Comparison of milk protein composition and rennet coagulation properties in native Swedish dairy cow breeds and high-yielding Swedish Red cows

Abstract

Recent studies have reported a very high frequency of noncoagulating milk in Swedish Red cows. The underlying factors are not fully understood. In this study, we explored rennet-induced coagulation properties and relative protein profiles in milk from native Swedish Mountain and Swedish Red Polled cows and compared them with a subset of noncoagulating (NC) and well-coagulating (WC) milk samples from modern Swedish Red cows. The native breeds displayed a very low prevalence of NC milk and superior milk coagulation properties compared with Swedish Red cows. The predominant variants in both native breeds were α-casein (α-CN) B, β-CN A and β-lactoglobulin (β-LG) B. For κ-CN, the B variant was predominant in the Swedish Mountain cows, whereas the A variant was the most frequent in the Swedish Red Polled. The native breeds displayed similar protein composition, but varied in content of α-CN with 9 phosphorylated serines (9P) form. Within the Swedish Mountain cows, we observed a strong inverse correlation between the relative concentration of κ-CN and micelle size and a positive correlation between ionic calcium and gel firmness. For comparison, we investigated a subset of 29 NC and 28 WC milk samples, representing the extremes with regard to coagulation properties based on an initial screening of 395 Swedish Red cows. In Swedish Red, NC milk properties were found to be related to higher frequencies of β-CN A, κ-CN E and A variants, as well as β-LG B, and the predominant composite genotype of β- and κ-CN in the NC group was AA/AA. Generally, the AA/AA composite genotype was related to lower relative concentrations of κ-CN isoforms and higher relative concentrations of α-, α-, and β-CN. Compared with the group of WC milk samples, NC milk contained a higher fraction of α-CN and α-lactalbumin (α-LA) but a lower fraction of α-CN 9P. In conclusion, milk from native Swedish breeds has good characteristics for cheese milk, which could be exploited in niche dairy products. In milk from Swedish Mountain cows, levels of ionic calcium seemed to be more important for rennet-induced gel firmness than variation in the relative protein profile. In Swedish Red, lower protein content as well as higher fraction of α-CN and lower fraction of α-CN 9P were related to NC milk. Further, a decrease in the frequency of the composite β-κ-CN genotype AA/AA through selective breeding could have a positive effect on milk coagulation properties.

Milk protein fractions strongly affect the patterns of coagulation, curd firming, and syneresis

“…The high content of α-LA is generally associated with poorly coagulated and noncoagulated milks, which is often explained in terms of a positive correlation between α-LA and β-LG contents (Jensen et al, 2012b;Ketto et al, 2017;Poulsen et al, 2017). In the present work, no clear effect seems to be triggered by an increase in the amounts or proportions of this whey protein ( Figure 5).…”

“…It is worth noting that some of the discrepancies of other work with our results could be due to the fact that the majority of these studies did not analyze or include the genetic variants of β-LG in the statistical model. In fact, several authors did indeed find a strong effect of β-LG genetic variants on milk coagulation and curd firmness (Marziali and Ng-Kwai-Hang, 1986;Heck et al, 2009;Poulsen et al, 2017).…”

The effects of cow genetic group on the density of raw whole milk

“…The results from their study showed a significant impact of breed on the relative overall concentrations of proteins (as shown in the results of this study, milk of Jersey cows have highest protein content, compared to EHF and NAHF strains of Holstein Friesian). Protein content, as well as its composition, is known to impact the processability of milk (Malossini et al, 1996;Tyrisevä et al, 2004;Wedholm et al, 2006;Ketto et al, 2017;Poulsen et al, 2017), however, its impact on milk density is not clearly established. The impact of seasonal and compositional variation on milk density has been assessed in a study by the same authors (Parmar et al, 2020), which showed that variation in milk constituents including protein over different seasons significantly impacted milk density (P < 0.05).…”

Quantification of the Effect of the Cattle Breed on Milk Cheese Yield: Comparison between Italian Brown Swiss and Italian Friesian

“…For instance, Italian Friesian cows, whose population corresponds to about 80% of dairy cows raised in Italy, produce milk with lower fat (−0.21 or −1.35 g/100 g) and casein (−0.27 or −0.38 g/100 g) contents than milks of Brown Swiss [ 4 , 5 ] or Jersey [ 3 ]. However, differences among breeds also include other specific properties such as the ratio among the casein fractions, genetic variants, level of post translational modifications and content of calcium phosphate [ 5 , 6 , 7 ]. All these “molecular” aspects influence the structural characteristics of the casein micelle, the aptitude of milk to rennet coagulation and the rheological properties of the resulting curd [ 8 , 9 , 10 ].…”