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

Abstract

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.

Selected Emerging Technologies to Enhance the Drying Process: A Review

“…The impact of ultrasound intensity and time of pretreatment was ambiguous, but it seems that when the ultrasound intensity is higher the time of pretreatment should be longer, as well. Such indistinct results were also presented by Opalić et al [60] for air-dried apple tissue treated at 37 kHz for varied times (0-45 min). They obtained the highest content of phenolic compounds in apple tissue dried for the same time (720 min) after 22.5 min of ultrasound application, compared with 0 and 45 min.…”

The impact of ultrasound and steam blanching pre-treatments on the drying kinetics, energy consumption and selected properties of parsley leaves

“…Interestingly, when parsley was dried with higher microwave power, the type of pre-drying processing did not alter the chlorophyll's quantity significantly, with the exception of blanched and untreated leaves at 30°C. Beneficial effect of the US treatment on the biological components and their activity was also observed in the case of polyphenols in apple [22], antioxidant activity in thyme [25], chlorophyll a and b [31] and polyphenols contents in parsley leaves [29]. However, the character of influence on the chemical composition was always linked to the drying conditions and in some dried material a significant decomposition of the molecules was observed.…”

Effects of Ultrasound on Polyphenol Retention in Apples After the Application of Predrying Treatments in Liquid Medium

“…During tissue sonication, ultrasound affects the matrix structure by formation of microscopic channels that favor both mass transfer intensification during osmotic treatment, and higher water diffusivity during subsequent air-drying (Nowacka et al 2014). From a technological point of view, the ultrasound seemed to be very promising, but unfortunately, in some cases, especially when a liquid medium during sonication was applied, substantial losses of bioactive compounds were reported (Stojanovic and Silva 2007;Opalić et al 2009;Pingret et al 2013). Although the available literature presents many experiments with ultrasound application before and during fruit and vegetable dehydration process (Siucińska and Konopacka 2014), the majority of them focus on monitoring the dynamics of mass transfer or physical properties, such as sugar gain, water loss, or changes in color or microstructure of plant tissue (Cárcel et al 2007;Deng and Zhao 2008;Garcia-Perez et al 2012;Nowacka et al 2012;Schössler et al 2012).…”

“…Although the available literature presents many experiments with ultrasound application before and during fruit and vegetable dehydration process (Siucińska and Konopacka 2014), the majority of them focus on monitoring the dynamics of mass transfer or physical properties, such as sugar gain, water loss, or changes in color or microstructure of plant tissue (Cárcel et al 2007;Deng and Zhao 2008;Garcia-Perez et al 2012;Nowacka et al 2012;Schössler et al 2012). With regard to phenolic compound retention during ultrasound-assisted fruit tissue treatment, the reports on negative effect of sonication on phenolic compound content and antioxidant activity (Stojanovic and Silva 2007;Opalić et al 2009), more often than not, indicate a positive influence (Keenan et al 2012). However, in both cases, the data is based on the total phenolic content measurements.…”