I need destructive testing methods (not necessarily) and devices information for determining the shelf life of fruits and vegetables based on their internal properties.
In order to study shelf life of different fruits and vegetables , we need different evaluation conditions , you will hardly find these details through one source. You will have to find information with particular fruit or vegetables. Shelf life of any fruit or vegetable depends upon the conditions under which they are evaluated.
I guess you are looking for basic fruit quality testing instruments, e.g., hand held digital refractometer (Atago), Penetrometer (firmness tester e.g., FR-5120, Lutron), color reader (CR 10 plus, Konica Minolta), pH, and EC meter (Hanna), The best way is to follow the Materials and Methods section of some selected papers of your interests, preferably of MDPI journals (Horticulturae, Agronomy, Agriculture), where details are provided. Then search for those instruments. Similarly, for biochemical analyses, you follow the papers and methods given therein.
Some of the device you need are available in the university. You can borrow. In other hand, for biochemical measurements you must act according to the protocols in the articls, specially.