Analysis of Free Amino Acids in Russula griseocarnosa Harvested at Different Stages of Maturity Using iTRAQ®-LC-MS/MS

Abstract

Free amino acids are closely related to the savory taste and beneficial effects of mushrooms. A novel, sensitive, and selective LC-MS/MS method was developed on the simultaneous determination of 20 free protein amino acids as well as 22 non-protein amino acids in Russula griseocarnosa at different stages of maturity by stable isotope isobaric tags for relative and absolute quantitation (iTRAQ) labeled. The results indicated that the content of total free amino acids increased slightly from 19.88 mg/g dry weight (DW) at stage 1 to 20.57 mg/g DW at stage 2, and then dramatically decreased to 14.42 mg/g DW at stage 3. The MSG-like components, including aspartic and glutamic acids were downtrend with the development of fruiting bodies. The contents of monosodium glutamate-like components were in the range of 0.99–2.28 mg/g DW and lower than those of sweet components (2.61–4.35 mg/g DW) or bitter components (1.89–3.39 mg/g DW). Contents of total tasteless components fluctuated in the range of 0.37–0.61 mg/g DW. Glutamine, glutamic acid, and alanine were the most predominant protein amino acids occurring in the free form, and argininosuccinic acid, γ-amino-n-butyric acid, β-alanine, and L-ornithine were the most plentiful non-protein amino acids. Furthermore, it could be noted that the quantitative differences in free amino acids between individuals at the same stages of maturity become larger with the development of fruiting bodies. Our findings provide further evidence regarding the selection of appropriate stages of maturity of R. griseocarnosa for its nutritional value and beneficial effects.