Samples (120) of ewes' raw milk collected over a 12-month period on arrival at the dairy and freshly drawn ewes’ milk samples (30) collected at the farm were analysed for total viable counts and staphylococci. Total viable counts reached on the average 54 × 106/ml in dairy samples and 6·0 × 105/ml in farm samples, whereas mean levels of staphylococci were 5·9 × 104/ml and 3·3 × 103/ml, respectively. A high proportion (62%) of coagulase-positive isolates from Baird-Parker agar plates was detected in spring months. Staphylococcus aureus (42%), Staph. haemolyticus (23%) and Staph. epidermidis (10%) were the predominant species in 210 characterized isolates of staphylococci from ewes' raw milk. Seven coagulase-positive, maltose-negative staphylococci could not be identified with any of the recognized Staphylococcus species. Eighteen Micrococcus strains were identified as M. varians, whereas 111 Micrococcus strains of uncertain taxonomic status were separated into three groups, according to their physiological characters.

Short-term associations between disease and milk yield were studied in 1594 lactations occurring between 1977 and 1982 in 732 Friesian, Ayrshire and Holstein crossbred cows. Statistically significant differences in milk yield between one week before and one week after clinical diagnosis were observed for ketosis (5·l kg/d), hypomagnesaemia (4·1 kg/d), mastitis occurring after peak yield (2·1 kg/d) and lameness (1·1 kg/d). Milk yield declined for as much as 2–4 weeks before diagnosis of disease, and total losses in milk yield associated with ketosis or hypomagnesaemia were estimated to be 60–70 kg. No significant differences were found for endometritis or for mastitis when it occurred before peak yield. Milk yield was suppressed for about 4 weeks after calvings with retained placenta, but there were no corresponding effects of dystocia or hypocalcaemia on milk yield. It is suggested that if automatic daily milk recording is available it may be possible to detect deviations from normal, and hence detect subclinical disease 2 or more weeks before its clinical appearance.

Half-udder comparisons were made using 56 cows for 2 months, in an experiment involving high bacterial challenge, to assess the combined effects of 5 min overmilking and pulsation failure (resulting from the use of shortened teatcup liners) on teat condition and mastitis. Only three new infections were confirmed in over 12500 quarter milkings in quarters milked with control liners (of 148 mm effective length) indicating little or no effect of prolonged overmilking in these quarters. A 3·5-fold increase in the new infection rate (NIR) based on bacteriological diagnosis alone (P < 0·01), or a 9-fold increase in NIR based on bacteriological diagnosis plus raised cell count and/or N-acetyl-β-D-glucosaminidase (P < 0·01), occurred in quarters milked with the same liners shortened to an effective length of 120–130 mm. The mean interval to infection or teat canal colonization (41 ν. 60 milkings), and for a quarter infection to be confirmed by other diagnostic tests (45 ν. 79 milkings) was significantly less in quarters overmilked with short liners. The results confirm that NIR increases whenever pulsation fails. Overmilking may increase NIR when it is associated with pulsation failure.

Several ionic components of ultrafiltrate were measured in bulk and individual cow milks and an assessment was made of their relationship with the parameters of the corresponding ethanol (EtOH) stability/pH profiles. From linear regression analysis the strongest relationships (P < 0·001) were between soluble salt balance [expressed as (Ca+Mg) minus (Pi+Cit) or as the ratio to (Pi+Cit)] and pK (correlation coefficient, γ ∼ 0·82) or Smax, the maximum stability at high pH (γ ∼–0·72), and between Pi and pK(γ = –0·84)or Smax (γ = –0·61). These relationships agree with the view that the parameters of the EtOH stability/pH profile are determined by pH-induced changes in concentration of divalent cations. Natural variations in these parameters may be attributed to variations in relative concentrations of divalent cations and their chelators. EtOH stabilities at the natural pH of bulk milks from winter/spring- and autumn-calving animals were lowest in early and late lactation. The most important contributory factors appeared to be a high salt balance ratio in late lactation and a low natural milk pH in early lactation. The main component responsible for variable salt balance ratio was usually soluble Pi. Decrease in EtOH stability at the natural pH of late lactation milks reflected a more general change in the characteristics of the EtOH stability/pH profile, seen as an increase in pK and, in extreme cases, a decrease in Smax and profile gradient.

