Exploration of natural enzyme inhibitors with hypoglycemic potentials amongst Eucalyptus Spp. by in vitro assays

Table 1 List of phytochemicals of Eucalyptus Spp. inhibiting the enzymes

Phytochemicals	Enzymes inhibited ↓
Flavonoids, like quercetin, kaempferol, myricetin; Phenolics-tannins, ellagic acid, and gallic acid; terpinoids-ursolic acid, oleanolic acid, p-cymene, and 1,8-cineole, 1-(S)-α-pinene	α-amylase
Polyphenols, proanthocyanidins, anthocyanins	α-glucosidase
Flavonoids, flavonols, terpenoids, mono-terpenes	Aldose reductase
Flavonoids, flavonols, terpenoids, mono-terpenes	Angiotensin converting enzyme
Terpenoids	Peroxisome proliferator activated receptor
Triterpenoids, phenolic compounds	Di-peptidyl peptidase 4

Table 2 Total polyphenol, flavonoid, flavonol and tannin contents of E. globulus, E. citriodora and E. camaldulensis

Extract1	Polyphenol(mg/g extract2)	Tannins(mg/g extract2)	Flavonoid(mg/g extract2)	Flavonol(mg/g extract2)
EG	496.85 ± 3.98	329.06 ± 6.25	7.15 ± 0.02	4.98 ± 0.01
EC	341.75 ± 3.63	199.75 ± 5.49	4.89 ± 0.01	3.87 ± 0.05
ECA	429.91 ± 4.03	253.15 ± 4.96	5.01 ± 0.02	4.09 ± 0.01

¹Content expressed per gram of relevant extracts (EG, EC and ECA);

²Values are expressed as mean ± SD from triplicate determination. EG: E. globulus; EC: E. citriodora; ECA: E. camaldulensis.

Table 3 Color test results for the presence of 1,8-cineole in E. globulus, E. citriodora and E. camaldulensis extracts

Extracts	Marquis test	Gallic acid test	Concentrated H2SO4	Phloroglucinol
EG	Orange	Yellow	Dark yellow	No color
EC	Orange	Dark Yellow	Dark yellow	No color
ECA	Orange	Yellow	Bright orange-yellow	Pink

EG: E. globulus; EC: E. citriodora; ECA: E camaldulensis.

Table 4 IC₅₀ inhibitory values of Eucalyptus extracts E. globulus, E. citriodora and E. camaldulensis in different assays

Assays	EG	EC	ECA
α-amylase	3.01 ± 0.01	4.13 ± 0.09	3.65 ± 1.04
α-glucosidase	2.08 ± 0.01	2.68 ± 0.11	2.11 ± 0.19
Aldose reductase	2.06 ± 0.03	6.72 ± 0.65	2.56 ± 0.84
Angiotensin converting enzyme	4.31 ± 0.09	30.83 ± 0.45	6.85 ± 0.98
Dipeptidyl peptidase	3.098 ± 0.09	6.138 ± 0.68	3.99 ± 0.91
1,1-diphenyl-2- picrylhydrazyl (DPPH)	12.32 ± 0.91	68.42 ± 0.05	14.44 ± 1.91

EG: E. globulus; EC: E. citriodora; ECA: E. camaldulensis.