Rheological, Physical and Sensory Characteristics of Lactose Fee Frozen Yoghurt

This study investigated the effect of lactose hydrolysis on the rheological and sensory characteristics of frozen yoghurt. Commercial lactase enzyme was added to hydrolyzed frozen yoghurt mix before the fermentation step. The obtained data showed that the hydrolyzed samples had slightly shorter fermentation time and higher acidity. Also, lactose hydrolysis affected considerably the rheological properties of the frozen yoghurt mix. At shear rate range of 2.6 to 50 s-1, the maximum apparent viscosity value of hydrolyzed frozen yoghurt mix was 50% less than the control samples. Moreover, shear stress value of the hydrolyzed samples was 30% less than that obtained for the control samples. Additionally, the hydrolyzed samples showed higher melting rate and significantly lower overrun (39.33±0.732%) compared to the control samples (44.63±0.645%). Hydrolyzed sample had lower viscosity and shear stress values, while both samples had shear thinning property following Power Law model. Furthermore, sensory evaluation results showed that both creaminess and texture attributes were significantly (P 0.05) different. It is concluded that lactose hydrolysis can significantly reduce some of frozen yoghurt quality attributes including its overrun. Therefore, these negative impacts should be addressed through product and process optimization.