Comparative study on the effect of extraction solvent on total phenol, flavonoid content, antioxidant and antimicrobial properties of red onion (Allium cepa)

Effect of solvents on TPC and TFC
Table 
2
summarizes the TPC and TFC results obtained from 
red onion skin extract using various solvents. The highest 
contents of phenolic and flavonoids were obtained for ethyl 
acetate and n-butanol extract. In turn, the lowest phenolic 
Table 1
Yield of red onion skin 
extract using different solvents
Solvent used
Yield % (w/w)
Distilled water 4.8 ± 0.06
Ethanol
4.5 ± 0.06
Methanol
5.6 ± 0.07
n-butanol
3.8 ± 0.05
Ethyl acetate
4.1 ± 0.03

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S. Khalili et al.
1 3
and flavonoid levels were presented by water extract show-
ing that onion skin contains compounds which have lower 
solubility in water phase. In general, the results depicted that 
the solvent with a lower polarity yielded higher phenolic and 
flavonoid contents. In addition, the results of the analysis 
of variance showed that the TPC and TFC of ethanol and 
methanol extract had no statistically significant difference.
In this sense, Singh et al. [
15
] reported extraction with 
distilled water yielded to minimum TPC and TFC of onion 
waste, which is in agreement with the results of the present 
study. In another study, some differences were observed in 
TPC extracted from different cultivars of Italian onion by 
Lisanti et al. [
26
]. Similarly, Bagherloo et al. [
1
] showed 
differences between the TPC amounts of two varieties of 
Iranian onion. In contrast, Davarinejad et al. [
27
] revealed 
that high polarity and viscosity of the solvent are effec-
tive in releasing the phenolic compounds. The discrepancy 
among the obtained results carried out on onion plant may 
contributed to genetic variations, environmental condi-
tions, method of sample preparation or extraction methods. 
Moreover, although phenols solubility in different solvents 
can be based on their polarities,solubility is a complicated 
phenomenon which differs with the stereochemistry of phe-
nols, the degree of conjugation of the aromatic rings and 
intermolecular forces between them and the solvent [
28
]. 
In this study, high correlation between TPC and TFC was 
found (R = 0.9168).