Inhibitory Effects of Onion Against α-Glucosidase Activity and its Correlation with Phenolic Antioxidants

Figures & data

Table 1 Total phenolic contents and antioxidant activities of onions and reference foods ^a

	Total phenolic content(mg GAE/100 g)		DPPH scavenging capacity(μmol L-ascorbic acid equivalents/g)
Samples	Wet weight basis	Dry weight basis	Wet weight basis	Dry weight basis
White onion	30.8 ± 3.3 c ^b	531.1 ± 56.7 B	0.52 ± 0.05 c	8.9 ± 0.8 B
Red onion	39.5 ± 3.9 c	531.4 ± 52.6 B	0.59 ± 0.07 c	7.9 ± 0.9 B
Onion powder	429.9 ± 73.0 b	508.9 ± 86.6 B	10.5 ± 0.39 a	12.5 ± 0.5 A
Bitter melon	43.7 ± 1.8 c	644.0 ± 26.4 A	0.65 ± 0.01 c	9.6 ± 0.1 B
Pumpkin	16.4 ± 0.6 c	183.1 ± 6.31 C	0.14 ± 0.04 d	1.6 ± 0.5 C
Yam	29.8 ± 3.7 c	134.8 ± 16.6 C	0.62 ± 0.13 c	2.8 ± 0.6 C
Medlar	565.5 ± 77.7 a	693.3 ± 95.2 A	6.50 ± 0.18 b	8.0 ± 0.2 B
^a Results were expressed as mean ± standard deviation (n = 3).
^b Values marked by the same letter within each column are not significantly different (p < 0.05).

Figure 1 The porcine α-amylase inhibitory activities of 70% ethanol extracts and boiling water extracts. Results were expressed as mean ± SD (n = 3). Values marked by the same letter are not significantly different (p < 0.05). The concentration of each test sample was 20 mg/mL.

Figure 2 α-glucosidase inhibitory activities of 70% ethanol extracts and boiling water extracts. Results were expressed as mean ± SD (n = 4). Values marked by the same letter are not significantly different (p < 0.05). The concentration of each test sample was 20 mg/mL.

Table 2 The correlation between various variables

	Porcine α-amylaseinhibitory activity	α-Glucosidaseinhibitory activity
DPPH scavenging capacity
70% ethanol extracts	−0.94	0.86
Boiling water extracts	−0.84	0.87
Total phenolic content
70% ethanol extracts	−0.83	0.94
Boiling water extracts	−0.93	0.92
The values of Pearson's correlation coefficient between different variables were calculated at p < 0.05.