Hydrolysis and acidogenic fermentation of a protein, gelatin, in an anaerobic continuous culture

Abstract

Model studies of anaerobic protein digestion were performed using gelatin dissolved in a mineral medium, which was fed to a mixed population of bacteria in a carbon-substrate limited chemostat culture. The dilution rate and culture pH value were varied progressively in order to determine the optimal conditions for hydrolysis and acidification (i.e., fatty acids formation). The optimum pH value appeared to be in the neutral region (pH>6.3), and the maximal dilution rate allowing steady state growth was 0.23 h-1. At this dilution rate and at pH 7 hydrolysis of gelatin was 78% complete, and 79% of the protein hydrolysed was fermented to identifiable products. At submaximal dilution rates both these values were higher. The main fermentation products were acetate, propionate, and valerate, and minor amounts of other volatile fatty acids. The product composition was relatively independent of the dilution rate, but varied substantially with the pH value.