Microencapsulation of Capsaicin in Chitosan Microcapsules: Characterization, Release Behavior, and Pesticidal Properties against Tribolium castaneum (Herbst)

SIMPLE SUMMARY: Grains are a major food resource for humans and ensuring food safety is essential. However, stored grains can be heavily infested by insect pests, leading to serious losses. Traditionally, fumigation based on chemical insecticides has been used for pest control, which include broad spectrum insecticides with high insecticidal efficiency. Unfortunately, this leads to food contamination and environmental pollution. Moreover, insects have evolved a higher resistance to these pesticides after long-term exposure. Developing new alternative insecticides has become important work in the field of grain storage. In this paper, we prepared a microcapsule using capsaicin, chitosan, and carboxymethyl chitosan, which has a high chemical stability and insecticide activity. Modern analytical methods such as FTIR, XRD, and SEM were used to determine these materials’ morphologies, crystal structure, and components, revealing that the particles had an amorphous nature, a uniform size, good adhesion, and significant slow-release characteristics. Tribolium castaneum (Herbst), an important pest insect, was selected as the experimental object. The results showed that this material had a higher insecticidal efficiency than pure capsaicin, both in inhibiting larvae development and in distorting the normal adult insect reproduction, revealing that this microcapsule has application potential as an insecticide for the insect control of stored products. ABSTRACT: Capsaicin is a capsaicinoid in hot chili peppers, with excellent antibacterial and antimicrobial activities and a good safety profile, but its poor solubility and instability restrict its effectiveness. This limitation may be mitigated by encapsulation. Herein, capsaicin microcapsules (CCMs) were prepared through layer-by-layer self-assembly, using chitosan and carboxymethyl chitosan as shell materials. The chemical and microstructure structural characterization was evaluated by the methods of Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The SEM indicated the microcapsules were irregular in shape with an average size of about 100 μm. The encapsulation had a high loading efficiency of 64.31%. FTIR and XRD revealed the absence of the interaction between the core and shell materials and the amorphous nature of the CCMs. The analysis results of the microcapsules’ release behavior showed the burst release of capsaicin in 7 days and a slow progression afterward in three solutions, with the highest release properties in a basic solution, followed by acidic and neutral salt solutions. The entomotoxicity of CCMs was conducted against Tribolium castaneum (Herbst), and its efficacy was compared with pure capsaicin. The CCMs were found to be highly effective against this pest. The LC(50) value for capsaicin and its microcapsules was 31.37 and 29.75 mg/kg on adults, respectively. According to these values, T. castaneum’s development and reproduction were significantly inhibited compared with the control group. The excellent physicochemical characteristics and insecticidal performance show a high application value for integrated pest control.