New Composite Hydrogel Based on Whey and Gelatin Crosslinked with Copper Sulphate

Abstract

By-products from the meat and dairy industries are important sources of high biological value proteins. This paper explores possibilities for improving the swelling and integrity of a cross-linked whey and gelatin hydrogel with different amounts of CuSO4 × 5H2O. Overall, swelling tests demonstrate that cross-linked samples show a better hydration capacity and stability in the hydration medium, but different copper concentrations lead to different swelling behavior. At concentrations smaller than 0.39%, the sample lasts for 75 h in a water environment before beginning to disintegrate. At a concentration of copper sulphate higher than 0.55%, the stability of the sample increased substantially. The swelling kinetics has been investigated. The diffusion constant values increased with the increase in copper concentration, but, at the highest concentration of copper (0.86%), its value has decreased. Spectroscopy analyses such as Fourier transform infrared (FT-IR), X-ray diffraction (XRD), ultraviolet-visible spectroscopy (UV-VIS), and nuclear magnetic resonance (NMR) relaxometry analyses revealed changes in the secondary and tertiary structure of proteins as a result of the interaction of Cu2+ ions with functional groups of protein chains. In addition to its cross-linking ability, CuSO4 × 5H2O has also shown excellent antibacterial properties over common bacterial strains responsible for food spoilage. The result of this research demonstrates the potential of this hydrogel system as a unique material for food packaging.

Characterization of a Graphene Oxide-Reinforced Whey Hydrogel as an Eco-Friendly Absorbent for Food Packaging

“…More than that, the increase in the GO content resulted in a decrease in the distance between the turns of the helical structures. A similar situation has been observed in the case of Cu (II)-cross-linked hydrogels [ 14 ] when the increase in the Cu(II) content determined a decrease in the size of the helical structures. Although the interactions of Cu (II) ions with protein chains resulted in the formation of amorphous hydrogels with no helical structures at a high concentration of copper sulphate (0.7%), the interaction between carbon-containing compounds and protein chains was not as strong as ionic interactions involving Cu [ 14 ] of Ca [ 17 , 87 ] ions, as helical structures still formed in all samples of our GO-containing hydrogels (see Table 2 ).…”

“…A similar situation has been observed in the case of Cu (II)-cross-linked hydrogels [ 14 ] when the increase in the Cu(II) content determined a decrease in the size of the helical structures. Although the interactions of Cu (II) ions with protein chains resulted in the formation of amorphous hydrogels with no helical structures at a high concentration of copper sulphate (0.7%), the interaction between carbon-containing compounds and protein chains was not as strong as ionic interactions involving Cu [ 14 ] of Ca [ 17 , 87 ] ions, as helical structures still formed in all samples of our GO-containing hydrogels (see Table 2 ). Similar results have been obtained for hydrogels containing whey and carbon nanotubes or nano-onions, whose diffraction patterns proved that secondary helical structures were formed in their hydrogels [ 88 ].…”

“…on the polymer chains allow a large amount of liquid to penetrate between the polymer chains to a level at which they can break, causing the hydrogel to dissolve. Therefore, many studies have investigated improvements in the entrapment capacity of the absorbed liquid by cross-linking the hydrogels with various compounds such as graphene oxide (GO) [ 7 , 8 , 9 , 10 , 11 ], copper compounds [ 12 , 13 , 14 , 15 ], alkaline salts [ 16 , 17 ], nanoparticles [ 18 , 19 , 20 , 21 ], and organic acids [ 22 ]. In addition, these materials impart specific properties that allow hydrogel formulations to meet desired application requirements such as antimicrobial properties, which are mandatory for food packaging [ 7 , 14 , 23 ], UV-VIS barriers for light-sensitive food [ 23 , 24 ], or water and gas barriers [ 23 ] to extend the shelf-life of food.…”

“…The globular proteins present in whey—namely, α-Lactalbumin, β-Lactoglobulin, and serum albumins [ 45 ]—are the main components involved in the whey gelation process, both through hydrophilic functional groups (-OH, -CONH, -CONH 2 , -COOH, and -SO 3 H) and ionic groups. Whey imparts poor mechanical qualities to hydrogels, but, by tuning with different reinforcing materials, it is a valuable precursor for hydrogels [ 7 , 14 , 15 , 46 , 47 , 48 ].…”

“…Similar to whey, gelatin proteins are characterized by a wide range of qualities: their nutritional value, high hydration and gelation capacity, biocompatibility, and biodegradability. The proteins of both precursors exhibit mechanical properties requiring reinforcement with materials such as graphene oxide [ 11 , 57 ], nanoparticles [ 14 , 58 , 59 , 60 ], nanofibers [ 60 ], hydroxyapatite [ 61 ], and montmorillonite [ 62 ].…”