Modeling of coagulation, curd firming, and syneresis of milk from Sarda ewes

Abstract This study investigated the modeling of curd-firming (CF) over time (CF t ) of sheep milk. Milk samples from 1,121 Sarda ewes from 23 flocks were analyzed for coagulation properties. Lactodynamographic analyses were conducted for up to 60min, and 240 CF individual observations from each sample were recorded. Individual sample CF t equation parameters (RCT eq , rennet coagulation time; CF P, asymptotic potential value of curd firmness; k CF , curd-firming instant rate constant; and k SR , curd syneresis instant rate constant) were estimated, and the derived traits (CF max , the point at which CF t attained its maximum level, and t max , the time at which CF max was attained) were calculated. The incidence of noncoagulating milk samples was 0.4%. The iterative estimation procedure applied to the individual coagulation data showed a small number of not-converged samples (4.4%), which had late coagulation and an almost linear pattern of the ascending part of the CF t curve that caused a high value of CF P , a low value of k CF , and a high value of k SR . Converged samples were classified on the basis of their CF t curves into no-k SR (18.0%), low-k SR (72.6%), and high-k SR (4.5%). A CF t that was growing continuously because of the lack of the syneresis process characterized the no-k SR samples. The high-k SR samples had a much larger CF P , a smaller k CF , and an anticipation of t max , whereas the low-k SR samples had a fast k CF and a slower k SR . The part of the average CF t curves that showed an increase was similar among the 3 different syneretic groups, whereas the part that decreased was different because of the expulsion of whey from the curd. The traditional milk coagulation properties recorded within 30min were not able to detect any appreciable differences among the 4 groups of coagulating samples, which could lead to a large underestimation of the maximum CF of all samples (if predicted by a 30 ), with the exception of the no-k SR samples. Large individual variability was found and was likely caused by the effects of the dairy system, such as flock size (on CF max , t max , and % ewes with no-k SR milk), flock within flock size (representing 11 to 43% of total variance for % ewes with no-k SR milk and CF max , respectively), days in milk (on all model parameters and CF max ), parity (on RCT eq , k SR , and CF max ), daily milk yield (on RCT eq and CF max ), and position of the individual pendulum that significantly affected model parameters and derived traits. In conclusion, the results showed that the modeling of coagulation, curd-firming, and syneresis is a suitable tool to achieve a deeper interpretation of the coagulation and curd-firming processes of sheep milk and also to study curd syneresis.