Effect of process parameters and soy flour concentration on quality attributes and microstructural changes in ready-to-eat potato–soy snack using high-temperature short time air puffing

High-temperature short time (HTST) air puffing has been found to be very useful process for production of potato–soy ready-to-eat snack food as it ideally produced highly porous and light texture. The process parameters considered viz. puffing temperature (185–255 °C) and puffing time (20–60 s) with constant initial moisture content of 36.74% and air velocity of 3.99 m/s for potato–soy blend with varying soy flour content from 5% to 25% were investigated using response surface methodology with central composite rotatable design (CCRD). The optimum product in terms of maximum expansion ratio (3.69), minimum hardness (2754.3 g) and maximum overall acceptability (7.3) were obtained with 10.31% soy flour blend in potato flour at the process conditions of puffing temperature (230.06 °C) and puffing time (25.46 s). Microstructural changes were evaluated at different stages (with an interval of 5 s) of HTST puffing for product obtained with the optimum processing conditions. The maximum expanded porous structures with larger cracks and smaller pits were recorded in the SEM micrographs at 20 s of HTST air puffing.