Characterization of cold plasma-induced covalent epigallocatechin gallate conjugates of β-lactoglobulin: a comparison with free-radical and alkaline treatments

The characteristics of cold plasma (CP)-induced β-lactoglobulin-epigallocatechin gallate (β-LG-EGCG) covalent conjugates were investigated in comparison with the conventional free -radical (FR) and alkaline treatment (AT) methods. Results indicated CP achieved a high EGCG grafting degree (116.73 ± 0.82 μmol/g, equivalent to 38.91 ± 0.27 % of grafting) after 45 s treatment, comparable to AT (131.79 ± 1.75 μmol/g, equivalent to 43.93 ± 0.58 % of grafting) and far exceeding FR (18.29 ± 0.67 μmol/g, equivalent to 6.10 ± 0.22 % of grafting). In addition, CP conjugates exhibited 27.51 % less browning than AT counterparts. Different from AT and FR, CP uniquely expanded EGCG-binding sites to include hydroxyl- and cyclic alkyl-containing residues. Multiple structural analyses revealed covalent grafting with EGCG induced conformational unfolding of β-LG and exposed buried hydrophobic groups. The CP-induced β-LG-EGCG conjugates yielded improvements comparable to AT in emulsifying and antioxidant properties. Moreover, CP-induced conjugates exhibited superior digestibility and lower antigenicity during gastrointestinal digestion. These findings demonstrated CP is a robust means of promoting covalent grafting between proteins and polyphenols, with high efficiency and enhanced functionality.