Study On Edible Film Based On Whey Protein Concentrate

Edible film packaging is more and more popular for its convenience and innocuity. It's a kind of edible and protecting film which can be used as a barrier layer to control water permeability, oxygen permeability, fat oxidation, and volatile flavor loss, hence keeping food in good condition and prolonging food shelf-life. This work focused on edible film based on whey protein concentrate (WPC), studying the film forming procedure, enzyme treatment mechanism and the application properties of whey protein edible film, which is helpful to the further application of edible film.The influences of protein concentration, glycerol concentration, and heating temperature on film formation were studied. The results showed that water vapor permeability (WVP) and oxygen permeability (OP) increased with increase in both protein and glycerol concentrations in the film forming solution. As increasing protein and glycerol concentration elongation increased by 46% and 87% respectively. WVP and OP values reached the lowest when the heating temperature was 70℃. Combined grade of WVP and OP, barrier property was investigated using Response Surface Methods. Mixture proportions of protein concentration 100 g/L, glycerol concentration 27 g/L, heating temperature 69℃, would yield an edible film with WVP 0.435 g·mm/m2·h·kPa and OP 0.134 cm3·mm/m2·d·kPa.Enzymatic treatment showed that, when enzymatic reaction time was 120 min, WVP, OP and film solubility (FS) decreased by 47%, 44% and 13%, respectively, while elongation of film increased by 41%. Enzyme reaction time had no significant effect on tensile strength and film color. As a result, enzyme reaction time fixed at 120 min is advisable for edible film property. When enzyme content was 0.4 g/L, WVP, OP, FS decreased by 48%, 41% and 12%, respectively, while E increased by 56%, and no significant effect on TS and film color were observed. 0.4 g/L was the optimum enzyme amount for film properties.The enzymatic treatment mechanism was investigated. Enzymatic treated protein contained more high weight molecular component according to HPLC result, which induced cross-link between proteins molecular. Denatured temperature of edible film increased according to DSC result. Besides, whey protein hydrophobic property was developed according to fluorescence analysis, while surface–SH content increased, which suggested that protein chains unfolded and hydrophobic group was uncovered, total–SH content decreased suggested that cross-linking promoted forming new S-S bound among protein chains. The SEM picture showed film had a smoother surface. It could be concluded that enzymatic treatment help protein to form more compact structure, all these transformation improve the barrier and mechanical properties of edible film.WPC-coating with and without enzymatic treatment can lower the fat acid value of walnut by 9%~51%, 10%~48%, respectively, and decreased peroxide value by 21%~38% and 22%~43%, respectively. Coating can improve the sensory properties.