Rheological characterization of particulate collagen edible films

MARIEL L. OTTONE; MARTA B. PEIROTTI; JULIO A. DEIBER

Buenos Aires

Jornada; VI Jornadas Internacionales de Proteínas y Coloides Alimentarios JIPCA VI; 2011

UBA

    The production of edible collagen films is an important area of research and development with a strong impact on the food industry. For instance, these membranes may be used as casing tubes and films in the meat industry. Applications involve mainly wrapped foods for better commercial presentation, food maturation and preservation. In addition these films are biodegradable avoiding the environmental damage caused by synthetic polymers. The collagen films, as obtained from precursor collagen colloidal particle suspensions, must satisfy several quality requirements. In the present work a rheological characterization of collagen edible films is proposed through the experimental evaluation of shear elastic modulus, toughness, hydration capability, and stress and stretch ratio at fracture (Deiber et al., Food Hydrocolloids, 2011). These properties are obtained from hydration, simple extension and compression tests and analyzed through the BST hyperelastic rheological model (Blatz, Sharda & Tschoegl, J. Rheology, 1974). Film rheological properties are evaluated for different concentrations of collagen present in the precursor particle colloidal suspensions. Also the concentration of coagulating salt solution used to fix the collagen particles must be accounted. Furthermore, when covalent cross-links of the particulate matrix are introduced with this purpose, different concentrations of cross-linker agent affect the film final mechanical properties, and hence the determination of concentration optimal values is required. Here films are fixed through three different procedures: (a) coagulation of the casting film with a 60 % w/w aqueous saline mixture, (b) formation of covalent bonds in the particulate matrix with glutaraldehyde, and (c) combination of (a) and (b). Isochoric extension and compression tests for plasticized films are carried out in the characterization process to obtain, for instance, the film linear elastic module and toughness. The film swelling capability, when it is immersed in formulated aqueous solutions, is also evaluated and studied, which is one of the required information to visualize the specific functions of these edible materials.     The basic theoretical background and rheological model are presented in details to interpret appropriately the experimental data obtained from rheometric and swelling tests. Results indicate that these collagen films behave as colloidal particulate networks composed of both particles and clusters. The evaluation of the BST rheological parameters allows one the estimation of the energy amount required to get film fracture for different collagen and cross-linker concentrations. Since final films have to satisfy several quality requirements before using, the interplay between their stiffness and toughness is presented and discussed. A clear distinction between chain and particulate networks is also analyzed taking into account film rheological responses and the deformation mechanisms associated with their elastic matrixes in simple extension. Also aspects for future researches are provided concerning the microstructure of these edible collagen materials.