Add a Levels layer, and immediately put it on "Luminosity" blend mode.
Hold down the Option key while dragging the white slider, until the background is almost all white (doesn't matter if there's still a bit of colour around the edges).
Paint black on the mask over the fruit. Be as accurate as possible, using this.
Add a white "Solid Color" layer, invert its mask to hide it, then paint it on over the edges where the background isn't quite white yet.