MICROSTRUCTURE AND PHYSICAL PROPERTIES OF QUARG CHEESE AS AFFECTED BY DIFFERENT HEAT TREATMENTS

Abstract

ABSTRACT The effects of different heat treatments on the rheological properties, microstructure and yield of production of quarg cheese were investigated. Three levels of time–temperature combination were used: 72C–16 s, 82C–5 min, 90C–5 min. Rheological properties were studied by means of frequency sweep experiment with the measurement of elastic modulus (G′). Microstructures of samples were observed by scanning electron microscopy (SEM). Maximum and minimum G′ and cheese yield were obtained at 90 and 72C, respectively (P < 0.05). Yield at 82 and 90C was higher than 72C but difference between heat treatment at 82 and 90C was not significant (P < 0.05). G′ values at 82 and 90C were higher than that at 72C. The difference between 82 and 90C was initially low; subsequently increase in frequency made G′ at 90C higher than 82C. SEM micrographs of samples at 82 and 90C were closely similar and no differences were observed between them. Micrographs showed the regular microstructure with branched clusters and numerous small pores at 82 and 90C, whereas micrographs of heat treatment at 72C had larger protein aggregates and fewer but larger pores. This study showed that heat treatments at 82 and 90C were more suitable for quarg cheese making than that at 72C. PRACTICAL APPLICATIONS Quarg cheese is one of the most popular acid-coagulated cheeses. This study shows that heat treatment at 82C–5 min is preferred for quarg production compared with other heat treatments. Contribution of denatured whey proteins in gel network led to higher cheese-making yield as well as high nutrition value. Heat treatment at 82C is also suggested in economic and energy consumption aspect.