Chemical composition, hygiene characteristics, and coagulation aptitude of milk for Parmigiano Reggiano cheese from herds yielding different milk levels

ABSTRACT The objective with this research was to compare milk quality parameters among herds characterized by different levels of milk production. The research involved 1080 bulk milk samples collected from 30 dairy herds, which produce milk for Parmigiano Reggiano cheese, during three years. Each milk sample was analysed for fat, crude protein, titratable acidity, total bacterial count, somatic cells, coliform bacteria, and Clostridia spores. Least mean values were obtained by ANOVA using milk production intervals from 6000 to 7999 (L-group), from 8000 to 9999 (M-group), and from 10000 to 12000 kg/cow/lactation (H-group) as fixed milk production classes. Increased milk production was associated with a reduction in milk fat content (from 3.54 in the L-group milk to 3.29 g/100 g in the H-group milk). An improvement in the hygienic-sanitary quality of milk was observed with increasing milk production. In fact, a progressive decrease in the total bacterial count (from 95 in the L-group milk to 45 103 cfu/mL in the H-group milk), number of coliforms (from 2294 in the L-group milk to 1342 cfu/mL in the H-group milk), and somatic cell number (from 382 in the L-group milk to 209 103 cells/mL in the H-group milk) was observed with the increase in milk production level. Finally, it appears that higher milk yield is connected with significant positive effects on the lactodynamometric properties of milk.

摘要 本研究旨在比较不同产奶水平奶牛群的牛奶品质参数。本研究于三年周期内，从30个用于生产帕马森·雷吉亚诺干酪(Parmigiano Reggiano)的奶牛群中采集了1080份批量乳样(bulk milk samples)。针对每份乳样，检测分析了其乳脂肪、粗蛋白、滴定酸度、总细菌数、体细胞数、大肠菌群及梭菌孢子含量。以泌乳期每头牛产奶量区间（6000~7999kg记为L组、8000~9999kg记为M组、10000~12000kg记为H组）作为固定产奶等级，通过方差分析(ANOVA)计算得到各组的最小二乘均值。研究结果表明，产奶量提升与乳脂肪含量降低呈显著负相关：L组乳样的乳脂肪含量为3.54g/100g，H组则降至3.29g/100g。随着产奶量升高，乳的卫生安全品质得到显著提升：总细菌数从L组的95×10³菌落形成单位每毫升(cfu/mL)降至H组的45×10³cfu/mL，大肠菌群数从L组的2294cfu/mL降至1342cfu/mL，体细胞数从L组的382×10³个/mL降至209×10³个/mL。最后，较高的产奶量对乳的泌乳动力学特性具有显著的正向影响。