Chemical, rheological and surface morphologic characterisation of spent hen proteins extracted by pH-shift processing with or without the presence of cryoprotectants

The chemical and rheological properties of spent hen proteins recovered by acid and alkaline extraction have been studied with/without cryoprotectants (CP) after 3 weeks of frozen storage. Four pH values (2.0, 2.5, 11.5, and 12.0) were used for extraction. CP addition prevented freeze-induced denaturation and oxidation in all extracted proteins, as revealed by significant increases in reactive sulphydryl groups (p < 0.0001), and a decrease in the formation of carbonyl groups (p < 0.0001). The alkaline extracted proteins with CP formed more viscoelastic gels compared to the others, while samples without CP failed to form a gel network. FTIR of the protein isolates with CP showed a protective effect on the secondary structure of the isolated proteins. Scanning electron micrographs showed a protective shield of CP around the isolated proteins.