Abstract
The aim of this work was to analyse the effect of ultrasound-assisted osmotic dehydration of apples v. Elise on mass transfer parameters, water activity, and colour changes. Ultrasound treatment was performed at a frequency of 21 kHz with a temperature of 40 °C for 30–180 min using four osmotic solutions: 30% concentrated syrups of erythritol, xylitol, maltitol, and dihydroxyacetone (DHA). The efficiency of the used solutes from the polyol groups was compared to reference dehydration in 50% concentrated sucrose solution. Peleg’s model was used to fit experimental data. Erythritol, xylitol, and DHA solutions showed similar efficiency to sucrose and good water removal properties in compared values of true water loss. The application of ultrasound by two methods was in most cases unnoticeable and weaker than was expected. On the other hand, sonication by the continuous method allowed for a significant reduction in water activity in apple tissue in all tested solutions.
Highlights
Osmotic dehydration (OD) is a simple technique for removal of water from fruits and vegetables, a more correct term is “osmotic dewatering” since the final product still has a high moisture content
The raw apple tissue was characterized by a water content (WC) of 5.69 ± 0.25 g H2 O/g dry matter (Table 1)
A 50% reduction in the Water Content (WC) of raw apple was obtained after 60 min in the case where sucrose used as osmotic agent, and after 120 min and 150 min in the case of erythritol and xylitol, respectively (Table 1)
Summary
Osmotic dehydration (OD) is a simple technique for removal of water from fruits and vegetables, a more correct term is “osmotic dewatering” since the final product still has a high moisture content. The amount of water remaining in the material does not ensure its stability, as water activity is generally higher than 0.9 [1] This partial dehydration is performed by immersion of the fruit or vegetable material in a concentrated aqueous solution, where there are two major simultaneous countercurrent flows: one flow of solutes from the solution into the food matrix and another from the food into the osmotic solution (principally water) [2]. The relevance of osmotic dehydration is related to the improvement of some nutritional, functional, and organoleptic properties of the product [3]. Different substances such as sweeteners or sweetness enhancer were proposed as an alternative to the use of sucrose. One of them was steviol glycoside, the additive which was used in OD [4]
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