The shelf life of custard apple is very short and also it is very delicate. How can I keep it fresh for a longer time? Till now I have tried freezing it and also keeping it in a air tight box but they didn't work. Any better ideas?
In order to preserve your custard applies I would suggest canning them since you have already frezing it. It does lose it's freshness to an extent, however, the shelf life would last longer.
Canning is also a good method as is can use vacuum sealed packaging which restricts air into the packaging which is what causes micro-organism growth an multiplication.
You could try sous-vide, or fermenting it depending on what you plan to do with it ?