Profiling of phenolics in cashew nut (Anacardium occidentale L.) testa and evaluation of their antioxidant and antimicrobial properties

Abstract

Most of agricultural by-products are rich sources of bioactive compounds. The present study deals with profiling phenolic compounds from various phenolic fractions of cashew nut (Anacardium occidentale L.) testa. The antioxidant and antimicrobial properties of phenolic fractions (free, esterified and bound) were also evaluated. About 20, 5 and 7 phenolic compounds were identified from free, esterified, and bound phenolic fractions, respectively. UPLC-HRMS/MS analyses of phenolic fractions revealed that condensed tannins and flavanols are the primary testa polyphenols. (+)-catechin, (−)-epicatechin, epicatechin gallate and procyanidins were identified in all the fractions. Most of the phenolic compounds were concentrated in the free form (62.5%), followed by the bound (21.8%) and esterified fractions (15.62%). The free phenolic fraction (FPF) showed the highest total polyphenol and flavonoid content. The FPF showed the highest radical scavenging activity (FPF IC50 12.35 ± 1.48 μg/ml (DPPH assay), 33.77 ± 1.04 μg/ml (ABTS assay) and 62.89 ± 2.1 μmol of Fe2+ equivalent per gram of cashew nut testa (FRAP assay)). The antimicrobial activities of phenolic fractions were tested against food-borne pathogens such as Staphylococcus aureus FRI722, Escherichia coli EFR02, Micrococcus luteus ATCC 9341 and Bacillus cereus ATCC 11778. All the phenolic fractions possess antimicrobial activity; the FPF has shown a maximum zone of inhibition at a lower concentration of 3 mg/ml. The antioxidant and antimicrobial activities of the testa were strongly influenced by its total phenolic and flavonoid contents. In conclusion, cashew nut testa is a suitable source to extract phenolic compounds with strong antioxidant and antimicrobial properties.