Valorization of three pecan nutshell cultivars by ultrasound assisted extraction of polyphenolic compounds and its potential free radical inhibition

Abstract

The present study was performed to identify the effects of ultrasound assisted extraction (UAE) conditions over total phenolic content, total flavonoid content, and antioxidant activity of pecan nutshell extracts of Western, Wichita, and Mahan cultivars. The analyzed UAE conditions were extraction time, amplitude, and sample-solvent ratio. Antioxidant activity was evaluated through ABTS, DPPH, and FRAP assays. Optimal extraction conditions were used to obtain an extract for the determination of medium inhibitory concentration (IC 50 ) and FTIR analysis. Results indicate that extraction time of 25 min favored the extraction of phenolic compounds and flavonoids; in addition, extract with an extraction time of 1 min exhibits antioxidant activity by ABTS, while extraction time of 5 min presents higher DPPH and FRAP activity. The highest concentration of phenolic compounds and flavonoids was obtained with a 50% amplitude. Antioxidant activity by ABTS was higher for an extract with 80% amplitude, while extract with 30% amplitude had higher antioxidant activity by DPPH and FRAP. Sample-solvent ratio of 1/50 had the highest content of phenolic compounds while flavonoid content was higher in the extract with a 1/30 sample-solvent ratio. Sample-solvent ratio using UAE did not have an effect over antioxidant activity by ABTS and DPPH; however, antioxidant activity by FRAP was increased by UAE were a 1/30 sample-solvent ratio exhibited the highest value. FTIR spectra suggests the presence of phenolic compounds, proteins, and polysaccharides; therefore, bioactive compounds can be recovered from pecan nutshell through ultrasound assisted extraction.