Application of back extrusion in rheological evaluation of quark cheese: effect of probiotic strain type and storage time on sensorial and textural characteristics

Back extrusion testing was used to evaluate the rheological properties of probiotic quark cheese. Effect of probiotic strain type including L.acidophilus (LA) and L.casei (LC) was studied on sensory and textural characteristics of quark cheese upon storage time. Results showed that LC quark cheese had firmer and harder texture (higher σmax, Young’s modulus) compared to that of LA sample in all storage days. Increasing storage time to 7 days, led to a significant (p<0.05) increase in the firmness of all samples. After 7 days, the firmness and hardness decreased again. There was no significant difference between LC and LA samples in terms of firmness from 14 to 21 days of storage. Sensorial results showed that there was no significant difference in sensory attributes of all samples in day 1. By increasing storage time differences in sensory properties appeared and LC sample obtained higher sensory scores compared to LA cheese. For all samples increasing storage time led to significant decrease in all sensory properties except for surface color and appearance. Especially between 14 and 21 days interval the greatest decrease in sensory scores occurred. The results of this study revealed probiotic quark cheese can be kept unchanged in terms of sensory properties for 14 days. Quark cheese supplemented with L.casei provided better sensory and textural properties compared to those of L.acidophilus.