The effects of level of dietary protein on the milk production and rumen physiology of dairy cows fed a diet based on a tropical grass hay

zFour rumen-fistulated, multiparous Holstein-Friesian cows in early lactation were offered mixed diets based on rhodes grass hay (Chloris gayana) cv. Callide containing 13, 14, 15 or 16% crude protein (CP) on a dry matter basis, in a 4 x 4 latin square design. The estimated undegradable protein concentration in these diets was similar with rumen degradable protein concentration varying. Cows fed a diet containing 13% CP had lower (P = 0.07) milk yields than cows in other treatments (20.4 vs 21.9, 22.0 and 22.2 L/d for 13, 14, 15 and 16% CP, respectively). A positive linear relationship was found (P = 0.06) between organic matter intake and dietary CP%. There were negative linear relationships between dietary CP% and digestibilities of dry matter (P = 0.09), organic matter (P = 0.06) and neutral detergent fibre (P = 0.02). Feeding a diet containing 13% CP resulted in significantly lower (P = 0.001) molar proportions (%) of rumen valerate in comparison with other treatments. The molar proportions of isovalerate differed (P = 0.001) between treatments (0.66, 0.78, 0.89 and 1.04%) for 13, 14, 15 and 16% CP, respectively). Dietary protein level had no effect on rates of passage, in situ digestion of rhodes grass hay or ratios of allantoin: creatinine in urine. These data showed that increasing the dietary CP concentration of lactating cows fed diets based on rhodes grass hay increased intakes and not significantly improved at dietary CP concentrations above 14% DM.

Heat-induced changes in UHT milks - Part 1

Raw milk was stored for 0, 2 and 4 days and processed in a UHT pilot plant by either direct or indirect heating. The unstored raw milk was also pasteurised. The thermally induced changes resulting from these treatments were investigated by examining a number of indices of heat damage. Lactulose, furosine, total and free hydroxymethylfurfural (HMF) and acid-soluble beta-lactoglobulin were analysed by high performance liquid chromatography (HPLC) while soluble tryptophan was examined by fluorescence spectroscopy. The directly heated UHT milk showed less heat damage than the indirectly heated milk, while the pasteurised milk displayed the least heat damage. During storage of the UHT milk for 12 weeks at similar to20degreesC, the levels of lactulose remained constant, while the furosine concentration increased. Both the total HMF and undenatured beta-lactoglobulin contents showed a general decrease during storage; however free HMF values initially rose but then decreased after four weeks' storage. As the age of the milk at the time of UHT processing increased, the levels of some of the indicators decreased. It is concluded that lactulose is the most reliable index of heat treatment, as it is virtually unaffected by refrigerated storage of the milk before or ambient storage after UHT processing. Reliance on other indicators may give misleading information on the heat load that UHT milk has received during processing.

Quantitative description of the interaction between folate and the folate-binding protein from cow's milk

A detailed study has been carried out on the dependence of folate binding on the concentration of FBP (folate-binding protein) at pH 5.0, conditions selected to prevent complications arising from the pre-existing self-association of the acceptor. In contrast with the mandatory requirement that reversible interaction of ligand with a single acceptor site should exhibit a unique, rectangular hyperbolic binding curve, results obtained by ultrafiltration for the FBP-folate system required description in terms of (i) a sigmoidal relationship between concentrations of bound and free folate and (ii) an inverse dependence of affinity on FBP concentration. These findings have been attributed to the difficulties in determining the free ligand concentration in the FBP-folate mixtures for which reaction is essentially stoichiometric. This explanation also accounts for the similar published behaviour of the FBP-folate system at neutral pH, which had been attributed erroneously to acceptor self-association, a phenomenon incompatible with the experimental findings because of its prediction of a greater affinity for folate with increasing FBP concentration.

Milk thistle and indinavir: a randomized controlled pharmacokinetics study and meta-analysis

Objectives: To determine whether ingestion of milk thistle affects the pharmacokinetics of indinavir. Methods: We conducted a three-period, randomized controlled trial with 16 healthy participants. We randomized participants to milk thistle or control. All participants received initial dosing of indinavir, and baseline indinavir levels were obtained (AUC(0-8)) (phase I). The active group were then given 450 mg milk-thistle extract capsules to be taken t.i.d. from day 2 to day 30. The control group received no plant extract. On day 29 and day 30, indinavir dosing and sampling was repeated in both groups as before (phase II). After a wash-out period of 7 days, indinavir dosing and sampling were repeated as before (phase III). Results: All participants completed the trial, but two were excluded from analysis due to protocol violation. There were no significant between-group differences. Active group mean AUC(0-8) indinavir decreased by 4.4% (90% CI, -27.5% to -26%, P=0.78) from phase I to phase II in the active group, and by 17.3% (90% CI, -37.3% to +9%, P=0.25) in phase III. Control group mean AUC(0-8) decreased by 21.5% (90% CI, -43% to +8%, P=0.2) from phase I to phase II and by 38.5% (90% CI, -55.3% to -15.3%, P=0.01) of baseline at phase III. To place our findings in context, milk thistle-oindinavir trials were identified through systematic searches of the literature. A meta-analysis of three milk thistle-indinavir trials revealed a non-significant pooled mean difference of 1% in AUC(0-8) (95% CI, -53% to 55%, P=0.97). Conclusions: Indinavir levels were not reduced significantly in the presence of milk thistle.

