Nine West African dwarf (Fouta djallon), Red Sokoto (Maradi) and Saanen lactating goats, hand-milked, were used for these studies, which lasted 12 weeks. The Saanen goats' milk was obtained weekly from the Western State Ministry of Agriculture and Natural Resources Urban Dairy Farm at Iwo Road, while similar samples were collected from the herd at the University of Ibadan Teaching and Research Farm. The goats were balanced for stage of lactation, namely early, mid- and late-lactation. They were each maintained on giant star grass (Cynodon nlemfuensis) ad lib. and 1kg dairy concentrate mixture daily.

The mean contents, with standard deviations, of the milks of Saanen, West African dwarf and Red Sokoto goats at mid-lactation respectively were: (in percentages), total solids 12·25±0·078, 18·18±0·392, 15·85±0·077; solids-not-fat (SNF) 8·91±0·142, 10·48±0·471, 10·53±0·140; butterfat 3·34±0·141, 7·78±0·621, 5·32±0·098; protein 3·04±0·139, 5·30±0·292, 4·74±0·021; lactose 4·56±0·167, 5·19±0·176, 4·77±0·053; energy (kJ/g dried milk), 21·08±1·11, 25·51±1·74, 22·17±0·51. Breed differences were significant (P < 0·01). The milk of West African dwarf goats contained more of these milk components than the milk of the Red Sokoto or Saanen goats. The Red Sokoto goats gave milk of higher content than did Saanen goats, even at an early stage of lactation.

Butterfat, protein, lactose and energy values were significantly affected by stages of lactation (P < 0·05) and tended to rise with advancing lactation; this was particularly so with West African dwarf goats.

The equipment tested (Fossomatic) is a fully automatic electronic instrument for counting the somatic cells in milk samples. The results are printed on a paper strip and displayed on a digital counter. The capacity is 180 samples/h.

Counting results obtained with the instrument have been compared with direct microscopic cell counts and particle counts by Coulter counter. The correlation coefficient with microscopic cell counts was 0·922–0·988, and with counts by the Coulter counter it was 0·916–0·992.

Reproducibility showed a coefficient of variation of 2–5 %. The carry-over between the samples was 2·0 %. Preserving milk samples with 0·05 % potassium dichromate did not influence cell counts, whereas freezing the samples reduced the counts 30 %.

The release of the enzymes xanthine oxidase and alkaline phosphatase from the milk fat globule membrane is shown to be an index of milk churning. The factors affecting globule breakdown in relation to this assay procedure are discussed.

A procedure is described for the determination of the lipolytic activity in milk using tributyrate as substrate. The method is based on the titration of liberated butyric acid in a diethyl ether: light petroleum (2·75:1, v/v) extract of the incubation mixture. Some of the fundamental factors involved in the procedure are discussed.

The lipoprotein lipase and tributyrate hydrolysing activities were found to be similarly distributed in the fractions obtained when whole milk was separated into skim-milk and cream, and when the cream was washed and freed from lipid. These enzyme activities in skim-milks and in extracts of lipid-free cream could not be separated by affinity chromatography on heparin-Sepharose. The enzymes were inactivated to the same degree when incubated at 37°C in the presence of 1·5 M-NaCl, pH 8·5, and both showed the same marked decrease in stability at 4°C in 1·5 M-NaCl, when the pH was changed from 8·3 to 9·0. Irradiation of skim-milk with UV-light caused the same decrease in both lipoprotein lipase and tributyrate hydrolysing activities. An antiserum against a highly purified skim-milk lipoprotein lipase caused total inhibition of the lipoprotein lipase and tributyrate hydrolysing activities in skim-milk and in extracts of lipid-free cream. It is suggested that in bovine milk there is only one major lipase and that it is identical to lipoprotein lipase.

Carboxymethyl cellulose (CMC) formed insoluble complexes with β-lactoglobulin, bovine serum albumin and Na caseinate. Maximum precipitation of the β-lactoglobulin-CMC complex occurred at pH 3·2, whereas maximum precipitation of the bovine serum albumin-CMC complex and the Na caseinate-CMC complex occurred at pH 2·8. The ratio of CMC to protein for maximum precipitation depended on the protein, being greatest for Na caseinate and least for bovine serum albumin. The percentage of protein precipitated by CMC decreased with increasing ionic strength of the solution, the rate of decrease being least for bovine serum albumin. At a given ionic strength, more protein was precipitated by CMC of high degree of substitution than by CMC of low degree of substitution. The change in pH (ΔpH) occurring on mixing CMC and unbuffered protein solutions, each initially at the same pH, was measured. ΔpH was negative for β-lactoglobulin-CMC mixtures over the pH range 7–2 (minimum at pH 5·5). For bovine serum albumin-CMC and Na caseinate-CMC mixtures, ΔpH was positive between pH 7 and 3·2 (maximum at pH 4·5), zero at pH 3·2 and negative between pH 3·2 and 2·0 (minimum at pH 2·8).

Starch-gel electrophoresis (SGE) and formol titration methods for detecting proteolysis in cold-stored raw milk have been studied to establish their value as quality indices. When examined by SGE, the first evidence of proteolysis in raw milks stored at 5°C was the formation of para-κ-casein. However, this fraction could not be detected on the starch gels until the total bacterial count (TBC) exceeded 107/ml. The SGE method appeared more reliable than the previously discussed tyrosine value method. Formol titration did not appear to have any application in the screening of cold-stored raw milks with TBC < 107/ml, but would detect some milks of poorer bacteriological quality.

