Write out the equation C = m/V, where m is the mass of the solute and V is the total volume of the solution. Plug in the values you found for the mass and volume, and divide them to find the concentration of your solution.

Your question is tricky because you started the work without knowing the concentration of your extract. You can not say your conc. is 50g/100mL or 0.5g/mL because 50g of dry fruit waste did not completely dissolve in 100mL of solvent and of course can not determine MIC if you do not have knowledge on the conc. of the starting material.

My humble advise is "re-do the assay, but this time after drying the fruit waste, grind and macerate (at least 48hours). Then filter and concentrate using rotary evaporation to obtain an extract prepared from fruit waste". From where you can prepare a 25mg/mL stock from which you can prepare you test concentrations.

Good luck..

As you did the work without knowing the concentration, ethically its better to do the extraction again and know your concentration first..

https://doi.org/10.3390/molecules26195918

https://doi.org/10.1016/j.foodchem.2009.07.019

https://doi.org/10.1016/j.jep.2017.04.003

https://doi.org/10.1080/10942912.2010.526274