Correlation between total phenolic content, flavonoid content and antioxidant activity
From the Pearson correlation tests in table 3, there were a very strong positive and significant (p < 0.05) correlation found between total phenolic content and FRAP assay in both extracts (r = 0.969 for 60% ethanol extract; r = 0.973 for aqueous extract). In EC50 of DPPH assay, there was a very strong negative and significant correlation (p < 0.05) occur in 60% ethanol extract (r = -0.939) but no correlation was found in aqueous extract. It might be feasible to suggest that phenolics do not act as the major antioxidant
Table 3. Pearson’s correlation coefficient between total phenolic content, FRAP assay and DPPH free radical scavenging assay (EC50)
Total Phenolic content Pearson correlation
FRAP
EC50
60% ethanol r value 0.969** -0.939**
p value 0.001 0.005
Aqueous r value 0.973** 0.654
p value 0.001 0.159
**Correlation is significant at the 0.05 level (2-tailed)
Table 4. Pearson’s correlation coefficient between total flavonoid content and FRAP assay and DPPH free
radical scavenging assay (EC50)
Total Flavanoid content Pearson correlation
FRAP
EC50
60% ethanol r value 0.985** -0.933**
p value 0.000 0.007
Aqueous r value 0.984** -0.592
p value 0.000 0.216
**Correlation is significant at the 0.05 level (2-tailed)
components in the aqueous extracts. There might be possibility of other active constituents, which are nonphenolic in nature that can be extracted in water extracts. According to Chye et al. (2008) and Perez-Jimenez and Saura-Calixto (2006), the presence of non-antioxidant compounds especially amino acids and uronic acids in the test solutions may produce higher antioxidant capacity to that produced by the polyphenols alone.
Besides, table 4 displayed that the total flavonoid content in 60% ethanol extract showed a very strong positive and significant (p < 0.05) correlation with FRAP assay (r = 0.985) but a very strong negative and significant (p < 0.05) correlation with FRAP assay in aqueous extract (r = -0.984). The positive and highly significant relationship between this effective compound with antioxidant activity indicates that flavonoid plays a major role in the antioxidant activity of mushrooms. The compounds such as flavonoids, which hold hydroxyls groups, are responsible for the radical scavenging activity in the plants (Mohamed Imran et al., 2011). There was a negative and significant correlation (p < 0.05) found betweenn EC50 and total flavonoid content in 60% ethanol extract (r = -0.933) but no correlation was found between them in aqueous extract. The negative linear correlations obtained in this study means sample with the highest flavonoid content shows higher antioxidant activity and lower EC50 values. This was in accordance to the findings by several authors who reported that total flavonoid content was negatively correlated with the EC50 of the edible mushroom Leucopaxillus giganteus (Barros et al., 2007b). The moderate to high scavenging effects of medicinal mushrooms might be associated with some antimutagenic properties (Mau et al., 2002).
Conclusions
A relationship between the EC50 of DPPH scavenging activity, FRAP assay, phenolic and flavonoid was established among different types of mushrooms and solvent extraction. In brief, the antioxidant activity was exhibited to a certain extent are probably due to other antioxidant components present in these mushroom extracts besides the phenolic compound and also depends on solvents used. This also indicates that phenolic compounds extracted might cover from moderate polarity to low polarity due to different antioxidant activity. This study suggests that high antioxidant activity in ethanol extract of mushrooms can potentially be used as a source of natural antioxidants due to presence of phenolic compounds since mushrooms are readily available and acceptable to the public. Further investigations on the isolation and purification of the active components from crude extracts of mushrooms can be done by using high performance liquid chromatography (HPLC).
Acknowledgements
We would like to acknowledge Department of Nutrition and Dietetics, Faculty of Medicines and Health Sciences, Universiti Putra Malaysia for the help and support of this work.