The influence of various factors on milk clotting time

Abstract

The influence of pH (6.5 and 5.8), amount of added CaCl2 (0, 200 and 400 mg/l)), coagulation temperature (30?C and 35?C) and heat treatment of milk (65?C/30 min and 87?C/10 min) on the rate of rennet induced milk coagulation (s) were investigated. The time (s) from rennet addition to onset of gelation (as indicated by the first visible floccules) was measured. The milk samples heat-treated at 87?C/10 min, with 400 mg/l added CaCl2, which were coagulated at 35?C and pH 5.8, coagulated 23.28-fold faster than the same samples without added CaCl2, which were coagulated at 30?C and pH 6.5. The results of investigations related to the influence of particular coagulation factors on the coagulation rate of heat-treated milk showed that at pH 6.5 the most pronounced influence was demonstrated by the amount of Ca2+ and temperature of coagulation. At pH 5.8, different amounts of Ca2 and used temperatures of coagulation did not influence coagulation rate regardless of the used heat treatment of milk. The influence of used heat treatment of milk was particularly pronounced during coagulation of samples without added CaCl2 that coagulated at 30?C and pH 6.5. The used heat treatment of milk practically did not influence the milk coagulation rate at pH 5.8. The greatest influence on milk coagulation rate was showed by pH. This influence was the most marked in coagulation of samples in which the coaggregates were formed, regardless of the amount of added Ca2+ and used coagulation temperatures.U okviru ovih istrazivanja ispitivana je brzina koagulacije mleka (s) u zavisnosti od pH mleka (6.5 i 5.8), kolicine dodatog CaCl2 (0, 200 mg/l i 400 mg/l), temperature koagulacije (30?C i 35?C) i rezima termicke obrade mleka (65?C/30 min i 87?C/10 min). Kod svih ogleda odredjivano je vreme (s) od momenta dodavanja sirila do pojave prvih vidljivih pahuljica grusa. Uzorci mleka termicki tretirani na 87?C/10 min kojima je dodato 400 mg/l CaCl2, cija je temperatura koagulacije bila 35?C, a pH 5.8 koagulisali su 23.28 puta brze u odnosu na iste uzorke kod kojih nije dodat CaCl2, ciji je pH bio 6.5, a temperatura koagulacije 30?C. Rezultati istrazivanja koji se odnose na uticaj pojedinacnih faktora koagulacije pokazala da je uticaj Ca2 s jedne strane i temperatura koagulacije s druge strane bio jace izrazen kod mleka u kojem su obrazovani koagregati, pri cemu je ovaj uticaj bio narocito izrazen pri pH 6.5. Pri pH 5.8 razlicite koncentracije Ca2+ i primenjene temperature koagulacije nisu imali veliki uticaj na brzinu koagulacije bez obzira na primenjeni rezim termicke obrade. Uticaj termickog tretmana narocito je bio izrazen kod uzoraka bez dodatog CaCl2, cija je temperatura koagulacije bila 30?C, a pH 6.5. Pri pH 5.8 brzina koagulacije prakticno vise nije zavisila od primenjenih rezima termicke obrade mleka. pH mleka imao je najveci uticaj na brzinu koagulacije mleka. Uticaj pH najvise je bio izrazen kod uzoraka u kojima su prethodno obrazovani koagregati pri svim koncentracijama Ca2+ i primenjenih temperatura koagulacije.