## 3 Discussion  
Fresh ginseng was harvested in October each year, and the development of modified atmospheres packing (MAP) enables research on fresh ginseng [14; 19; 20; 21; 22]. Ginseng is an important traditional folk medicine in China, Japan, and Korea [5], and its medical effect may be better than wild ginseng [15]. The age of ginseng root is essential to the development of the ginseng industry. Our results have provided correlations between the activity of key enzymes and ginseng content in ginseng of different years in Ji'an, China. The results might yield insight into a new strategy for identifying the age of individual ginseng plants. Several studies have reported other methods to discriminate the different ages of ginseng, such as telomere length [23], allometry [24] Fourier transform infrared spectroscopy (FTIR) [25], and taste-sensing [26]. Figure 7: The correlation analysis of total ginseng and the individual ginseng. (** The correlation is significant, with a confidence level (double test) of 0.01. * The correlation is significant, with a confidence level (double test) of 0.05. Underscore 1 (_1) represents the gene expression of a key enzyme. Underscore 2 (_2) represents the activity of a key enzyme). To the best of our knowledge, we systematically report for the first time, the change in the activity of seven key enzymes in fresh ginseng. Through correlation analysis, we propose a potential new strategy for discriminating the age of fresh ginseng roots by measuring the content of ginseng, gene expression, and enzyme activity. First, we successfully measured total saponins and developed an HPLC-based method for the simultaneous determination of four types of individual ginseng. Moreover, the HPLC method presented here was a rapid and sensitive way to quantify the content of major individual ginsengides in fresh ginseng samples [17]. The observed trend in the change and content of total saponins and monomer saponins is consistent with previous research [27; 28; 29]. The correlation of total ginsengides and individual ginsengides had statistical significance and obviously increased with age. Their common metabolic pathway results in a correlation between saponins and ginsengides. To further understand the molecular mechanisms of ginseng biosynthesis at different ages, we determined the transcription level of seven key genes (_HMGR, FPS, SS, SE, DS, CYP450_, and _GT_) in the ginseng biosynthetic pathway. Gene expression exhibited different variation trends for different phases of growth. Gene expression during the first stage (_HMGR_) and the third stage (_GT, CYP450_) had a similar tendency across the different ages. The two enzymes are required throughout all stages of ginsengide biosynthesis [30]. The genes encoding the three key enzymes presented the same trend during the second biosynthesis stage, and the trend was similar to results of the present study [17]. \(DS\) gene expression rapidly increased from years 2-4 and then remained stable during years 4-6; these results were consistent with changes in ginsengide. The \(DS\) gene is relevant to dammarenediol, which is the direct precursor of the dammarane tetracyclite triterpenoids. However, the correlation of gene expression with total saponins and years did not reach statistical significance. Key enzyme activity was measured, and the data were normalized for processing. The activity for all seven enzymes significantly increased between the second and fourth years, indicating a rapid increase of ginsengide during this period. This phenomenon was consistent with the change in ginsengide. The correlation was analyzed, and only DS and GT activities were statistically significant. Previous studies reported that the initial committed step in ginsengide synthesis is the transformation of 2,3-oxidosqualene to dammarenediol II catalyzed by DS, which is the first dedicated enzyme for ginsengide biosynthesis in _P. ginseng._ Several studies have shown that the up-regulation of DS expression resulted in increased ginsengide.