Composition and effect of blending of noncoagulating, poorly coagulating, and well-coagulating bovine milk from individual Danish Holstein cows

Abstract

The aim of the present investigation was to study the underlying causes of noncoagulating (NC) milk. Based on an initial screening in a herd of 53 Danish Holstein-Friesians, 20 individual Holstein-Friesian cows were selected for good and poor chymosin-induced coagulation properties; that is, the 10 cows producing milk with the poorest and best coagulating properties, respectively. These 20 selected cows were followed and resampled on several occasions to evaluate possible changes in coagulation properties. In the follow-up study, we found that among the 10 cows with the poorest coagulating properties, 4 cows consistently produced poorly coagulating (PC) or NC milk, corresponding to a frequency of 7%. Noncoagulating milk was defined as milk that failed to form a coagulum, defined as increase in the storage modulus (G') in oscillatory rheometry, within 45min after addition of chymosin. Poorly coagulating milk was characterized by forming a weak coagulum of low G'. Milk proteomic profiling and contents of different casein variants, ionic contents of Ca, P and Mg, κ-casein (CN) genotypes, casein micelle size, and coagulation properties of the 4 NC or PC samples were compared with milk samples of 4 cows producing milk with good coagulation properties. The studies included determination of production of caseinomacropeptide to ascertain whether noncoagulation could be ascribed to the first or second phase of chymosin-induced coagulation. Caseinomacropeptide was formed in all 8 milk samples after addition of chymosin, indicating that the first step (cleavage of κ-CN) was not the cause of inability to coagulate. Furthermore, the effect of mixing noncoagulating and well-coagulating milk was studied. By gradually blending NC with well-coagulating milk, the coagulation properties of the well-coagulating samples were compromised in a manner similar to titration. Milk samples from cows that consistently produced NC milk were further studied at the udder quarter level. The coagulation properties of the quarter milk samples were not significantly different from those of the composite milk sample, showing that poor coagulation traits and noncoagulation traits of the composite milk were not caused by the milk quality of a single quarter. The milk samples exhibiting PC or NC properties were all of the κ-CN variant AA genotype, and contained casein micelles with a larger mean diameter and a lower fraction of κ-CN relative to total CN than milk with good coagulation properties. Interestingly, the relative proportions of different phosphorylation forms of α-CN differed between well-coagulating milk and PC or NC milk samples. The PC and NC milk samples contained a lower proportion of the 2 less-phosphorylated variants of α-CN (α(S1)-CN-8P and α(S2)-CN-11P) compared with samples of milk that coagulated well.

Dairy processing and cold storage affect the milk coagulation properties in relation to cheese production

“…An increase in viscosity is observed followed by branching of the aggregates, thus characterizing the second stage (Dalgleish and Corredig 2012). It has been questioned whether κ-CN molecules in poor and non-coagulating milks are actually cleaved to the same extent as κ-CN in good coagulating milk by chymosin, but in an earlier study, it was observed that the first phase occurred to comparable extent in both good and non-coagulating milk (Frederiksen et al 2011a).…”

“…It is clear that the majority of samples present not only good coagulation properties but also poor coagulating and even non-coagulating milk (Ikonen et al 2004;Frederiksen et al 2011a;Poulsen et al 2013). The reasons behind this variability can be many, as a variety of factors influence the milk coagulation properties, including lactation stage, somatic cell count, breed, and parity, and these factors influence the properties by manifestation of changes in the milk composition (Devold et al 2000;Ikonen et al 2004;Frederiksen et al 2011b).…”

“…Commonly identified risk factors for poor coagulating and non-coagulating milk include low casein (CN) content, especially low ĸ-CN content, ĸ-CN genetic polymorphism, larger CN micelles, and lower Ca content (Tsioulpas et al 2007;Frederiksen et al 2011a;Jensen et al 2012;Gustavsson et al 2014;Malacarne et al 2014), but the underlying reasons are still not completely elucidated. Indeed, there is no report in the literature on how milks with distinct coagulation abilities respond to cold storage.…”

Mapping and fine-mapping of genetic factors affecting bovine milk composition

“…Consequently, non-coagulation of milk can be considered as a new phenotype that accounts for the needs of the cheese industry. Non-coagulation (NC) of milk is prevalent among several dairy cattle breeds, such as Swedish Red, Finnish Ayrshire, Holstein-Friesian, and Italian Brown Swiss, to name a few (e.g., Frederiksen et al, 2011;, Gustavsson et al, 2014. The prevalence of NC milk varies among these breeds ranging from 4% in Italian Brown Swiss (Cecchinato et al, 2009) up to 13% in Finnish Ayrshires (Ikonen et al, 2004).…”

“…Since total milk production is about 3 million tons per year (LRF Dairy Sweden, 2015) and the market price of milk produced is about 0.28 euros per kg, the problem of NC milk affects milk with a value of approximately 63 million euros per year. Frederiksen et al (2011) has estimated in 25% the proportion of NC milk in a batch of wellcoagulating milk that is sufficient to deteriorate the MCP of well-coagulating milk. Van Hooydonk et al (1986) showed that the addition of calcium would restore coagulation of NC milk but not to the level of well-coagulating milk according to Hallén et al (2010).…”