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ARS Home » Pacific West Area » Albany, California » Western Regional Research Center » Healthy Processed Foods Research » Research » Publications at this Location » Publication #218794
Title: Thermal Transitions and Extrusion of Glycerol-Plasticized Whey Protein Mixtures

Author
item HERNANDEZ-IZQUIERDO, VERONICA - UC DAVIS, DAVIS, CA
item REID, DAVID - UC DAVIS, DAVIS, CA
item McHugh, Tara
item Berrios, Jose
item KROCHTA, JOHN - UC DAVIS, DAVIS, CA

Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/15/2008
Publication Date: 5/1/2008
Citation: Hernandez-Izquierdo, V.M., Reid, D.S., Mc Hugh, T.H., Berrios, J.D., Krochta, J.M. 2008. Thermal Transitions and Extrusion of Glycerol-Plasticized Whey Protein Mixtures. Journal of Food Science. V73(4):169-175.

Interpretive Summary: The effects of glycerol and water contents on the thermal changes of whey protein isolate (WPI) powder-glycerol-water mixtures were studied. Mixtures of 100 to 0, 70 to 30, 60 to 40, and 50 to 50 of WPI to glycerol were adjusted to specific values of moisture before submitting the mixtures to heat treatment to evaluate changes in their physical attributes. Temperatures in the ranges of 146 to 148 degrees C Differential scanning calorimetry (DSC) showed the existence of an endothermic peak starting at 148.3+/-0.7 degrees C caused significant changes in the texture and appearance of the mixtures. This temperature fell in the range of temperatures required to form flexible, transparent whey protein sheets by extrusion (a process of making sheets and other forms by forcing semisoft material through a specially-shaped mold or nozzle). In the present study, whey protein-based sheets containing 45.8, 48.8 and 51.9% glycerol were obtained using a twin-screw extruder. All samples were obtained at a screw speed of 250 rpm and melt temperature, at the time of sheet formation, of 143-150ºC. Average thickness of the sheets was 1.31 mm. Samples with 45.8% glycerol had higher tension strength than samples with higher glycerol contents. Also, as glycerol concentration increased, sheet elasticity decreased significantly. Extrusion of whey protein-based sheets is an important step towards extrusion of thinner edible films for food wraps, layers, or pouches.

Technical Abstract: The effects of glycerol and moisture contents on the thermal transitions of whey protein isolate (WPI) powder-glycerol-water mixtures were studied. Mixtures with ratios of 100:0, 70:30, 60:40 and 50:50 WPI:glycerol on a dry basis (db) were pre-conditioned to 0.34+/-0.01 (25.4±0.4ºC) and 0.48+/-0.02 (25.9±2.2ºC) water activity. Differential scanning calorimetry (DSC) showed the existence of an endothermic peak starting at 148.3+/-0.7 degrees C for 100% WPI pre-conditioned to a water activity of 0.34+/-0.01. The onset temperature of this peak decreased with addition and increase of glycerol content, as well as with the increase in water activity. Another endothermic transition occurred in mixtures containing 50% glycerol db, pre-conditioned to 0.48+/-0.02 water activity. The onset temperature of the peak was 146+/-2.0 degrees C. This temperature fell in the range of temperatures required to form flexible, transparent whey protein sheets by extrusion. Whey protein-based sheets containing 45.8, 48.8 and 51.9% glycerol db were obtained using a Haake-Leistritz co-rotating twin-screw extruder. All samples were obtained at a screw speed of 250 rpm and a final barrel temperature profile of 20-20-20-80-110-130ºC. Melt temperature at the time of sheet formation was 143-150ºC. Average thickness of the sheets was 1.31±0.02 mm. Samples with 45.8% glycerol db had significantly higher tensile strength (TS) than samples with higher glycerol contents. Also, as glycerol concentration increased, sheet elastic modulus (EM) decreased significantly (p<0.05). Extrusion of whey protein-based sheets is an important step towards extrusion of thinner edible films for food wraps, layers, or pouches.