Samples of reduced whole casein from genetically typed individual cows were quantitatively separated into their main components, αsl-, αs2-, β- and κ-caseins by reverse phase high performance liquid chromatography (RP-HPLC) using a mobile phase of phosphate-buffered aqueous propan-2-ol containing sodium dodecyl sulphate and an octadecylsilyl stationary phase. One casein sample was found to give two peaks of β-casein of approximately equal areas. RP-HPLC of tryptic digests of the two separated peak fractions gave identical patterns with the exception of one peptide peak with different retention times. Amino acid analyses performed on both fractions showed that they corresponded to peptide 114–169 of β-casein A1. The atypical β-casein differed from the typical one by a Pro→Leu substitution in region 114–169.

Fast protein liquid chromatography was used to study the κ-casein fraction of casein micelles from bulk milk and from milk from individual animals homozygous for κ-caseins A and B. The extent of glycosylation of the κ-casein appeared to have no effect on its distribution in casein micelles of different sizes, nor did it affect the rate at which κ-casein was destroyed during renneting. The rate of breakdown of κ-casein during renneting was also almost independent of micellar size. The results may indicate a difference between methods which analyse for intact κ-casein or for the product macropeptide during renneting.

High performance gel chromatography of the casein micelles disaggregated by 6 m-urea was carried out on a TSK-GEL G4000SW column using 6 M-urea synthetic milk serum as the effluent. The eluate was divided into two fractions. Fast eluted fraction 1 decreased from 67·5 to 57·3% on reduction of casein micelles and was not observed in reduced colloidal phosphate-free casein micelles. Fraction 1 from reduced casein micelles contained 1·7 times as much Ca and Pi bound to casein as did whole casein micelles, while fraction 2 essentially contained only bound Ca. These facts indicated that fraction 1 of reduced casein micelles consisted of the casein aggregates cross-linked by colloidal Ca phosphate (CCP). Polyacrylamide-gel electrophoresis showed that fraction 1 of reduced casein micelles contained more αs1- and αs2-caseins and less β-casein than whole micellar casein. No κ-casein was detected in fraction 1 of reduced casein micelles. It is suggested that the ester phosphate groups of casein are the sites for interaction with CCP.

AS the break-up of weak curd during processing leads to fines losses, the mechanical strength of acid casein curd is important. When different techniques were investigated to evaluate objectively the strength of acid casein curd a plate extrusion method was found to require the least preparation of the curd and to give rapid and reproducible results. The optimum condition for mechanical testing of samples was after acidulation or after cooling for 2h at 25 °C.

The precipitation stage in acid casein manufacture controls the initial strength of the casein curd, which is an important factor in determining fines losses during processing. A plate extrusion method was used to determine the mechanical strength of casein curd, precipitated batchwise at temperatures from 25 to 53 °C over a pH range of 3·9 to 5·1. Curd strength was determined either immediately after acidulation or after cooling for 2 h at 25 °C. Curd was stronger immediately after acidulation than after cooling and increased in strength as precipitation temperature and pH were increased. Curd precipitated at high temperature and high pH was mechanically strong, had a large particle size, and had high total solids and Ca contents. The relationship between these curd properties is discussed, and it is concluded that Ca retention at high precipitation temperature and pH is largely responsible for the characteristic curd properties under these precipitation conditions.

