With difficulty.  You definitely would need to extract it, given that berry by-products contain polyphenols that react posibively in the concentrated sulfuric acid assays such as mhdp that might be used for quantifgication of galacturonic acid, plus there are lots of sugars and hence another source of interference. and even after extraction, which is never quantitative, they will be risqks of interference by phenolics and neutral sugars.

See for example Kosmala M., Kołodziejczyk K. , Markowski J., Mieszczakowska M. , Ginies C. &  Renard C.M.G.C.: Co-products of black-currant and apple juice production: hydration properties and polysaccharide composition. LWT-Food Science and Technology 43 (2010) 173-180.

 Kosmala M., Kołodziejczyk K. , Markowski J., Mieszczakowska M. , Ginies C. &  Renard C.M.G.C. Cherry fruit and cherry pomaces - polysaccharide composition.Plant Foods for Human Nutrition 64 (2009) 279-285