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

Determination of minimum bactericidal concentration 
(MBC) and minimum fungicidal concentration (MFC)
To determine the MBC and MFC, 10 μL of each well con-
taining the different concentrations of the onion extract with 
the respective bacteria and fungi were plated onto a plate 
containing Mueller Hilton agar and potato dextrose agar, 
respectively. Each well was plated onto the same plate with 
different partitions indicating concentration. A total of 6 
plates, one for each bacterium and fungus, was incubated 
for 24 h at 37 ºC and 48 h at 28 ºC, respectively and observed 
for the growth on the surface of the agar. An empty plate of 
Mueller Hinton agar and potato dextrose agar incubated at 
37 ºC for 24 h and 28 ºC for 48 h, respectively, which was 
considered as negative control. This was done to check the 
sterility of media [
22
].
Statistical analysis
Each test was performed in triplicate, and all data analysis 
was expressed as a mean ± standard deviation. Significant 
differences between means were analyzed statistically using 
a one-way analysis of variance (ANOVA) according to SAS 
9.4 TS Level 1M3 software package SAS [
23
]. Duncan’s 
multiple range test was used to test the significance of the 
means of three replicates of samples.
Results and discussion
Effect of solvents on the extraction yield
The extraction yield is affected by the chemical nature of 
phytochemicals, the extraction method, sample particle size, 
the extraction solvent, extraction pH, temperature and time 
as well as the presence of interfering substances [
24
]. The 
application of a proper solvent plays a vital role in the extrac-
tion of phytochemicals [
15
]. The extraction yields obtained 
using different solvents used in this study are reported in 
Table 
1
. Methanolic extract was found to be the best extract-
ant for red onion skin, achieving the highest extraction 
yield of the plant component (5.6 ± 0.07% w/w), more than 
any other solvents. According to the results of our study, 
the extraction yield decreased in following order: metha-
nol > distilled water > ethanol > ethyl acetate > n-butanol. It 
confirms that the extraction yield increased with an increase 
in polarity of the extraction solvent. Skerget et al. [
25
] 
showed that when pure acetone and ethanol were used as 
solvents, the yields obtained for onion skin were much lower 
compared to the aqueous mixtures of acetone or ethanol.