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 (30ºC and 35ºC) and heat treatment of milk (65ºC/30 min and 87ºC/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 87ºC/10 min, with 400 mg/l added CaCl2, which were coagulated at 35ºC and pH 5.8, coagulated 23.28-fold faster than the same samples without added CaCl2, which were coagulated at 30ºC 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 30ºC 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 istraživanja ispitivana je brzina koagulacije mleka (s) u zavisnosti od pH mleka (6.5 i 5.8), količine dodatog CaCl2 (0, 200 mg/l i 400 mg/l), temperature koagulacije (30ºC i 35ºC) i režima termičke obrade mleka (65ºC/30 min i 87ºC/10 min). Kod svih ogleda odredjivano je vreme (s) od momenta dodavanja sirila do pojave prvih vidljivih pahuljica gruša. Uzorci mleka termički tretirani na 87ºC/10 min kojima je dodato 400 mg/l CaCl2, čija je temperatura koagulacije bila 35ºC, a pH 5.8 koagulisali su 23.28 puta brže u odnosu na iste uzorke kod kojih nije dodat CaCl2, čiji je pH bio 6.5, a temperatura koagulacije 30ºC. Rezultati istraživanja koji se odnose na uticaj pojedinačnih faktora koagulacije pokazala da je uticaj Ca2 s jedne strane i temperatura koagulacije s druge strane bio jače izražen kod mleka u kojem su obrazovani koagregati, pri čemu je ovaj uticaj bio naročito izražen pri pH 6.5. Pri pH 5.8 različite koncentracije Ca2+ i primenjene temperature koagulacije nisu imali veliki uticaj na brzinu koagulacije bez obzira na primenjeni režim termičke obrade. Uticaj termičkog tretmana naročito je bio izražen kod uzoraka bez dodatog CaCl2, čija je temperatura koagulacije bila 30ºC, a pH 6.5. Pri pH 5.8 brzina koagulacije praktično više nije zavisila od primenjenih režima termičke obrade mleka. pH mleka imao je najveći uticaj na brzinu koagulacije mleka. Uticaj pH najviše je bio izražen kod uzoraka u kojima su prethodno obrazovani koagregati pri svim koncentracijama Ca2+ i primenjenih temperatura koagulacije.