I'm trying to make Turkish delight with apple juice concentrate and tapioca starch instead of refined sugar and cornstarch. However, I haven't been able to get the consistency for two times, it becomes more viscous and spreads. In fact, after adding tapioca starch, it thickens very quickly, at this stage I thought that I shouldn't cook for a long time as with cornstarch, because tapioca is more unstable to heat? What do you think, is there a way to get a stable Turkish delight by changing these two main ingredients?
The tapioca starch shouldn't be that much of a problem. It has a very slightly different texture than cornstarch, but it produces the same firmness. The end result is only slightly gummier, in many cases imperceptebly so.
What won't work is the apple juice concentrate. Turkish delight is a type of candy; it is made out of sugar. The apple juice has nowhere enough sugar for that, it is still mostly water (I found a nutrition facts label stating it only has 38 g of sugar per 100 g). And the sugar in it is not sucrose, but fructose, which has a different consistency. Worse yet, it may also contain other stuff such as pectin, which will further do weird things to the final texture. So that is a big no-no. Even if you were using pure refined fructose, you couldn't expect to substitute it for sucrose (table sugar) and get the same results.
So, in the end, you are quite free in your choice of starch, but the sugar has to stay, and in the exact amount as prescribed in the recipe, you cannot reduce it either. I cannot think of a product that will work well as a substitute. If the "white" sugar is what you object to, you could use brown sugar - the amount of molasses used to color it is so miniscule, it won't interfere with the candy-making process, beside giving you a bit of a discoloration.