Fast quantification of free amino acids in food by microfluidic voltage-assisted liquid desorption electrospray ionization-tandem mass spectrometry.

A method based on microfluidic voltage-assisted liquid desorption electrospray ionization-tandem mass spectrometry (VAL-DESI-MS/MS) has been developed for fast quantification of free amino acids in food. Food extracts were transferred to the microfluidic platform and analyzed by liquid desorption ESI-MS/MS. Deuterated aspartic acid (i.e., 2,2,3-d3-Asp) was used as internal standard for analysis. The method had linear calibration curves with r2 values > 0.998. Limits of detection were at the level of sub µM for the amino acids tested, i.e., glutamic acid (Glu), arginine (Arg), tyrosine (Tyr), tryptophan (Trp), and phenylalanine (Phe). To validate the proposed method in food analysis, extracts of Cordyceps fungi were analyzed. Amino acid contents were found in the range from 0.63 mg/g (Tyr in Cordyceps sinensis) to 4.44 mg/g (Glu in Cordyceps militaris). Assay repeatability (RSD) was ≤ 5.2% for all the five amino acids measured in all the samples analyzed. Recovery was found in the range from 95.8 to 105.1% at two spiking concentrations of 0.250 mg/g and 1.00 mg/g. These results prove that the proposed microfluidic VAL-DESI-MS/MS method offers a quick and convenient means of quantifying free amino acids with accuracy and repeatability. Therefore, it may have potential in food analysis for nutritional and quality assessment purposes. Graphical abstract.

Simultaneous Quantification of Adenosine and Deoxyadenosine Isomers in Foods with High Sensitivity.

Simultaneous quantification of adenosine and deoxyadenosine isomers, including 2'-deoxyadenosine (dA) and 3'-deoxyadenosine (cordycepin, COR) is a challenge because they are very similar in chemical structure. In some previous studies on food ingredients, adenine and dA might be mistakenly detected as COR that has been shown to have multiple health benefits. In this work, we developed a novel HPLC method with fluorescence detction (HPLC-FD) to simultaneously quantify COR, adenosine and dA. Pre-column derivatization with chloroacetaldehyde (CAA) was deployed. The proposed method has a limit of detection at the nM level for COR and adenosine, and is far more sensitive than the methods previously deveopled for COR determination. Using the present method, caterpillar fungi were analyzed as model food samples. The analysis revealed that COR was present in cordyceps militaris and cordyceps flowers in a concentration range from 0.314 to 0.735 mg/g, but not in cordyceps sinensis (C. sinensis), a natural and the priciest caterpillar fungus. These results suggest that the profile of active ingredients in C. sinensis has been wrongly claimed for many years. This finding was also supported by the results from further HPLC-MS/MS analyses.