Determination of the content of free amino acids and their profiling

When assessing sourdough maturity, the quantification of free amino acids (FAA) is of utmost importance, since their concentration is one of the biochemical indicators commonly used to describe its performances. The difficulty of analyzing amino acids with conventional chromatographic systems is mainly due to the complex nature of samples and unique chemical properties of amino acids, which require chemical derivatization, either before or after chromatographic separation, to improve their detection. For good chromatographic separations, the right combination of resins, buffer, pH, and temperature is necessary, which is why automated systems like the Biochrom amino acid analyzer have been developed. In the Biochrom system, amino acids are separated by ion exchange chromatography and quantified using dual wavelength photometric detection following ninhydrin post-column derivatization. Notwithstanding the high reproducibility and the possibility to quantify up to 56 amino acids and derivatives, the long time of analysis can be inconvenient if large numbers of samples are to be analyzed or if the goal is to just quantify total FAA. In such cases, rapid spectrophotometric assays like the ninhydrin method are available. This chapter describes the determination of FAA in sourdough according to two methods: (i) the spectrophotometric quantification of total free amino acids with the cadmium-ninhydrin assay, which is rapid and does not require elaborated and expensive equipment, and (ii) the chromatographic technique using the Biochrom system, which, although more time consuming than the former, allows the quantification of the single free amino acids.