Effects of dairy factory, milk casein content and titratable acidity on coagulation properties in Trentingrana dairy industry

The objective of the present study was to investigate the effect of environmental factors, milk casein content and titratable acidity on milk coagulation properties (MCP) of samples routinely collected in the Trento province (northeast Italy) under field conditions. Rennet coagulation time (RCT, min), curd-firming time (k(20), min) and curd firmness (a(30), mm) were determined by Formagraph on 14 971 samples from 635 herds associated to 17 dairy factories. Besides MCP, fat, protein, and casein percentages, titratable acidity (TA), and somatic cell and bacterial counts were available. A standardised index of milk aptitude to coagulate (IAC) was derived using information of RCT and a30. An analysis of variance was conducted on MCP and IAC using a fixed effects linear model. Approximately 3% of milk samples did not form a curd within the testing time (30 min) and k(20) was missing for 26% of milks. The percentage of samples without information on k(20) largely differed among dairy factories (1.7-20.9%). Significant differences were estimated between the best and the worst dairy factory for RCT (-2 min), k(20) (-1.2 min), a(30) (+3.4 mm) and IAC (+2.6 points). Milk casein content and TA were important factors in explaining the variation of MCP and IAC, supporting the central role of these two traits on technological properties. The Trento province is heterogeneous in terms of dairy systems and this could explain the differences among dairy factories.