Comparison of phenolic composition in date (Phoenix dactylifera L.) flesh and seeds extracted by an ultrasonic-assisted and conventional method

Date palm (Phoenix dactylifera L.) is an important fruit of the Middle East and North Africa with a high content of phenolic compounds. This study applied ultrasonic-assisted and conventional methods to extract phenolic compounds from date flesh and seed. The efficacy of the extraction methods is compared in terms of quantity, content, and antioxidant capacity of phenolic compounds. The highest total phenolic content (TPC) was found in ultrasonic-assisted date seed samples extracted by ethanol (18.53 mg GAE/g). In contrast, the TPC content of conventionally extracted seed samples ranged from 1.30 to 14.46 mg GAE/g. The TPC and antioxidant capacity values of phenolic compounds extracted from date flesh samples were lower than those extracted from seed samples. Liquid chromatography electrospray ionization quadrupole time-of-flight mass spectrometry (LC-ESI-QTOF-MS/MS) was used to characterize phenolic compounds. A total of 47 different phenolic compounds were identified, including 21 phenolic acids, 21 flavonoids, and 5 other polyphenols. High-performance liquid chromatography equipped with a photodiode array detector (HPLC-PDA) was used to quantify the phenolic compounds in different date samples. The highest content was found in ultrasonic-assisted date seed samples extracted in methanol solvent. The extract also contained epicatechin (36.12 μg/g), coumaric acid (27.05 μg/g), p-hydroxybenzoic acid (21.03 μg/g), syringic acid (19.85 μg/g), and epicatechin gallate (11.67 μg/g). The results showed that ultrasonic-assisted extraction could significantly increase the quantities of functional components of the extracts obtained from fresh date fruit samples.