## 3 Results and Discussion
### Folin-Ciocalteu Determination of Z. officinal Extracts  
Recent studies [30; 31] in polyphenolic compounds of diverse structure have showed that the Folin-Ciocalteu assay, broadly used to measure total polyphenolic contents, is an adequate method to evaluate the polyphenolic reducing capacity, which occurs through a single electron transfer mechanism [32; 33]. Table 3 summarizes the results for Folin-Ciocalteu (FC) reducing capacity of extracts from _Z. officinal_ rhizomes (\(n=12\)), performed as described in Section 2.3, Materials and Methods.  
Results for FC reducing capacity in _Z. officinal_ extracts show variability, with values ranging from 49.5 mg of gallic acid equivalents (GAE)/g extract up to 150.5 mg GAE/g extract. One-way ANOVA followed by Tukey post hoc test indicated significant difference (\(p<0.05\)) between samples from the Northern and Western regions. Samples from the Northern region show some of the highest values with an average FC content of 105.7 mg GAE/g compared to results for samples from Western region, which hold an average 45% lower (58.0 mg GAE/g). Individually, WR-2 shows the lowest value (49.5 mg GAE/g) among all 12 samples, while SR-1 shows the highest FC reducing capacity (150.5 mg GAE/g), followed by NR-4 (146.7 mg GAE/g) and NR-3 (121.1 mg GAE/g).  
Compared with the literature, results obtained for FC assay were shown to be higher than values reported in the literature for _Z. officinal_ samples from Malaysia (18.44 mg GAE/g dry material), Sudan (60.34 mg GAE/g dry material) and China (9.69 mg/g dry material) [28; 34; 35]. On the other hand, the UPLC analysis results proved to agree with FC determinations, where samples with the highest TG content, SR-1 (48.17 mg/g), NR-3 (39.59 mg/g) and NR-4 (42.05 mg/g) also presented the highest FC values. A similar trend was observed for the samples with the poorest contents of TG, namely WR-1 (23.52 mg/g) and WR-2 (23.26 mg/g), which was also in agreement with FC lowest findings.  
Finally, as shown in Figure 12a, correlation analysis between TG and FC reducing capacity in samples determined by UPLC demonstrated to have significant positive correlation (r = 0.941, \(p<0.05\)), thus suggesting a role of gingerols contents in the reducing capacity FC, in agreement with previous reports on polyphenols [36; 37].  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Product** & **FC (mg/g) 1,2,3** & **Product** & **FC (mg/g) 1,2,3** \\ \hline NR-1 & 99.5 \({}^{\mathrm{c},\mathrm{d}}\)\(\pm\) 0.9 & NW-2 & 103.7 \({}^{\mathrm{c}}\)\(\pm\) 1.4 \\ NR-2 & 97.1 \({}^{\mathrm{d},\mathrm{e}}\)\(\pm\) 0.9 & NW-3 & 95.2 \({}^{\mathrm{d},\mathrm{e}}\)\(\pm\) 1.5 \\ NR-3 & 121.1 \({}^{\mathrm{b}}\)\(\pm\) 1.2 & SR-1 & 150.5 \({}^{\mathrm{a}}\)\(\pm\) 1.9 \\ NR-4 & 146.7 \({}^{\mathrm{a}}\)\(\pm\) 4.8 & WR-1 & 49.8 \({}^{\mathrm{h}}\)\(\pm\) 0.9 \\ NR-5 & 64.2 \(\pm\) 1.2 & WR-2 & 49.5 \({}^{\mathrm{h}}\)\(\pm\) 0.8 \\ NW-1 & 93.7 \({}^{\mathrm{e}}\)\(\pm\) 1.0 & WR-3 & 74.9 \({}^{\mathrm{f}}\)\(\pm\) 1.1 \\ \hline \hline \end{tabular} \({}^{1}\) mg of gallic acid equivalent/g extract. \({}^{2}\) Values are expressed as mean \(\pm\) standard deviation (S.D.). \({}^{3}\) Different superscript letters indicate differences are significant at \(p<0.05\) using one-way analysis of variance (ANOVA) with a Tukey post hoc as statistical test.  
\end{table}
Table 3: Folin–Ciocalteu (FC) reducing capacity for extracts of _Z. officinal_ rhizomes.  
In turn, correlation analysis between FC and the individual phenolic compounds showed correlation only with 6-gingerol and 10-gingerol, where the highest correlation is presented by 6-gingerol (r = 0.905, \(p\) < 0.05), as shown in Figure 12b, therefore aligning with the antioxidant role of this compound as previously reported [38; 39].