Beneficial sterols in selected edible insects and their associated antibacterial activities

Abstract

Edible insects are increasingly gaining popularity as research reveals multiple benefits. However, the rediscovery of natural products from insects as medicinal agents has received limited attention. This study aimed at evaluating the diversity of sterols in extracts of nine edible insects and potential antibacterial activities. Dichloromethane extracts of these insects were analyzed using gas chromatography-mass spectrometry to identify important sterols, followed by evaluation of their anti-bacterial activities. Nineteen sterols were identified with the highest recorded in African fruit beetle [Pachnoda sinuata (47.37%)], crickets [Gryllus bimaculatus (36.84%) and Scapsipedus icipe (31.58%)]. Cholesterol was the most prevalent, except in black soldier fly (Hermetia illucens). Bioactivity revealed S. icipe as the most potent extract against Escherichia coli and Bacillus subtilis whereas G. bimaculatus was highest against Methicillin-susceptible Staphylococcus aureus 25923. These findings unravels the diversity of sterols in edible insects and their possible application in food, pharmaceutical and cosmetic industries.

Figure 1

Total ion chromatogram indicating the abundance of phytosterols/stanols identified in African fruit beetle larvae P. sinuata.

Figure 2

Abundance of sterols in crickets: G. bimaculatus, S. icipe and the desert locust S. gregaria.

Figure 3

Quantification of the stigma-7-en-3β-ol sterol in H. illucens and R. differens.

Figure 4

An overlay of R. differens and G. krucki showing the presence of desmosterol (labelled B). The peak denoted by letter D contained different sterols at 38.79 (γ-sitosterol) and at 38.81 (stigma-7-en-3β-ol (5α, 24S) in G. krucki and R. differens.

Figure 5

Mass spectra of (A) desmosterol and (B) cholesterol indicating the possible fragment peaks.

Figure 6

Chromatogram indicating sterols from silkworm-B. mori and Macrotermes sp. extracts.

Figure 7

The chemical structures of the identified sterols in the selected edible insects.

Figure 8

The percentage area mean (± SE) of fatty acids and sterols in the DCM extracts. Bars are capped with different letters shows how significantly the given data correlate (Tukey's HSD test: p < 0.05).

Figure 9

Biosynthesis of selected sterols identified from the edible insects. HMGR 3-hydroxy-3-methylglutaryl-CoA reductase, SQE1 squalene epoxidase, CAS1 cycloartenol synthase, LAS1 lanosterol synthase, SMT1/2 C24-sterol methyltransferase, DIM/DWF1 sterol-∆²⁴-isomerase/reductase, CYP710A C-22-sterol desaturase. The double arrows indicate several steps of enzymatic reactions.

Figure 10

Proposed biosynthesis of taraxasterol identified from the cricket species—G. bimaculatus.