Characterization of heat cured and transglutaminase cross-linked whey protein-based edible films.

Edible whey protein films were produced using whey protein isolate (WPI), glycerol and candelilla wax. Films were also produced with the addition of microbial transglutaminase (TG) to the film forming solution after heating. Both sets of films were vacuum heat cured for 0, 12 and 24h at 90°C. The effect of heat curing and transglutaminase treatments on mechanical properties [tensile strength (TS), elongation at break (%E) and toughness], the free suflhydryl, disulfide, and lysine contents and degree of cross-linking of WPI films were assessed. Heat curing increased the TS of WPI and WPI/TG films compared to uncured films. Heat curing films for 24h had increased %E compared to other films. Heat curing increased the toughness of WPI films. Heat curing decreased the free sulfhydryl content of WPI and WPI/TG films. The disulfide bond content of WPI films heat cured for 12h was higher than for films heat cured at 0 and 24h. The disulfide content of WPI/TG films heat cured for 12 and 24h was higher than for films at 0 and 48h. Heat cured WPI films had lower lysine content compared to uncured films. WPI/TG films heat cured for 24h had lower lysine content compared to films heat cured at 0 and 12h. SDS-PAGE was used to confirm heat curing and TG treatment resulted in the formation of covalent cross-links, between whey protein fractions. The water vapor permeability (WVP) of WPI and WPI/TG films heat cured for 0 and 24h was determined at 37.8°C and 85% RH as well as the oxygen permeability at 23°C and 0% RH. Moisture sorption isotherms (MSI) of films were determined at 23°C and 5°C using the Guggenheim-Anderson-de Boer equation (GAB). Heat curing WPI/TG films reduced the WVP compared to uncured WPI, WPI/TG and cured WPI films. The addition of TG reduced the oxygen permeability (O2P) compared to films without TG. Heat curing reduced the O2P of films compared to uncured films. Heat curing of WPI/TG films produced the greatest reduction in O2P of films tested. The moisture sorption isotherm of WPI and WPI/TG films heat cured for 0 and 24h at 90°C were found to closely follow the GAB mode) at 5 and 23°C. The films MSI, at 5°C were higher than the MSI of films at 23°C. The ultraviolet and visible light transmission and the color characteristics of WPI and WPI/TG films heat cured for 0 and 24h were assessed. Heat curing increased the yellowness of films. All films had low transmission of ultraviolet light. The effect of heat curing and transglutaminase treatments on the thermal properties (melting onset temperature, peak melting temperature and enthalpy of fusion) of whey protein isolate films with and without transglutaminase, and heat cured at 90°C for 0, 12 and 24h was assessed. The peak melting temperatures for films increased with heat curing and time. ...Read more

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Characterization of heat cured and transglutaminase cross-linked whey protein-based edible films.