Ohmic Treatment of Pear Purées (cv. ‘Conference’) in Terms of Some Quality Related Attributes

The effect of ohmic treatment on some quality related characteristics of pear puree (cv. ‘Conference’) such as color, reducing sugars, total phenols, rheological behavior and microbial counts, was analyzed. The inactivation kinetics of pectin methyl esterase (PME) in pear crude extract and puree were studied by conventional thermal and ohmic treatments. Thermal inactivation of PME in crude extract was described by a first-order kinetic model. The activation energy values suggested the presence of two isoenzymes with different thermostability. The ohmic heating reduced PME activity by 96% at 25 V·cm -1 . Minimal changes induced by ohmic heating on above quality related aspects were observed. Supporting this statement, there were no significant changes in the nutritional and sensorial attributes. It was reported an increase of 3% of reducing sugar content for the ohmic heated samples. The phenolic content of the treated samples registered a reduction of 59% in comparison with fresh pear puree. The pear puree presented a non-Newtonian pseudoplastic behaviour. The Ostwald de Waele model was fitted to rheograms and the consistency coefficient ( m ) and flow behavior index ( n ) were determined. Results obtained for the microbial charge were higher in the control samples. Thus, microbial counts showed complete inactivation of yeast and mold at voltage gradient higher than 17.5 V·cm -1 .