Abstract:
The objective of this study were to investigate the effects of invert sugar on drying kinetics and the quality changes of osmotically dehydrated-air dried storage. This study was divide into three parts. Initially, cantaloupe slices were soaker in a mix solution containing 0.5% sodium metabisulfite, 1% citric acid and calcium chloride at different levels (0,0.5,1.0,1.5 and 2.0% (w/v)). Calcium content and hardness of cantaloupe slices were determined everyday until the amount of calcium was constant. Calcium chloride concentration significantly affected calcium content of cantaloupe slices (p≤0.05). The hardness of cantaloupe slices was significantly affected by calcium chloride concentration (p≤0.05) while the effect of immersion time was not significant (p>0.05). The results from calcium content, hardness and microstructure under Cryo-SEM showed that the cantaloloupe treated with a mix solution containing 1% calcium chloride for 6 days were the best condition for pretreatment. Further study, four levels (0,5,10 and 15% (v/v)) of invert sugar in the final step of osmotic dehydration were applied. The cantaloupe slices were then dried in hot-air dryer at 60°C. The result showed that cantaloupe without invert sugar had the fastest drying rate. The drying rate was lower when increasing the amount of invert sugar. The moisture ratio data were fitted to ten different mathematical models. The modified Henderson and Pabis model was found to be the best model to predict the drying kinetic of all treatments. The quality changes during drying process of four treatments showed a similar trend. The increase in invert sugar in osmotic solution led to decrease in aw: whist reducing sugar content and browing increased; the pattern of changes in hardness, cutting work and sulferdioxide content were not different during drying. The result from sensory analysis showed that the product containing 10 and 15% invert sugar were most acceptable. However, the final product containing 15% invert sugar was sticky. Therefore in the further study, cantaloupe containing 0, 5 and 10%, being kept in PP bag at room temperature (30°C), were selected for quality study during storage. Among all treatments, the produce containing 10% invert sugar showed the best quality after 24 week storage, only small changes in physical qualities were found. The microstructure Cryo-SEM showed that the use of invert sugar in osmotic solution can retard the sucrose crystal formation on the surface of osmotically dehydrated-air dried cantaloupe over 24 weeks storage period.