Effect of Pre-Treatments and Drying Temperatures on Physicochemical Properties and Microbial Counts of Dried Indigenous Vegetables
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Abstract
This research aimed to study the effect of pre-treatments prior to drying and drying temperatures on physical, chemical and microbiological properties of some indigenous vegetables, namely cowslip creeper, ceylon spinach and star gooseberry. These vegetables were pre-treated prior to drying for 12 conditions i.e., immersing in a solution of potassium metabisulfite (KMS), citric acid and sodium hydroxide (NaOH) for 5, 10 and 15 minutes, and blanching for 30, 45 and 60 seconds compared to fresh vegetables as a control sample. After that, they were dried with a tray hot-air dryer with 3 different temperatures (50, 60 and 70 °C). It was found that the pre-treatments prior to drying and drying temperatures significantly affected drying processes and properties of these dried cowslip creeper, ceylon spinach and star gooseberry. At higher drying temperatures, the drying time was shorter. It was also observed that blanching led to the shortest drying time compared with KMS, NaOH and citric acid soaking, respectively. The total color change value of vegetable soaking in KMS for 15 minutes before drying gave the lowest value compared with fresh vegetables (p < 0.05), followed by NaOH, citric acid soaking and blanching, respectively. When drying at higher temperatures, the water activity, vitamin C, moisture and protein contents of all dried vegetables were reduced, whereas the rehydration, fiber and ash contents were increased significantly (p < 0.05). In addition, the KMS soaking before drying led to a low number of total microbial counts, and yeast and mold count of all dried vegetables. Also, drying at high temperature resulted in decreasing of their microbial counts. According to the results, it could be concluded that KMS soaking for 15 min and then drying at 70 ºC was the optimum condition for drying these indigenous vegetables.
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References
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