Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 14, 2005
Publication Date: December 26, 2005
Citation: Onwulata, C.I., Isobe, S., Tomasula, P.M., Cooke, P.H. Properties of whey isolates extruded under acidic and alkaline conditions. J. Dairy Science. 89: 71-81. 2005. Interpretive Summary: Some snack foods containing textured proteins and meat-like products are made from starch and proteins cooked in a machine called an extruder. The extruder consists of a long, heated barrel with two mixing screws inside. The starch and protein are cooked as the screws mixes and pushes the materials through the extruder to form the snack or meat-like food. The crispness of the product is determined by its moisture content and its temperature as it leaves the extruder. It was determined that addition of WPI in its native globular form adversely affected the crunchiness, color, and the texture of extruded snack or meat-like foods. To improve the usefulness of the protein used in the snack or meal-like foods, the texture of whey protein isolates are first changed in the extruder using different pH conditions. The temperature, moisture and pH conditions of the WPI leaving the extruder were adjusted to modify the structure of the WPI. This created a form of WPI that makes better snack or meat-like product. This knowledge allows the creation of nutritious expanded crunchy snack foods, and utilizes whey protein, a byproduct of the cheesemaking process.
Technical Abstract: Whey proteins have wide acceptance and use in many products due to their beneficial nutritional properties. To further increase the amount of whey protein isolates (WPI) that may be added to products such as extruded snacks and meats, texturization of WPI is necessary. Texturization changes the folding of globular proteins improving interaction with other ingredients and creates new functional ingredients. In this study, WPI pastes (60% solids) were extruded in a twin screw extruder at 100°C with four pH-adjusted water streams; an acidic (pH 2.0 ± 0.2), HACI, and alkaline (pH 12.4 ± 0.4), NALK streams, from 2 N HCl and 2 N NaOH respectively, and two electrolyzed water streams, acid (pH 2.5 ± 0.2), EACI, or alkaline (pH 11.5 ± 0.4 ), EALK; these were compared to WPI extruded with deionized water, NEUT. The effects of water acidity on WPI solubility at pH 7, color, microstructure, Rapid Visco-Analyzer (RVA) pasting properties and physical structure were determined. Alkaline conditions increased insolubility caused yellowing and increased pasting properties significantly (p<0.05). Acidic conditions increased solubility and decreased WPI pasting properties. Subtle structural changes occurred under acidic conditions, but were more pronounced under alkaline conditions. Overall, alkaline conditions increased denaturation in the extruded WPI resulting in stringy texturized WPI products which could be used in meat applications.