beta-lactoglobulin polymorphism in ovine breeds: Influence on cheesemaking properties and milk composition

Milk samples from 340 Merino and 234 Lacha sheep were analyzed by isoelectric focusing in thin gels with carrier ampholytes. Five different beta-lactoglobulin (beta-Lg) phenotypes (A, B, AB, AC and BC) were observed in milk from the Merino breed, but only three phenotypes were found in milk from the Lacha breed (A, B and AB). Differences in gene frequencies between flocks were observed. The gene frequencies were A: 0.58, B: 0.41, C: 0.01 in milk from the Merino breed and A: 0.47, B: 0.53 in milk from the Lacha breed. Rheological parameters, coagulation time (r), rate of firming (K-20) and curd firmness (A(max)) were determined, and chemical parameters (protein, lactose, fat and total solid content) were studied for the Merino breed; the pH was measured in all samples. No relationship was found between beta-Lg polymorphism and renneting properties in milk from the Merino breed. Protein content and pH were positively correlated with r.