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

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.

Urinary N-acetyl-beta-D-glucosaminidase activity in type I diabetes mellitus.

We measured urinary albumin excretion rate (AER) and N-acetyl-beta-D-glucosaminidase (NAG) activity in relation to disease duration, acetylated hemoglobin (HbA1c), hypertension and puberty in 44 children and adolescents with type 1 diabetes mellitus. AER and Urinary NAG activity were significantly higher in the patients compared to controls (AER 19.4 +/-; 35.8 vs 4.7 +/- 4.4, NAG activity 5.6 +/- 0.6U vs. 1.6 +/- 0.2U). Microalbuminuria was present in seven patients (15.9%), all of whom were pubertal. There was no correlation between AER and urinary NAG activity. There was a significant direct correlation between AER and disease duration (P <0.05), HbA1c (P < 0.05), diastolic blood pressure (P <0.05) and puberty (P <0.05). None of the microalbuminuria related variables was significantly correlated with urinary NAG activity. Puberty was an independent factor for elevated urinary NAG activity. This study shows that urinary NAG is elevated in children and adolescents with type 1 diabetes mellitus, but is not associated with AER related factors except for puberty. Urinary NAG activity does not appear to be a useful marker for early detection of diabetic nephropathy in children and adolescents with type 1 diabetes mellitus.