Dear Dr Ashraf

There are different models available to describe the flow behavior of puree based products. For example shear rate shear stress models: Power law, Herschel-Bulkeley, Casson etc... and some Viscosity-shear rate models such as moore, cross model etc..

There are plenty of literature on the issue. Well it depends upon how you are treating your data or the instrument you are using. For simplicity, if there is no suspended particles (filtered juice) Power law is the best. If there is pulp, try HB model. If you are using oscillatory rheology then try to match Cox-Merz rule.

You may see this link:

http://www.tetrapak.com/usprocessing/documents/Rheology_Dairy%20Processing%20Hand%20Book.pdf

Thanks for all

Dr Ashraf

as suggested by other scientists, though there are several mathematical models available with us to solve your problem. but depending upon the problem u can select few from them or you can test all of them. and if you r not satisfied with all of them you can try inbuilt non linear models in curve expert software.

One mathematical model I really like is Power Low, applied to shear stress data obtained from increasing and then decreasing shear rate. It is a simple model that gives you many answers.

Power law  and HB model have wide application among food materials or non-Newtonian fluid. However, comparing these with other selected models as presented in books like Food Rheology by James F. Steffe and other research articles with the aid of software package like Matlab (this is robust) . The best may be selected using appropriate criteria (highest R2, and lowest sse and Rmse). 

there is published data on things like apple sauce and the like.  they are generally fitted by a Herchel Bulkey model which exhibits both shear thinning and yield stress behaviors.