opinion. Contrary to her beliefs it was found:

(1) that the mean firmness for normal Cheshire and Double Gloucester curds was the same as that for normal Cheddar curds,

(2) that normal curds, regardless of type, were softer in the summer months than in the winter.

Though confident opinions are often expressed on very small differences in firmness, the smallest difference in modulus which can be correctly appreciated appears to be of the order of 8%.

Traces of certain metallic contaminants (copper, iron, lead, zinc, aluminium and manganese), when added at the rate of 3 and 7 p.p.m. to milk used for the manufacture of Cheddar cheese, cause certain flavour (and colour) defects in the matured cheeses, of which, however, no indication is given when the cheese is plugged and graded at about 14 days after manufacture.

The distribution of copper, iron, manganese and lead between curd and whey during the cheese-making process is recorded and the action of traces of various metals on the acidity development in a typical "starter" culture has been followed.

The discolorations noted for copper- and iron-contaminated cheeses are considered to be due not to the formation of their sulphides (although this is the case for lead discoloration), but to the atmospheric oxidation of a colourless metal: protein complex.

The vitamin A and carotene content of 14 samples of butter fat churned from milk in the usual way has been compared in spectrophotometric and Lovibond tintometer tests with figures similarly obtained for the ether-extracted fat from the same milks. On the assumption that there is no loss of either carotene or vitamin A in the course of the ether extraction, it has been found that some carotene is lost in churning but that vitamin A is not appreciably affected.

Dioxins are lipophilic compounds with a small molecular weight and are highly persistent, bioaccumulative and toxic. Dioxin detoxification is associated with an increased production of reactive oxygen species (ROS). In physiological conditions the body is protected against ROS and their toxic products by a wide range of antioxidant systems. We hypothesize that the imbalance between ROS production, associated with dioxin exposure, and the antioxidant defence capacity, may lead to oxidative stress, with consequent increased consumption of antioxidants and accumulation of toxic compounds in blood and tissues. The objective of this study was to evaluate the effect of exposure to dioxins on the plasma redox status of lactating buffalo cows. To this aim, the major liposoluble (retinol and α-tocopherol) and water-soluble (ascorbate) antioxidants, the superoxide dismutase (SOD) and glutathione peroxidase (GPx) activity, the total antioxidant capacity (TAC), as well as specific protein oxidation markers (protein bound carbonyls and nitro-tyrosine) and lipid oxidation markers (hydroperoxides), were chosen as indices of blood redox status. The concentration of antioxidants, protein-bound carbonyls (PC), nitro-tyrosine (N-Tyr), and hydroperoxides (LPO), the SOD and GPx activity, and the TAC were measured in plasma samples obtained from buffalo cows exposed to environmental levels of dioxins higher (n=21, group A) or lower (n=29; group B) than those permitted. Plasma titres of antioxidants, as measured by HPLC, and the total antioxidant capacity, as measured by trolox equivalents capacity, were higher in group B than in A. Similarly, SOD and GPx activities were higher in group B than in A. Conversely, plasma levels of PC, N-Tyr and LPO, as measured by ELISA, were higher in group A than in B. Our results suggest that exposure to dioxins impairs the plasma antioxidant defence system of lactating buffalo cows, and that metabolic processes associated with dioxin detoxification might induce or enhance oxidation of protein and lipids. This adverse effect on blood redox status might have negative implications for animal health and reproduction, and might compromise animal welfare.

