Metabolite Transformation and Enzyme Activities of Hainan Vanilla Beans During Curing to Improve Flavor Formation

Enzymatic Activity and Its Relationships with the Total Phenolic Content and Color Change in the High Hydrostatic Pressure-Assisted Curing of Vanilla Bean (Vanilla planifolia)

Diverse enzymatic reactions taking place after the killing of green vanilla beans are involved in the flavor and color development of the cured beans. The effects of high hydrostatic pressure (HHP) at 50-400 MPa/5 min and blanching as vanilla killing methods were evaluated on the total phenolic content (TPC), polyphenoloxidase (PPO), and peroxidase (POD) activity and the color change at different curing cycles of sweating-drying (C0-C20) of vanilla beans. The rate constants describing the above parameters during the curing cycles were also obtained. The TPC increased from C1 to C6 compared with the untreated green beans after which it started to decrease. The 400 MPa samples showed the highest rate of phenolic increase. Immediately after the killing (C0), the highest increase in PPO activity was observed at 50 MPa (46%), whereas for POD it was at 400 MPa (25%). Both enzymes showed the maximum activity at C1, after which the activity started to decrease. As expected, the L* color parameter decreased during the entire curing for all treatments. An inverse relationship between the rate of TPC decrease and enzymatic activity loss was found, but the relationship with L* was unclear. HHP appears to be an alternative vanilla killing method; nevertheless, more studies are needed to establish its clear advantages over blanching.

Candidate genes involved in the biosynthesis of lignan in Schisandra chinensis fruit based on transcriptome and metabolomes analysis

Schisandra chinensis Turcz. (Baill.) is a plant species with fruits that have been well known in Far Eastern medicine for a long time. It has traditionally been used as a stimulating and fortifying agent in cases of physical exhaustion and to inhibit fatigue. The major bioactive compounds found in S. chinensis are lignans with a dibenzocyclooctadiene skeleton, but little is known about their biosynthesis in plants. S. chinensis is the ideal medicinal plant for studying the biosynthesis of lignans, especially the dibenzocyclooctadiene skeleton. Genomic information for this important herbal plant is unavailable. To better understand the lignan biosynthesis pathway, we generated transcriptome sequences from the fruit during ripening and performed de novo sequence assembly, yielding 136 843 unique transcripts with N50 of 1778 bp. Putative functions could be assigned to 41 824 transcripts (51.57%) based on BLAST searches against annotation databases including GO (Gene ontology) and KEGG (Kyoto Encyclopedia of Genes and Genomes). Furthermore, 22 candidate cytochrome P450 genes and 15 candidate dirigent proteins genes that were most likely involved in the lignan biosynthesis pathway were discovered based on transcriptome sequencing of S. chinensis. The genomic data obtained from S. chinensis, especially the identification of putative genes involved in the lignan biosynthesis pathway, will facilitate our understanding of lignan biosynthesis at the molecular level. The lignan metabolite profiles were analyzed by metabolomes, the accumulation patterns of 30 metabolites involved in the lignan pathway were studied. Co-expression network of lignan contents and transcriptional changes showed 355 strong correlations (correlation coefficient, R² > 0.9) between 21 compounds and 153 transcripts. Furthermore, the comprehensive analysis and characterization of the genes involved in lignan pathways and the metabolite profiles of lignans are expected to provide better insight regarding the diversity of the chemical composition, synthetic characteristics, and regulatory mechanisms of this medical herb.