Effect of blanching on thermal color degradation kinetics and rheological behavior of rocket (Eruca sativa) puree

Rheological behavior and green color retention are important parameters during thermal processing of pureed leafy vegetables. In this study, an attempt was made to investigate thermal effect on the color and rheological characteristics of rocket (Eruca sativa L.) purees made from leaves with and without stems. The color degradation kinetics of rocket puree was studied at temperatures between 60 and 110 °C using fractional conversion technique. The degradation kinetics of puree followed a 1st order reaction kinetics and the activation energy values for puree with and without stems were ranged between 38.90 and 51.21 kJ/mol. Effects of blanching on oscillatory and steady flow rheology of puree made from leaves with and without stems were studied in the temperature range of 25 to 70 °C. All puree samples exhibited an elastic modulus that is larger than the loss modulus in the tested frequency range. Blanched leaf puree exhibited the highest mechanical strength at 70 °C. The steady flow data fitted the Herschel-Bulkley model well. The complex viscosity and the apparent viscosity at similar frequency and shear rate range failed to follow the Cox-Merz rule. Scanning electron microscopy and sieve-analysis revealed that the leaf puree had smaller particle sizes than puree with stems.