Abstract
The effect of different concentrations of sugar solution (hypertonic) (30%, 45% and 60% w/v) and carboxyl methyl cellulose (CMC) (0%, 1% and 2% w/v) coating on freeze drying of apple slices was studied. In total, nine treatments with respect to concentrations of hypertonic solution and coating layer were prepared to analyze their influence on the physical and chemical properties of freeze dried apple slices. It was observed that increase in the sugar solution concentration, decreased the moisture content of the apple slices significantly impacting its water activity, texture and sugar gain. Application of different concentrations of CMC coating had no significant effect on the properties of dried apple slices. A significant change was observed for color of CMC coated freeze dried apple slices pretreated with 60% sugar solution. Drying kinetics of pretreated apple slices were fitted by using two drying models, Newton’s and Page’s. Page’s model showed higher R-square and lower root mean square error (RSME) compared to Newton’s model.
Highlights
Osmotic dehydration of food materials includes partial removal of water when they are immersed in a hypertonic solution for a particular time and solution temperature
It was found that different concentrations of carboxyl methyl cellulose (CMC) coating did not have any significant effect on the moisture content and moisture loss ratio (Figures 1–3), while, by increasing the concentration of sugar solution, it notably decreased the moisture content
Our results were in agreement with the work, conducted by Falade et al in 2003 [14], they reported a decrease in instantaneous moisture content of cashew apples by increasing osmotic solution concentration
Summary
Osmotic dehydration of food materials includes partial removal of water when they are immersed in a hypertonic solution for a particular time and solution temperature. Freeze drying causes the least damage on the texture of the dried products and as such can be used as a substitute to other methods of drying such as hot air, vacuum, microwave, and osmotic dehydration [9] This drying process involves primarily freezing the food samples in a freezer, followed by keeping them under low pressure condition with the use of sufficient heat for ice sublimation [10]. Agnieszka and Andrezej studied the structural impact of osmotically pretreated freeze dried strawberries on their mechanical properties and reported that osmotic dehydration can limit the shrinkage of freeze dried strawberries They found that this process strengthened the fruit structure by increasing their cell wall thickness [11]. In this study the effect of carboxylmethyl cellulose coating prior to osmotic dehydration pretreatment on physical and chemical properties of freeze dried apple slices was evaluated
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