Not just for beer: evaluation of spent hops (Humulus lupulus L.) as a source of eco-friendly repellents for insect pests of stored foods

Spent hops is a waste produced in large amount by the brewing industry. Rhyzopertha dominica and Sitophilus granarius are insects that cause important economic losses of stored foods. In this study, for the first time, spent hops has been evaluated as a source of essential oil (EO) and chemicals with repellent activity against R. dominica and S. granarius. Spent hops EO yield was 0.11 %. The terpenes myrcene, α-humulene, and β-caryophyllene were its main components (47 %). Spent hops EO RD₅₀ values were 0.01 and 0.19 μL cm⁻² for R. dominica and S. granarius, respectively. Among the chemicals, myrcene was able to exert the highest repellency against R. dominica (RD₅₀ = 0.27 µM cm⁻²), while limonene was the most effective compound against S. granarius (RD₅₀ = 0.89 µM cm⁻²). These results indicate spent hops as an excellent source of EO and chemicals to be utilized as low-cost, eco-friendly insect pests repellents in the protection of stored food.