Impact of Pretreatment and Drying Methods on Quality Attributes of Onion Shreds

Nihar R. Sahoo1, Lalit M. Bal2*, Uma S. Pal1 and Dipika Sahoo3

1Department of Agricultural Processing and Food Engineering, Orissa University of Agriculture and
 Technology, Bhubaneswar, Odisha-751003, India
2Post Harvest Process and Food Engineering, College of Agriculture, Jawaharlal Nehru Agricultural
 University, Tikamgarh, Madhya Pradesh-472001, India
3Department of Horticulture, College of Agriculture, Bhawanipatna, Orissa University of Agriculture and
 Technology, Bhubaneswar, Odisha-751003, India

Article history
Received January 14, 2014
Accepted December 10, 2015

Key words
pretreatment, hot air drying, heat pump drying, microwave-assisted convective 
drying, onion

Experiments were conducted on dry untreated onion shreds (2 mm thickness) or treated with salt (5 % solution) and potassium metabisulphite (0.5 % solution) in convective drier at 50 °C ((46±4) % relative humidity (RH)), 55 °C ((35±4) % RH), 60 °C ((28±4) % RH) and 65 °C ((20±4) % RH), heat pump-assisted convective drier at 35 °C ((32±2) % RH), 40 °C ((26±2) % RH), 45 °C ((19±2) % RH) and 50 °C ((15±2) % RH) and microwave-assisted convective drier at four microwave power levels, i.e. 120, 240, 360 and 480 W. The quality parameters of the dried onion shreds, namely rehydration ratio, colour difference, pyruvic and ascorbic acid contents and sensory scores were evaluated. The quality of dehydrated onion shreds was observed to be comparatively better when treated in heat pump drier at 50 °C, followed by that in microwave-assisted convective drier at 240 W and 50 °C, and last in convective drier at 60 °C. The onion shreds pretreated with potassium metabisulphite retained better colour of the dried product irrespective of drying methods. Therefore, heat pump drying may be recommended as one of the best drying methods for onion shreds, because it maintains the final product quality, which has practical importance for the food industry.

*Corresponding author:  
  +91 674 256 2360

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