The effect of feed intake on abomasal digesta outflow and gastrointestinal motility of preruminant calves given whole milk was studied. Digesta collections were made from calves fitted with re-entrant duodenal cannulas. In other calves myoelectric activity was recorded from electrodes implanted on the abomasum and proximal small intestine, sometimes concurrently with recordings from an electromagnetic flow sensor on the duodenum. After a feed of 2–8 kg milk recurring patterns of intestinal myoelectric activity associated with fasting were temporarily interrupted by a period of continuous irregular spike activity; the duration of the post feeding activity increased with intake of milk. Patterns of abomasal digesta flow were characterized by alternating periods of rapid and slower flow with a frequency that corresponded to cyclic change in myoelectric activity of the small intestine. Hourly rates of abomasal emptying of digesta during a 6-h collection period were significantly greater (P < 0·05) after giving feeds of 6–8 kg milk compared with measurements of flow rate when 2 kg feeds were given. It is concluded that myoelectric activity of the proximal small intestine exercises control over abomasal emptying of digesta by a mechanism which adjusts the mixing and propulsive functions of gut motility in accordance with the amount of milk consumed.

A series of short duration experiments has shown that infections caused by the milking machine or the way in which it is used can be controlled by fitting deflector shields in the teatcup liners. This not only provides a simple means of controlling such infections, but demonstrates that they result from penetration of the streak canal of the teat by contaminated milk particles impacting on the teat ends.

The mammary glands of conventionally reared cows, never exceeding a live weight gain (LWG) of 0·74 kg/d, weighed 39% more and contained 68% more secretory tissue than glands of rapidly reared animals grown at 1·1 kg/d. In 11-month-old heifers reared at 3 rates of LWG (L, 0·57; M, 0·76 and H, 1·18 kg/d) gland weight was related to LWG, but dissected mammary parenchyma was heavier in animals on treatment L than on treatment H and followed a quadratic relationship. Parenchymal composition on treatment H was correlated to both age and body weight at puberty. No similar trend was observed in treatments L and M although group L animals had more ductal tissue and less fat than those of group M. Heifers from treatment L were reared during pregnancy at either 0·68 or 0·84 kg/d LWG (treatments LL and LH respectively) and heifers from treatment H at 0·58 kg/d (treatment HL). Total gland weight was unaffected by treatment, but the percentage by weight of secretory tissue in the gland in treatment HL was less than for treatments LL and LH. These experiments confirm that mammary development is permanently impaired by high rates of LWG in the first year of life. There was no impairment of mammary development in heifers reared moderately in the first year and more rapidly during pregnancy.

Seven lactating goat mammary glands from 6 goats were perfused for several hours in the presence of [U-14C]L-leucine (4 experiments) or [2-3H; l-14C]DL-leucine (3 experiments) and received adequate quantities of glucose, acetate and amino acids. Radioactivity in casein was mainly recovered in leucine and 90% of casein leucine was derived from free plasma leucine. About 64% of the leucine molecules were used for casein synthesis. Up to 12% of the molecules were channelled into lipid synthesis, while the remaining (up to 24%) were metabolized to CO2. From the 3H/14C ratio of casein and casein leucine, it was calculated that 70–80% of the leucine molecules were reversibly transaminated before their incorporation into milk protein. However, only 4–8% of the plasma leucine molecules were transaminated during passage through the udder. Different pools for oxidation and for protein synthesis may be present in the goat mammary gland.

The ethanol (EtOH) stability characteristics of skim-milk concentrates were found to be governed by their chloride ion content. This effect appeared to be largely one of ionic strength. At pH values around 7·0 and above, EtOH stability showed a linear decrease with increasing chloride content but at pH values < 7 the relationship was non-linear. This empirical observation allows the EtOH stability of a skim-milk concentrate to be predicted from simple measurements on the original milk sample. Moreover, predicted increases in the EtOH stability of concentrated milks were obtained when the levels of monovalent ions in the system were reduced either by dialysis before or after concentration or by ultrafiltration.

The composition of casein in Irish milk for manufacturing was examined throughout the year. Large changes in composition were observed in the final quarter of the year as a result of the influence of late lactation when the proportion of αs- and β-caseins declined and the proportion of κ- and γ-caseins and of minor casein components increased. Similar changes in casein composition were induced by treatment of milk with porcine plasmin. The activity of plasmin-like milk proteinase in milk was quantified from the rate of conversion of added [14C]β-casein to [14C]γ-caseins. This activity was considerably higher in a late lactation milk than in a mid lactation milk and was ∼ 20 times higher at 37 °C than at 4 °C. It was concluded that casein compositional changes in late lactation were largely the result of proteolysis of individual caseins by plasmin-like milk proteinase.

Fourteen samples of milk fat, representing a wide range of individual fatty acid contents, were subjected to stereospecific analysis to determine fatty acid contents at the sn-l-, sn-2- and sn-3-positions of the triglycerides. Highly significant linear relationships were found between the content of a fatty acid at the 3 positions and the content of the same acid in the intact triglycerides. As the content of an acid increased in the triglycerides there were increases in the content of that acid at the 3 positions. When the content of an acid changed in the triglycerides, the content at the 3 stereospecific positions did not change at the same rate. The positions with the highest slope values corresponded to the positions where the individual fatty acids were preferentially esterified.

A study of the inhibitory action of Debaryomyces hansenii (31 strains) on Clostridium tyrobutyricum (5 strains) and Cl. butyricum (2 strains) on laboratory media showed that Deb. hansenii inhibited the growth of these organisms, and that this effect was due not only to competition for nutrients but also to the production of both extra-and intracellular antimicrobial metabolites. The inhibitory effect varied with strain and occurred whether the yeasts were grown aerobically or under reduced O2 tension.

