Modeling Color Parameters during Plums Drying Pretreated with Ultrasound and Osmotic Dehydration

The aim of this study was to investigate the effect of simultaneous application of ultrasound and osmotic dehydration pretreatments on changes of color parameters as well as sensory evaluation during hot air drying. In this evaluation, pretreatments including ultrasound time at two levels (10 and 30 minutes), osmotic solution concentrations at two levels (50 and 70 Brix) and immersion time in osmotic solution at four levels (60, 120, 180 and 240 min) were applied on plums and then the samples were dried at 80°C temperature and 1.4 m/s air velocity. The results showed that with decreasing moisture content during drying, the samples lightness "L" and yellowness "b" is reduced while the redness "a" is increased. The simultaneous application of ultrasound and osmotic dehydration pretreatments led to a significant increase in "L" and "b" and a significant decrease in "a" compared to control samples. In addition, application of the pretreatments improved the other color indices (Total color change, Chroma index, Hue angel and browning index). Sensory evaluation results of the dried plums showed an improvement in terms of appearance, color, taste and overall acceptability of the samples pretreated with ultrasound and osmotic dehydration. Moreover, modeling the color parameters changes of the plums during drying was done through the models available in the literature as well as the models proposed in this study. Then, one of the proposed models was selected as the best model to predict color parameters changes of the plums under the selected experimental conditions.