EFFECT OF HEAT TREATMENT ON PROPERTIES OF PROTEIN AND RENNETABILITY OF CAMEL MILK

Abstract

The current study was conducted at Haramaya University Dairy laboratory with the main objective of investigating how heat treatment affects whey proteins and rennetability property of camel milk for cheese making. Completely randomized design (CRD)was used by evaluating effect temperature (heated at 400C,650C/30min,720C/30 sec, 750C/5 min, 850C/5 min and 900C/5 min).Unheated milk used for alternative reference during chemical and whey protein denaturation evaluation. Similar experimental setup was also used for cow milk for reference. Heat treatment was done in thermostatically controlled water bath. The chemical composition of milk analysed using milkoscan, whey protein denaturation analysis was done using gel electrophoresis and kjeldahal method. While for rennetabilty properties parameters Rheometery ReoRox G2-4 was used. The result showed that raw camel milk significantly (P<0.05) had lower percentage of protein, solid non-fat, casein and lactic acid than cow milk. Heat treatment have no significant effect (P>0.05) on gross chemical content of camel and cow milk. Total whey protein denaturation % increased (P<0.05) as heating temperature increased in both camel and cow milk. In camel milk α- lactalbumin (α-La)showed less denaturation while Camel serum albumin denatured at higher heat treatment as band become invisible. While in cow milk β-lactoglobulin and α- La denatured as temperature level increased while bovine serum albumin the denaturation percentage increased constantly as temperature increased. Gelation time, and Time to G'max were significantly increased(P<0.05) as heat treatment increased while G'max was lowered as heating temperature increased for camel and cow milk. For camel milk short (6min) gelation time was observed for heated at 400C while it increased to 14 min at 650C. Significantly lower G'max observed at 75,85 and 900C/5min for camel while for cow milk at 900C/5min. From heat treated higher at 650C/30min (51pas for camel and 111 for cow) than the other temperatures. Similarly, time to G'max was also increased as heat treatment increased. Pre heat treatment of milk can determine the gelation time and curd aggregation property of cheese. Therefore, lower Pasteurization temperature that results less denaturation of whey protein was optimal for cheese milk treatment. Pasteurization temperature at 720C/30 sec can also be an alternative for cheese milk treatment to utilize whey proteins without affecting coagulation processes.