Submitted to: Journal of Food Processing and Preservation Research
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/31/2003
Publication Date: 12/31/2003
Citation: Onwulata, C.I., Konstance, R.P., Phillips, J.G., Tomasula, P.M. Temperature profiling: solution to problems of co-extrusion with whey proteins. Journal Of Food Processing And Preservation Research. Vol. 27, Number 5, pp. 337-410. December 2003. Journal of Food Processing & Preservation. Interpretive Summary: Most crunchy snack foods are made from corn meal in a machine called an extruder. The extruder consists of a long, heated barrel with two mixing screws inside. The corn meal is cooked as the screws mix and push the corn meal through the extruder to form the snack food. The crunchiness of the snack is determined by its moisture content and its temperature as it leaves the extruder. In order to improve the nutritional profile of crunch snack foods, the addition of proteins to the corn meal, such as whey protein isolate (WPI)-a concentrated form of whey - was proposed. However, in experimental tests, addition of WPI adversely affected the crunchiness, color, and texture of extruded snack foods. To determine why this occurs, a series of experiments were carried out by extruding corn meal containing various amounts of WPI. Results indicated that addition of WPI to corn meal causes a surge in temperature of the product as it moves through and leaves sthe extruder, far above the temperature of the product if corn meal alone is extruded. Temperature conditions were then established and linked to a range of desirable product characteristics for WPI - corn meal blends. This knowledge allows the creation of nutritious snack foods and utilizes whey protein, a byproduct of the cheesemaking process and an underutilized milk protein.
Technical Abstract: Corn meal was extruded with whey protein isolate (WPI) using high shear extrusion processing conditions and preset barrel temperatures ranging from 100 to 150 degrees C. High shear resulted in increased melt temperatures, which produced two temperature-dependent product responses. WPI was added at concentrations of 15, 25 and 35 percent, and the effect of these amounts on product melt temperatures was recorded. Moisture loss, expansion, texture and color were recorded. There was a significant (P less than 0.05) increase in temperature and moisture flash off (loss) in products substituted with whey proteins in excess of 25 percent. Melt temperatures below 125 degrees C, reduced expansion and increased product density. However, at temperatures above 130 degrees C, density decreased, resulting in crispier, easy-to-break products, with densities below 0.8 g/cm-3. Substituting WPI in expanded products increased product lightness color value even at high temperatures (greater than 140 degrees C), where browning as expected. The melt temperature of a WPI substituted product measured at the die, was the best indicator of quality, and correlated with physical attributes more than any other indicator