Collagen arrangement and strength in sausage casings produced from natural intestines

Abstract

Natural sausage casings are made from the submucosa of intestines, a collagen-rich layer traditionally obtained from bovine, porcine and ovine sources. Collagen provides strength to animal tissues, in part due to the structural arrangement of the collagen fibrils. The collagen arrangement through the intestinal submucosa is not well characterised and the relationship of this structure with strength in not well understood. Synchrotron-based small angle X-ray scattering (SAXS) was used to determine the collage fibril orientation, orientation index (OI) and D-spacing of bovine, porcine and ovine sausage casings. Tear strength was measured both parallel and perpendicular to the length of the intestine. The D-spacing is similar (64.8–65.2 nm) in materials from all three species. The collagen fibrils are arranged in planar layers (OI = 0.86–0.91 measured with X-rays edge-on) and is similar in the three species. The fibril orientation is within 7° of the longitudinal direction of the intestine. OI measured normal to the surface is highest for bovine 0.49 (0.13), then porcine 0.35 (0.06) and ovine 0.33 (0.11). When normalized for thickness the tear strengths are similar for all species: bovine 8.8 (2.3) N/mm, porcine 6.4 (0.4) N/mm and ovine 8.3 (2.5) N/mm where the differences in absolute strength (bovine 4.1 (1.0) N, porcine 2.0 (0.3) N and ovine 1.0 (0.3) N) are due to differences in thickness. The material properties of the sausage casings from all three species is similar. This is a surprising finding since in other tissues (such as dermis of different animals, and pericardium of cattle of different ages) there are marked differences in the structural arrangement of collagen and these differences lead to fundamental differences in the mechanical properties of these materials. In summary, sausage casings from different species are structurally similar, other than thickness, and it is the thickness that is responsible for the different properties in use.