Abstract:
The aims of this work were to study the effect of polyhydric alcohol on mass transfer during osmosis and drying kinetics as well as study quality changes of osmotically dehydrated-air dried cantaloupe during storage. Firstly, the effect of polyhydric (sorbitol or glycerol) partially replace sucrose at 10 and 15% (w/v) on mass transfer rate during osmosis was studied. The treatment with 0% polyhydric alcohol and the 10% (v/v) invert sugar replacement were set as a control and a reference, respectively. The treatment with sorbitol and reference showed significantly higher solid gain (SG) and lower water loss (WL) (p≤0.05) than the control. The treatment with glycerol presented significantly lower SG and higher WL (p≤0.05) than the control. Mass transfer rate increased with increasing concentration of polyhydric alcohol. Secondly, the osmosed cantaloupe was then dried in hot air drier at 60 ℃. The rate of drying was as follows: control > sorbitol > glycerol > reference. The drying rate decreased as the concentration of polyhydric alcohol increased. Page's model showed a better fit with experimental data of all treatments than did the Henderson and Pabis model. During drying process, it was found that the treatment with polyhydric alcohol and reference resulted in the decreasing in a[subscript w]. Water mobility was monitored using NMR technique. The use of polyhydric alcohol and the reference resulted in decreasing of NMR relaxation time. Based on result from sensory analysis and drying kinetics, the product containing 10% sorbitol, 10% glycerol, the control and the reference were selected for further study. Thirdly, BET monolayer value (m₀) was calculated using BET equation. The m₀ of the products was as follows: reference > glycerol > sorbitol > control. Finally, the dried products, in polypropylene bag, were randomly selected for the study of quality changes during storage for over 20 weeks at temperature of 30 ℃ as storage time increased, moisture content and a[subscript w] of all treatments slightly decreased while hardness and cutting work increased. The result from sensory analysis showed that the product treated with sorbitol, glycerol and the reference had a significantly higher overall appearance acceptability score (p≤0.05), as compared to the control. The storage at 40 ℃ accelerated dramatic changes in product qualities.