Effects of extrusion parameters on physicochemical properties of third generation corn snacks expanded by microwave heating

Abstract

Corn grits were extruded then extrudates were expanded by microwave-heating. Effects of addition of xanthan gum (XG) (0%–1%), feed moisture content (37%–47%) and screw speed (100–300 rpm) level on physicochemical properties of snacks were evaluated with response surface methodology (RSM). All suspensions of expanded samples exhibited shear-thinning behavior. Apparent amylose content of samples ranged from 22.47% to 37.97%. Screw speed and feed moisture content had positive effect on apparent viscosity and amylose content but XG level had negative effect on them. Increasing screw speed increased expansion and luminosity but decreased browning index and total color difference. Increasing feed moisture content resulted in reduced expansion, luminosity but increased browning index. In contrast to the initial effect, expansion and browning index decreased when XG addition level was above 0.5%. Optimum conditions were determined to obtain the maximum values for expansion index and luminosity and minimum value for the total color difference by desirability function. They were found as 300-rpm screw speed, 47% feed moisture content and 0.34% XG level. Practical applications Extrusion process occupies an important place in the food industry for production of snacks and breakfast cereals. This technology is especially preferred due to its versatility, high productivity, relative low cost energy efficiency for snack production. However, extrusion process conditions (feed moisture, screw speed, and barrel temperature) and additives used in this process have critical importance for snack characteristics. Gum addition provides lubrication during extrusion process. Expansion and color characteristics of product may be change according to gum addition level. Response surface methodology (RSM) can be used as an optimization tool to achieve a better product considering multiple quality characteristics for snacks. A better evaluation of simultaneous interactive effects of process variables on the products can be achieved with RSM technique. Application of RSM in this study may be employed as baseline information for further scale-up of third generation snack production with several additives and under different production conditions.