UNLOCKING THE PROTEIN FRACTION OF COFFEE SILVERSKIN: FROM MATRIX-RELATED CONSTRAINTS TO A NOVEL EXTRACTION STRATEGY

Coffee is one of the most worldwide consumed beverages, with coffee silverskin (CS) representing the primary byproduct of the roasting step. This matrix is predominantly composed of dietary fiber (50–60%, both soluble and insoluble), lignin (18–30%), proteins (12–20%), and a minor lipid fraction (~3%) (Prandi et al., 2021). Thus, CS represents a valuable opportunity for developing biotechnological approaches to generate new products with added value promoting the circular bioeconomy. In literature the protein fraction has been a poorly explored and characterized. The high temperatures characteristic of the roasting process deeply affects the molecular organization of the matrix. The resulting CS is therefore characterized by Maillard reaction products and colored pigments (e.g. melanoidins), together with and a complex network of recalcitrant polysaccharides. These structural molecular rearrangements trap the protein fraction, severely limiting their extractability. In this work, different molecular approaches were evaluated in the attempt to overcome the matrix effect and enable extraction and characterization of the CS protein fraction. Conventional alkaline extraction (CAE), alongside ultrasound- and microwave-assisted methods, has been widely explored for protein recovery from CS; however, the resulting fractions frequently exhibit poorly resolved electrophoretic profiles characterized by diffuse smearing. The protein fraction was further characterized for the presence of glycosylation, confirming a highly glycosylated matrix, which likely contributes to limiting the extractability and the diffuse electrophoretic profiles observed. Notably, to overcome these limitations, a novel approach combining an alkaline pretreatment with H₂O₂ and a selective extraction step was developed here for the first time, successfully enabling the recovery of well-defined protein bands at approximately 66 kDa — a level of resolution not achieved by conventional methods. These findings provide a foundation for further optimization to maximize extraction yields and limiting the interference by pigments and polysaccharides. References: Prandi, B., Ferri, M., Monari, S., Zurlini, C., Cigognini, I., Verstringe, S., Schaller, D., Walter, M., Navarini, L., Tassoni, A., Sforza, S., & Tedeschi, T. (2021). Extraction and chemical characterization of functional phenols and proteins from coffee (Coffea arabica) by- products. Biomolecules, 11(11). https://doi.org/10.3390/biom11111571