Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/8/2005
Publication Date: 1/1/2006
Citation: Luthria, D.L., Mukhopadhyay, S. 2006. Influence of sample preparation on assay of phenolic acids from eggplant. Journal of Agricultural and Food Chemistry. 54:41-47. Interpretive Summary: This paper depicts the importance of sample preparation on analysis of phenolic compounds from food samples. Direct comparison of over ten extraction procedures or conditions was performed in our laboratory to show the importance and influence of sample preparation on assay of phenolic compounds. This is critical for accurate quantitation of total phenolic compounds and their antioxidant potentials present in various food matrices. This will enable researchers to accurately evaluate the role of phenolics phytonutrients in diet and health and establish appropriate dietary intakes and guidelines.
Technical Abstract: Sample preparation is often overlooked and is frequently considered as “means to an end”. This systematic study with a phenolic enriched substrate, eggplant (Solanum melongena L.), was undertaken to evaluate the substantial variations in the extraction techniques, solvents and parameters as described in the published literature. Direct comparison of over ten extraction procedures or conditions was performed in our laboratory to show the importance and influence of sample preparation on assay of phenolic compounds. Chlorogenic acid (CA) was the most abundant phenolic acid accounting for over 75% of the total phenolic acids content extracted from the eggplant sample. Optimum extraction of CA and total phenolics (TP) from Black Bell cultivar of eggplant were obtained when extractions were performed with mixture of MeOH:H2O at a ratio of 80:20 (% v/v) using pressurized liquid extractor (PLE) at 100 oC. The amount of CA and TP extracted from eggplant by the previously reported procedures using a wrist shaker, rotary shaker, stirring, sonication or reflux with different extraction solvents (acetone or varying composition of MeOH:H2O solvent mixtures) varied significantly between 5-95% as compared to PLE. The predominant phenolic acids in the free phenolic acid fraction of Black Beauty cultivar of eggplant were CA isomers. However, caffeic acid isomers were the major phenolic acids extracted from the base hydrolyzed fraction. The total amount of caffeic acid extracted from Italian Neon cultivar was more that twice as compared to other four eggplant cultivars (Orient Express, Calliope Zebra Stripe, Orient Charm Neon, and Black Beauty)