The final properties of biopolymeric materials are directly related to the structure of the biopolymer at mirco- or nanoscale. With this regard, the extent of the cross-linking in biopolymers can be controlled by the type of cross-linker but also by the conditions used during the preparation of biocomposites. In this work, the reaction between gelatin and lactose was analyzed as a function of lactose content and both processing methods and conditions. It was observed that soluble films can be prepared at acidic pHs, when the extent of cross-linking was lower, as shown by colour and UV-vis spectroscopy measurements, indicating the inhibition of cross-linking when pentosidine, a soluble compound, was formed. These results highlight the potential use of these films as active films in contact with gastrointestinal fluids, in which the pH is acid. In contrast, cross-linking reaction progressed at higher pHs, resulting in films with high UV-vis protection and tensile strength higher than 50 MPa, which could be used as packaging films. In all cases, the lactose-modified materials were transparent and hydrophobic, functional properties required for many applications.