Variation in protein profile of bulk milk from Northern Sweden

Sammanfattning: The protein composition of milk samples from Norrland, Sweden was investigated by capil-lary electrophoresis, in order to evaluate the variation in protein profile from different breeds at different collection periods during the year. The protein profile is of importance for pro-cessability of the milk, and is known to be influenced partly by genetics. Bulk milk samples from 13 farms with Swedish Mountain Breed (SMB), Swedish Jersey (SJB), Swedish Red and White (SRB) and Swedish Holstein (SH) were analysed for content of αs1-, αs2-, β-, and κ-casein, as well as α-lactalalbumin and β-lactoglobulin. The samples were also analysed in regard to total protein content, fat content and casein micelle size (CMS). Sampling took place during three periods; November, February and September, and the breeds were com-pared between the “indoor period” (November and February) and “outdoor period” (Sep-tember) as well as during the whole period of investigation. For analysis during the indoor versus outdoor period, SMB and SJB was set as one cluster. The analysis showed significant differences between the breeds during the period of investigation as well as between the indoor and outdoor period. During the period of investigation SJB had the highest inclusion of κ-casein, which was 3.29 percentage points higher compared to SRB and 1.67 percentage points higher than SH. SJB was found to have a significantly lower inclusion of β-casein compared to SH, SRB and SMB with a difference of 7.20, 5.92 and 5.64 percentage points respectively. SJB was found to have a significantly higher inclusion of β-lactoglobulin com-pared to SH by 1.24 percentage points. Significant differences was found between the clus-ters when the indoor and outdoor period was compared. The SMB/SJB cluster (indoor) and SMB/SJB (outdoor) was found to have a significantly higher inclusion of κ-casein by 2.31 and 2.99 percentage points respectively compared to SH (indoor). SH (indoor) was found to have a significantly higher inclusion of total β-casein compared to SMB/SJB (indoor) and SMB/SJB (outdoor) by 3.47 and 4.67 percentage points respectively. No significant differ-ences regarding protein composition within any breed was found between the indoor and outdoor period. The fat content in SJB milk was found significantly higher compared to SMB, SRB and SH during the period of investigation by 2.44, 2.21 and 2.53 percentage points respectively. The CMS differed significantly between the breeds between the indoor and outdoor period. SH (outdoor) was found to have a significantly larger CMS compared to SH (indoor), SMB (indoor), SRB (indoor) and SJB (indoor) (p=0.018, p=0.023, p=0.012 and p=0.034 respectively). It was concluded that the protein profile varies between breeds, and that season of collection only had a limited effect on the milk- and protein composition. The small variance regarding season could partly depend on the low sample size. More ex-tensive studies are needed in order to support the results.