1. Introduction
Ketchup, one of the most important tomato products, is produced basically from either cold or hot extracted tomatoes; or directly from concentrates, purees and tomato paste (Sahin and Ozdemir, 2004). Although ketchup is known worldwide; information on this product is limited in the literature (Sharoba et al., 2005). Ketchup is time-independent, semi-solid non-Newtonian fluid having a definite yield stress (Sharoba et al., 2005). Based on dynamic shear data, it was also reported that the Cox–Merz rule was not applicable for commercial tomato ketchup samples (Bistany and Kokini, 1983), exhibiting properties similar to weak gels (Rao and Cooley, 1992).
