Influence of micellar calcium and phosphorus on rennet coagulation properties of cows milk.

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.

Dairy maturation of milk used in the manufacture of Parmigiano-Reggiano cheese: effects on physico-chemical characteristics, rennet-coagulation aptitude and rheological properties.

The aim of this research was to study the effects of dairy maturation on the physico-chemical characteristics and technological properties of milk used for Parmigiano-Reggiano cheese manufacture. Three different operating conditions (CF1, CF2 and CF3) were considered. Full cream milk from the evening milking was stored on the farm and delivered to the cheese factory in churns (CF1) or in thermoregulated tanks at a temperature not lower than 18 degrees C (CF2 and CF3). The natural creaming (10-12 h overnight) was performed in a traditional large flat vat containing 10-12 hl (CF1 and CF2) or in thermoregulated large flat vats containing 60 hl at about 15 degrees C (CF3). Twenty-four, 24 and 22 maturation trials were performed in CF1, CF2, and CF3, respectively, during 2 consecutive years. A significant increase (P

Composition, coagulation properties and Parmigiano-Reggiano cheese yield of Italian Brown and Italian Friesian herd milks.

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.