Microwave-assisted solid-liquid extraction using propylene glycol as solvent in the recovery of bioactive compounds from umbu seeds

Umbu (Spondias tuberosa) is a Brazilian Caatinga native fruit that has an economic-social importance since its cultivation increases the income of the local population. Pulp is the main product of its agro-industrialization. However, depulping gives rise to about 25% of residue. It is known that fruit peels and seeds are composed of macro and micronutrients as well as bioactive compounds, becoming the use of umbu residue an opportunity to add value to the fruit agro-chain. As the recovery of bioactive compounds from umbu seeds has not yet been optimized, this work aimed to evaluate their recovery through a more sustainable approach, using propylene glycol as solvent in microwave-assisted solid-liquid extraction. For that, an experimental design varying the propylene glycol percentage (15-85%) and temperature (59-201 °C) was adopted. The power in the microwave device was automatically adjusted by the system in the range of 0–600 W to maintain the working temperature during extraction (10 min). The total phenolic compounds (TPC) and antioxidant capacity by DPPH• were evaluated as responses. The highest values were found at 201 °C and 50% propylene glycol (3242 mg AGE/100 g and 162 µmol Trolox/g for TPC and DPPH•, respectively). The values observed were, at least, 8 times higher than those obtained in the worst experimental condition (25% propylene glycol and 80 °C), showing that the independent variables had effect on the evaluated responses (p<0.05). All models were significant as the calculated F-values (36 and 295 for TPC and DPPH•, respectively) were higher than the listed F-value (F5,5=5.05) at α=0.05. No lack of fit was observed. Adjusted R² values of the models were higher than 0.95, accounting for, at least, 95% of data variability. Thus, microwave-assisted extraction employing propylene glycol as solvent can be a more sustainable way for the use umbu seeds.