Enhanced NMR-based profiling of polyphenols in commercially available grape juices using solid-phase extraction.

Grapes and related products, such as juices, and in particular, their polyphenols, have previously been associated with many health benefits, such as protection against cardiovascular disease. Within grapes, a large range of structurally diverse polyphenols can be present, and their characterisation stands as a challenge. (1)H NMR spectroscopy in principle would provide a rapid, nondestructive and straightforward method for profiling of polyphenols. However, polyphenol profiling and identification in grape juices is hindered because of signals of prevailing carbohydrates causing spectral overlap and compromising dynamic range. This study describes the development of an extraction method prior to analysis using (1)H NMR spectroscopy, which can, potentially, significantly increase the number of detectable polyphenols and aid their identification, by reduction of signal overlap and selective removal of heavily dominating compounds such as sugars.

Nutrimetabolomics: development of a bio-identification toolbox to determine the bioactive compounds in grape juice.

BACKGROUND: Grape juice and related products have previously been associated with many health benefits, such as protection against cardiovascular disease. Current consensus is that the polyphenols are the likely bioactive species in these products. RESULTS: Extracts of commercially available grape juices exhibited biological antioxidant activities ranging from 19.30 to 3099.51 µM trolox equivalents, as determined by cell-based assay in which J774 macrophages were stimulated with lipopolysaccaride at a concentration of 100 µg/ml for 1 h. Partial least-squares regression was then used to determine covariance between the antioxidant activity and 400 MHz (1)H NMR spectral profiles using models with R(2)X and R(2)Y values of 0.64 and 0.95, respectively, using three latent variables: the Q(2)(cum) was 0.63. Hydroxycinnamic acids and their derivatives were identified as being the most positively correlated with the antioxidant activity. CONCLUSION: The work presented here describes a strategy for the bioinformatic linkage of plant metabolomic data with in vitro biological activity as an initial step towards determining structure-activity relationships.