Protein hydrolysate from organic fraction of municipal solid waste compost as nitrogen source to produce lactic acid by Lactobacillus fermentum ATCC 9338 and Lactobacillus plantarum NCIMB 8826

In this work a strategy for obtaining free amino-acids concentrate from an organic fraction of municipal solid waste compost and its use as a nitrogen source for lactic acid production, a compound widely used in different industries, using L. fermentum ATCC 9338 and L. plantarum NCIMB 8826 strains is described. Enzymatic digestion is based on the combined action of endoprotease Alcalase 1.5 MG and exoprotease Flavourzyme 500 MG. The highest degree of hydrolysis obtained under the optimal conditions was 41%. The use of glucanase Viscozyme L prior to protein hydrolysis helped to reduce the viscosity of the solution and promote the action of proteases, increasing its hydrolysis degree by 76%. The hydrolysate contained all 21 amino-acids, making it ideal for lactic acid bacteria growth. During shake flask cultivations the culture media was complemented with glucose as carbon source. Finally, with the hydrolysate, a maximum lactic acid concentration of 9.0 ± 0.2 g·L⁻¹ and 11.1 ± 0.1 g·L⁻¹ for L. fermentum ATCC 9338 and L. plantarum NCIMB 8826 respectively was obtained after 27 h. The innovation of the approach lies in exploiting the overproduction of compost for the production of lactic acid.