Collagen is widely used in the food industry, e.g. in the manufacturing of coextruded sausage casings. The diverse functionalities of collagen depend on various factors including origin, collagen type, extraction, pH, and ionic strength. We hypothesized that the addition of acids may modify electrostatic molecular interactions, and affect key process parameters such as the critical overlap concentration (C*) and entanglement concentration (Ce), due to screening effects, interactions with corresponding bases, as well as modifications in collagen triple helices. Therefore, the aim of this study was to evaluate the impact of acids and pH on C* and Ce of telopeptide-poor collagen (TPC). Thus, dilute, semidilute and concentrated regimes of TPC in 0.1 N, 0.01 N, and 0.001 N acids (HCl, H2SO4, H3PO4, and HClO4) were assessed using dynamic rheometry to determine the intrinsic viscosity [η], C* and Ce .
The results showed that [η] of TPC increased with increasing pH independent of the acid applied, whereas C* and Ce decreased. The addition of 0.1 N HClO4 led to the highest C* and Ce, thus indicating the degradation of collagen fibrils due to strong oxidizing properties of HClO4. Besides, TPC diluted in H3PO4 and HClO4 exhibited the lowest C* and Ce followed by HCl and H2SO4. The results suggest a clear trend in enhanced entanglement when pH is adjusted closer to the isoelectric point (pI) of TPC (pI was measured as 4.9-5.1). Furthermore, C* and Ce showed that acid effects declined at pH closer to the pI. This suggests that pH plays a key role in entanglement rather than variations in ionic strength, or hydrophobic and hydration forces caused by the anions.
We demonstrated that collagen entanglement depends strongly on pH and acid type, thus highlighting the importance of the preparation step of collagen raw materials for subsequent processing that could offer new insights for food manufacturers.
Principal investigator: Prof. Dr. Jochen Weiss j.weiss@uni-hohenheim.de
