Continuous and conventional microwave heating effects on the antioxidant capacity of tomato juice

Abstract

Thermal processing extends the shelf life of fruits and vegetables by inactivating microorganisms and enzymes. The efficacy of heating depends on the properties of the food and mainly on the processing parameters. The microwave (MW) oven offers several advantages for keeping overall quality and safety of the foods products. A continuous MW oven is a new tool which can make the cooking process of plant products shorter. The present work evaluates the effect of a new industrial continuous MW oven at different heating powers (750, 900 and 1050 W) and times (from 120 to 420 s) on the antioxidant capacity of tomato juice. This treatment was compared to other tomato juice heated in a conventional MW oven (750 and 900 during 60 to 150 s). As control non heated juice was used. The results showed that the antioxidant capacity was lowered by the heating. In general, as longer the duration and higher the power applied the lower antioxidant capacity was found. However, a moderate high power dose (900 W) combined with shorter duration (120 or 150 s) kept better the antioxidant capacity than low power MW dose (750 W) combined with high treatment duration (360 or 420 s). At similar doses (time/power) the industrial MW provided a slightly lower antioxidant capacity than conventional MW. As main conclusion, when comparing the efficacy of the continuous MW oven versus the conventional one no advantage for keeping the antioxidant capacity of tomato juice was found.