Key role of collagen fibers orientation in casing-meat adhesion

Meat adhesion of collagen casings is important for the quality of sausages. In view of the crucial role of surface morphology in material adhesion, we hypothesize that the fiber orientation of collagen casings controls the meat adhesion. To verify this hypothesis, the casing-meat adhesion of four manufactured collagen casings (MCCs) was examined by the visual observation and the peeling force detection. The corresponding fiber orientation was investigated by using scanning electric microscope (SEM) and tensile tests. The results showed that MCC1 and MCC2 which had narrower directionality peak (-20° to -40° and -20° to 40°, respectively) and higher axial (σ_a) to radial (σ_r) strength ratios (1.90±0.07 and 1.31±0.02, respectively) demonstrated lower peeling forces than MCC3 and MCC4, indicating that a more isotropic structure is advantageous to the casing-meat adhesion. Further detection of the radial and axial shrink (including free shrinkage (S_r, S_a) and shrink force (F_r, F_a)) and observation of the local meat-casing interfaces by hematoxylin and eosin (HE) staining showed that appropriate S_r (15%-20%) and F_r (0.2-0.4N) values at 80°C helped to make the sausage tight whereas high F_a (>0.7N) promoted the peeling off of the casings from meat. These results imply that an isotropic structure leads to balanced radial and axial shrink of MCCs, which may enhance the casing-meat adhesion. Overall, controlling a uniform fiber orientation should be an effective way to enhance the meat adhesion of collagen casings. Besides, shrinking properties should be efficient indicators for the meat adhesion of collagen casings.