High resolution monochromated Electron Energy Loss Spectroscopy (EELS) at subnanometric spatial resolution and <200 meV energy resolution has been used to assess the valence band properties of a distributed Bragg reflector (DBR) multilayer heterostructure composed of InAlN lattice matched to GaN. This work thoroughly presents the collection of methods and computational tools put together for this task. Among these are zero-loss-peak subtraction and non-linear fitting tools, and theoretical modeling of the electron scattering distribution. EELS analysis allows to retrieve a great amount of information: Indium concentration in the InAlN layers is monitored through the local plasmon energy position, and calculated using a bowing parameter version of Vegard Law. Also a dielectric characterization of the InAlN and GaN layers has been performed through Kramers-Kronig analysis of the Valence-EELS data, allowing band gap energy to be measured and an insight on the polytypism of the GaN layers.