Antioxidant properties and aroma compounds of tree tomato fruits (Solanum betaceum) dried with different methods

The tree tomato or tamarillo (Solanum betaceum) is a tropical fruit which ranges in color from purple to yellow. This study was carried out to examine the changes in physical, morphological, antioxidant and aroma properties of tree tomato fruits dried with different drying methods. For this purpose, tree tomato fruits were dried in convective dryer at different temperatures (40, 50, 60, 70 and 80oC) at 1.5 m/s air speed, in microwave (350, 500 and 650W) and in freeze dryer. In this study, the dehydration and rehydration kinetics, physical, antioxidant properties and volatile compound profile of fruits were determined. For antioxidant properties, total phenolic compounds, total flavonoid, total anthocyanin, vitamin C, ferric reducing antioxidant power (FRAP) and 2,2-diphenyl-1-picrylhydrazil (DPPH) free radical scavenging assay were determined. Profiles of phenolic and anthocyanin compounds were determined by High Performance Liquid Chromatography (HPLC-DAD), and aroma profile was determined by gas chromatography (GC-MS). This study revealed that Midilli model best described the kinetics of convective and microwave drying methods. In the rehydration kinetics, it was determined that Weibull and Peleg models best fitted the rehydration process of convective dried tree tomato fruits while the microwave dried tree tomato fruits were better fitted with the Exponential model while the freeze-dried ones fitted with the Peleg model. The least total color change (∆E) was found in fruits that were convective dried at 40°C while the least shrunk fruits were those freeze dried. The least loss of ascorbic acid was in microwave at 650W, convective at 40°C and freeze-dried. Convective drying at 80°C is the most effective drying method in terms of total phenolic content, while freeze drying in terms of total anthocyanins, microwave drying at 650W in terms of flavonoid and DPPH free radical scavenging, microwave dried fruits have more gallic acid, catechin and epicatechin compared to other methods. The highest pelargonidin-3-glucoside content was found in freeze dried and the lowest in 350W microwaves dried fruits. A total of 39 volatile compounds were identified in fresh tree tomatoes. Ethyl and methyl esters of butanoic acid, methyl and ethyl esters of hexanoic acid, n-amyl acetate and eucalyptol were found to be high in fresh fruits. 54 volatile compounds were isolated in dried fruits. While some of the volatile compounds were formed during drying, some of them were lost during drying. As a result, microwave after freeze drying was effective in the good preservation of physical, antioxidant and volatile compounds in tree tomato fruits dried by different methods.