Mechanical and osmotic dehydration behavior of pineapple and retention of Vitamin C
The study was designed to observe the behavior of mechanical and osmotic dehydration of pineapple, retention of vitamin C content during drying and development of jam from fresh and dehydrated pineapple. Osmotic dehydration carried out with pineapples collected from local market of Mymensingh in July 2015 and found that pineapples contained higher moisture content (93.9%,wb) than normal (85-87%,wb) and showed contradictory osmotic behavior due to higher moisture content and hormonal effect. Then the studies were conducted using pineapples of Gaint Kew variety collected from Madhupur without hormone treatment which contained 86.11% moisture, 0.36% ash, 13.89% total solid, 0.54% protein and 17.38 mg 100g−1 vitamin C. The osmotic concentration behavior was investigated using sugar and combined sugar-salt solution for 6 mm thick pineapple slices and immersion time was 6 hr. The extent of water loss, solid gain and normalized solid content were strongly influenced by strength of osmotic solution. It was found that K-value (mass transfer coefficient) increases with increasing concentration and was the highest (0.15 min−1) for 55/5% sugar/salt solution and lowest (0.07 min−1) for 45% sugar solution. Three different temperatures (55, 60 and 65 °C) and thicknesses (4, 6 and 8 mm) were used to investigate the drying behavior of pineapple slices in a mechanical dryer. Activation energy value of 8.14 Kcal g-mole−1 was found for fresh pineapple slices. 55/5% sugar/salt osmosed and dried pineapple gave 5.46 times higher dryer throughput compared to nonosmosed dried pineapple. Degradation of vitamin C content of pineapple at different air-dry bulb temperatures (55, 60 and 65 °C) of 6 mm thickness was investigated and activation energy for degradation of vitamin C was found to be 14.38 Kcal g-mole−1. Osmotic dehydration prior to air drying, gave the lower rate of degradation of vitamin C during drying compared to that dried without osmosis. Developed jams were tested for their acceptability by sensory evaluation using 1-9 point hedonic scale and jam made from osmotically dehydrated (55/5% sugar-salt and then dried at 60°C) secured highest score (8.5) and ranked as ‘like very much’, while the other products were ranked as ‘like moderately’.
Keywords: Dehydration, osmosis, activation energy, vitamin C, jam