Narrow Results

The present work proposed the two-stage drying technique concerning on the drying of shrimp using superheated steam dryer followed by heat pump dryer (SSD/HPD) at different drying conditions. The effects of drying temperatures and intermediate moisture contents (IMC) on drying characteristics and dried product quality were investigated. Shrinkage, color and texture of dried shrimp were determined. The experiments were carried out in the two stages of SSD/HPD. The first-stage superheated steam drying was performed at the drying temperatures of 160°C and 180°C while the second-stage heat pump drying was operated at 50°C. The moisture content of shrimp at the end of the superheated steam drying stage (IMC) was varied between 30% and 40% (w.b.). For the comparison, purely SSD (superheated steam drying for the whole drying process) was also performed at the same drying steam temperature as used in the first-stage SSD. As for the effects of drying conditions, the results showed that higher drying steam temperature and higher IMC yielded better product quality only in terms of color. In addition, it was found that SSD/HPD dried shrimp had much lower degree of shrinkage, better color, softer and less tough than purely SSD dried shrimp.

Hot air drying, vacuum drying and low-pressure superheated steam drying (LPSSD) of Indian gooseberry flake were carried out at various drying temperatures (65 and 75°C) and absolute pressures (7, 10 and 13 kPa) to monitor the drying kinetics and quality changes, in terms of color changes and antioxidant activity, of the product. The dried gooseberry flake was then soaked in hot water at 70, 80 and 90°C to prepare Indian gooseberry tea. In terms of the drying kinetics, the drying temperature had an effect on the moisture reduction rate of the samples in all cases. Vacuum drying, however, took shorter time to dry the product to the desired moisture content. Regarding the nutritional quality of the dried flake, it was found that the amount of ascorbic acid in the flake dried by vacuum drying was higher than those dried by hot air drying and LPSSD. However, LPSSD could retain flavonoid compounds better than did other drying techniques. On the other hand, total polyphenolic compounds and the total antioxidant activity of the dried flake were not significantly different among all cases. Regarding the release of antioxidants from the flake during tea preparation, no significant difference was observed between using the water temperature of 70, 80 and 90°C. Due to the more porous structure of LPSSD flake, however, higher compound degradation was noted. Nevertheless, it could still be concluded that drying the flake by LPSSD at 75°C and 7 kPa could best retain the active compounds, i.e., 62% of ascorbic acid, 91% of flavonoid compounds, 81% of total polyphenolic compounds and 83% of antioxidant activity; appropriate water temperature and time for tea preparation was 90°C and 5 minutes, respectively.

The bombay duck or bombil (Herpadon nehereus) is often considered as a delicious fish by connoisseurs of Indian cuisine. It is native to the waters between Mumbai and Kutch in the Arabian sea. Bombay duck is often dried and salted in open air sun drying, however, it suffers from serious drawbacks of contamination due to flies, insects and soil. Solar drying is an excellent way to get rid of these problems as the fish is contained in cabinet or tunnel. In the present work, the solar drying was carried out in a pilot scale solar dryer provided with 20 m² solar collection area and having capacity to load upto 100 kg wet fish. The role of pretreatment, the inlet air temperature and gas velocity on drying of Bombay duck was studied. The dried fish was tested for its physical and organoleptic properties, besides microbial analysis.