Effects of Alkali and Acid on the Solubility and Molecular Weight of Collagen Hydrolysates Extracted from Bovine Hide

Abstract

Preparation of collagen hydrolysates with high molecular weight to meet its industrial demand is a crucial step for resource utilization of solid waste of animal skins/hides. However, it is very difficult to achieve both higher molecular weight and solubility of collagen hydrolysates through the traditional methods. In this study, we attempted to prepare bovine hide collagen hydrolysates with high molecular weight and solubility through the application of NaOH or different types of acid. Influences of the concentration of alkali and acid, hydrolysis temperature and time on the molecular weight and solubility were studied, respectively. The results showed that NaOH has a strong hydrolysis effect on bovine collagen, making it a suitable candidate for the preparation of collagen hydrolysates with medium or low molecular weight. Under these optimized NaOH treatment conditions, i.e., NaOH concentration of 0.13 mol/L, hydrolysis temperature of 60 - 70°C and time of 5 h, we achieved 96% of solubility for hide pieces and the molecular weight of collagen hydrolysates were in the range of 25 - 30 kDa. By contrast, the molecular weight of the hydrolysates prepared through H2SO4 hydrolysis method was higher than that of NaOH hydrolysis method. Under the optimized H2SO4 treatment conditions, i.e. H2SO4 concentration of 0.5 mol/L, hydrolysis temperature of 50°C and time in the range of 5 - 7 h, the solubility of hide pieces reached up to 80 - 97%. Additionally, in the H2SO4 hydrolysates, the proportion of macromolecular components with molecular weight of about 100 kDa was 41 - 55% and that of medium molecular components with molecular weight of about 20 kDa was 45 - 59%. This study showed that high solubility and high molecular weight collagen products can be obtained by H2SO4hydrolysis under specific conditions. Thus, this study provided a useful scientific method and process parameters to guide the controlling of molecular weight and the industrial application of collagen from waste on a bigger scale.