The phenolic groups in red grape juice are mainly Anthocyanins, marked with 1 in the table:
http://jn.nutrition.org/content/136/...expansion.html
Adding up,the total Anthocyanin concentration is 0.234 m-mol/L,for MW=450 this is 0.105g/L
For comparison the concentration of pyrogallol in 1:100 PMK Pyro is 0.5g/L
The Anthocyanins are subject to hydrolysis at high pH:
http://www.demochem.de/p26_anth-e.htm

GJ-1
Red Grape Juice pH 3.7....................600ml
Sodium Hydroxide...............................3g
Phenidone......................................... 0.2g
pH =10.9

HP5 at EI=200 was developed in GJ-1 60min 20C, ag 10s every 2min.
The negatives were underdeveloped but printable.
One negative was bleached in 100g/L ferricyanide+bromide and fixed.
A very faint relief image caused by the tanning of the gelatin by Anthocyanin or derivatives is shown in the attachment.(It is possible to provide a much better image from unbleached negative).
Anthocyanins are present at low concentration and may be hydrolysed but produce detectable tanning.
Other red/purple berries contain Anthocyanins, as a curiosity it may be possible to make staining developers from them.
Thanks for comment.