We had a cake which was made for our school opening and we need to find something to spray on to preserve the cake? For the future.  We called other cake shops but they didn't have anything we could how used. 
When I buy apples I also like to go for the most crispy ones.  To find these, what I do is I flick the apples with my finger and listen to the sound it makes. You will be looking for a clear, 'high pitch' sound. Try flicking different apples and you will notice the difference between the sounds. The ones that are more mushy make a soft, 'low pitch' sound. Hope this helps! 