Hello,
I found the same thing with the fruits too! Ella loved all the veggies you mentioned to start, then I started with fruit and I got this face as if it was sour. I tasted the banana, peach, pear etc in a jar and I found it sour too! Try them, they have ascorbic acid in them to preserve them (lemon juice) thus they do taste sour a little and I am sure to there fresh new palates even more sour than we taste them. What I did was mash a normal banana and she LOVED it, she also now eats in a mesh feeder. Other than that, I just made my own pears and she seems to like them. I recently found an organic brand called Earth's Best that doesn't use ascorbic acid and she loves the apple/banana together, as well as plan apple. Maybe that is what your lo is experiencing or it just may be a face he likes to make to new tastes (since he ate half a jar)? Good luck with most taste testing!