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Macamides are characteristically found in maca (Lepidium meyenii Walper). Fatty acid derivatives are also an important type of constituent in maca, since they not only relate to the biosynthesis of macamides in the postharvest process but also possess some bioactivities. To study their comprehensive profiles in maca tubers processed via the air-drying method, ultraperformance liquid chromatography quadrupole time-of-flight mass spectrometry (UPLC-QTOF-MS) analyses were performed to identify macamide and fatty acid molecules. Their contents in maca tubers that were processed via air drying and freeze drying, respectively, were further quantified using high-performance liquid chromatography (HPLC) analyses comparing with eight macamide and three fatty acid reference standards. A total of 19 macamides (including four novel ones) and 16 fatty acid derivatives (two found in maca for the first time) were identified. Quantification analyses results showed the eight macamides with contents ranging from 31.39 to 1163.19 μg/g (on dry tuber), and fatty acids from 18.71 to 181.99 μg/g in the air-dried maca, but there were only three macamides and one fatty acid detected with very low contents (3.97–34.36 μg/g) in the freeze-dried maca. The results demonstrated that the air-drying method can increase the accumulations of macamides and fatty acids in the metabolism of maca in the postharvest process. The biosynthesis of two types of macamides, i.e., N-benzyl-oxo-octadecadienamides and N-benzyl-oxo-octadecatrienamides, was further elucidated in detail. These results provide more valuable insights into the phytochemicals of maca, which is helpful to explain its health benefits.

Doubanjiang-meju, a major ingredient of Chinese fermented food for several centuries, is produced using broad bean, wheat flour and salt. In this study, we investigated prokaryotic community succession and metabolite changes using high-throughput sequencing and 1H-NMR methods. After 35 days, bacterial communities, except Lactobacillus and Acinetobacter, were relatively stable until the end of fermentation, and consisted predominantly of the genera Tetragenococcus, Lactobacillus, Staphylococcus, Acinetobacter, Pseudomonas and Streptococcus. Glucose, arabinose, fructose and mannitol were identified as major sugars, lactate and acetate as major organic acids, and amino acids as the major nitrogen compounds present in doubanjiang-meju. Correlation analysis revealed important links between bacterial populations and metabolites, e.g., Pseudomonas was significantly correlated with 10 nitrogenous metabolites, while Streptococcus was significantly correlated with six carbonic metabolite and eight nitrogenous metabolites. These results not only revealed bacterial succession and dynamic changes in metabolites as well as pH and color, but also elucidated their relationships during the doubanjiang-meju fermentation.

AIM To identify core bacterial communities and volatile compounds and to investigate their relationships in Doubanjiang, a Chinese traditional red pepper paste. METHODS AND RESULTS Two main culture-independent methods, polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) and MiSeq sequencing technique, were used to investigate bacterial composition. Headspace solid-phase microextraction combined with gas chromatography-mass spectrometry (HS-SPME-GC-MS) was used to isolate and identify volatile organic compounds. Partial least squares (PLS) regression and correlation coefficients analyses were used for elucidating the relationship between core bacterial community and volatile compounds. CONCLUSIONS Lactic acid bacteria (LAB) and Enterobacteriaceae family were identified primarily by the PCR-DGGE fingerprinting. Furthermore, the core microbiome (>1% average relative abundance) were indentified by Miseq sequencing technique, which mainly assigned to Proteobacteria, Cyanobacteria and Firmicutes phyla. For volatile profile, a total of 29 volatile compounds were identified by HP-SPME-GC-MS, mainly alcohols, esters, aldehydes, ketones and phenols. PLS regression and Pearson's correlation coefficients analyses revealed highly covariable relationships between volatile compounds and bacterial taxa. Notably, Pseudomonas most highly significantly associated with 3-methyl butanal, 2-methyl butanal, benzeneacetaldehyde and 2-acetylpyrrole (P