Hot Air Puffing Kinetics for Soy-fortified Wheat-based Ready-to-Eat (RTE) Snacks

The soy-fortified wheat-based flat cold extrudate, after requisite steaming, was puffed in hot air using the high-temperature short-time (HTST) whirling-bed puffing system. The hot-air puffing was conducted at five different hot air temperatures, 200 to 240 degrees C at constant fluidizing air velocity of 3.95 m s(-1) for 50 s of puffing time. The initial moisture of sample was 0.4617 kg kg(-1) dm. The already existing 15 different thin layer-drying models were applied to determine the hot air puffing kinetics, based on puffing temperatures. It was found that the Page model could represent hot air puffing kinetics of the steamed flat cold extrudate within 99.3% accuracy. The effective diffusivity was found to be between 1.15623 x 10(-9) and 2.58631 x 10(-9) m(2) s(-1) for steamed flat cold extrudate in the temperature range of 200 to 240 degrees C. The activation energy for diffusion was found to be 2,341.824 kJ kg(-1). The optimum puffing conditions with respect to expansion ratio (ER) and sensory color score were found at puffing temperature of 220 degrees C and puffing time of 30 s. The variation in ER for the product was found to follow a linear relationship with moisture content of steamed flat cold extrudate during puffing. The Dincer Number for steamed flat cold extrudate puffed in fluidizing air at temperature 220 degrees C and 3.95 m s(-1) velocity was determined to be 276,223.8. This Dincer Number was used to predict the puffing time required to achieve predetermined moisture content of product. The prediction was found to be effective within 10% deviation from the values of experimental puffing time except during the initiation of puffing.