Effect of osmotic pre-treatment and microwave heating on lycopene degradation and isomerization in cherry tomato

Cherry tomato were dehydrated by a combination of different techniques (osmotic dehydration, convective drying, and microwaves assisted air drying) in order to evaluate the effect of the process variables on the degradation and isomerization of lycopene, as well as on the optical properties. Specifically, the effect of prior osmotic treatment, air drying temperature (40, 55, and 80 degrees C) and level of microwave energy (0, 1, and 3 W/g) were studied. Obtained results showed that the osmotic pre-treatment limited the isomerization during the later stage of drying, whereas both the loss of total lycopene and the trans-as isomerization, mainly to the 13-cis form, were favored by an increase in temperature and the microwave power. Furthermore, a positive correlation between the degree of isomerization experienced by the samples during drying and the hue (h*) were obtained. This correlation was reflected in the colour of the sample with predominantly more orange tones and less reddish ones. (C) 2010 Elsevier Ltd. All rights reserved.