Phenolic enriched extracts obtained from commercial vegetable residues: optimized extraction, chemometrics and metabolomic screening

Vegetable residues are rich in phenolic compounds (PC), widely recognized for their health-promoting and technological properties especially as antioxidants. Phenolic-enriched extracts were obtained from vegetable residues applying ultrasound and optimized hydroalcoholic mixtures. The weight and volume of residues generated after food preparation in two food service units in Rio de Janeiro was registered during 20 days. The most discarded residues were selected: chard, papaya (seeds and peduncle), carrot and chayote. The extraction was optimized by applying simplex-centroid experimental design for mixtures (water and ethanol, 5 conditions 0-100%) and ultrasound probe (0, 5, 30, 60 min), using Folin-Ciocalteu and DPPH analysis as dependent variables. The optimized extracts were further characterized by FRAP and ORAC. Phenolic profiling was determined by UPLC-MSE and evaluated by PCA and OPLS-DA analysis. Ultrasound applied for 30 min was the most efficient method to extract antioxidant compounds, using 100% water (chard and chayote), 75% (papaya peduncle) and 50% (papaya seeds and carrot peels). As time of ultrasound extraction increased, the solvent diffused deeper into the matrixes, increasing the mass transfer to the solvent. However, an additional time (60 min) leads to a decrease of antioxidant activities. Carrot peels presented the highest antioxidant activity, followed by papaya peduncle and seeds. Globally, 154 PC were identified and relatively quantified in all samples, including isomers. Flavonoid was the most abundant class except for carrot peels were phenolic acids prevailed. Quercetin 3-O-glucuronide, 1,5-dicaffeoylquinic acid, chlorogenic, sinapic and 3-feruloylquinic acids were the most abundant PC. Ultrasound did not promote the extraction of unique PC, but the abundance was significantly increased, such as sinapic acid and esculin (12 folds). From the OPLS-DA model was possible to indicate 12 discriminant PC. The extracts showed a rich composition in bioactive compounds and can be effectively applied as natural additives or ingredients for functional foods.