Rheological behavior of whole and concentrated noni pulp

Summary The rheological behaviour of fruit pulps allows one to obtain important information about their flow under distinct conditions and at different stages of the process. Thus the present study aimed to analyse the rheological behaviour of whole noni pulp (Morinda citrifolia L.) and that concentrated to 30 and 50 °Brix. The rheological parameters determined were: shear stress, strain rate and apparent viscosity, using a Brookfield viscometer at rotational speeds of 5 to 200 rpm and temperatures from 5 to 65 °C. Of the models tested, the Mizrahi & Berk model best represented the rheograms of the whole and concentrated noni pulps with the following fittings: R2 ≥ 0.8219, X2 ≤ 0.1569 and P ≤ 2.26%. The pulps studied presented values for the fluid behaviour index of less than one (n<1), characterizing them as non-Newtonian fluids with pseudoplastic behaviour. The Arrhenius equation can be used to demonstrate the effect of temperature on the apparent viscosity for the whole and 30 ºBrix pulps at all speeds, and for the pulp with 50°Brix preferably at rotational speeds of 5, 10 and 20 rpm.