Antimicrobial properties of date palm (phoenix dactylifera) seed extracts

Abstract

Twelve extracts from four solvents (ethanol, methanol, acetone and distilled water) and three varieties of date palm seeds (Deglet Nour, Biruni and Mixture) were tested in vitro for their antimicrobial activity against two Gram-positive (Staphylococcus aureus and Bacillus subtilis) and two Gram-negative (Escherichia coli, Pseudomonas aeruginosa) bacteria species to establish whether or not they have antimicrobial activity. The extraction conditions for phenolic compounds from the best date palm seed extract were then optimized, a maximum Inhibition zone of 21mm was obtained under the experimental conditions of extraction temperature 35°C, extraction time 23hrs, and agitation 191rpm and the optimized extract was examined for the presence of phenolic acids. The agar disc diffusion and microbroth dilution methods were used to determine the zone of inhibition between the edge of the filter paper and the edge of the inhibition area (IZ) and the minimum inhibitory concentration (MIC) respectively. Response surface methodology (RSM) was used to determine the optimal conditions for extraction of the best extract. The central composite design was used to investigate the effects of three independent variables (extraction temperature, extraction time and agitation speed) on the dependent variable (inhibition zone). Phenolic acids in the optimized extract were determined using high-performance liquid chromatography (HPLC). All the twelve extracts of date palm seeds inhibited all the test microorganisms with minimum inhibitory concentration ranging from 10 to 42mg/ml and with minimum bactericidal concentration ranging from 21 to 167mg/ml. Extraction temperature, agitation, and extraction time significantly affected total antimicrobial contents extracted from date seeds. The five phenolic acids tested for (2- hydroxyl cinnamic acid, vanillic acid, 4-hydroxyl benzoic, 4- hydroxyl cinamic acid and coumaric acid) were detected in the optimized ethanolic extract of Deglet Nour (best extract). These results afford ground informations for the potential use of the extracts of these date palm seeds in prevention of bacterial infections and as food additives to prevent growth of undesirable microorganisms. In vivo toxicity tests, identification of active antimicrobial compounds and effects on the shelf-life of food products are some topics for further research.