Rennet coagulation of skim milk and curd drainage: effect of pH, casein concentration, ionic strength and heat treatment

Abstract

-The effect of the pH of skim milk (6.4 to 6.0), the casein concentration (27 to 36 g . kg -1 ), a reduction in the ionic strength to 0.6 compared to that of unmodified milk and the effect of heat treatment on rennet coagulation, gel syneresis and drainage were tested. Coagulation was measured using a formagraph and by viscoelasticimetry, while syneresis was studied using a centrifugation test. Drainage was followed under conditions similar to those of cheesemaking, using either a mesophilic or thermophilic process. The effects of pH and casein concentration on rennet coagulation, gel syneresis and drainage were in accordance with those reported in the literature. Reduction in ionic strength led to shorter coagulation time and firming time. It also led to an increase in gel firmness, gel syneresis, drainage rate, final amount of expelled whey, solids content and hardness of drained curd. Ionic strength appeared to have an interactive effect with pH on coagulation and with the concentration of casein on syneresis and drainage. This effect of the reduction in ionic strength is discussed. rennet coagulation / pH / casein concentration / ionic strength / drainageRésumé -La coagulation présure du lait écrémé et l'égouttage : effet du pH et de la concentration en caséine, de la force ionique et du traitement thermique. L'effet du pH du lait écrémé (6,4-6,0), de la concentration en caséines (27-36 g . kg -1 ), de la réduction de la force ionique du lait à 0,6 fois celle du lait natif et du traitement thermique a été testé sur la coagulation présure, l'aptitude à la synérèse et l'aptitude à l'égouttage des gels. La coagulation était suivie à l'aide du formagraph et d'un viscoélasticimètre, tandis que la synérèse était suivie par un test de centrifugation et l'égout-tage était étudié par une méthode proche d'une fabrication fromagère. Les résultats confirment ceux de la littérature pour l'effet des facteurs pH et concentration en caséine sur la coagulation, la synérèse et l'égouttage. La réduction de la force ionique a entraîné une réduction du temps de prise et de

Characterisation of whey drainage kinetics during soft cheese manufacture in relation with the physicochemical and technological factors, pH at renneting, casein concentration and ionic strength of milk

“…The methodology used involved centrifugation tests and collection of whey versus time by a manual method [7].…”

“…W was the total weight of whey expelled at time (t), W1 and W2 the whey amounts obtained at the end of steps 1 and 2, and τ1 and τ2 the kinetics times of the steps 1 and 2 of whey drainage. This equation was already used in a previous work [7]. A two step exponential equation was chosen to describe W, as it gave a better adjustment to experimental data than a single step equation.…”

Effect of barn airspace temperature on composition and technological parameters of bulk milk produced by dairy cows of Czech Fleckvieh and Holstein breeds

“…In addition Hanuš et al (2011) observed that herd, year, and season showed a signifi cant eff ect on milk composition and its technological parameters (including RCT) of milk produced by dairy cows of the Czech Fleckvieh breed. Daviau et al (2000) mentioned that shorter RCT was associated with a decrease in the content of protein, which usually associated also with a decrease in the content of casein. A signifi cant eff ect of season and herd on rennet coagulation time and other parameters of milk technological quality in Holstein cows was observed also by Chládek et al (2011).…”

Desenvolvimento de misturas instantâneas de mandioca e caseína: efeito do teor de proteína e parâmetros de extrusão sobre a viscosidade

“…As proteínas do leite compreendem duas frações: as caseínas, que se apresentam principalmente no estado de partículas coloidais, (micelas) e as proteínas do soro, que estão em solução (DAVIAN et al, 2000;GAUCHERON;LE GRAËT;BRIARD, 2000). O leite bovino tem um conteúdo de proteína, expresso como %N × 6,38, de 30-35 g.L -1 .…”