TY  - SER
AU  - EL-Zeini,Hoda M.
TI  - Impact of heat treatment of milk on rheological properties and microstructure of set-yogurt gel
KW  - Yogurt
KW  - Milk
KW  - Effect of heat on
N1  - Includes references
N2  -  Yogurt gels were made from milk heated at 72 °C /15 s, 85°C/IS min and 100°C/5 min by acidification with S. thermophilus (TH4) and L. delbrueckii subsp bulgaricus (LBI2). The pH, viscosity, shear stress and torque were measured during the yogurt gelation process. Images of sections of yogurt samples were obtained using scanning electron microscope in order to evaluate yogurt microstructure. Gel structure was examined for surface roughness, compactness, matrix area and pores area. With 100°C/5 min heat treatment, highest viscosity, shear stress, torque, surface roughness, compactness, and matrix area were exhibited, while, the lowest values were obtained with milk subjected to 72 °C C/15s. The acid-induced gelation properties of heated milk are consistently different in some aspects as shifting in gelation pH, rougher gels and a different microstructure of the gels. Heat treatment of milk had significant effect (p<0.001) on all the rheological parameters investigated. The matrix area of the protein aggregates was a useful parameter to describe the differences between casein networks obtained by high and low heat treatments. The parameter of the average pores area in the yogurt gel gave an indication of its permeability. Significant positive correlations were observed between heat treatments and gel rheological properties measured. It was concluded that rearrangements of casein particles in the gel network occurred
UR  - http://nile.enal.sci.eg/EALE/2007/AASM/4507/1/183.pdf
ER  -