Ultrastructural and physicochemical characteristics of rice under various conditions of puffing

Puffed cereals are processed grain formulations commonly used as ready-to-eat (RTE) breakfast foods and are appreciated mainly for their lightness and crispiness. Puffing process involves the release or expansion of gas within a product either to create an internal structure or to expand or rupture an existing structure. In this study, oven-puffing is performed using high-temperature, short-time (HTST) treatment with heated sand. Three varieties of parboiled milled rice namely Sukara, IR-64 and Ziri, commonly used for making puffed rice, are studied and their physicochemical characteristics observed. The degree of expansion of the rice kernels is found to be affected by parameters which are connected with the compositional characteristics and processing of the grain. The optimum puffing conditions were found to be 15 s, 250 A degrees C and 11 % (dry basis) for puffing time, sand temperature and final moisture content for all the three varieties respectively. Apart from physicochemical analysis, scanning electron microscopy images of transverse section of the kernels, under various conditions of puffing, are studied for their ultrastructural differences using image processing algorithms. Using these algorithms, the cellular structure of the grain is characterized to calculate the average area and the number density of pores as an indicator of the puffing quality.