Sensitive characterization of complex chemical reactions in black garlic preparation based on on-line extraction electrospray ionization mass spectrometry

Changes in chemical composition during food processing and handling are crucial for the alteration of food flavor and function, and accurate characterization of key chemical reaction pathways in complex food matrices is one of the core challenges in food chemistry research. Here, this study attempts to establish a strategy for sensitive characterization of chemical reactions during food processing based on on-line extraction electrospray ionization mass spectrometry (oEESI-MS). The process of making garlic into black garlic, a traditional global flavor food, was chosen as an exemplary research template. The direct MS characterization of raw garlic as well as black garlic samples with different processing times was achieved by using the self-constructed oEESI-MS device. Benefiting from the high tolerance of oEESI-MS to complex matrix interferences, all samples can be fingerprinted directly without any pre-processing or pre-separation. As a result, oEESI-MS achieved a sensitive characterization of the changes of key substances during the preparation of black garlic. Further, a new chemical reaction pathway, the degradation of γ-L-glutamyl-S-allyl-L-cysteine to S-allyl-l-cysteine, was completely demonstrated by analyzing the differential substances before and after the treatment, and verified by standard substances and chemical theory calculations. In conclusion, a complete oEESI-MS-based strategy for tracking the substance changes in food processing was established in this study, which has a widely applicable prospect for the precise setting of food processing time and parameters, and the innovation of processing technology.