Drying Kinetics, Effective Moisture Diffusivity, and Activation Energy of Osmotic Pretreated Hot-Air-Dried Paneer Cubes

Abstract

Paneer is a heat-acid-coagulated dairy product, and it has a very low shelf life due to its higher moisture content of about more than 50% (w.b). Drying is the best option to reduce moisture, but it takes time and affects the nature of the product. Here, osmotic dehydration (OD) is applied as pretreatment prior to drying to preserve the color and textural changes and reduce the drying time. Commercial NaCl was chosen as osmotic agent. The paneer samples were taken as ( $2\text{cm}\times 2\text{cm}\times 2\text{cm}$ ) cubes and pretreated with NaCl, viz., 6%, 12%, 22% $w/v$ , and surface treatment. The pretreated paneer was dried at 50, 55, and 60°C in a hot-air dryer with constant air velocity of 0.25 m/s. The equilibrium moisture content level was higher in osmotic treated samples compared to the control sample with range between 12.46 and 16.64% (w.b). The osmotic pretreated sample had shortened drying time compared to the control sample. Effective moisture diffusivity and activation energy were calculated, and the osmotic pretreatment impacted positively on it. The drying parameters were fitted with models and found that the Midilli model was ( $R^2>0.99$ ) best fit. The osmotic pretreated samples at 50°C drying temperature show ( $P\le 0.01$ ) better results in color, texture, and sensory profile of dried paneer, while pretreatment is not effective at 55 and 60°C drying temperatures. Except for the carbohydrate content, osmotic pretreated samples retain more fat and protein after the drying process. As a result, it can be concluded that osmotic pretreatment reduces the drying time and retains color, texture, and nutritional characteristics of dried paneer, especially at 50°C drying temperature.