L-lactic acid production from apple pomace by sequential hydrolysis and fermentation.
The potential of apple pomace (a solid waste from cider and apple juice making factories) as a source of sugars and other compounds for fermentation was evaluated. The effect of the cellulase-to-solid ratio (CSR) and the liquor-to-solid ratio (LSR) on the kinetics of glucose and total monosaccharide generation was studied. Mathematical models suitable for reproducing and predicting the hydrolyzate composition were developed. 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-solid and 8.5 IU/g-solid, respectively), 79% of total glucan was saccharified after 12 h, leading to solutions containing up to 43.8 g monosaccharides/L (glucose, 22.8 g/L; fructose, 14.8 g/L; xylose+mannose+galactose, 2.5 g/L; arabinose+rhamnose, 2.8g/L). These results correspond to a monosaccharide/cellulase ratio of 0.06 g/FPU and to a volumetric productivity of 3.65 g of monosaccharides/L h. 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 6 h (volumetric productivity=5.41 g/L h, product yield=0.88 g/g).
Gullón
Beatriz
B
Department of Chemical Engineering, Faculty of Science, University of Vigo (Campus Ourense), As Lagoas, 32004, Ourense, Spain.
Yáñez
Remedios
R
Alonso
José Luis
JL
Parajó
J C
JC
D001628:Beverages; D002480:Cellulase / Q000378:metabolism; D005285:Fermentation; D005511:Food Handling; D006867:Hydrolases / Q000378:metabolism; D006868:Hydrolysis; D019344:Lactic Acid / Q000096:biosynthesis*; D027845:Malus / Q000737:chemistry* / Q000378:metabolism*; D010936:Plant Extracts / Q000032:analysis
D010936:Plant Extracts; D019344:Lactic Acid; D006867:Hydrolases; D002480:Cellulase