Indirectly heated ultra-high-temperature (UHT) processed milk was prepared with initially high, medium, and low dissolved O2 contents of 8·9, 3·6 and 1·0 ppm respectively, aseptically bottled, and tested at intervals during storage at room temperature for 150 d. Flavour acceptability increased to a maximum after a few days, but declined slowly after about 6 d; the increase was associated with less off-flavour described as ‘cabbagey’, and the decrease with more ‘stale’ off-flavour descriptions. Milks with higher initial O2 contents were preferred up to 8–13 d, but thereafter acceptability was independent of initial O2 content. Sulphydryl group (–SH) contents rapidly decreased and O2 levels correspondingly declined in the first few days as the flavour improved. Loss of –SH was lower with lower initial O2 contents, and moderate –SH content remained in low O2 samples for several weeks. Ferricyanide reducing (FR) values did not satisfactorily measure stale flavour development. They were initially high and decreased during the first 13 d at rates dependent on O2 content. After 20 d the FR values began to rise in high O2 samples, but continued to decline slowly in low O2 samples up to 90d although stale flavour was increasing.

High initial O2 contents resulted in rapid depletion of ascorbic acid and folic acid during storage. Losses of vitamin B12 were small, but were higher with high O2 contents than with low.

The beneficial effect of O2 on flavour, therefore, appears to be so slight and confined to such a short period in the early life of the milk as to be completely outweighed by the adverse nutritional effects.

A simple test procedure was used to predict the most suitable mixture of Noury rennet (Mucor pusillus Lindt proteinase) and swine pepsin for Cheddar cheesemaking. Duplicate cheeses were made with 6 Noury rennet–swine pepsin mixtures and with each enzyme alone, with calf rennet as the control. There were slight differences in the course of the cheese-making process and in the yields of the cheeses. Sensory evaluation showed that the most acceptable cheeses were those made by coagulant mixtures closely similar to the predicted mixture and these were as acceptable as cheeses made with calf rennet. The survival rates of different groups of bacteria were similar in all cheeses. There were differences in the products of proteolysis in the various cheeses throughout ripening, particularly with respect to products derived from αs1-casein. The Noury rennet was characterized for the proportion of milk clotting activity associated with each of 4 components and its stability in solution was determined.

A method is outlined for accelerating ripening in Swedish semihard cheese by increasing the number of lactic starter bacteria present in the cheese without impairing characteristic texture and flavour. In addition to the normal starter inoculum, suitable lactic starter bacteria whose lactic-acid-producing activity had been greatly reduced by previous sublethal heat treatment, were added to the cheesemilk. When suspensions of streptococci and lactobacilli cultivated at a constant pH were heated at 59 and 69°C respectively acid production was retarded by 5–10 h, which was found to be sufficient for the cheese-making. Proteolysis was lowered only 10–30% by these heating temperatures. Bacterial cell suspensions, prepared by the methods outlined and added to the cheesemilk, were incorporated in cheese curd to extents depending on the amount added and the type of starter. The number in the final cheese could be increased to a maximum of 4–5 times that of control cheese. No adverse effect of the extra starter bacteria on pH, fat content and water content of cheeses 24-h old was observed. Proteolysis, measured as the increase in trichloroacetic acid and phosphotungstic acid (PTA)-soluble N, increased with increasing number of cells in the cheese. Organoleptic judgements showed a positive correlation (r = 0·81) between taste and PTA-soluble N, which in turn was influenced by the number of cells in the final cheeses.

The acid phosphatase activity levels in a number of Greek cheeses and in Cheddar cheeses were found to be unaffected by storage for up to 18 months and 12 months respectively. In Cheddar cheese, starter organisms made an insignificant contribution to this activity. Studies of acid phosphatase prepared from Streptococcus cremoris-lactis NCDO 762 starter cultures showed that the enzyme was of high molecular weight and largely particle-bound. The pH of optimum activity was 5·2 and the enzyme was inhibited by F−, Al3+, a number of heavy metals, oxidizing agents and sulphydryl-modifying reagents. Kinetic measurements at pH 5·2 gave a Km value for p-nitrophenyl phosphate of 1·2 mM. Orthophosphate, pyrophosphate and isoelectrically precipitated casein behaved as competitive inhibitors to the hydrolysis of p-nitrophenyl phosphate with K1 values of 1·2 mM, 1·0 mM and 1·1 mM respectively. In spite of this binding to the enzyme, casein provided a very poor substrate for the starter acid phosphatase. The properties of acid phosphatase present in Cheddar cheese made with Str. cremoris NCDO 924 starter were consistent with the enzyme being exclusively of milk origin and small differences between this and the acid phosphatase previously isolated from bovine milk were attributable to the binding of peptides produced during the cheese maturation to the enzyme molecules. It was concluded that in cheese, phosphatase action was due largely to the enzyme of milk origin, with that provided by the starter being of minor importance.

In ripening and mature Cheddar cheese, 2 distinct types of birefringent microscopic crystalline inclusions are found. One of these is an irregularly shaped large aggregate of needle-like crystals (LAC). The histochemical demonstration of Ca in the LAC together with their total absence from cheese made with δ-gluconic acid lactone (GAL) instead of starter bacteria suggests that they are composed of Ca lactate.

The other type of inclusion is a smaller aggregate of crystals (SAC). They are more numerous than the LAC and are concentrated in areas which probably correspond to the lines of curd particle fusion. The SAC appear in cheese immediately after pressing and increase in number until the cheese is about 1 month old. They can be detected in unsalted, milled curd after 1 d and are present in large numbers in cheese made with GAL. These observations together with histochemical evidence that they may contain phosphate groups suggest that the SAC are probably composed of Ca phosphate. Their location in spaces between the fat and casein phases of the cheese indicates that they crystallize from pockets of residual whey. Each SAC is composed of a large number of very long (maximum length 4·5 μm), thin (maximum diam. 25 nm) crystals each of which is covered by a thin layer of electron-dense material tentatively identified as casein.