Perfil eletroforético das proteínas do leite e estabilidade no teste do álcool.

Abstract

Unstable non acid milk (LINA) characterizes for lack of stability of caseins, resulting in coagulation in the alcohol test, without high acidity, above 18°D and with changes in the milk s physic and chemical properties. Among chemical attributes, differences of total crude protein and protein fractions percentages are noticeable between stable and unstable milk. This study aimed to evaluate the relation between milk s electrophoretic profile and stability in the alcohol test with cows being fed with different diets. The trials were conducted at the dairy region of Pelotas, at the south of Rio Grande do sul State, Brazil.The first trial was held at the Embrapa Clima Temperado, from April to August, with two diets: control and feeding restriction, 100 and 60% of previous feeding amounts, with six Jersey cows, at the beginning of their lactation. The second trial was held at the Embrapa Clima Temperado, from May to June, with three diets: control (no additive inclusion), addition of sodium bicarbonate and addition of sodium citrate, with 17 Jersey cows at all lactation stages (76 to 293 days in milking). The third trial was held at the Colégio Agrícola Visconde da Graça UFPEL, from march to April, with three diets: control (deficient), 100% of energy nutritional requirements and 100% of protein-energy nutritional requirements, using 12 Holstein and Jersey cows, at the beginning and mid lactation. In all evaluations the following analyses were performed: alcohol test (with ethanol concentration from 68 to 80°GL v/v), titrable acidity, pH, boiling test, chemical composition, Somatic Cells Count (SCC). Besides, milk production, body weight, body condition score were 12 also evaluated. Milk s protein fractions were evaluate with electrophoreses in 12% poliacrilamide gel. In the first trial, diets did not change protein fraction of the milk not its composition and stability, just milk production. However, stable milk and unstable milk presented differences for κ-CN percentages. In the second, the addition of sodium bicarbonate and addition of sodium citrate, influenced protein fraction β e κ-CN. The unstable milk presented higher amounts of αs-CN. In the third, the adjusted diets could alter milk production, protein, total solids and levels of calcium in milk and blood.