Abstract:
The aim of this research was to investigate the effects of invert sugar and two-stage drying on qualities of osmotically dehydrated-air dried papaya and on the quality changes during storage. Papaya slices were soaked for various periods (1 to 10 days) in a solution containing 0.5% (w/v) sodium metabisulfite, 1.0% (w/v) citric acid, and different levels of calcium chloride (0, 0.5, 1.0, 1.5% w/v). The amount of infused calcium and hardness of papaya slices were determined. Calcium concentration and immersion time significantly affected hardness and calcium contents of papaya slices (p≤0.05). Papaya treated with solution containing 1.5% CaCl2 for 5 days was selected for further study as the treatment was the optimum condition for soaking time and amount of infused calcium. In the second part, effects of invert sugar and two-stage drying were studied. The conditions of invert sugar and drying were; Condition 1 : papaya slices containing no invert sugar and dried at 60ºC for 25 hour, condition 2 : papaya slices containing 10% invert sugar and dried at 60ºC for 19 hour, condition 3 : papaya slices containing 10% invert sugar and dried at 60ºC for 4 hour followed by 50ºC for 15 hour and condition 4 : papaya slices containing 10% invert sugar and dried at 60ºC for 4 hour followed by 40ºC for 21 hour. The results showed that moisture content and aw of product from each treatment were not significantly different (p>0.05). Moisture content of products was less than 18% (w.b) and aw was less than 0.65. Hardness and cutting work of products from condition 2, 3 and 4 were less than those of products from condition 1 significantly (p≤0.05). However, adhesiveness of products from condition 2, 3 and 4 were higher than those of products from condition 1 significantly (p≤0.05). Comparing between drying processes, it was found that hardness and cutting work of products from condition 3 and 4 were less than those of products from condition 2 but not significantly (p>0.05). Using invert sugar led to a better texture of products and two-stage drying could prevent case- hardening on surface of product. Qualities of product during storage were studied for over 18 weeks period. It was found that the products condition 2, 3 and 4 showed minor changes in colour and texture when compared to products from condition 1. Changing in colour and hardness of products with different drying process were less occurred in the products from condition 3 and 4 than those of condition 1 and 2. The score of acceptance test showed score more than 5 in the product containing invert sugar during storage period. The accepted score of the products from condition 3 and 4 in terms of colour, appearance and overall acceptability was more than those of products from condition 2. Therefore, the use of invert sugar combined with two-stage drying (60ºC followed by 50ºC) was possible strategy to apply to maintain the quality of osmotically dehydrated-air dried papaya since the drying time is shorter and the qualities was accepted over period of storage.