The extracellular acid lipase produced by Penicillium roqueforti strain 1173 was purified by precipitation with 50 % ethanol, DEAE Sephadex A 50 ion exchange chromatography and 2 successive treatments with SP Sephadex C 50. An ~ 400-fold purification with a 35 % yield was obtained. The enzyme was active from pH 1·7–10·5, with an optimum activity pH of 6·5 at 20 °C and 6·0 at 30 °C. A second minor optimum appeared close to pH 2·5 and there was a minimum activity at pH 3·6. In the presence of 0·1 M-CaCl2 at 30 °C, the optimum was at pH 5·5, also the pH value where inhibition by CaCl2 was least (9%). The pH stability curve at 30 °C showed no discontinuities and had a maximum between pH 3·7 and 6·0. At pH 6·5 activity at 5 °C represented 37 % of the maximum value, which was reached at 35–40 °C and the apparent activation energy was about 5·42 kcal mol-1. Between pH 4·0 and 7·0, the ratio of hydrolysis velocity at 30 °C compared to that at 20 °C ranged from 2·1 to 1·2. At pH 6·0, the enzyme began to be inactivated at temperatures above 35 °C with decimal destruction times (D values) of 150, 29 and 4 min for respective temperatures of 40, 45 and 50 °C. In terms of substrate specificity the maximum activity was obtained with tricaproin whilst with tributyrin, tricaprylin, butter oil and triolein relative velocities were 22, 6·7, 3·0 and 1·5% respectively of that for tricaproin whilst Tween 20 and triacetin were 2·5 and 2% respectively.

An extract of Kluyveromyces lactis 416 and a β-galactosidase preparation (Maxilact 40000) contaminated with proteinase, showed similar pH profiles of caseinolytic activity. Similar modes of casein hydrolysis (κ-, > αs-, ≥ β-) were observed at pH 5·0 (the pH of Cheddar cheese), without detection of bitterness. The contaminated Maxilact preparation contained similar proteinase types to those detected in an autolysate of K. lactis. Both the autolysate and the Maxilact preparation contained acid endopeptidase (proteinase A), serine endopeptidase (proteinase B) and serine exopeptidase (carboxypeptidase Y) activities. Some aminopeptidase activity was also detected in both preparations. There were some differences in apparent molecular weight and charge properties between proteinase A and B and carboxypeptidase Y from the 2 proteinase sources.

Hydrogen peroxide accumulated in aerated cultures of Streptococcus lactis C10, the amount depending on the sugar being utilized. When the energy source was galactose or (to a lesser extent) lactose or maltose, H2O2 reached autoinhibitory levels. With glucose, H2O2 reached levels which did not cause obvious inhibition, and then declined. Washed cell suspensions utilized several media ingredients including glucose, galactose and yeast extract as substrates for O2 uptake, but cell-free extracts utilized none of these. The only substrate which supported O2 uptake by cell-free extracts was NADH. The activity of NADH oxidase was not affected by several intermediates of carbohydrate metabolism. Evidence was obtained to show that its synthesis was regulated via induction by O2 with an overriding catabolite repression type control, when cells were grown at the expense of glucose.

A method has been developed, using the fluorogenic substrate 4-methylumbelliferyl oleate, to measure the activity of the extracellular lipase of the psychrotroph Pseudomonas fluorescens AR11 in milk. Inhibition of lipolysis by constituents of skim-milk was prevented by including both sodium taurocholate and cetyltrimethylammonium bromide in the reaction mixture. Cream also interfered with the reaction and skim-milk was used for high sensitivity. Natural milk lipase was readily inactivated by heat treatment to which AR11 lipase was relatively resistant.

A new technique is described for the microfiltration of cheese brine. Soft cheese brine with viable counts/ml of up to 1·2 × 106 bacteria and 2·2 × 104 yeasts and moulds was filtered using a pleated tangential flow filtration cartridge of 0·2 εm pore size membrane. This filtration resulted in a 3–4 orders of magnitude reduction of bacteria and the complete rejection of yeast and mould from the permeate. Hard cheese brine with similar bacterial loads was treated with a 1·2 εm pore size membrane cartridge and the resulting permeate contained 2–3 orders of magnitude fewer bacteria and no yeasts or moulds. Flux decline during the filtration was a function of the number of microorganisms and the amount of N in the brine. A cleaning procedure using enzyme and acid washes was established in order to prolong membrane performance.

The apparent diffusion coefficients for NaCl in Romano-type cheese salted by brining or dry salting were ∼0·23 cm2/d. A plot of the natural logarithm of % salt-in moisture against distance was almost linear, the slope of which is the distance over which the salt concentration decreases by a factor of 1/e (0·368). Such plots may be useful in predicting the concentration of NaCl at any point in the cheese after any period of brining. After 9 d brining, the water to salt flux (ratio of outflow of water to inflow of NaCl) decreased from 2·42 at the surface to ∼0·5 in the middle zone of the cheese and increased again to > 1 at greater distances from the cheese/brine interface.

Intracellular cell-free enzyme extracts (CFE) of cheese starter bacteria significantly enhanced the flavour-accelerating effect of commercial neutral proteinase without increasing the gross proteolysis in Cheddar cheese. Peptide and amino acid N were released more rapidly in CFE-treated cheeses, compared with those treated with neutral proteinase or untreated controls.

Blocks of Cheddar cheese ranging in weight from ¾ to 44 lb were vacuum-wrapped and stored for up to 6 weeks. Panel assessment after 0, 3 and 6 weeks showed that the quality decreased, and off-flavours increased with decrease in block size. Headspace analysis showed that the volatile substances H2S and CH3SH decreased in concentration in line with quality.