Polyphenol content and health benefits of raisins

The health benefits of grapes and wine have been studied and publicized extensively, but dried grapes (raisins, including “sultanas” and “currants”) have received comparatively little attention. The purpose of the review was to summarize the polyphenol, phenolic acid, and tannin (PPT) composition of raisins; predict the likely bioavailability of the component PPT; and summarize the results of human intervention studies involving raisins. The most abundant PPTs are the flavonols, quercetin and kaempferol, and the phenolic acids, caftaric and coutaric acid. On a wet weight basis, some PPTs, such as protocatechuic and oxidized cinnamic acids, are present at a higher level in raisins compared to grapes. In human intervention studies, raisins can lower the postprandial insulin response, modulate sugar absorption (glycemic index), affect certain oxidative biomarkers, and promote satiety via leptin and ghrelin. However, only limited numbers of studies have been performed, and it is not clear to what extent the PPT component is responsible for any effects. More research is required to establish the bioavailability and health effects of the PPT component of raisins, the effects of raisins on health biomarkers in vivo in humans, and how these effects compare to grapes and wine.