Thermal transitions and heat-sealing of glycerol-plasticized whey protein films: Fid-Bau Portal

Thermal transitions and heat-sealing of glycerol-plasticized whey protein films

Hernandez-Izquierdo, V.M. / Krochta, J.M.

Transparent, flexible whey protein-based edible films plasticized with glycerol were produced by wet (solution-casting) and dry (twin-screw extrusion followed by compression-molding) processes. The relationship between the thermal transitions and the heat-sealability of the whey protein-based edible films was investigated. Differential Scanning Calorimetry showed the existence of endothermic peaks with an onset transition temperature of 156.3 +- 1.4 deg C for both the solution-cast and extruded films. Films were heat-sealed using an impulse heat-sealer at an effective jaw pressure of 293.31 kPa, a voltage of 15 V and a cooling time of 4 s. Various impulse times, ranging from 1.5 to 2.5 s, were used to heat-seal the films. A thermocouple was used to measure the heat-sealing temperatures at each impulse time. Heat-sealing temperatures ranged between 126.1 +- 9.0 and 204.0 +- 5.4 deg C for the shortest and longest impulse times, respectively. Seal strengths were determined using an Instron Universal Testing Machine. Film thickness appeared to have an effect on seal strength; higher strengths were achieved for thinner films, which, in this case, were the solution-cast films. Thicker (extruded) films required a longer minimum impulse time to achieve a heat-seal. The highest seal strength (433.07 +- 39.37 N/m) was obtained with solution cast films (thickness of 0.13 +- 0.01 mm) sealed with an impulse time of 2 s (164.60 +- 5.1 deg C). Impulse times above 2.5 s (204.0 +- 5.4 deg C) resulted in degradation of both solution-cast and extruded films.