Three types of liner (wide bore tapered, wide bore and narrow bore) were compared in a change-over design experiment comprising three 3-d periods and using six lactating Holstein Friesian cows with a wide range in milk flow rate and teat dimensions. Vacuum levels measured within the liner showed a characteristic pattern of three distinct phases: 1, a mouthpiece chamber (MPC) vacuum that fluctuated with vacuum beneath the teat; 2, a stable MPC vacuum that coincided with the period of peak milk flow and 3, a MPC vacuum that fluctuated with pressure changes in the pulsation chamber and coincided with the period of no or reduced flow. Of the three liners examined, the Gascoigne 1030A (wide bore tapered) induced the highest MPC vacuum (29·4 ± 2·23 kPa, mean ± s.e.m), significantly higher (P < 0·01) than the Alfa-Laval 960000–01 wide bore (23·5 ± 2·32), regardless of teat size and milk flow rate. The Alfa-Laval 7275737–01 (narrow bore) gave a significantly lower value (16·5 ± 1·96) than either of the others (P < 0·001). It was not possible to link absolutely raised MPC vacuum to cow discomfort and teat trauma but circumstantial evidence encourages this view. Narrow teats in combination with slow flow rate appeared to exacerbate MPC vacuum and, because milking time for such animals was protracted, teats were exposed for longer periods.

AS previously described, the process consists essentially of the passage of milk at pH 5·2–5·25 through an ion exchange resin charged with a suitable mixture of the ions of Ca, K, Na and Mg.

When citric acid was used for reduction of the pH and 30 resin bed volumes (r.b.v.) were treated, the concentration of residual 85Sr was reduced to 2–4% whether it had been introduced in vivo or in vitro. There was no evidence that repeated use of the resin bed resulted in diminished radiochemical efficiency.

About the same efficiency of removal of 133Ba was obtained but this efficiency was achieved with 137Cs only if not more than 15 r.b.v. were treated. If 30 r.b.v. were treated the concentration of residual 137Cs was as much as 30%.

When hydrochloric acid was substituted for citric acid the residual concentration of 85Sr was 11%. Analyses of milks processed after adjustment of pH with either citric or hydrochloric acid showed the products to be satisfactory. The only important constituent lost was thiamine. Concentrations of heavy metals remained well below maximum values. Although the flavour of milk was detectably changed by the treatment it was still acceptable.

The results are discussed in relation to the problem of achieving maximum decontamination and to the design of a large scale plant.

Thirty-six lactating cows were used in a 3×2 factorial design experiment to study the effects of level of energy and fibre intake on milk yield and composition over an 8-week experimental period. Three levels of fibre intake — 1g of crude fibre per 25, 17·5 and 10 kcal of estimated metabolizable energy (ME) requirements — were given in diets supplying both 80 and 100% of energy requirements. The level of energy intake significantly affected milk yield, milk energy output and the percentage solids-not-fat (SNF) and protein in the milk. The effects of fibre intake on both milk yield and milk energy output were marked but not significant. Fibre intake had a significant curvilinear effect on both the SNF and protein in the milk with the highest fibre intake resulting in a significant decrease in both fractions. A significant linear decrease was obtained in the lactose fraction as the fibre intake increased.

The total volatile fatty acid (VFA) level in the rumen was significantly affected by both energy and fibre intake. The level of energy intake only significantly affected the proportion of propionic acid. Fibre intake significantly affected the proportion of both acetic and butyric acids resulting in mean proportions of acetic acid of 66, 70 and 72 at the low, medium and high fibre intakes. The correlations between the rumen acids and lactation efficiencies are also presented.

Multiple regression analysis within each fibre level has been used to partition the ME available for production between that used for milk energy output and liveweight change. The results showed efficiencies of utilization of ME for milk output of 66, 65 and 56 on the low, medium and high fibre diets respectively.

Nitrogen balance data are presented.

When milk was preheat-treated after either evaporation or homogenization with fat present the degree of heat stability induced in the resulting evaporated milk (EM) was considerably less than with the normal process in which the preheat treatment was carried out first. When the preheat treatment was carried out after both evaporation and homogenization, no heat stability was induced by the preheat treatment. Removal of the whey protein fraction from the milk increased the heat stability of both the EM homogenized before preheat treatment and the EM made by the normal process.

Regular testing at 3-monthly intervals for periods extending to 7 years of some 650 to 850 cows in fourteen herds indicated that the majority of the new infections caused by Sir. agalactiae were recorded in the autumn months, August, September and October.

