Polyphenols are a result of alcoholic fermentation. They aren't there as much before fermentation. In fact, phenols and polyphenols contribute a lot to a good red wine's structure and complexity.
My first guess would be that fresh grape juice will not get the same result.
I concur in spite of current advertising campaigns.
However the potato chips being consumed while surfing FR is more delightful than a natural laxative as in grape juice.
Nature can be cruel.