A prototype heat pump dryer has been developed for drying of fruits and vegetables at low temperature and relative humidity to maintain the quality of dried product. Onions, of Nasik red variety were peeled, trimmed and sliced to 2 mm thickness. The onion slices were dried in the heat pump dryer at 35ºC (32 % R.H.), 40ºC (26 % R.H.), 45ºC (19 % R.H.) and 50ºC (15 % R.H.). Samples were also dried in a hot air dryer at 50ºC (52 % R.H.) for comparison. The drying rate increased with increase in drying air temperature, associated with reduced R.H., in the heat pump dryer. Drying took place mainly under the falling rate period. The Page equation, resulting in a higher coefficient of determination and lower root mean square error, better described the thin-layer drying of onion slices than the Henderson and Pabis equation. Heat pump drying took less drying time of 360 min and yielded better quality dried product, with higher retention of ascorbic acid and pyruvic acid and lower colour change, as compared to a hot air dryer at the same drying air temperature of 50ºC.
Adam E, Mühlbauer W, Esper A, Wolf W, Spiess W. Quality changes of onion (Allium Cepa L.) as affected by the drying process. Nahrungfood. 2000. p. 2–6.
2.
Adapa P, Sokhansanj S, Schoenau G. Performance study of a re-circulating cabinet dryer using a household dehumidifier. Drying Technology. 2002. p. 1673–89.
3.
Chua K, Chou S, Ho J, Hawlader M. Heat pump drying: Recent developments and future trends. Drying Technology. 2002. p. 1579–610.
4.
Francis F, Clydesdale F. Food calorimetry: theory and applications. The AVI publishing Company Inc; 1975.
5.
Henderson S, Pabis S. Grain drying theory i. temperature effect on drying coefficient. Journal of Agricultural Engineering Research. 1961. p. 169–74.
6.
Hernandez J, Pavon G, Garcia M. Analytical solution of mass transfer equation considering shrinkage for modeling food-drying kinetics. Journal Of Food Engineering. 2000. p. 33–9.
7.
Holdsworth S. concentration and drying of foods. Elsevier Applied Science Publ; 1986. p. 293–303.
8.
Kalbasi M. Heat and moisture transfer model for onion drying. Drying Technology. 2003. p. 1575–84.
9.
Kaymak-Ertekin F, Gedik A. Kinetic modelling of quality deterioration in onions during drying and storage. Journal Of Food Engineering. 2005. p. 443–53.
10.
Lewicki W, Pp, Rajchert D, Nowark D. Effect of mode of drying on storage stability of coloured dried onion. Polish Journal of Food and Nutrition Sciences. 1998. p. 701–6.
11.
Madamba P, Driscoll R, Buckle K. The thin-layer drying characteristics of garlic slices. Journal Of Food Engineering. 1996. p. 75–97.
12.
Malchev E, Ioncheva N, Tanchev S, Kalpakchieva K. Quantitative Changes in Carotenoids During the Storage of Dried Red Pepper and Red Pepper Powder. Nahrung-food. 1982. p. 415–20.
13.
Pal U, Khan M. Heat pump drying of food materials: A critical review. Journal Of Food Science And Technology-mysore. 2007. p. 119–24.
14.
Pal U, Khan M. Calculation steps for the design of different components of heat pump dryers under constant drying rate condition. Drying Technology. 2008. p. 864–72.
15.
Pezzutti A, Crapiste G. Acta Horticulturae. 1st International Symposium on Edible Alliaceae. 1997. p. 455–62.
16.
Ranganna S. Handbook of analysis and quality control for fruit and vegetable products. 2nd Ed. Tata Mc Graw Hill Publishing Co; 1986.
17.
Rapusas R, Driscoll R. Kinetics of Nonenzymatic Browning in Onion Slices During Isothermal Heating. Journal Of Food Engineering. 1995. p. 417–29.
18.
Sarsavadia P. Development of a solarassisted dryer and evaluation of energy requirement for the drying of onion. Renewable Energy. 2007. p. 2529–47.
19.
Sawhney R, Sarsavadia P, Pangavhane D, Singh S. Determination of drying constants and their dependence on drying air parameters for thin layer onion drying. Drying Technology. 1999. p. 299–315.
20.
Schwimmer S, Weston W. Onion Flavor and Odor -Enzymatic Development of Pyruvic Acid in Onion as a Measure of Pungency. Journal Of IJFS October. 1961. p. 159–67.
21.
Agricultural And Food Chemistry. p. 301–4.
22.
Sharma G, Verma R, Pathare P. Mathematical modeling of infrared radiation thin layer drying of onion slices. Journal Of Food Engineering. 2005. p. 282–6.
23.
Viswanathan R, Hulasare R, Jayas D. Drying characteristics of shredded onion (Allium cepa). Journal Of Food Science And Technologymysore. 2003. p. 521–4.
24.
Wang J. A single-layer model for far-infrared radiation drying of onion slices. Drying Technology. 2002. p. 1941–53.
25.
Williams S. Official methods of analysis of the association of official analytical chemists. 1984.
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