Rapid Quality Discrimination and Amino Nitrogen Quantitative Evaluation of Soy Sauces by Tri-Step IR and E-nose

Despite the fact that soy sauce has been one of the most popular seasonings in Eastern Asia, rapid and holistic methods for its authentication and discrimination are still lacking. This research is sought to develop a novel method for rapid discrimination and amino nitrogen quantitative evaluation of different qualities of soy sauces (Chinese traditional fermentation soy sauce (CTFSS), Japanese traditional fermentation soy sauce (JTFSS), high-salt liquid-state fermentation soy sauce (HLFSS), and low-salt solid-state fermentation soy sauce (LSFSS)) based on tri-step infrared spectroscopy (IR) and partial least squares (PLS). Global nutrition fingerprints (saccharides, proteins, amino acids, and other compositions) of each quality soy sauce at the three levels of enhanced spectral resolution and nutrition profile variations among different soy sauces are synthetically interpreted with fast evaluation of their relative contents based on spectral peak intensity. Complementarily, electronic sensory combined with SPME-GC-MS distinguishes four species of soy sauces effective in smell with 90 discrimination indexes. Specifically, FT-IR peak intensity at about 1409 cm −1 (C–N band) exhibits regular enhancement with the increasing concentration of amino acid nitrogen. Thus, a quantitative prediction model based on IR spectra is established by PLS ( R 2 , 0.9956; RMSEC, 0.233). It has been demonstrated that the developed method is applicable for rapid (5 min) discrimination and quantitative analysis of amino acid nitrogen in soy sauce.