Moisture sorption studies on onion powder

Moisture sorption studies were conducted on three samples of onion powders, i.e. freeze-dried, vacuum shelf-dried and through flow-dried onions. The data obtained for texture (flowability) and per cent moisture were used in determining critical moisture levels. The monolayer moisture contents, corresponding to Brunauer Emmett Teller (BET) theory were taken as the safe minimum moisture levels in onion powder. The moisture content values (moisture-free basis), which correspond to a monomolecular layer of adsorbed water computed by BET equation, were 2.09, 1.96 and 1.94%, for freeze-dried, vacuum shelf-dried and through flow-dried onion powders, respectively. This study on initial and critical moisture levels of dehydrated onion powders helps in the selection of the packaging materials for storage.