Advancements in Drying Techniques for Food, Fiber, and Fuel

Effect of drying techniques on the retention of antioxidant activities of Saskatoon berries

“…The observed antioxidant activity ranking of the fruit in terms of TEAC (ABTS radical scavenging) was frozen berries > freeze dried berries > microwavevacuum dried berries > thin layer hot air dried berries > vacuum dried berries. In the freeze drying process, the low temperature and solid state of water in the material during drying resulted in improved retention capacity of nutrients of the products (Dev & Raghavan, 2012;Ratti, 2001). Our results indicate that less thermal degradation and less leaching loss during freeze drying helped to retain the highest antioxidant activity (3.90 ± 0.01, mM Trolox 100 g −1 ) among the dried samples.…”

“…In the thin layer hot air drying, the berries were exposed under a continuous hot air stream flow for a relatively long time to increase the temperature to evaporate moisture from the fruit (Ratti, 2001). The high temperature, long drying time and presence of air led to oxidative degradation of the anthocyanins (Table 1), resulting in the deterioration of the color attribute of the dried fruit (Dev & Raghavan, 2012;Ratti, 2001). Thus thin layer hot air drying showed less antioxidant retention capacity than microwave-vacuum drying.…”

“…Vacuum drying can be performed at a low temperature and this drying system is suitable for heat sensitive materials. The vacuum drying can result in greater retention of nutrients as well as volatile compounds in the dried products, but this drying method is limited in use because of higher costs and prolonged drying time (Dev & Raghavan, 2012;Mitra & Meda, 2009;Ratti, 2001;Sagar & Kumar, 2010). The selectivity of the drying system for particular products or retention of particular elements in the products is very important for suitable and efficient drying of the products.…”

“…In practice, there are many methods of drying such as freeze drying, microwave-vacuum drying, vacuum drying and hot air drying, etc. Although the purpose of all drying methods is the same, the heat generation and heat transfer phenomena to the materials are quite different from each other (Dev & Raghavan, 2012;Ratti, 2001). Freeze drying is one of the best drying methods to retain the quality of dried products; however, this method is relatively expensive for commercial drying of fruits.…”

Water Content Determinations for Peat and Other Organic Soils Using the Oven-Drying Method

“…The oven-drying temperature and period adopted for the removal of water are of great importance, influencing the measurement result since different physical states are produced. The same is also true for other biological materials, as reported, for example, in studies on foods [4][5][6] , pharmaceuticals, [7] fibers, [4] fuels [4,8] and animal manure, [9] although pertinent drying temperature ranges may be different.…”