Investigation of the dynamic changes in the chemical constituents of Chinese "Laba" garlic during traditional processing.

"Laba" garlic is a famous traditional garlic product, particularly popular with the people in Northern China. The processing time plays an important role on the chemical constituents of "Laba" garlic. Here, we investigated the composition of "Laba" garlic during traditional processing using a non-targeted metabolomics approach. Through using gas chromatography mass spectrometry (GC-MS) and liquid chromatography mass spectrometry (HPLC-MS/MS) with multivariate analysis, a total of 20 volatile metabolites, 16 primary metabolites and 15 phenolic compounds were identified as notable changed compounds due to the traditional processing ( < 0.05). The characteristic flavor of "Laba" garlic was formed mainly by the decreased content of organosulfur compounds and the increased content of non-organosulfur compounds. In addition, this study also proposed the metabolic pathway of primary metabolites and phenolic compounds in garlic samples during processing. Most primary metabolites including lactic acid, isocitric acid, l-leucine, l-proline, d-fructose, d-glucose and erythritol increased from day 3, and reached the maximum level at day 12, which were thought to be the foundation for the sweet and sour taste of "Laba" garlic. Although the concentration of the 15 phenolic compounds from day 3 to day 42 was notably higher than the raw garlic (0 day), the antioxidant activities showed a decreasing trend from day 0 to day 28. The correlation analysis result revealed that notable positive associations were presented between organosulfur compounds, organic acids, amino acids and antioxidant activities. Furthermore, day 12 was found to be the most suitable time to obtain the "Laba" garlic considering its colour, flavor, taste and physiological function. These results are helpful in comprehending metabolism changes and physiological function of "Laba" garlic traditional processing.