THIXOTROPY OF ORANGE CONCENTRATE AND QUINCE PUREE

Orange juice with pulp and pectins is thixotropic at soluble solids co ncentrations of 55 and 60 degrees Brix in the range of temperatures fr om 0 to 20C and sheer rate from 72 to 57.6 s(-1). Quince puree is thix otropic at soluble solids concentrations of 12.3 to 28 degrees Brix in the range of temperatures between 0 to 20C and shear rate from 7.2 to 57.6 s(-1). The thixotropic behaviour of orange juice and quince pure e increases with increasing concentration and decreasing temperature a nd they can be described by the kinetic model proposed by Figoni and S hoemaker (1983): sigma = sigma(e) + (sigma(0i) - sigma(e)) exp (- kt) The thixotropic structure of orange juice was destroyed by applying a shear rate of 57.6 s(-1) for 5 min, and for quince puree for 10 min. Q uince puree shows a greater thixotropic character than orange juice, b ecause it has a higher content of fiber, pulp and pectins and also bec ause it shows a microscopic structure consisting of long particles and heterogeneous fibers.