Characterization of red prickly pear peel (Opuntia ficus-indica L.) and its mucilage obtained by traditional and novel methodologies

Prickly pear is an exotic fruit with a high amount of peel (40-45%), which is generally discarded. However, this by-product may be a good source of bioactive compounds that could be obtained using different technologies. Thus, the objective of this research was to characterize the red prickly pear peel and its mucilage obtained by both magnetic stirring and power ultrasound using water as solvent. Magnetic stirring at different temperatures (30, 40 and 50 degrees C) and times (10, 20 and 30min) was applied as traditional extraction methodology. Power ultrasound at different amplitudes (30, 60 and 90%) and times (30, 60 and 90s) was used as novel extraction methodology. Proximate chemical composition, structural polysaccharides, bioactive compounds, antioxidant capacity and microstructure were evaluated in prickly pear peel and mucilages. The maximum yield obtained with magnetic stirring and ultrasound was 41.8 +/- 1.8% (40 degrees C for 10min) and 33.6 +/- 0.2% (30% of amplitude for 60s), respectively. The chemical analysis of mucilages showed that contains structural polysaccharides such as cellulose and lignin. Phenolic compounds (12.00-18.60mg GAE/g), betalains (1.12-1.48mg/g) and antioxidant capacity by DPPH (3.12-4.88mg GAE/g) and FRAP (28.45-30.08mg AAE/g) assays were higher in mucilage obtained by magnetic stirring. Microstructural analysis showed the formation of agglomerated fibrils in prickly pear peel and mucilage extracted by magnetic stirring, whereas mucilage obtained by ultrasound exhibited more organized fibrils.