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

Abstract

Milk samples from 340 Merino and 234 Lacha sheep were analyzed by isoelectric focusing in thin gels with carrier ampholytes. Five different β-lactoglobulin (β-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 (K20) and curd firmness (Amax) 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 ß-Lg polymorphism and renneting properties in milk from the Merino breed. Protein content and pH were positively correlated with r.