What is the enzyme that makes apples's pectin heat resistant? And can it be added to other fruits to achieve similar results?
I don't know for sure if it is the same enzyme naturally that naturally occurs in apples, but there is a commercial product called NovoShape that serves this purpose. It is a pectin esterase. You can find it in small quantities at Modernist Pantry: http://www.modernistpantry.com/novoshape.html