%0 Journal Article
%T Optimization of Microwave-Osmotic Pretreatment of Apples with Subsequent Air-Drying for Preparing High-Quality Dried Product
%A Elham Azarpazhooh
%A Hosahalli S. Ramaswamy
%J International Journal of Microwave Science and Technology
%D 2011
%I Hindawi Publishing Corporation
%R 10.1155/2011/687548
%X Prepared apple (Red Gala) cylinders were subjected to microwave-osmotic dehydration treatment under continuous flow medium spray (MWODS) conditions and then air-dried to a final 20% moisture content. The dried samples were evaluated for color and textural properties, and rehydration capacity. The MWODS pretreatments were based on a central composite rotatable design and a response surface methodology using five levels of sucrose concentration, temperature, and contact time at a constant flow rate of 2800£¿mL/min. The air-drying was carried out at 60¡ãC, % relative humidity, and £¿m/s air velocity. The results were compared to untreated air-dried (AD) (worst-case scenario) and freeze-dried (FD) (best-case scenario) apples without the MWODS treatment. Color properties were affected regardless of the type of treatment. Conventional AD apples were darker in color, whereas MWODS-treated samples were lighter with higher and values, higher Hue and Chroma values but lower value and . Further the color parameters of MWODS-treated samples were closer or equal to the FD apples. The texture properties were also affected by the osmotic variables with MWODS treatment resulting in softer and chewier products. The AD samples were hard, and FD apples were brittle. 1. Introduction Food industry interest in enhancing quality and marketability of dried foods has been continuously increasing. Osmotic dehydration (OD) pretreatment has long been recognized to improve product quality and reduce energy consumption. Osmotic drying is only a pretreatment, and hence a second-stage drying such as air, freeze, and vacuum drying is necessary to complete the process. It has been shown that the quality of air-, freeze-, or vacuum-dried fruits and vegetables could be improved by an osmotic pretreatment [1]. Freeze-drying (FD) is considered to be the best for keeping the quality attributes, but it is expensive [1]. In an earlier study [2], it was shown that a microwave-osmotic dehydration (MWODS) pretreatment could be used to accelerate the moisture removal from the fruit. The pretreatment resulted in removal of almost 50% of the fruit moisture in a short 30£¿min treatment time [2]; however, the influence of the treatment on product quality was not reported. There have been several studies on the evaluation of color change during osmotic dehydration. Osmotic dehydration (OD) reduces the discoloration of fruits by enzymatic browning by limiting exposure of fruits to oxygen [2], and the sugar uptake increases the stability of pigments during further drying and subsequent storage period.
%U http://www.hindawi.com/journals/ijmst/2011/687548/