* To whom correspondence should be addressed. Lebensm.-Wiss. u.-Technol., 33, 354 } 361 (2000) Formulation of Extruded Snack Food (Gum Based Cereal}Pulse Blend): Optimization of Ingredients Levels Using Response Surface Methodology Sushma Thakur and D. C. Saxena* S. Thakur: Department of Microbiology and Bioengineering, Central Food Technological Research Institute, Mysore (India) D. C. Saxena: Department of Food Technology, Sant Longowal Institute of Engineering and Technology, Longowal 148 106 (India) (Received November 25, 1999; accepted April 4, 2000) Response surface methodology (RSM) was used to analyse the e+ect of corn -our, green gram -our, xanthan, guar gum, arabic gum and carboxymethyl cellulose (CMC) on the sensory and objective (expansion ratio) attributes of an extruded snack food. A rotatable central-composite design was used to develop models for the sensory and objective responses. ¹ he experiments were run at 160 3C with a feed rate of 70 g/min. Responses were most a+ected by changes in corn -our, green gram -our and guar gum levels and to a lesser extent by xanthan, gum arabic and CMC levels. Individual contour plots of the di+erent responses were superimposed, and regions meeting the maximum sensory score of 21.4 and an expansion ratio of 13.2 were identi,ed at 692 g/kg corn -our, 307 g/kg green gram -our, 0.302 g/kg xanthan, 0.216 g/kg guar gum, 0.196 g/kg gum Arabic and 0.262 g/kg CMC levels.  2000 Academic Press Keywords: extrusion; cereal-pulse blend; gum; RSM; optimization Introduction Snack foods have become an integral part of the eating habits of the majority of the world's population. Basically, they are prepared from natural ingredients or components according to predesigned plans to yield products with speci"ed functional properties. Extrusion technology, in recent times, has become one of the major processes for producing varieties of food. Ex- truded foods range from breakfast cereals, snack foods with modi"ed starches and #ours to sweets. Extruders provide thermal and shear energy to the food material, which then undergoes signi"cant physical and chemical change. The geometry of extruders and complex physicochemical transformations such as starch gelatin- ization, protein denaturation and hydrogen bond rup- ture take place during extrusion. Cereal grains tend to be low in protein and to have a poor biological value; the essential amino acids being the limiting factor in cereals (1). Remarkable progress has been made in the utilization of new protein sources such as oilseed, cereal, leguminous seed, leaf and single cell proteins (2, 3). To produce nutritious products, cereals are usually forti"ed with lysine or pulse proteins. Legumes are an important source of food protein and other nutrients (4, 5, 6). How- ever, most legumes do not provide enough viscosity, caus- ing problems of binding and retaining texture and shape, especially for low moisture shelf-stable snack foods (7). The e!ectiveness of response surface methodology (RSM) in the development and optimization of cereal products has been highlighted by di!erent authors (8}11). The basic principle of RSM is to relate product properties of regression equations that describe inter- relations between input parameters and product proper- ties (12). Some good examples of appropriate applications of this technique in food extrusion are the optimization of complex products or properties (13) or of many process variables (14). In the present study, investigations were undertaken to formulate a starch (corn #our) and green gram (Phaseolus aureus) based low moisture nutritious snack, by extrusion process. The well-established functional property of poly- saccharide as binder and viscosity enhancer formed the basis for incorporation of gums in a cereal}pulse blend. The objective of our work was to optimize the formula- tion of raw ingredients, i.e. corn #our, green gram dhal #our, polysaccharides such as carboxymethyl cellulose 0023-6438/00/050354 #08 $35.00/0 doi:10.1006/ fstl.2000.0668  2000 Academic Press All articles available online at http://www.idealibrary.com on 354