Extreme frequencies of the α_s1-casein “null” variant in milk from Norwegian dairy goats – Implications for milk composition, micellar size and renneting properties

Abstract

Caprine α s1 -casein polymorphism is one of the key factors which determines important technological properties of milk, such as rennetability and cheese yield. The indigenous Norwegian goat breed is characterized by a remarkably high frequency (>70%) of a "null" variant of α s1 -casein unique to this population. This mutation, referred to as the exon 12 D allele, involves a single base deletion in exon 12 of the α s1 -casein gene. The aim of this study was to provide more detailed information on how α s1 -casein polymorphism affects composition and rennet coagulation properties of milk from Norwegian dairy goats. Class of α s1 -casein significantly affected milk composition; crude protein, casein and pH. The mean casein micelle size was larger in milks containing α s1 -casein "null" variant when compared to "strong" milks; in contrast, the heat-induced changes in micelle size appeared to be least pronounced in this group. Compositional differences between "strong" and "null" milks may explain these differences. α s1 -Casein class had a significant effect on gel strength recorded 30 min after the addition of rennet, with the "strong" milks giving the greatest firmness. However, a considerable fraction of the milk samples in this study were unable to form a strong clot, regardless of the α s1 -casein variant. These results indicate that environmental and compositional factors not considered in this study may be important in the curd formation process.

Effect of production season on protein fraction content in milk of various breeds of goats in Poland

“…; Devold et al . ). In the study of Mayer and Fiechter (), which included six breeds of goats (coloured, Pinzgau, Saanen, Strahlen, Toggenburg and white) maintained in Austria, only small (statistically insignificant) differences in the chemical composition of milk were found.…”

Effect ofCSN1S1gene polymorphism and stage of lactation on milk yield and composition of extensively reared goats

“…The analysis of Sarda goat milk composition revealed higher protein and casein percentages when compared with other goat breeds (Kusza et al 2007;Strzałkowska et al 2009;Devold et al 2010;Pagano et al 2010). The effect of CSN1S1 polymorphism on protein and casein content is in agreement with the aforementioned studies, while differences emerged regarding the expression level of α s1 -CN, in fact, the AA goats produced on average 4·42 g/l per allele and the BB produced 4·94 g/l per allele, both higher than the values reported so far (Grosclaude et al 1987;Caravaca et al 2009).…”

Phenotypic factors affecting coagulation properties of milk from Sarda ewes

“…Noncoagulating samples are those samples that do not coagulate within 30 min from rennet addition to milk. They have been very frequently evidenced for both individual and bulk milk samples in cattle (Ikonen et al, 1999), water buffaloes , sheep (Pazzola et al, 2013;Bittante et al 2014), and goats (Devold et al, 2011;Pazzola et al, 2012Pazzola et al, , 2014. The presence of NC samples also affects the actual meaning of average values of MCP and the possibility to estimate breeding values of animals (Ikonen et al, 2004;Cecchinato et al, 2011).…”