Encapsulation of Fennel and Basil Essential Oils in β-Cyclodextrin for Novel Biopesticide Formulation

Abstract

β-cyclodextrin (β-CD) is a good host for the encapsulation of fennel and basil essential oils (FEO and BEO, respectively) and the formation of inclusion complexes (ICs) using the co-precipitation method. According to the results of the GC/MS analysis conducted in this study, monoterpenes and monoterpenoids were the dominant chemical groups in total FEO, while in BEO, these two groups occurred along with sesquiterpenes and sesquiterpenoids. The presence of dominant compounds from both EOs was validated using the FT-IR spectra of ICs, which indicated successful complexation. Analyses conducted using SPME/GC-MS showed the continuous emission of volatiles over 24 h from both ICs. Under SEM, particles of both ICs appeared to have a rectangular or rhomboid morphology and few aggregates. The insecticidal properties of EOs and ICs with β-CD were tested on the Colorado potato beetle (CPB) as a model pest. The inclusion complex of β-CD with FEO altered the developmental dynamic and body mass of the CPB. The initial increase in the proteolytic activity of CPB larvae fed with potato plants sprayed with ICs was not maintained for long, and the proteolytic efficacy of treated larvae remained in line with that of the control larvae. Future investigations will focus on manipulating the volume of EOs used and the treatment duration for optimal efficacy and potential application.

Keywords: Colorado potato beetle; FT-IR; SPME/GC-MS; inclusion complex.

Figure 1

Chemical structure (A) and 3-D model (B) of β-cyclodextrin molecule.

Figure 2

Chemical composition (A); dominant constituents (B); and chemical groups (C) of fennel (Foeniculum vulgare Mill.) essential oil. RI—retention index; RT—retention time; %m/m—% of compound in total oil. Colored bars represent the contribution (%m/m) of the compound in total EO.

Figure 3

Chemical composition (A); dominant constituents (B); and chemical groups (C) of basil (Ocimum basilicum L.) essential oil. RI—retention index; RT—retention time; n.i.—non-identified; %m/m—% of the compound in total oil. Colored bars represent the contribution (%m/m) of the compound in total EO.

Figure 4

FT-IR spectra of fennel EO (FEO), β-cyclodextrin (β-CD), and IC of β-cyclodextrin and fennel EO (β-CD-FEO) (A) and FT-IR spectra of basil EO (BEO), β-cyclodextrin (β-CD), and IC of β-cyclodextrin and basil EO (β-CD-BEO) (B).

Figure 5

SPME/GC-MS chromatograms of β-CD-FEO (A), β-CD-BEO (B), and volatile release from ICs after 0, 3, 6, and 24 h (n = 3, p < 0.05) (C). At 13.71 and 21.43 min, there are cyclomethylsiloxane signals from the SPME GC/MS system.

Figure 6

Scanning electron micrographs of β-CD-FEO at 2000× and 15,000× (A); scanning electron micrographs of β-CD-BEO at 1500× and 15,000× (B).

Figure 7

Effect of fennel (FEO) and basil (BEO) essential oils and β-CD inclusion complexes (β-CD-FEO and β-CD-BEO) on growth, development, and proteolysis of Colorado potato beetle (CPB) larvae. Application of EOs (A), spraying with ICs (B), and feeding of CPB larvae with EOs or ICs on treated or non-treated (control) potato plants (C). Larval mass (D), percentage of larvae in 2nd, 3rd, and 4th instars (E), and proteolytic activity of larvae and adults (a) (F) are presented before treatment (day 0) and after larvae were fed with potato plants for 4 and 8 days. Results in (D,F) are presented as means ± standard errors (n = 10). Means denoted by the same letter within the same time point are not significantly different (p ≤ 0.05) according to the LSD test.