Table 4.

Concentration of amino acids as measured by LC–MS/MS with isotope dilution three different hydrolysis methods

Analyte	H2O2 + 6 M HCl + β-ME	6 M HCl + β-ME	4 M  MetS + 0.2% tryptamine	Reference*
Ala	1.6 ± 0.13	1.54 ± 0.08	1.53 ± 0.05	2.28 ± 0.16
Arg	2.86 ± 0.07	2.64 ± 0.08	2.85 ± 0.24	3.72 ± 0.31
Asx	5.2 ± 0.24	5.65 ± 0.38	5.77 ± 0.46	6 ± 1.2
Glx	7.8 ± 0.05	8.04 ± 0.76	8.5 ± 0.15	10.2 ± 1.4
Gly	1.69 ± 0.13	1.78 ± 0.01	1.82 ± 0.04	2.22 ± 0.15
His	1.25 ± 0.08	1.55 ± 0.1	1.72 ± 0.08	1.22 ± 0.09
Ile	2.59 ± 0.14	2.62 ± 0.22	2.37 ± 0.11	2.31 ± 0.23
Leu	4.62 ± 0.15	4.56 ± 0.49	5.13 ± 0.12	4.03 ± 0.42
Lys	3.49 ± 0.12	3.69 ± 0.2	4.03 ± 0.03	3.2 ± 0.25
Phe	2.22 ± 0.05	2.93 ± 0.06	3.21 ± 0.17	2.54 ± 0.13
Pro	2.73 ± 0.1	3.05 ± 0.08	3.22 ± 0.12	2.71 ± 0.23
Ser	3.03 ± 0.23	3.09 ± 0.24	2.92 ± 0.2	2.69 ± 0.32
Thr	1.97 ± 0.06	2.52 ± 0.18	2.33 ± 0.11	2.02 ± 0.11
Val	2.51 ± 0.1	2.41 ± 0.11	2.72 ± 0.13	2.45 ± 0.41
Tyr	0 ± 0	2.55 ± 0.24	3.13 ± 0.33	1.76 ± 0.43
Trp	0 ± 0	0 ± 0	0 ± 0	0.66 ± 0.14
Cys**	1.14 ± 0.04	0.81 ± 0.05	1.02 ± 0.13	0.74 ± 0.15
Met**	0.97 ± 0.07	0.74 ± 0.04	0.91 ± 0.07	0.69 ± 0.13
Total protein	48.04 ± 0.99	50.17 ± 0.89	53.19 ± 1.47	53.24 ± 0.36***

Values are expressed as mg/100 mg biomass, amino acids represented by three letter abbreviations

*Values were obtained from NIST certificate of analysis for standard reference material^® 3234. Variability is expressed as standard error of mean (n = 3)

**Cysteine was measured as cysteic acid in hydrolysis that involved prior oxidation and as cystine for the other two methods. Similarly, methionine was measured as methionine suloxide upon oxidation and as methionine in the two methods that did not involve prior oxidation

***Total protein reported by NIST used a combination of Kjeldahl, thermal conductivity and pyrolysis methods [48]. Summation of amino acids from NIST reference gives 51.44 mg/100 mg biomass