TMT-labelled quantitative proteomics reveals the mechanism of Rhodotorula mucilaginosa on proteolysis of dry-cured ham: Structural protein degradation, amino acid release and taste improvement

To investigate the mechanism of Rhodotorula mucilaginosa on structural protein degradation and taste development of Jinhua ham, the effects of Rhodotorula mucilaginosa and Pichia kudriavzevii on proteolytic enzyme activities, surface hydrophobicity, myofibril microstructure, protein degradation, free amino acids and sensory attributes were investigated during the dry-ripening of Jinhua ham. The inoculation of Rhodotorula mucilaginosa EIODSF019 (RE) and Rhodotorula mucilaginosa XZY63-3 (RX) consistently exhibited higher proteolytic enzyme activities compared with Pichia kudriavzevii XS-5 (PK). The decrease of alpha-helix exposing more internal hydrophobic groups of myofibrillar proteins, contributed to higher surface hydrophobicity of RE compared with PK and RX. RE showed the highest proteolysis index among all groups, which could be attributed to more degradation of myosin, actin and troponin; the changes were confirmed by the intense breakdown of myofibrils observed by atomic force microscopy and transmission electron microscopy. 36 down-regulated proteins mainly derived from myofibrils and catalysis-related enzymes were identified in RE by TMT-labeled quantitative proteomics analysis. The degradation of myosin, actin and troponin showed the most intense response to the accumulation of glutamic acid, lysine and alanine. Partial least square regression analysis and correlation analysis revealed that the breakdown of MYH14, MYH3, TNNI1 and TNNTI was highly correlated with improvement of umami, richness and aftertaste.