The effects of solvents and extraction method on the phenolic contents and biological activities in vitro of Tunisian Quercus coccifera L. and Juniperus phoenicea L. fruit extracts

The effects of different extracting solvents, used in two extraction methods, on the total polyphenol contents of Quercus coccifera L. and Juniperus phoenicea L. fruits were studied. The antioxidant and antibacterial activities of these extracts were evaluated. Water and organic solvents, used individually, such as acetone and chloroform, or in mixtures: acetone/water/acetic acid (90/9.5/0.5) and ethyl acetate/methanol/water (60/30/10), significantly affected total polyphenol content. The antioxidant activity of these extracts was investigated by the widely used ABTS+ method and the β-carotene bleaching test. The results showed that solvents with different polarities had significant effects on antioxidant activity. A few of these extracts are as strong as some common synthetic antioxidants. Extracts were also tested for their antibacterial effects on spoilage and pathogenic bacteria. Results showed that acetone/water/acetic acid extracts exhibited the highest antibacterial activities against all tested germs. It is also noteworthy that the Gram-positive bacteria, Staphylococcus aureus ATCC 25923 and Enterococcus faecalis ATCC 29212, were inhibited more easily than were the Gram-negative ones. Since a strong correlation between polyphenol contents and biological activities was noted (correlation ranging between R2 = 0.76 and R2 = 0.84), we suggest the use of these extracts to prevent the deterioration of stored foods by bacteria, if any resulting organoleptic effects are acceptable.