Toomas Allmere

Flavour and texture in sourmilk affected by thickeners and fat content

When reducing fat content or replacing fat with thickener in reduced fat foods, flavour and texture may change. The objective of this study was to investigate effects of thickener and fat content o ...

Comparison of milk protein composition in a Swedish and a Danish dairy herd using reversed phase HPLC

Abstract The milk composition in a Swedish herd, consisting of Swedish Red and White cows (SRB) and Swedish Holstein cows (SLB), and in a Danish herd, consisting of Danish Holstein-Friesian cows (SDM), was evaluated. Concentrations of the major milk proteins (κ-casein, αS1-casein, β-casein, β-lactoglobulin A, β-lactoglobulin B and α-lactalbumin) of 134 individual milk samples were determined by reversed phase (RP) HPLC. Other parameters determined included milk fat, urea, lactose, calcium, lactoferrin, somatic cell count and protein degradation (determined as level of free amino-terminals). Analysis of variance was used to compare concentrations of analysed milk variables between SRB and SLB or between SLB and SDM. Concentration of total protein, total casein, β-casein and κ-casein were significantly higher in SRB milk compared with SLB milk. Concentration of α-lactalbumin and calcium were significantly higher in SDM milk than in SLB milk. The concentration of urea was higher in SLB than in SDM milk and is suggested to reflect differences in feeding regimes between the investigated Swedish and Danish herd.

Comparative studies on the gelling properties of cardosins extracted from Cynara cardunculus and chymosin on cow's skim milk

A comparative study was developed on the clotting activities and gelling properties of cardosins A and B, extracted from dried flowers of Cynara cardunculus, and chymosin on cows skim milk, at various pH values. The determination of the total milk-clotting activity was performed following an international standard, whereas a rheometer was employed to measure the viscoelastic properties of the gels subsequently formed: the evolution of the complex modulus (G*) and the phase angle (δ) was monitored with time. The G* values of the milk gels were higher for cardosins than for chymosin at pH 6.6, but the reverse held at pH 6.4 and 6.2. The δ values were identical for all three enzymes tested. Chymosin exhibited the highest specific milk clotting activity, followed by cardosin B. The clotting activity of chymosin seems to be more influenced than that of cardosins by the pH of milk.

Studies on Rheological Properties of Stirred Milk Gels Made from Milk with Defined Genetic Variants of κ-Casein and β-Lactoglobulin

The rheological properties of acidified milk gels made from milk with defined genetic variants of κ-casein and β-lactoglobulin have been investigated. Gels were prepared from skim milk after heating for 4 min at 90°C by acidification with glucono-δ-lactone and gentle stirring after holding for 24 h at 20°C. Stirred acidified milk gels were then kept at 6°C for 96 h and thereafter measured for the rheological properties using a Bohlin VOR Rheometer. The milk gels containing only the B variant of β-lactoglobulin (homozygous cows) were found to have a significantly higher elastic modulus as compared to milk gels containing both β-lactoglobulin A and B or only A. An explanation could be that more β-lactoglobulin B had aggregated with the casein micelles, since a strong correlation was found between the loss of native β-lactoglobulin in the milk serum and the gel firmness. No correlation was found between gel firmness and any of the κ-casein genetic variants, dry matter content and the total protein concentration, respectively. Furthermore, viscous properties did not vary between the acidified milk gels in this experiment.

Casein retention in curd and loss of casein into whey at chymosin-induced coagulation of milk

Impact of milk protein composition on casein (CN) retention in curd during the milk coagulation process was studied using a model cheese making system. Individual milk samples from 110 cows in mid lactation of the Swedish Red and Swedish Holstein breeds with known genotypes of beta-casein, kappa-casein and beta-lactoglobulin were defatted, coagulated with chymosin, subjected to syneresis and subsequent pressing simulated by centrifugation. The results indicated that kappa-casein concentration of milk plays an important role in the curd formation process and initial syneresis (whey after cutting), whereas an increased CN ratio was associated with less casein in whey after simulated pressing. Increased kappa-casein concentration of milk also characterized the milk samples with no measurable loss of casein in whey, compared with milk samples with casein lost in whey, both after cutting and after simulated pressing. Concentrations of alphas1-casein, beta-casein, and total casein in milk were positively associated with fresh curd yield, which showed a strong correlation with amount of casein retained in curd. No effect of protein genotype on fresh curd yield or casein in whey was found. The beta-lactoglobulin BB genotype was associated with increased casein retention in curd, most likely due to the association of this genotype with CN ratio.