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

Abstract 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°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°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 (164.6 ± 5.1°C). Impulse times above 2.5 s (204.0 ± 5.4°C) resulted in degradation of both solution‐cast and extruded films. Copyright © 2009 John Wiley & Sons, Ltd.