Enzymatic activity and half-lives of capsaicin, dihydrocapsaicin, and pentadecanoic acid methyl ester in soil sprayed with hot pepper extract

Abstract

Pest management is facing economic and ecological challenges in the United States and worldwide due to pest resistance, human and environmental hazards caused by use of synthetic pesticides. Natural product-based pesticides offer advantages that they are specific to the target species and typically have unique modes of action with little mammalian toxicity. Studies conducted at Kentucky State University revealed that the insecticidal and acaricidal performance of crude extracts from the fruits of Capsicum species justified the need for developing a natural pesticide formulation for agricultural use. Analysis of hot pepper extracts indicated the presence of three compounds having pesticidal efficacy: capsaicin, dihydrocapsaicin, and pentadecanoic acid methyl ester. The main objectives of this investigation were to: i) determine the half-live (T_1/2 value) of capsaicin, dihydrocapsaicin, and pentadecanoic acid methyl ester in soil sprayed with hot pepper formulation and ii) assess the impact of hot pepper formulation on total soil enzyme activity. Analysis of soil sprayed with pepper extracts indicated that T_1/2 values of capsaicin, dihydrocapsaicin, and pentadecanoic acid methyl ester were 7.3, 1.5, and 10.2 d, respectively. Hydrolysis of the fluorescein diacetate [3, 6-diacetylfluorescein (FDA)], used for measuring overall soil enzyme activities, indicated that total enzyme activities was slightly enhanced by 2% in soil sprayed with hot pepper extracts.

Keywords:

• Natural pesticides
• soil enzymes
• mass spectrometric analysis

Acknowledgments

The author acknowledges Dr. Robert Jarret (USDA/ Agricultureal Research Service) for his assistance in providing hot pepper seeds, and Mr. Hank Schweickart for preparing the field plots. This investigation was supported by a Capacity Building Grant No. 2012-02483 from USDA/National Institute of Food and Agriculture to Kentucky State University.