Moisture sorption isotherms and quality characteristics of onion powder during storage as affected by sprouting

The present investigation was carried out to study the impact of sprouting on the moisture sorption isotherm at 20, 30, 40 and 50 °C and storage study at 25 °C of onion powder developed from PRO-6 variety using a gravimetric technique. The sorption isotherms obtained were of typical type II sigmoidal curves according to BET classification. The experimental data obtained was fitted to mathematical models (GAB, BET, Oswin, Smith, Caurie, Iglesias and Chirife, and Halsey). A non-linear least square regression analysis was used to evaluate the model constants. The GAB model followed by BET, Oswin and Smith best fitted the experimental data. The effect of storage time on the physicochemical properties of onion powder packed in low-density polyethylene (LDPE), aluminum laminated polyethylene (ALP) and glass was evaluated at ambient temperature (25 °C) condition. Storage stability of onion powder in terms of moisture content, colour parameters, bulk density and flowability varied to a different extent during storage, in three different types of packaging materials. In all the types of packaging materials, sprouted onion powder showed minimum changes in all analyzed physicochemical properties as compared to raw onion powder during storage. The extent of the change in physicochemical composition suggested the use of sprouting process for long-term storage of onion powders in ALP and glass packaging.