Hot air drying kinetics of novel functional carrot snack: Impregnated using polyphenolic rich osmotic solution with ultrasound pretreatment

In this study, osmotic impregnation technique combined with ultrasonic pretreatment was applied to carrot slices followed by hot air drying in order to production of functional and healthy snack enriched with polyphenolic compounds derived from roselle extract (at least 400 ppm). The purposes of osmotic impregnation‐dehydration process were the maximum amount of dehydration and phenolic compounds diffusion along with the minimum sugar gain. Results revealed that increasing osmotic solution concentration and process time over optimal points, resulted in reduction of phenolic compounds saturation inside the samples. Also, it was found that prolonged ultrasound pretreatment had a damaging effect on fruit tissue microchannels and led to a decrease in the mass transfer rate. The optimal conditions of this stage were osmotic solution concentration of 60% and the process time of 60 min without ultrasonic pretreatment. In the second stage, the results of hot air drying showed that the highest amount in the total phenolic content was achieved at 70°C. Furthermore, among the several models evaluated, Jena & Das model with a determination coefficient of 0.99 and minimum error indexes, was the best fitted to drying experimental data and activation energy for effective diffusivity coefficient was calculated as 35.987 kJ/mol. PRACTICAL APPLICATIONS: Due to elevation in consumer's awareness in recent decades about the importance of food composition for healthier life and diseases prevention, demand for functional foods has been increasing. Food enrichment with bioactive compounds like polyphenol compounds from different plant sources is an applicable method for this purpose. In this study, carrot, which is a valuable vegetable itself, was further extended to a more functional food by enrichment with rosella plant extract and then hot air dried to produce a snack which has more nutritional quality than conventional ones. Also, osmotic dehydration results in lower moisture content of carrot slices which helps reduced hot air drying time and lower energy consumption. Overall, results from this research is usable to develop a functional snack based on carrot and rosella extract.