When infections were considered in relation to the stage of lactation, although higher new infection values were recorded at the first test after calving than at later stages, the differences were not statistically significant.

We are indebted to Dr D. N. Lawley for advice on the statistical interpretation of the results of this investigation.

Acknowledgement is also made to the Agricultural Research Council for grants in aid of the investigation.

The changes in the volatile acidity and other factors during the ripening process of Stilton cheese have been studied. The growth of the mould was characterized by an increase in the fat-soluble fatty acids derived from the cheese fat.

Pricking the cheese ensured a more uniform blueing and hastened the ripening. There was no evidence that judicious pricking at 2 months after manufacture seriously affected the course of the ripening. Excessive pricking, however, produced abnormal cheese of poor keeping quality.

Concentrations of IgA and IgM in milk from normal lactating cows were measured to determine whether they were affected by lactation number, lactation stage, daily milk production, milk composition and somatic cell score (SCS). A total of 284 Chinese Holstein cows showing no signs of mastitis were selected from more than 1600 cows from one farm. Concentrations of IgA and IgM in normal milk were determined by ELISA. Results revealed that average milk IgA and IgM concentrations were 235±11 and 32±3 μg/ml, respectively. IgA and IgM concentrations in milk were found to have an association with lactation number, stage of lactation, daily milk production and SCS. Both SCS and daily milk production were found to be strong significant (P<0·01) direct factors correlating to IgA concentration. Stage of lactation and SCS were found to be strong significant (P<0·01) direct factors correlating to IgM concentration.

The development of free volatile fatty acids (FVFA) in Ras cheese treated with lipases was investigated. Ras cheese was made with the addition of Italase, Capalase K and Capalase KL and then analysed periodically for the FVFA by quantitative gas-liquid chromatography. Lipase treatment markedly increased the total FVFA content of the cheese during storage, particularly when Capalase K was used. The FVFA of Ras cheese were found to consist of propionic, butyric, caproic, caprylic and traces of acetic acid. The relative concentration of FVFA varied with storage and lipase treatment.

The enzymatic hydrolysis of cheese whey was optimised using the enzymes iZyme, Alcalase or Flavourzyme under different conditions. Hydrolysates supplemented with commercial nutrients were evaluated as fermentation broths to produce DL-3-Phenyllactic acid (PLA) from phenylalanine (Phe) by Lactobacillus plantarum CECT-221. Optimised hydrolysates were obtained using Flavourzyme at 50 °C and 100 rpm during 12 h, and assayed in 250 ml Erlenemyer flasks using different proportions of vinasses as economic nutrient. The process was then scaled up using a 2 litres Bioreactor working under the continuous modality. Under the intermediate dilution rate of 0·0207 h−1 0·81 ± 0·026 mM of PLA and 38·8 ± 3·253 g/l of lactic acid were produced. A final evaluation revealed that lactic acid, and bacteriocins exerted the highest inhibitory effect among the extracted components of cell-free supernatants.

In this Research Communication we describe the optimisation of spray drying conditions in the production of microencapsulated cream powder. Oil-in-water emulsions were prepared using maltodextrin (18 DE) and sodium caseinate as wall materials (with the total wall material per total solid content ratio of 30%) and then converted into powder by spray drying. Response surface methodology was used to optimise the factors of spray drying system i.e. inlet drying temperature, feed flow rate, and aspiration rate, where the levels were in the range of 150–190°C, 9–30 ml/min, and 50–100%, respectively. Our objective was to perform spray drying with the highest drying yield and to obtain a microencapsulated cream powder with the highest bulk density, the shortest wetting time, and the lowest surface fat content. The calculated and validated optimum conditions for the spray drying process were found to be 162.8°C for inlet drying temperature, 11.51 ml/min for feed flow rate, and 72.8% for aspiration rate. At these optimum conditions, drying yield, bulk density, wettability, and surface fat content values were 36.37%, 269.9 kg/m3, 115.2 s and 26.2%, respectively.