Dynamics of ADH and related genes responsible for the transformation of C₆‐aldehydes to C₆‐alcohols during the postharvest process of oolong tea

Abstract

Aroma is an important index of tea quality. The volatile C6‐compounds formed from linoleic and linolenic acids in tea leaf lipids are essential components of tea. C6‐compounds are formed and transformed during the postharvest process of tea leaves. However, the metabolic flux of these C6‐compounds, the activities of related enzymes, and the transcription of related genes during the postharvest process of oolong tea remain unclear. In this study, the chemical profiles of C6‐aldehydes and C6‐alcohols, the pattern of ADH enzyme activity, and the level of CsADH gene expression during the postharvest process of oolong tea were investigated. We found that the turnover process had a positive effect on the accumulation of C6‐alcohols and simultaneously induced ADH activity, especially during the withering stage. The expression of CsADH peaked during the turnover stage. The relative expression level of CSA019598 typically increased during the postharvest process. Correlation analysis demonstrated that CSA019598 expression increased as ADH activity increased. This finding suggests that CSA019598 may play a prominent role in regulating ADH. These results advance our understanding of C6‐compound formation during the postharvest process of oolong tea. We aim to evaluate how green leaf volatiles affect the enzymatic formation and genetic transcription of aromatic compounds in oolong tea in future studies.

The Genetic Basis of Tomato Aroma

“…In tomato fruit the latter is the most important for the production of volatiles, which occurs through two steps: (i) fatty acids are deoxygenated by means of lipoxygenases (LOX), which are classified as 13-LOX and 9-LOX and are leading respectively to 13-hydroperoxides and 9-hydroperoxides [67,108]; (ii) hydroperoxides are catabolized by means of hydroperoxide lyases (HPL), also classified as 13-HPL and 9-HPL, leading to an oxoacid and a volatile aldehyde. Volatile aldehydes can be converted into alcohols by means of alcohol dehydrogenases (ADH; [109][110][111][112][113][114]). According to the literature ( [68]), 13-LOX enzymes are mainly involved in the synthesis of (Z)-3-hexenal from linolenic acid and hexanal from linoleic acid.…”

Metabolic Flow of C6 Volatile Compounds From LOX-HPL Pathway Based on Airflow During the Post-harvest Process of Oolong Tea

“…CK, ODT, and OT showed transcription levels of the CsADH genes. Three ADH regulatory genes were selected based on previous studies, designated as CSA019598, CsADH, and CL822.Contig4 (Zhou et al, 2020). The CL822.Contig4 expression level of ODT was significantly higher than those of CK (P <0.01) and OT (P <0.05), which was significantly positively correlated with the change in ADH activity (Figure 5B).…”

“…Enzyme activity measurements were performed using an ADH activity detection kit following the instructions of the manufacturer (Beijing Solarbio Science & Technology Co., Ltd., China). The ADH activity was calculated using the mass of the original sample, as reported previously (Zhou et al, 2020).…”

“…cDNA was generated with the PrimeScript RT Reagent Kit with a gDNA Eraser (TaKaRa Biotech Co., Ltd., Dalian, China). Quantitative real-time PCR (qRT-PCR) was performed as previously described using a LightCycler 480 Real-Time PCR System (Roche Molecular Systems, Alameda, CA, USA) (Zhou et al, 2020). The reaction mixture had a total volume of 20 µL, comprising cDNA (1 µL), 2 × TB Green Premix Ex Taq II (TaKaRa; 10 µL), 10 µM forward primer (0.8 µL), 10 µM reverse primer (0.8 µL), and double-distilled water (ddH 2 O, 7.4 µL).…”

“…Volatile compounds that constitute oolong aroma are divided into four classes based on their origin, namely, fatty acid derivatives, phenylpropanoids/benzenoids, terpenoids, and norisoprenoids (Fu et al, 2017). Fatty acid (FA) derivatives of carboxylic 6 (C6) volatile compounds are considerably accumulated and transformed during the postharvest processing of oolong tea (Zhou et al, 2020). Postharvest processing imparts the oolong tea with a rich and varied natural floral and fruity aroma.…”