Inhibition of enzymes linked to type-2 diabetes and hypertension by essential oils from peels of orange and lemon

Figures & data

Table 1. Chemical composition of essential oil.

	Orange peels		Lemon peels
Compounds^a	KI^b	%^c	KI^b	%^c
α-Phenandrene	1088	0.14	–	–
Sabinene	1149	0.11	1094	4.18
Limonene	–	–	1188	53.07
α-Pinene	1225	0.70	1228	3.82
β-Pinene^d	1267	0.02	1306	9.53
Limonene	1309	92.14	–	–
Cis-ocimene	1356	0.12	1385	0.01
β-Myrcene	1382	2.7	1391	3.33
Allo-ocimene	1400	0.07	1396	0.04
Pinene-2-ol	–	–	1429	–
α-Thujene	1424	0.19	1450	0.05
Decanal	1448	0.22	–	–
γ-Terpinene	1461	0.23	1483	0.11
Geijerene	1468	0.12	–	–
Fenchone	1514	0.13	–	–
Neral	1529	0.09	1502	4.70
Geranial	1539	0.07	1516	3.33
Isoartemisia	1550	0.05	1559	0.04
1,8-cineole	1569	0.33	0.33	0.33
Geraniol	1599	0.06	–	–
Nerol	1620	0.08	–	–
Linalool	1639	0.05	1622	3.70
Borneol	1662	0.17	1628	5.57
α-Terpineol	1689	0.17	1677	0.25
Terpinen-4-ol	1703	0.09	1681	0.23
Thymyl methyl ether	1731	0.16	1634	0.06
Ascaridole	1749	0.08	1741	0.06
Linalyl acetate	1652	0.13	–	–
Ethyl cinnamate	1694	0.14	1709	0.10
Borneol acetate	1688	0.12	1689	0.13
Neryl acetate	1697	0.06	–	–
β-Bisabolene	–	–	1715	0.11
Linalyl acetate	–	–	1705	–
Geranyl acetate	1703	0.15
β-Caryophyllene	1668	0.12	1731	1.49
Trans-α-bergamotene	1760	0.12	–	–
Cardinene	1777	0.08	–	–
β-Elemene	1789	0.03	1778	0.61
Germacrene D	–	–	1800	0.10
Bicyclogermacrene	1811	0.19	1800	0.08
α-Copane	1850	0.03	–	–
Germacrene D	1886	0.09	–	–
Acetyleugenol	1891	0.05	–	–
Elemicin	1912	0.02	–	–
Benzyl benzoate	1959	0.09	–	–
α-Humulene	2010	0.09	–	–
Viridiflorol	–	–	2042	0.05
Torreyol	–	–	2049	0.04
Tetradecanoic acid	–	–	2039	0.08
Total identified		99.84		99.76
Grouped components (%)
Monoterpene hydrocarbons		58.00		74.10
Oxygenated monoterpenes		32.10		21.28
Sesquiterpene hydrocarbons		9.70		2.48

^aCompounds are listed in order of their elution from a DB-5 FID column.

^bKovat Index.

^cPercentages obtained by FID peak-area normalization [Sources: Oboh et al. (2014) and Oboh et al. (2016)].

^d Main compounds in bold font.

– Not determined.

Table 2. IC₅₀ values of α-amylase, α-glucosidase, and ACE inhibition.

Parameter (unit)	Orange	Lemon	Acarbose	Lisinopril
α-Amylase (µg/mL)	11.51 ± 0.83^a	8.16 ± 0.43^b	7.45 ± 0.43^b	–
α-Glucosidase (µg/mL)	11.53 ± 0.41^a	7.56 ± 0.84^b	8.44 ± 0.43^b	–
ACE (µg/mL)	31.79 ± 0.52^a	26.17 ± 0.52^b	–	24 ± 0.43^b

Values represent means of triplicate reading. Values with different letters along the rows are significant different at p < 0.05. – Not determined. Acarbose and lisinopril were used as standards.

Table 3. R² values of α-amylase, α-glucosidase, and ACE inhibition.

Parameter	Orange	Lemon	Acarbose	Lisinopril
α-Amylase	0.98	0.95	0.76	–
α-Glucosidase	0.96	0.81	0.86	–
ACE	0.29	0.22	–	0.56

– Not determined.

Figure 1. α-Amylase inhibitory activity of essential oils from orange and peels.

Figure 2. α-Glucosidase inhibitory activity of essential oils from orange and lemon peels.

Figure 3. Angiotensin-I-converting enzyme inhibitory activity of essential oils from orange and lemon peels.