Microwave exposure of tomato varieties before catalytic oven drying and its effect on physicochemical and bioactive components studied by Fourier transform infrared (FTIR) spectroscopy

Abstract

This study investigates the microwave-oven drying process to dehydrate two tomatoes (Solanum lycopersicum) varieties for the enhancement of its quality. Roma and grape tomato slices were pre-dried using microwave power densities of 10, 15 and 20 W, respectively for 10 min before catalytic hot-air oven drying temperature at 60 °C for 8 h. The dried tomato slices were cooled and milled into powder. Physicochemical, bioactive, phytonutrients, colour, textural and fourier transform infrared spectroscopy (FTIR) characterization of the dried grape and Roma tomato were carried out according to standard method. Decrease in the pH of the microwave pre-dried tomato slices was accompanied by significant increase (p < 0.05) in the total titratable acidity as the microwave power densities increased. The ascorbic acid value increased significantly (p < 0.05) with increasing power densities for Roma tomato while colour profile reduced. The phenolic compounds decreased with a corresponding increase (p < 0.05) in total carotenoid, lycopene and beta-carotene in Roma tomato variety. Majority of the textural properties decreased with increased in power densities. FTIR revealed the presence of diverse functional groups ranging from alkanes, alcohols, quercetin, aldehydes and phenolic compounds in all the samples evaluated. This study revealed that pre-dried process using microwave at varied power densities retained some of the quality characteristics of dried tomato. Thus, application of microwave power densities prior to oven-drying process could serve as an alternative method towards commercialization of good quality dried tomato for the agro-food processing industry.