Sustainable Augmentation of Chickpea Protein Functionality and In Vitro Digestion via Spent Coffee Phenolics: A Protein–Phenolic Interaction Study

Plant-based proteins exhibit low functionality compared to animal-based counterparts. In this regard, protein–phenolic interaction is one of the promising methods for boosting the functional properties of proteins as well as improving the stability of phenolic compounds. This study evaluated the binding ability and the effect of interaction between phenolic extracts from spent coffee grounds, chosen to be a sustainable and abundant phenolic source, and chickpea protein isolate (CPI). Extracted phenolics were identified as chlorogenic acid, cryptochlorogenic acid, caffeic acid, and catechin. Also, the effect of interaction on the protein functionality and in vitro digestion properties of the protein-phenolic complex was assessed. Different interaction conditions were tested, including varying concentrations of phenolic extract (PE) (0, 0.5, 1.0, and 1.5 mg/mL) at two different pH levels (pH 7.0 and 9.0, for better protein solubility) since these conditions affect the bond formation. The formation of the bond was also assessed to be affected by pH and concentration. Although there were no significant improvements in the protein solubility, the foaming and emulsifying properties of CPI were improved after its interaction with phenolic compounds. The highest improvements were observed for the emulsion activity index, emulsion stability index, and foaming capacity up to 71%, 82%, and 69%, respectively. On the other hand, the antioxidant properties of the protein-phenolic complex before and after digestion were increased by 71% and 37%, respectively. The best interaction condition for antioxidant properties and protein functionality was found at pH 9.0 and the phenolic concentration of 1.5 mg/mL PE sample. This study demonstrated that the functionality of CPI can be improved by spent coffee phenolics; however, the conditions can be enhanced by the investigation of individual phenolic compounds and optimization of interaction conditions. With the improvement of protein functionality, CPI can be used in combination with phenolics from sustainable sources like spent coffee grounds in various plant-based alternative foods as well as new product formulations.