Abstract
Abstract Osmotic dehydration of kiwi was evaluated using 45, 55 and 65 °Brix sucrose solutions. Free moisture, water activity and solutes gain decreased in fruit during the process. Water loss rates were higher in the beginning of drying. Water activity decrease was higher when the product was in 65 °Brix solution. The equilibrium moisture content estimated by the Peleg model decreased significantly with increasing concentration of the osmotic solution, and the diffusivity values of water loss were in the range from 1.5 × 10-9 to 1.9 × 10-9 m2 s-1. The osmotic pressures of the solutions were also predicted.
Highlights
Candied fruits and vegetables are produced by osmotic dehydration (OD) when they are immersed in hypertonic sugar solution, which is used as a method of partial removal of water from foods (Sareban & Souraki, 2016; Abraão et al, 2013; Souraki et al, 2014b)
Samples of fresh kiwi used in the experiments had the following physicochemical characteristics: moisture content of 87.73% ± 1.05%; water activity of 0.990 ± 0.001; 3.06 ± 0.25 of pH and 12.15 ± 0.75 °Brix; these values are close to those reported by Gerschenson et al (2001): moisture of 84%, water activity of 0.99 and soluble solids between 11 and 14 °Brix
The output rates of free water were higher as the solution concentration increased. This is explained by the fact that higher concentration differences between fruit and osmotic solution promote greater water losses (Robbers et al, 1997), as a consequence of the osmotic pressure gradient and the existing mass transport, with mass transfer rates dependent on concentration and temperature of osmotic solution (Rastogi & Niranjan, 1998)
Summary
Candied fruits and vegetables are produced by osmotic dehydration (OD) when they are immersed in hypertonic sugar solution, which is used as a method of partial removal of water from foods (Sareban & Souraki, 2016; Abraão et al, 2013; Souraki et al, 2014b). Due to difference between the osmotic pressure of the food and that of the solution, water is transported from the material into the solution. During OD the rate of water loss is directly proportional to: osmotic solution concentration; immersion time; temperature; weight ratio of the feed solution; agitation; and depends on food structure, solid size and geometry, and the area of mass exchange and system pressure (Herman Lara et al, 2013; Conceição Silva et al, 2012; Ruiz Lopez et al, 2010; Rastogi & Niranjan, 1998)
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