Effects of extraction solvents on phenolic contents and antioxidant activities of Tunisian date varieties (Phoenix dactylifera L.)

Second-grade dates (Phoenix dactylifera L.), with hard texture, from six Tunisian cultivars were analysed for their composition and antioxidant activities. Results showed predominance of total sugars and a relatively low content of protein, fat and ash. On the other hand, optimisation of extraction of antioxidant was carried using five different solvents.The highest level of phenolic compounds for all dates varieties was found in the 70% acetone extract. This level ranged from 199.43 to 576.48 mg of GAE/100 g fresh weight. However, extraction into 50% methanol gave the highest antioxidant activity from 89.55 to 109.67 mg equivalents of ascorbic acid/g fresh weight. For both two solvents, Bejo exhibited the highest phenolic content and total antioxidant activity, while Baydh El Hamam presented the lowest. A positive linear correlation between total antioxidant activity and phenolic contents was observed (R2 = 0.83; R2 = 0.74 for acetone/H2O and methanol/H2O, respectively).The antioxidant activity of acetone/H2O and methanol/H2O extracts was carried using DPPH radical-scavenging activity and reducing power. These results showed that dates had strongly scavenging activity on DPPH reaching 90.12% in methanol/H2O from Deglet Nour. Whereas, acetone/H2O showed the best reducing power which Bejo was significantly higher than the other varieties.This study demonstrates the potential antioxidant activity with Tunisian date, that we can use these natural extracts as food additives in replacement of synthetic compounds.

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► We tested the antioxidant activity of Tunisian date by product using different solvents.
► 70% acetone was found to be the most efficient solvent for extracting phenolic compounds.
► 50% methanol gave the highest antioxidant activity.
► A strong correlation existed between antioxidant activity and phenolic compound.