Influence of selected factors on induced syneresis

Abstract

Syneresis is the process of whey separation induced by gel contraction resulting in rearranging or restructuring of casein matrix formed during enzymatic coagulation. Numerous factors can influence the process of syneresis. The influences of pH, calcium concentration, temperature of coagulation of milk and applied heat treatment on the syneresis induced by different intensity of centrifugal force have been investigated. Coagulated samples were centrifuged at 1000, 2000 and 3000 rpm for 5 min, respectively. Reconstituted skim milk powder (control sample) and reconstituted non-fat milk heat treated at 87ºC/10 min (experimental sample) are coagulated at temperatures of 30ºC and 35ºC, at pH value of 5.8 and 6.2, and with the addition of 100, 200 and 400 mg/l of CaCl2, respectively. Centrifugation at 1000 rpm of both control and experimental samples didn’t recover any sera, regardless of the applied coagulation conditions. This indicates that the intensity of centrifugal force wasn’t strong enough to disrupt gel structure and cause syneresis. When the intensity of centrifugal force was increased up to 2000 rpm, the syneresis was induced, but the degree of syneresis depended on the applied factors of coagulation, primary on the applied heat treatments and temperature of coagulation. The amount of added CaCl2 didn’t have a significant influence on the induced syneresis at 2000 rpm. The induced syneresis was very significant for both control and experimental samples when the intensity of centrifugal force of 3000 rpm was applied. It was also noted that curd produced from heat treated milk in which milk protein coaggregates were formed, released less sera regardless of the applied coagulation factors.

Sinerezis je proces izdvajanje surutke usled kontrakcije gruša, pri čemu dolazi do rearanžiranja, ili prestruktuiranja kazeinske mreže, koja je nastala tokom enzimske koagulacije, na koji utiče veliki broj faktora. U ovom radu je ispitivan uticaj pH, koncentracije Ca2+, temperature koagulacije mleka i uticaj termičkog tretmana na indukovani sinerezis pod uticajem različitog intenziteta centrifugalne sile. Koagulisani uzorci mleka centrifugirani su pri 1000, 2000 i 3000 o/min u vremenu od 5 minuta. Rekonstituisano obrano mleko u prahu (kontrolni uzorak) i rekonstituisano obrano mleko termički tretirano na temperaturi 870C/10 minuta (ogledni uzorak) je koagulisalo pri različitim temperaturama 30ºC i 35ºC, pH vrednostima 5.8 i 6.2, kao i pri dodatku 100, 200 i 400 mg/l CaCl2. Centrifugiranjem kontrolnih i oglednih uzoraka pri 1000 o/min, bez obzira na uslove koagulacije nije dovelo do izdvajanja seruma iz gela, pa se može zaključiti da intenzitet primenjene centrifugalne sile nije bio dovoljno veliki da naruši strukturu gela i izazove sinerezis. Sa povećanjem intenziteta centrifugalne sile (2000 o/min), dolazi do većeg, ili manjeg stepena pojave indukovanog sinerezisa, a uočava se uticaj ispitivanih faktora koagulacije, pre svega primenjenih termičkih tretmana, pH vrednosti temperature koagulacije, a u manjoj meri i količine dodatog CaCl2 na količinu izdvojenog seruma. Pri delovanju centrifugalne sile većeg intenziteta (3000 o/min), kod kontrolnih i kod oglednih uzoraka u znatno većoj meri je uticalo na količinu izdvojenog seruma. Takodje je uočeno da gel dobijen od mleka u kojem su obrazovani koagregati, pri svim ispitivanim faktorima koagulacije, izdvaja manju količinu seruma u odnosu na kontrolne uzorke.