The anthocyanin content of grapes, and the wines made from them, are believed to have several health benefits, including mopping up of harmful free radicals and as anti-inflammatory agents.
The research, published in the Journal of Agricultural and Food Chemistry (Vol. 54, pp. 5344-5349), reports that by spraying the grapes with an anti-bacterial agent called benzothiadiazole (BTH) leads to a tripling of the main anthocyanins in the grape, and offers a "simple way to increase the nutraceutical content".
BTH is not associated with any toxicological risk for humans. Indeed, it is recognized by the European Commission as fulfilling the safety requirements for plant protection products and has no reported harmful effects on human or animal health.
Moreover, the concentrations used in this study are similar to those used to protect tomato plants from bacterial disease, said the researchers from University of Milan and the Experimental Institute of Viticulture.
The scientists, led by Giancarlo Folco, sprayed vines (Vitis vinifera cv. Merlot) with a solution of BTH (0.3 millimoles) on the first, fourth and seventh day of the last week prior to harvest. The concentration was based on previous results from bean experiments.
After harvesting some grapes were subjected to a standard wine making process.
Using high-performance liquid chromatography (HPLC) the anthocyanin content of the grapes and the wine was assessed, and the researchers found that, compared to the control (unsprayed) grapes, the concentration of the five main anthocyanins: delphinidin; cyaniding, petunidin, peonidin, and malvidin, as well as there acetylated and para-coumaroyl derivatives, had more than tripled in the BTH sprayed grapes.
However, when the experimental wines (from BTH sprayed grapes) were tested, the concentrations were not significantly different from control wines.
Not content to have shown such an interesting result, the researchers continued to examine the effect of grape skin extracts, or wine solutions, on vasodilation of rabbit endothelium cells in vitro. Endothelium cells line the inner wall of blood cells and improve blood flows by expanding (dilating).
Dysfunction of endothelial cells is a major risk factor for a serious of cardiovascular diseases, including high blood pressure (hypertension), hardening of the arteries (atherosclerosis), heart attack and stroke.
The results showed that the extracts from the grape skins significantly improved the vasodilation in the rabbit aorta samples in a dose-dependent manner. No effect was observed for differing concentrations of the wine, compared to the control wine.
It should be stressed that the concentrations used in these tests were pharmacological and not nutraceutical.
"The vasodilation of the berry skin extracts reported clearly represent an effect observed at pharmacological concentrations, and any extrapolation to an actual nutraceutical value will require further in vivo studies," said the researchers.
The effect of the BTH on the anthocyanin concentration is proposed to be a response by the plant to the agent. Spraying the crop with BTH, said the researchers, triggers an inducible response from the plant to produce more anthocyanins, which help the plant's resistance to the chemical challenge.
The difference in results between the grapes and the wine, said the scientists, was due to changes in anthocyanin concentrations that occur as different compounds present in the wine react and change as the wine matures.
"In conclusion, we propose that plant (Vitis vinifera) treatment with the resistance activator BTH at preharvest may represent an interesting strategy to enrich the nutraceutical potential of grape," they said.