Does Genistein remain in resonance stabilised form in physiological pH or acidic pH?
The first acid dissociation constant for genistein ($\mathrm{p}K_\mathrm{a1}$) is $6.51 \pm 0.20$ (Ref.1), mainly because of hydrogen bonding between $\ce{C_{(4)}}$ carbonyl oxygen and $\ce{C_{(5)}-OH}$, similar to that in acetylacetone (see the diagram):

Therefore, in physiological $\mathrm{pH}$ ($\mathrm{pH} \approx 7.3$) it should be partially ionized. If it is in acedic solution, $\ce{C_{(4)}}$ carbonyl oxygen would be partially or fully protonated based on the acid strength of the solution. Furthermore, the energy minimized three-dimensional structure of genistein shows the hydrogen bonding as depicted in following image (See Figure A; Ref.1):

References:

Yoshiyuki Mizushina, Kazuaki Shiomi, Isoko Kuriyama, Yoshihiro Takahashi, Hiromi Yoshida, “Inhibitory effects of a major soy isoflavone, genistein, on human DNA topoisomerase II activity and cancer cell proliferation,” International Journal of Oncology 2013, 43(6), 1117-1124 (https://doi.org/10.3892/ijo.2013.2032).