| Abstract: | Heat-induced protein polymerization, gelation and the associated molecular scale changes were investigated during conductive and microwave heating (CH and MH, respectively). Given identical temperature-time profiles, polymerization of bovine serum albumin, ovalbumin, egg white (EW) and wheat gluten protein occurred faster and to a greater extent with CH than with MH. Moreover, lanthionine cross-links were present in some MH but in none of the CH samples. Gelation of EW protein by CH or MH was studied in more detail. Differential scanning calorimetry and fluorescence spectroscopy indicated that EW proteins initially denatured to a larger extent with CH than with MH. Size exclusion high performance liquid chromatography demonstrated that CH resulted in more heavily cross-linked EW protein networks than MH. Homogeneous EW gels were obtained by 15 min CH at 80 °C while 120 min MH at this temperature still resulted in inhomogeneous (with liquid and solid zones) gels. This was affirmed by low resolution 1H nuclear magnetic resonance measurements which indicated more mobile water in MH than in CH samples. However, MH gels had higher firmness than the corresponding CH gels. Thus, MH here led to less covalent cross-linking than CH, but still resulted in firmer gels most likely because its protein network relied heavily on non-covalent interactions.Industrial relevanceThis study highlighted differences between microwave and conventional, conductive, heating of different protein materials. While literature is divided about the origin of differences noted between these different heating modes, it is clear from our data that heating mode, given identical temperature-time profiles, impacts the changes that proteins undergo during heating. The knowledge that microwave heating favors protein unfolding, aggregation and cross-linking to a lower extent than conductive heating can likely be exploited in industrial applications. |
