The main requirement for milk processed in most cheese typologies is its rennet coagulation ability. Despite the increasing number of studies, the causes for abnormal coagulation of milk are not fully understood. The aim of this study was to ascertain relationships between milk characteristics and its rennet coagulation ability, focusing on the influence of calcium (Ca) and phosphorus (P). Ca and P are essential constituents of the micelles. Micellar P can be present as part of colloidal calcium phosphate (inorganic-P) or covalently bound to caseins as phosphate groups (casein-P). Eighty one herd milk samples (SCC<400 000 cell/ml) were classified as Optimal (8), Suboptimal (39) Poor (29) and Non-coagulating milk (5), according to their rennet coagulation parameters as assessed by lactodynamographic test. Samples were analysed for their chemical composition (basic composition, protein fractions, minerals and salt equilibria), physicochemical parameters (pH and titratable acidity) and rheological properties. Optimal milk was characterised by the highest contents of major constituents, protein fractions and minerals, lowest content of chloride and highest values of titratable acidity. Non-coagulating milk was characterised by the highest values of pH and the lowest of titratable acidity. At micellar level, Optimal milk showed the highest values of colloidal Ca, casein-P and colloidal Mg (g/100 g casein), while Non-coagulating milk showed the lowest values. Interestingly, there was no statistical difference regarding the content of colloidal inorganic-P (g/100 g casein) between Optimal and Non-coagulating milks. Overall, high mineralisation of the micelle (expressed as g inorganic-P/100 g casein) positively affect its rennetability. However, excessive mineralisation could lead to a reduction of the phosphate groups (g casein-P/100 g casein) available for curd formation.
The authors report the results of a study aimed at the comparison of the basic chemical composition, the main protein fractions distribution, rennet coagulation properties and Parmigiano-Reggiano cheese yield of vat milk from Italian Brown and Italian Friesian herds. Parmigiano-Reggiano cheese factories which manufacture milk separately from Italian Brown herds and Italian Friesian herds were used in the study. Thirteen cheesemaking trials were performed at 10 different commercial cheese factories. The study was carried out from March to October 2003. For each cheesemaking trial in each factory, approximately 1100 kg milk from Italian Brown cows and from Italian Friesian cows were processed in parallel. The animals involved in the study came from farms with comparable management practices, size, location, number of lactation and days in milking. Each vat contained milk obtained by combining milk collected during the evening milking (partially skimmed milk by natural creaming) and the following morning milking (full-cream milk), from at least 2 dairy herds. Milk from Italian Brown cows is characterised by a higher casein content (27.1 v. 23.7 g/kg; P < or = 0.0001) than Italian Friesian cows' milk. Curd firming time (k20) of Italian Brown cows' milk was markedly lower than that of Italian Friesian cows' milk (6.6 v. 10.0 min; P < or = 0.001). This implies a higher rate of aggregation of para-casein micelles for Italian Brown cows' milk. The coagulum of Italian Brown cows' milk had better rheological properties and lower losses of fat in the cheese whey. Parmigiano-Reggiano cheese yield at 24 h was also higher for Italian Brown cows' milk, + 0.99 kg cheese for every 100 kg vat milk.
-The trends of the physicochemical properties, chemical constituents and main nitrogen fractions of Haflinger mare milk were studied. Milk samples were collected at d 4,20,40, 60, 80, 120, 150 and 180 post-partum, by hand-milking from 5 mares, 7-14 years old (4-11 parities) and 400-490 kg live weight. Density, pH, titratable acidity, fat, protein, lactose and ash varied significantly during the first lactation period, while the freezing point showed statistically no significant modifications. The contents of fat, protein and ash diminished. In addition, the gross energy value tended to decrease and the lactose content increased. Total N content decreased significantly (P < 0.0001), especially between d 4 (515 mg) and d 40 (286 mg) and, to a lesser degree, until d 180 of lactation (255 mg . 100 g -1 milk). The casein number varied significantly (P < 0.001), particularly between the beginning (56.32%) and the end (45.40%) of lactation. The trend of non-protein N and globulin N fractions was different; both the 2nd and 3rd month showed the lowest values of the entire lactation (P < 0.05). The non-protein N proportion (NPN × 100 / total N) increased significantly (P < 0.001) from the beginning (7.74% at d 4) to the end (12.37% at d 180) of lactation. The globulin N proportion increased from the end of the 4th lactation month, reaching in the final period an average value of about 10% of total N, but with an irregular trend (P > 0.05).Haflinger horse / nursing mare / lactation stage / milk properties / milk composition / nitrogen fractions Résumé -Propriétés physico-chimiques, composition chimique, valeur énergétique et fractions azotées du lait de jument de race Haflinger pendant 6 mois de lactation. L'évolution des propriétés physico-chimiques, des constituants chimiques et des principales fractions azotées du lait de jument de race Haflinger a été étudiée. Les prélèvements de lait ont été effectués à 4,20,40, 60, 80, 120, 150 P. Mariani et al. 416
The goat CSN1S2 locus is characterized by the presence of three alleles, A, B and C, all associated with about 2.5 g/l of protein per allele. The SDS-PAGE analysis of 441 individual milk samples obtained from goats belonging to a population reared in Southern Italy showed that the milk produced by three goats did not apparently contain alpha s2-casein, whereas milk produced by 37 goats showed a less intense electrophoretic band of this casein fraction (about 50%). These results can be explained by hypothesizing the presence of another allele at this locus, CSN1S2o, associated with a 'null' content of alpha s2-casein. Southern blot, PCR and PCR-RFLP analyses of the DNA region containing the CSN1S2 gene of individuals producing milk with and without alpha s2-casein did not show differences between the two groups. As a consequence, goats producing milk without alpha s2-casein carry an apparently intact gene. The first results obtained by sequencing part of the CSN1S2o allele revealed a G-->A transition at nucleotide 80 of the 11th exon which creates a stop codon and could be responsible for the absence of the alpha s2-casein in goat milk. This mutation eliminates a NcoI restriction site. A test based on this polymorphism has been established in order to identify carriers of the CSN1S2o allele.
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