Methods of detecting fouling caused by heating of milk

Fouling is the deposition of milk solids on heat transfer sur aces, particularly heat exchangers. It is a major industrial problem, which causes a decrease in heat transfer efficiency and shortens run times. The resultant effect is a decrease in process efficiency and economy. For studying and monitoring deposit formation, suitable fouling detectors or methods of measuring the deposit are required. This can be achieved through direct means, whereby the deposit is analyzed after a certain time, or indirectly through instrumentation for monitoring parameters such as temperature, pressure, flow rate, overall heat transfer coefficient, heat flux, and other physical properties. This article reviews the various reported fouling detection methods.

Impacts of feeding system and season on milk composition and Cheddar cheese yield in a subtropical environment

Milk obtained from cows on 2 subtropical dairy feeding systems were compared for their suitability for Cheddar cheese manufacture. Cheeses were made in a small-scale cheesemaking plant capable of making 2 blocks ( about 2 kg each) of Cheddar cheese concurrently. Its repeatability was tested over 10 separate cheesemaking days with no significant differences being found between the 2 vats in cheesemaking parameters or cheese characteristics. In the feeding trial, 16 pairs of Holstein - Friesian cows were used in 2 feeding systems (M1, rain-grown tropical grass pastures and oats; and M5, a feedlot, based on maize/barley silage and lucerne hay) over 2 seasons ( spring and autumn corresponding to early and late lactation, respectively). Total dry matter, crude protein (kg/cow. day) and metabolisable energy (MJ/cow.day) intakes were 17, 2.7, and 187 for M1 and 24, 4, 260 for M5, respectively. M5 cows produced higher milk yields and milk with higher protein and casein levels than the M1 cows, but the total solids and fat levels were similar (P > 0.05) for both M1 and M5 cows. The yield and yield efficiency of cheese produced from the 2 feeding systems were also not significantly different. The results suggest that intensive tropical pasture systems can produce milk suitable for Cheddar cheese manufacture when cows are supplemented with a high energy concentrate. Season and stage of lactation had a much greater effect than feeding system on milk and cheesemaking characteristics with autumn ( late lactation) milk having higher protein and fat contents and producing higher cheese yields.

Lipoprotein lipase and lipolysis in milk

Bovine milk contains a lipoprotein lipase that accounts for most, if not all, of its lipolytic activity. The total lipase activity in raw milk is sufficient to cause rapid hydrolysis of a large proportion of the fat. However, in reality this does not happen, because the lipase is prevented from accessing the fat by the milkfat globule membrane. Physical damage to this membrane in raw milk initiates lipolysis. Furthermore, simply cooling certain individual milks soon after secretion can initiate the so-called spontaneous lipolysis. The biochemical basis of spontaneous lipolysis is still poorly understood, but it appears to be related to a balance between activating and inhibiting factors in the milk. Lipolysis in milk and milk products causes rancid off-flavours and other problems, and is a constant concern in the dairy industry. A thorough understanding of the mechanism of lipolysis and constant vigilance by operatives is required to minimize lipase-related problems. (c) 2006 Elsevier Ltd. All rights reserved.

Effect of extrusion parameters on flavour retention, functional and physical properties of mixtures of starch and D-limonene encapsulated in milk protein

The purpose of this research was to investigate the retention of flavour volatiles encapsulated in water-insoluble systems during high temperature–short time extrusion process. A protein precipitation method was used to produce water-insoluble capsules encapsulating limonene, and the capsules were added to the extruder feed material (cornstarch). A twin-screw extruder was used to evaluate the effect of capsule level of addition (0–5%), barrel temperature (125–145 °C) and screw speed (145–175 r.p.m.) on extruder parameters (torque, die pressure, specific mechanical energy, residence time distribution) and extrudate properties [flavour retention, texture, colour, density, expansion, water absorption index, water solubility index (WSI)]. Capsule level had a significant effect on extrusion conditions, flavour retention and extrudate physical properties. Flavour retention increased with the increase in capsule level from 0% to 2.5%, reached a maximum value at capsule level of 2.5% and decreased when the capsule level increased from 2.5% to 5%. The die pressure, torque, expansion ratio, hardness and WSI exhibited the opposite effect with the presence of capsules.