Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 12/28/2004
Publication Date: 7/20/2005
Citation: Hernandez, V.M., Reid, D.S., Mc Hugh, T.H., Berrios, J.D., Olsen, C.W., Olson, D.A., Pan, J., Krochta, J.M. 2005. Thermal transitions and extrusion of glycerol-plasticized whey protein mixtures. Meeting Abstract No. 54D-7. p. 60., IFT Annual Meeting, July 2005, New Orleans, LA.
Technical Abstract: Whey-protein-based edible films provide the opportunity to protect foods and reduce packaging waste. The solution-casting method, currently used to study the properties of films that would be formed as coatings on foods, does not lend itself to large-scale production of films that could be used as stand-alone food wraps and layers between food components, or be sealed to form food pouches. Manufacture of such films via extrusion would increase their commercial potential due to a more efficient and continuous process. It was hypothesized that extruder operating conditions required to form whey protein-glycerol-water mixtures into sheets are dependent on the thermal transitions of such mixtures. The objective of this research was to study the effect of glycerol plasticizer and moisture content on the thermal transitions and extrusion of whey protein powder-glycerol-water mixtures. Mixtures with 100, 70, 60 and 50% whey protein isolate (WPI) powder and 0, 30, 40 and 50% glycerol by weight were pre-conditioned to two different water activities (0.339±0.007 and 0.475±0.017). Moisture content was determined using a vacuum oven. Differential scanning calorimetry (DSC) was used to determine the thermal transitions of the mixtures. A co-rotating twin-screw extruder with six independent heating and cooling zones and an L/D ratio of 30:1 was used to extrude whey protein sheets. DSC peak onset temperatures were significantly affected by moisture and glycerol content of the samples (p<=.05), indicating lower temperature endothermic transitions for samples with higher moisture and/or glycerol contents. Transparent flexible whey protein extruded sheets could be formed with 68% glycerol content (d.b.), a screw speed of 275 rpm and a barrel temperature profile of 20-40-80-100-120-130°C. Average melt temperature was 130°C. Extrusion of whey protein sheets constitutes the first step towards extrusion of thinner films for food wraps, layers and pouches, which can work together with conventional packaging to improve food quality.