It can take 15-20 exposures before a child is ready to try a new food! Some kids need time to interact with foods in many different ways before deciding on putting in in their mouthes. If you were introduced a new food that you've never seen before you would probably appreciate being able to explore it as opposed to being pressured to put it straight in your mouth!
Remember interaction with a new food doesn't necessarily need to involve actually eating it. Every non pressure and positive exposure is a step in the right direction!
Have you tried any of these ideas?