Application of ultrasound assisted vacuum drying for improving quality properties during peppers dehydration

The use of various pretreatment applications and novel drying techniques have been recently considered very crucial for drying of food to improve the quality properties of the products and preserve nutritional values at maximum. For this purpose, ultrasound treatment which has been used to increase heat and mass transfer was combined with vacuum drying method so that ultrasound assisted vacuum (USV) drying method could be obtained and it was used to dry some food products. Dried red peppers are important spices consumed traditionally. USV drying method was used to dry them in the thesis study. In this thesis study, red peppers were dried at 45, 55, 65 and 75 °C by applying USV drying method to examine drying kinetics, rehydration ratio and effects of drying methods on bioactive compounds such as total phenolic content and antiradical activity under these conditions, total yeast and mold count and color changing values. USV control treatments not included ultrasound waves were applied under the system in the same property to determine real effect of USV drying method. In addition, vacuum drying and oven drying methods were used to examine these drying, quality and microbial parameters. USV drying method could provide 25 % shorter drying period (180 min shorter at 45 °C) and the increasing effective moisture diffusivity (Deff) (between 9% and 89%) as compared to USV control technique. Total yeast and mold count of peppers were more inactivated with USV drying method as compared to control treatment. Rehydration properties of red peppers dried by USV drying method were mostly similar or slightly decreased. However, the antioxidant capacities of red peppers dried by USV drying method were generally affected more than USV control method. Keywords: Red pepper, vacuum drying, ultrasound treatment, USV, bioactive properties, drying kinetics.