Mixed vegetable powders -composed of purple sweet potato, red cabbage and beetroot at a 2:1:1 ratio -were incorporated with cereal base by an extrusion process to obtain a functional, ready-to-eat breakfast cereal. This study investigated the effects of mixed vegetable powder level (8, 12 and 16%), screw speed (300, 350 and 400 rpm) and feed moisture content (13, 15 and 17%) on the physical and functional properties of extrudates in breakfast cereal production using response surface methodology (RSM) and Box-Behnken experimental design. The results showed high correlation coefficients (R 2 ) of multiple regression equations about the relationship among product responses and process variables, and no significant lack of fit (indicating a best-fit model). The optimum conditions were determined from the overlaid area found by superimposing the individual contour plots of responses. Correspondingly, the verification of results showed good agreement between the responses of experimental values at selected optimum conditions and the predicted values from regression equations.Keywords: extrusion, mixed vegetable powder, optimization, ready-to-eat breakfast cereal, response surface methodology (RSM) *To whom correspondence should be addressed. E-mail: ch.chulaluck@gmail.com
IntroductionReady-to-eat breakfast cereal is an ideal food for people's modern-day lifestyle, where speed and convenience, as well as complete nutritional values, are desirable food characteristics. Due to efforts to reduce the amount of in-home preparation time, breakfast cereal technology has evolved from the simple procedure of milling grains for cereal products that require cooking to the manufacturing of highly sophisticated ready-to-eat products that are convenient and quickly prepared. Nowadays, extrusion cooking technology is still recommended for the commercial applications of ready-to-eat breakfast cereal manufacturing, and remains one of the most widespread because of numerous advantages over conventional processing methods, such as faster processing times, lower processing costs, less square footage required, shorter response time, and greater flexibility (Riaz, 2000).Extruded breakfast cereals are typically based on whole or milled fractions of cereal grains which provide a high starch component. A high-carbohydrate breakfast cereal can positively influence the body's internal processes, fueling brain function and muscle action. But manufacturers must continue to develop new and improved products in line with consumers' changing needs and tastes, widening product categories and shifting market share. Apart from promoting breakfast cereal with whole grains and fortification with micronutrients, breakfast cereal production should provide health or functional benefits over and above basic nutrition. For example, dietary fiber concentrates from vegetables showed a high total dietary fiber content and better insoluble/ soluble dietary fiber ratios than cereal bran (Grigelmo-Miguel and Martin-Belloso, 1999). This research is focused on creatin...
