Rennetability, rheological, geometrical and microstructural properties of buffalo milk gel during coagulation process: impact of heat treatments [electronic resource].

Includes references.

In this paper, three different milk heating temperatures often described in the literature, 63°C/30 min, 72°C/15 s and 85°C115 s were compared to unheated milk (control treatment), for their influences on the enzymatic hydrolysis of "-casein (primary phase) and the entire coagulation. process (primary and secondary phases) by monitoring the shear stress (SS) and torque (T) forces. The impact of milk heating was also followed by measuring the rheological and microstructural properties of the induced gels. Heating buffaloes' milk decreased the rate of rennet-induced flocculation compared to unheated milk. Heat-induced enzymatic inhibition was showed by increasing the rennet onset time from 4 to 11, 7 and 12 min for raw milk and milk heated at 630C/30 min, 72°C/15 sand 85°C/15 S, respectively. Heat treatment at 72°C/15 s caused a slight decrease in S5 (70.09 D/cm²) compared to unheated milk (74.6 D/cm2), while those of 63°C/30 min and 85°C/15s decreased 55 significantly. Torque showed similar profile to that of 55. The rheological properties of rennet-induced gels (intensity, sphericity, compactness, surface roughness, matrix area and pores area) were significantly affected by heat treatments (p<0.001). Raw milk gel exhibited the lowest intensity, roughness, compactness, sphericity and matrix area (42.60/0, 0.57, 0.44, 0.58 and 44.50/0, respectively). Heating milk at 63°C/30 min, 72°C/15 s and 85°C115 s significantly (p<0.001) decreased the gel pores area (30.90/0, 27.4% and 40.7%, respectively) compared to that of unheated milk (55.4%). Raw milk gel seemed to be homogenous and have more connections between particles in a three-dimensional network and more pores producing a porous structure. No noticeable heat-induced effects were observed on the structure of the casein micelle fraction gel of heated milk at 72°C/15 s.

Summary in Arabic.

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