Effect of milk urea content on characteristics of matured Reblochon cheeses

Abstract

According to a crossed experimental design, two groups of 14 Montbéliarde dairy cows received in the winter two hay-based diets, with a normal or a high nitrogen level, obtained by substituting in the diet 2.5 kg of soybean meal to 2.5 kg of cereal concentrate. During the last week of the two experimental periods of 3 weeks, four batches of Reblochon cheese were manufactured with three different milks: control milk, milk from soya-fed cows and control milk with 0.25 g/L of added urea. Twenty-four batches were manufactured under identical conditions with full fat raw milk. A high nitrogen level diet increased milk urea content, which rose from 0.24 to 0.49 g/L, and decreased the protein content slightly. Rennet clotting time and curd firming time were slightly higher in the high nitrogen level. Milk fat, casein, total and soluble Ca and P were not modified by the diet. A high milk urea content, whether it comes from addition to milk or from feeding, leads to a lower acidification rate in mould and at demoulding to moister ripened cheeses. Nitrogen fractions, pH, and Ca content of cheeses were not modified by milk urea content. While eating, compared with control cheeses, cheeses from soya-fed cows were significantly less firm, less pasty, less chalky. Their taste was creamier, less acid and sweeter. Cheeses from added urea milk were close to cheeses from soya-fed cows in their chemical composition and texture, and to control cheeses in their taste. This suggests that milk urea, whether it comes from addition to milk or from feeding, influences directly acidification kinetics, chemical composition and texture characteristics of matured cheeses, however, urea is not directly involved in taste differences.