Investigation of the effect of pH on the formation of deposit from milk during ultra high temperature treatment using a plate-type plant showed that deposit formation was greatly increased when the pH of whole milk was reduced to 6·54, irrespective of whether the adjustment was made through the addition of HCl or lactic acid. Most of the increase in deposition took place in the higher temperature sections of the plant. Conversely, an increase in milk pH to 6·8 using NaOH resulted in considerably less deposit being formed during heat treatment. Reducing the pH of whole milk increased the deposition of both protein and fat, but reduced the deposition of minerals. Despite very high concentration of fat in the deposits, it is unlikely that fat per se was responsible for increased deposit formation. Deposition also increased when the pH of skim milk was reduced to 6·51 before processing. Electron micrographs of the milks after heat treatment indicated that pH reductions caused the formation of large aggregates containing casein micelles during heating. Fat globules were also present in aggregates formed in whole milk with reduced pH. Slight reductions in the pH of milk before processing appear to enable the pH during heat treatment to fall below a critical value at which coagulation of milk takes place at the heated surfaces.

The effect of heating raw milk at 75 °C for 30 min and at 95 °C for 15 s in the presence of varying concentrations of three oxidizing agents on the denaturation of total and individual whey proteins was measured. At 75 °C, ±-lactalbumin could be protected against denaturation by both iodate and H202 and ²-Lactoglobulins A and B by H202 and dichromate. However, at concentrations above ∼ 15 MM, the oxidizing agents tended to increase denaturation. At 95 °C, where the extent of whey protein denaturation was much reduced in the absence of oxidizing agents, little or no protective effect was observed. It is suggested that H202 may prove a suitable alternative to iodate in reducing deposits in ultra high temperature plants.

The physicochemical properties of eight extracellular proteinases secreted by psychrotrophic bacteria of dairy origin have been studied. Seven of these proteinases were able to withstand ultra heat treatment (UHT) with D values at 140 °C ranging from 2 to 300 s. The six Pseudomonas fluorescens proteinases were glycoproteins of mol. wt 47000–49500. The two Serratia marcescens proteinases, of mol. wt of 51000, did not contain carbohydrate but in other respects were similar to the Pseudomonas proteinases. The proteinases were inhibited by various metal chelators and all contained Ca and Zn in similar proportions. Their amino acid compositions were similar, with alanine as the N-terminal group, cysteine completely absent and very low levels of methionine. Isoelectric points ranged from 5·10 to 8·25. Their physical and chemical properties enabled them to be classified as alkaline metalloendopeptidases. A similarity index (S▵n) was used to predict sequence homology between ten proteinases of known amino acid composition. Comparisons of S▵n of these proteinases showed only minor sequence differences except for those of Ps. fluorescens MC60. Heat resistance could not be related wholly to similarities in protein sequence, but could be related both to the strength of stabilizing Ca2+–protein interactions and to the randomness inherent within the folding of the peptide chain.

Conditions necessary for the determination of crude extracellular lipase activity from Pseudomonas fluorescens B52 using β-naphthyl caprylate (β-NC), an 8-carbon ester, as the substrate were examined. Maximum enzyme synthesis occurred at 20 °C in pyruvate mineral salts medium containing 1 mM-CaCl2. Bile salts were necessary for enzyme activity; 6 mM-Na taurocholate or Na deoxycholate gave maximum activity but the latter compound was inhibitory at higher concentrations. Activity was optimal in N-Tris[hydroxymethyl]methyl-2-aminoethane sulphonic acid buffer pH 8·0 at 40 °C. A comparison of β-NC with β-naphthyl butyrate (a 4-carbon ester) and β-naphthyl myristate (a 14-carbon ester) showed that β-NC was the best substrate; Km values of 0·0415, 0·141 and 0·200 mM and Vmax values of 67·2, 20·1 and 5·28 μmol ml-1 h-1 were obtained for those substrates respectively. The enzyme was inhibited 50% in its activity against β-NC by 0·009 mM-EDTA, 0–0007% (w/v) mixed alkyltrimethylammonium bromide and 0·00275% (w/v) Triton X-100. The biochemical properties determined using β-NC as substrate are consistent with those reported for the lipases of other strains of Ps. fluorescens using natural substrates.