ZS10 - Exposure "Locking"
Caveat: I have a ZS7, not a ZS10... but I think the hint below should be the same for both these cameras.
Also try this for obtaining AF Lock... but am not sure whether shooting in this scene mode will always be helpful.
Switch your ZS10 to Scene Mode 'Underwater'. Toggle the left navigation key on the rear of the camera switch AF Lock on and off. You can continue to change the EV independently.
There is no combined AF/AE Lock feature on my ZS7 available in any Scene Mode. Only the Scene Mode 'Underwater' has the AF Lock feature.
Hope this also helps you a bit with your query above.