RHEOLOGICAL BEHAVIOR OF KIWI FRUIT JUICE CONCENTRATES

The theological behaviour of diluted kiwi concentrates (22.5-63.0 degrees Brix) over the temperature range 4 to 70C, was studied. The values below 55.7 degrees Brix fit the power law while above 55.7 degrees Brix fit the Herschel-Bulkley equation. Maximum and minimum consistency index values were 62225 and 16 mPa.s(n). Concentrates showed a yield stress at 55.7 degrees Brit, from 5 to 11 Pa, and 63.0 degrees Brit, from 19 to 53 Pa. Yield stress was correlated with temperature by means of a linear equation. Arrhenius activation energies were in the range of 28.97 to 33.89 kJ/mol. The average value of the flow behaviour indexes varied from 0.85 (sample at 22.5 degrees Brix) to 0.59 (sample at 63.0 degrees Brix). Simple equations are proposed to describe the combined effect of temperature and soluble solids content on consistency index and rheological behaviour index.