Assessment of polyphenol composition, antioxidant and antimicrobial properties of various extracts of Date Palm Pollen (DPP) from two Tunisian cultivars

Abstract

This study aimed to investigate and compare the total phenolic content (TPC) and total flavonoid content (TFC) and antioxidant and antibacterial activities of different extracts recovered from Date Palm Pollen collected from Tunisian cultivars of Kerkennah (DPP-K) and Tozeur (DPP-T) using various solvents, including hexane, chloroform, ethyl acetate, acetone, ethanol and water. The results revealed that DPP-T had higher TPC than DPP-K for all solvent extracts, except for hexane, with a value of 237.74 ± 9.58 mg GAE/g for the water extract. The highest level of TFC (75.10 ± 4.37 mg QE/g) was recorded in the acetone DPP-T extract, which was about twice as high as that of DPP-K. A total of eight phenolic compounds were identified and quantified in both extracts by HPLC, namely gallic acid, catechin, caffeic acid, epicatechin, vanillic acid, coumarin, quercitin and rutin. The antioxidant activities of the extracts were screened using DPPH and β-carotene bleaching assays. The results indicated that the DPP-T acetone extract showed the best DPPH scavenging activity (IC50 = 46.56 ± 0.28 μg/ml), with no activity being recorded for DPP-K. The DPP-T extract also showed significant effects in terms of the β-carotene test (28.12 ± 0.04 μg/ml) when compared to BHT as a reference standard. The extracts were screened for antimicrobial activity against 10 bacterial and 7 fungal strains, and the results showed that ethyl acetate DPP-K extract exhibited the strongest activity against Listeria monocytogenes and that the Staphylococcus aureus strain was most sensitive to DPP-T, with MIC and MBC values of 0.98 mg/ml and 1.95 mg/ml, respectively. Both DPP-T and DPP-K showed strong inhibition effects on the growth of oxysporum. Further time kill assays demonstrated the potency of DPP-K and DPP-T ethyl acetate extracts to inhibit the growth of L. monocytogenes and S. aureus, respectively. Overall, the findings suggest that DPP could be considered a promising source of new natural antioxidant and antimicrobial agents for use in various food and pharmaceutical products and formulations. This suggested that the DPP extract is a good potential inhibitor of food spoiling microbial growth and could be a highly effective therapeutic choice for human and plant infections. Keywords: Date Palm Pollen (DPP), Solvent extracts, HPLC, Antioxidant activity, Antimicrobial activity, Kill-time assay