Bound phenolic acids present in fruit requires extreme conditions in vitro to release them from a complex matrix. How does human physiology release and make them available for biological functions?
Do you mean phenolic acids like ferulic acid, bound by an ester-bond to either arabinogalactans of pectins or xylans? Actually, it is very rare in fruits, being mostly present in Cereals (bound to xylans) and Chenopodiaceae (sugar beet etc, bound to pectin); the mechanism for its bioavailability is likely to be linked to colonic degradation of the fibers of which it is an integral component, I saw recently: DOI: 10.1186/1743-7075-11-1 and DOI: 10.1021/jf4001814 on phenolics from wheat bran.
The "normal" phenolic acids, present in the vacuoles of the cells, are actually very easy to extract (just press, you'll get almost quantitative transfert to the juice provided you avoid oxidation), see for apple juice Food Chemistry 124 (2011) 117-125