methane yield was promoted during propionate anaerobic digestion process.The total proteins of three samples were extracted, and the concentration and quality of proteins were determined by BCA Protein Assay Kit and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), respectively. Next, protein was digested, and the peptides after protein digestion were vacuum dried, and then re-suspended with 2% acetonitrile and 0.1% trifluoroacetic acid (TFA). The samples were desalted with a Waters Oasis HLB and vacuum dried. The assay of samples was performed on a Q-Exactive HF-X coupled with Easy-nLC 1200.