Extrusion is a versatile and state-of-art technology and provides enormous opportunity for modifying the functionality of food materials for improved digestibility and high sensory quality. With considerable previous research on cereal based products, the current focus has now shifted towards millets and pulses for enhancing nutritional and functional quality for high-end consumer. The present review highlights the current advances made in development of cereal, millet and pulse based extruded products. In addition, the current trends in use of extruded flours as novel green ingredients as hydrocolloids, fat replacers and for developing gluten-free, phenolic-rich, lowglycemic and functional foods has also been reviewed. al., 2014b;Roman et al. 2015b). Parallel to the increased applications, concern has grown in the physico-chemical, functional and nutritionally relevant effects of extrusion processing.The present review outlines the effect of extrusion on physicochemical (hydration), functional (antioxidants, phenolics) and viscometric/pasting properties of cereal grains and pulses. An attempt has also been made to summarize current trends and perspectives in extending application of extruded flours as novel green ingredients and additives for developing quality gluten free and low fat products.
Effect of Extrusion on Functionality of FloursDuring extrusion, flour is subjected to high temperature and high shear at relatively low levels of moisture content, which can effectively modify the functionality of composite cereal matrices by the way of gelatinization and degradation of starch, solubilization of dietary fibre, protein aggregation and inactivation of anti-nutritional factors (Hagenimana et al., 2006; Martinez et al., 2014c). Extrusion process offers significant opportunity to modulate feed rate, feed moisture, screw speed and barrel temperature, suited to product composition; accentuating the changes in their hydration properties, texture, bioactive compounds and pasting profile or viscometric properties (Martinez et al., 2015b). However, selection of appropriate processing conditions is must, as the extent of modifications is governed by severity of the process variables involved. Effect of extrusion on hydration properties Extruded products are characterized by several physicochemical properties such as water absorption index (WAI), water solubility index (WSI), wateroil absorption index, protein solubility index, nitrogen solubility index, gelatinization capacity, emulsion solubility index etc. In particular, the hydration properties such as the WAI and WSI are important and predict how the materials behave if further processed into extruded products (Oikonomou and Krokida, 2011). The changes in hydration properties during extrusion can be attributed to structural changes in polymeric (starch and protein) and/or nonpolymeric (lipid) macromolecular components. These properties are influenced mainly by size and structure of starch granules (Nura et al., 2011). WAI indicates the amount of water immobili...