A less energy intensive process for dehydrating onion

Abstract

Onion powder has an extensive demand and wide application worldwide as flavour additive in convenience foods and medicinal products. Conventionally onion powder is prepared by hot air drying of onion slices followed by grinding. Convective air drying when used alone demands longer drying time and thus has a high expense of energy. As bulk of onion is water (82-87 %), removal of moisture prior to drying can reduce moisture loading on dryer and hence the energy consumption. Keeping this in view, onions were partially dewatered using centrifugal force before convective drying. The effect of partial mechanical dewatering and drying air temperature was studied on drying time, specific energy consumption and onion powder quality (colour and flavour). The combination process was also optimized to achieve increased drying rate and product quality comparable to products obtained using convective drying alone. Onions subjected to 60 % partial mechanical dewatering and hot air drying at 70°C exhibited significantly (p≤0.5) shortened drying time, decreased energy consumption and maintained colour and flavour of the dried product.

Applicability of Pulsed Electric Field (PEF) Pre-Treatment for a Convective Two-Step Drying Process

“…This also demonstrates a higher impact of the PEF-induced moisture leakage while drying at lower temperatures. This is in good correspondence with the previously reported data [15,17,45,46].…”

“…The trend of less drying time reduction caused by PEF at higher drying temperatures is in agreement with previously made studies [15,17,45,46]. On the contrary, longer drying times at 75 °C f untreated samples in comparison to the PEF-treated sample resulted in a greater reduction, comparin paper with the first paper out of this study [17].…”

“…An explanation for the colour change of the PEF-treated sample dried at 85/55 • C might be the time of heat expose, meaning the overall drying time, that might resulted in colour changes [15,55,67].…”

“…Onions are valued for their flavors and for their nutritional value, and these quality attributes should be maintained during processing [13,14]. Grewal et al, 2015 andLaw, 2010, name the drying time and the drying temperature as proportional factors of the thermal damage of the product [15,16].…”

Optimization of Chemical Pretreatment for Osmotic Dehydrated Talaja Red Onion Slices Using Response Surface Methodology

“…Also it is a well-known fact that each 1 % reduction in feed moisture leads to 4 % less dryer energy input [5] [21]. Effect of mechanical dewatering prior to hot air drying was investigated on drying time, specific energy consumption, flavour, and colour of dried product [12]. Osmotic dehydration is a method for the partial dehydration of water-rich foods, such as fruits and vegetables, by immersing them in a concentrate solution of sugar or salt.…”