The Effect of Ultrasound Pre-Treatment and Air-Drying on the Quality of Dried Apples

Abstract

In order to develop environmentally sound, energy inexpensive and well scalable drying techniques that maintain high quality of dried fruit, optimisation of integrated process (ultrasound and air-drying) in the production of dried apples was conducted. Selected quality parameters of fresh and dried apples (variety Goldparmâne) resulting from different duration of ultrasonic pre-treatment and air-drying were compared. Sugars were determined spectrophotometrically using an enzymatic method. Content of total phenols and flavonoids was determined spectrophotometrically with the Folin-Ciocalteau assay, while the antioxidant capacity was evaluated by using ABTS (2,2-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) and FRAP (Ferric Reducing/Antioxidant Power) assays. Sensory properties of dried apples were investigated according to the Quantitative Descriptive Analysis. In combination with the same air-drying conditions, prolonged ultrasound pre-treatment led to a decrease in total phenols and flavonoids, as well as in the antioxidant capacity of dried apples. Difference in drying time had no significant effect on the content of total phenols and flavonoids, as well as antioxidant capacity. The sample dried without the ultrasound pre-treatment was evaluated as the most sensory acceptable. The content of glucose and fructose correlated well with total phenols and flavonoids, as well as with antioxidant capacity of apple samples.

Keywords

• fresh apple
• dried apple
• ultrasound and air-drying process
• sensory properties
• phenols
• flanonoid
• antioxidant capacity