Détermination d’un rendement fromager de laboratoire en relation avec les caractéristiques chimiques de laits de brebis
Table 1 : Mean extreme values and standard deviation of parameters describing the cheese making ability of milk - Table 2 : Regression equations for the solid cheese yield - Figure 1 : Relationship of
A number of studies have shown the effects of the chemical, physical and bacteriological characteristics of milk on cheese making and the cheese yield in particular. Research tends to focus on the butterfat and protein content and, to a lesser extent, the mineral characteristics (calcium and phosphorus) of the milk. Most of the studies are concerned with cow’s milk, with studies of ewe’s milk being rarer.
Objectives
The aim of this project is to investigate the main physico-chemical parameters affecting the cheese making ability of ewe’s milk.
Results obtained
A laboratory curd is made in order to assess the cheese making ability of milk. This enables the chemical composition of the milk to be described in greater detail by determining the following criteria : protein content (TP), milk butterfat content (TB), milk solids (MSL) and serum solids (MSLA), solid cheese yield (RFs) and fresh cheese yield (RFf), cheese making protein (MPF) and milk mineral content (calcium and phosphorus). The cheese making protein content is determined by the difference between the milk protein content and the serum protein content after coagulation with rennet. The mean protein and fat content of ewe’s milk (Table 1) is considerably higher than in cow’s milk, accounting for the superior cheese yield with ewe’s milk. The fresh cheese yield of cow’s milk is in fact 16.5% compared to 41.5 % for ewe’s milk. Ewe’s milk is considerably richer in minerals (calcium and phosphorus) than cow’s milk. The mean density is 1.036. The MPF/TP ratio is slightly higher for ewe’s milk (82 % as opposed to 77 % for cow’s milk). This higher ratio expresses the greater efficiency of use of ewe’s milk proteins in making curd, with the cheese making protein representing the milk caseins. The correlation matrix based on the data collected reveals close links between the parameters studied. RFs correlates strongly with MSL, RFf, MPF and (R2> 0.75). The lowest correlations, which occur between the minerals (Ca or P) and the other criteria (R2 = ۪.50), can be accounted for by the low variation in mineral levels during lactation. However, the mineral content correlates relatively well with the protein content (R2 =0.75). As RFs is a good indicator of the cheese yield in manufacture, several regression equations have been established in order to estimate the solid cheese yield from simple criteria (Table 2). A regression equation based on Roquefort-type micro-manufacture was used to calculate the fresh cheese making yield from our data. The manufacturing RFf was then related to the corresponding laboratory RFf. A manufacturing RFs was also estimated from the milk solid content. Laboratory cheese making yield correlates well with Roquefort-type manufacturing yield in terms of fresh matter and solids (R2 0.75 and 0.81 respectively ; Figures 1 and 2). The laboratory RFf are markedly higher than the manufacturing RFf (Figure 1). This difference could be due to better draining of the curd in manufacture. The relative error between the laboratory and manufacturing RFf is 71%, as opposed to only 11% for the corresponding RFs. These results indicate that the solid cheese yield is a good basis for estimating the manufacturing yield. However, the relationship in Figure 1 applies only to Roquefort-type manufacture, as the manufacturing yield is specific to each type of cheese.
Contribution
CRA-W
Partners
Agricultural University of Gembloux
CRAW off coordinator
BARTIAUX-THILL Nicole (Inspecteur général scientifique) Rue de Liroux, 8 B-5030 Gembloux Téléphone direct :62 67 71 Téléphone département :+ 32 (0) 81/61.27.39 - 61.27.40 Fax département :+ 32 (0) 81/61.58.68 E-mail :bartiaux@cra.wallonie.be
