Antioxidants and biomethane production from Opuntia varieties

In this study, Opuntia varieties were investigated for their potential to fit a biore-finery approach. This work proposed the extraction of antioxidants and the production of biomethane from their solid effluents. Three Opuntia varieties –O. ficus-indica var. Milpa Alta (OfiM), O. ficus-indica var. Copena (OfiC) and O. engelmannii (Oe)– were subjected to solvent extraction. Our results revealed that 80% methanol yielded the highest amount of phenolic compounds (8.99 mg/g) and flavonoids (1.67 mg/g) in OfiM. Subsequently, biomethane potential experiments compared raw and residual biomasses, as well as inoculum-to-substrate ratio (ISR, 0.5, 1.5 and 2.5). Biomethane yields were lower with residual biomass compared to raw Opuntia. The highest biomethane yield of 552 mL CH4/g VS was achieved with raw OfiM at ISR 2.5. For the second assay of OfiM, biomethane yields were 412 and 458 mL CH4/g VS, respectively for residual and raw biomasses. Despite a decrease of approximately 10% in biomethane yield due to extraction operation, the coupling of both processes becomes highly desirable to obtain high-value extractable compounds and substantial biomethane production, which is a step towards the Opuntia biorefinery.