Hemp globulin heat aggregation is inhibited by the chaperone-like action of caseins

Hemp (Cannabis sativa L.) seed contains high-quality storage proteins (mainly globulins) that are easily digested. However, hemp globulins (HG) are almost insoluble at low ionic strength, which limits the use of hemp protein in many food systems. The aim of this study is to make soluble aggregates by inducing interactions between HG and sodium caseinate (SC, a mixture of four milk casein proteins) through heating. HG was mixed with SC in pH 7 solution with high ionic strength (0.5 M) and heated at 90 °C for up to 15 minutes. Heating HG alone led to extensive aggregation and precipitation. SC dramatically reduced the turbidity of the heated hemp-caseinate protein solution, exhibiting the chaperone-like effect against heat stress. According to the results of a high-throughput fluorescence method, this chaperone-like effect could be partly explained by hydrophobic interactions between HG and αS1- and β- casein. Adsorption of these caseins to the exposed hydrophobic regions of hemp globulin may thus sterically inhibit the disulphide bond exchange/formation between hemp globulins, resulting in the change of aggregation regime from diffusion limited to reaction limited aggregation. The disulphide bonding between HG and κ-casein may also stabilise the HG|SC aggregates. Dynamic light scattering data demonstrated that the hemp-caseinate protein complexes were stable at room temperature. These complexes remained colloidal stable when the ionic strength was lowered to 0.17 M. The hemp-caseinate protein complexes have possible applications in emulsions and beverages.