Sunday, April 29, 2007

Sequential hydrolysis and fermentation of apple pomace to lactic acid

B. Gullón1, R. Yáńez2, J.L. Alonso1, and J.C. Parajó1. (1) Department of Chemical Engineering, Faculty of Science, University of Vigo, As Lagoas, Orense, 32004, Spain, (2) Department of Chemical Engineering, Faculty of Experimental Science, University of Huelva, Avda. de las Fuerzas Armadas s/n, Huelva, 21007, Spain

Lactic acid has a number of applications in food technology, pharmaceuticals and chemicals. The worldwide market growth is expected to be between 10 and 15% per year. Lactic acid is mainly produced by fermentation of enzymatic hydrolyzates from starch extracted from grain. Utilization of industry wastes residues, like apple pomace, as the substrate for fermentation of lactic acid makes the production process more attractive in both environmental preservation and production cost reduction.
Apple pomace is the main solid waste generated in cider and apple juice making factories, and it accounts for between 25-35% of the weight of the processed raw material. In Spain, the cider making industries produced more than 20000 metric tonnes of apple pomace in 2003.
In this work the potential of apple pomace as a source of sugars for fermentation was evaluated. The effect of the cellulase-to-solid ratio and the liquor-to-solid ratio on the kinetics of glucose and total monosaccharide generation was studied. When samples of apple pomace were subjected to enzymatic hydrolysis, the glucose and fructose present in the raw material as free monosaccharides were extracted at the beginning of the process. Using low cellulase and cellobiase charges (8.5 FPU/g and 5 IU/FPU, respectively), 79% of total glucan was saccharified after 12h, leading to solutions containing up to 43.8 g monosaccharides/L.
Liquors obtained under these conditions were used for fermentative lactic acid production with Lactobacillus rhamnosus CECT-288, leading to media containing up to 32.5 g/L of L-lactic acid after 6h (volumetric productivity = 5.41 g/Lh, product yield =0.88 g/g).