Polyacrylamide gel with switchable trypsin activity for analysis of proteins.

Trypsin was immobilized on a variety of materials to improve digestion efficiency. However, because the immobilized trypsin will digest proteins during electrophoresis, direct immobilization of active trypsin in polyacrylamide gel will compromise the protein separation. To overcome this problem, here we report a novel polyacrylamide gel with switchable trypsin activity. It was prepared by copolymerization of the PEG-trypsin-aprotinin complex during the gel-casting step. Because the inhibitor aprotinin binds strongly with trypsin at alkaline pH, this novel gel does not display hydrolytic activity during electrophoresis. After electrophoresis, the activity of trypsin embedded in gel could be recovered by simply washing away the bound inhibitor at a low pH. It was demonstrated that this unique switchable activity design allowed high resolution of the complex protein mixture during electrophoresis and highly efficient digestion of the separated proteins in situ in the gel after electrophoresis.

Application of metabolomics profiling in the analysis of metabolites and taste quality in different subtypes of white tea.

Three subtypes of white tea, Silver Needle (SN), White Peony (WP), and Shou Mei (SM), differ in their taste, aroma, bioactivity, and commercial value. Here, a metabolomics investigation on the chemical compositions combining taste equivalent-quantification and dose-over-threshold (DoT) determination on the taste qualities were applied to comprehensively characterize the white tea subtypes for the first time. Significant differences in the contents of catechins, dimeric catechins, amino acids, phenolic acids, flavonol/flavone glycosides, and aroma precursors were observed among these 3 white teas. Metabolite content comparison and partial least-squares (PLS) analysis suggest that theanine, aspartic acid, asparagine, and AMP were positively correlated with the umami taste in white tea, and flavan-3-ols, theasinensins, procyanidin B3, and theobromine had positive correlations with higher bitterness and astringency tastes. In addition, puckering astringent (-)-epigallocatechin gallate (EGCG), (-)-epicatechin gallate (ECG) and theogallin, bitter-tasting caffeine, and the mouth-drying/velvety-like astringent γ-aminobutyric acid (GABA) were identified as key taste compounds of white tea infusion by absolute quantification and DoT factor calculations. This work provided systematic and comprehensive knowledge on the chemical components, taste qualities, and sensory active metabolites for the subtypes of white tea.