Twin-screw extrusion puffing of nonfat dry milk and starch - the effects of acid addition, fluid addition rate and nonfat dry milk concentration on extruded products

Nonfat dry milk (NDM) and a modified cornstarch were extruded at three NDM concentrations (45, 65, 85%), three lactic acid concentrations (0, 33 and 50% of the added fluid) and two fluid addition rates (6.5, 7.3kg/h) to alter extrudate characteristics. Process responses (die temperature, die pressure, motor torque and specific mechanical energy) and product responses (color, solubility, expansion ratio, bulk density and peak viscosity) were analyzed statistically and response surface plots were generated using the results to graphically illustrate relationships present. It was demonstrated that NDM provided structural integrity to the extrudates, and formula conditions altered product characteristics such as density and color to change its fitness for use in extruded products. The response surfaces generated allow for the selection of formula conditions to produce desired product attributes.