The effects of manothermosonication on tomato pectic enzymes and tomato paste rheological properties

The effect of manothermosonication (MTS), the simultaneous application of heat and high energy ultrasound waves under moderate pressure, on tomato juice rheology and on tomato pectinmethylesterase (PME) and polygalacturonase (PG) activity in tomato juice was examined. Tomato juice was subjected to MTS treatments (20 kHz, 2 kg pressure, 117 mum amplitude and 70degreesC), or to control thermal treatments (TT), for 1 min. Flow curves, yield stress and apparent viscosity were measured on both kind of samples. Apparent viscosity of MTS samples were 1.6-fold higher than that of TT samples. Yield stress values were also 2.2-fold higher in MTS than in TT samples. Flow curve values were fatted to the power law equation; MTS samples showed about 1.9-fold higher consistency values and lower flow indexes, n = 0.190 vs. n = 0.126, than TT samples. MTS samples retained about 20% more serum than TT samples after centrifugation. TT inactivated about 38% of the initial PME activity whereas PME activity was undetectable in MTS-treated tomato juice. TT left PG unaffected whereas MTS treatments inactivated 62% of total PG activity. These results suggest, that MTS could be an useful technology to obtain high viscosity and consistency tomato juice. (C) 2002 Elsevier Science Ltd. All rights reserved.