Effects of stage of lactation, milk protein genotype and body condition at calving on protein composition and renneting properties of bovine milk

Abstract

The lactational variation in milk protein composition and renneting properties and their relationship to the cow's body condition at calving were investigated in 39 Danish Holstein first lactation cows fed on a well balanced standard diet. All milk characteristics measured were significantly affected by stage of lactation (P<0·01). Casein as a proportion of total milk nitrogen reached a maximum in mid lactation. The proportion of αs- and κ-casein in total casein decreased and the proportion of β-casein increased systematically during lactation while the proportion of γ-casein was lowest in mid lactation. The α-lactalbumin content of milk and its proportion of total whey proteins decreased during lactation. Renneting time was highest and curd firmness lowest in mid lactation. These results appeared to reflect a low degree of proteolysis in late-lactation milks compared with several other investigations, probably because of the good nutritional state of the cows. The body condition at calving affected proteolysis and the renneting properties of milk. A good body condition increased the content of whey protein in total milk nitrogen and of γ-casein in total caseins (P<0·05); in addition, curd firmness was improved (P<0·01) and aggregation time was reduced (P<0·05). We suggest that these effects were related to the fat metabolism and energy status of the cows during lactation. The interrelationships between the milk characteristics were evaluated by factor analysis to support the interpretation.

Effect of oxytocin on milk proteins and fatty acid profile inSahiwal cows during lactation periods

“…Similar results were found by Lucey and Fox (18), who reported that late lactation milk could have markedly lower casein concentrations than middle lactation milk. In casein protein, αs-CN contributing a major portion of total casein and being maximum at middle lactation in the control milk is supported by the findings of Ostersen et al (19), who found that the proportion of αs-CN in total casein decreased at end lactation. Barry and Donnelly (20) reported that αs-CN increased in early lactation and then fell for the rest of lactation.…”

Effect of Asparagus racemosus (shatavari) extract on physicochemical and functional properties of milk and its interaction with milk proteins

“…Decrease in pH probably also affected the stability of caseinate particles directly as well as indirectly by release of calcium ions from dissolved and colloidal complexes as the pH is lowered. Grandison et al (1984) and Ostersen et al (1997) found that milk pH affects predominantly the rennet coagulation time. Shatavari supplimented milk showed a decrease in pH compared to control milk and hence, decreased the rennet coagulation time.…”

Milk quality – a future approach from a researcher’s point of view

“…Milk containing the so-called BBphenotype of β-lactoglobulin have been shown to contain more casein and a higher casein number than the AA-phenotype. The BB-milk is therefore expected to be more suitable for cheese production than the AA-milk (McLean et al, 1984;van den Berg et al, 1992;Ikonen et al, 1997;Ostersen et al, 1997). The BB-phenotype of к-casein has been associated with superior cheese making properties of the milk and with increased cheese yield (Schaar, 1984;Schaar et al, 1985, Walsh et al, 1995, 1998a.…”