Yield, Pesticide Residues and Bioactive Compounds in Flowers of Ugandan-Grown Arabica and Robusta Coffee

Abstract

Coffee flowers are byproducts of coffee cultivation that are gaining interest due to their various potential applications. However, little information existed on their safety and composition of bioactive compounds. This study evaluated the coffee flower yield per plant and pesticide application practices of coffee farmers (n=100) in Bulambuli (Arabica coffee) and Luwero (Robusta coffee) districts, Uganda. A cross sectional survey employing questionnaires was used to collect information from respondents. Samples of coffee flowers were then picked from selected farmers for laboratory analysis. Analysis for pesticide residues and bioactive compounds was done by a Gas Chromatography Mass Spectrometry (GCMS) and data were analysed using SPSS. It also studied pesticide residues in fresh Arabica and Robusta coffee flowers. Bioactive compounds were studied in fresh, air-dried and oven-dried Arabica and Robusta coffee flowers. The average coffee flower yield per tree was 350g. Pesticide application mainly targeted the entire coffee plant. The use of synthetic pesticides was more in Arabica coffee. Residues from the pesticides used were mevinphos, phorate, fonofos, parathion-methyl, parathion, triazophos, anthraquinone, allethrin-1, 2, resmethrin-1, phenothrin-1, deltamethrin-1, and piperonyl butoxide. Pesticide residue levels in the flowers varied significantly (p<0.05) with maturity stage, and coffee variety. Robusta coffee flowers had the highest level of anthraquinone (301.7±86.7μg/L) while Arabica coffee flowers had the highest level of mevinphos (137.4±56.5μg/L). Overall, Arabica coffee flowers of 6-10 years old retained more pesticide residues. The level of bioactive compounds varied significantly (p<0.05) with maturity stage, drying method, and coffee variety. The predominant bioactive compounds in Robusta coffee flowers were caffeine (689.3±104.1mg/100g), squalene (93.7±21.1mg/100g), and pentadecanoic acid (41.8±33.5mg/100g). In Arabica flowers, they were caffeine (346.1±150.0mg/100g), and n- hexadecanoic acid (142.4±34.3mg/100g). Retention of bioactive compounds was in the order; fresh, air-dried and oven-dried coffee flowers. Most coffee plants had a flower yield of 1 to 500g per plant in both Arabica and Robusta coffee plants. Bioactive compounds were higher in oven- dried Robusta and air-dried Arabica coffee flowers with maturity affecting their levels. Generally, pesticide usage was rampant indicating the need to educate coffee farmers on correct pesticide application.