Food Additive Lactic Acid Production by Immobilized Cells of Lactobacillus brevis on Delignified Cellulosic Material ORNEL ELEZI, ² YIANNIS KOURKOUTAS, ² ATHANASIOS A. KOUTINAS, ² MARIA KANELLAKI, ² EUGENIA BEZIRTZOGLOU, § Y. A. BARNETT, # AND POONAM NIGAM* ,# Food Biotechnology Group, Section of Analytical Environmental and Applied Chemistry, Department of Chemistry, University of Patras, GR-26500 Patras, Greece; Laboratory of Microbiology, School of Medicine, University of Ioannina, GR-45110, Greece; and School of Biomedical Sciences, Faculty of Life and Health Science, University of Ulster, Coleraine BT52 1SA, Northern Ireland, U.K. Improvements in yield and productivity in lactic acid fermentation by Lactobaccilus brevis cells immobilized on delignified cellulosic (DC) material are reported. The system proved to be more efficient in comparison with the work reported by other workers. Yields of 80 and 100% conversion using glucose were obtained at 30 °C in 1 day of fermentation time. Lactic acid fermentation using whey as substrate was obtained at 30 °C in 1-1.5 days, resulting in 70% yield, whereas the remaining lactose in whey was converted to alcohol byproduct, leading to a 90% lactose exploitation and 100% conversion. Cell immobilization of L. brevis on DC material was proved by its reuses in repeated batch fermentations and through electron microscopy. A series of 10 repeated batch fermentations without any loss in cell activity showed a tendency for high operational stability. The presence of DC material resulted in a drastic drop of the fermentation time from 48 to 13 h. KEYWORDS: Lactic acid production; Lactobacillus brevis; delignified cellulosics; whey fermentation INTRODUCTION Lactic acid is an important chemical used in a wide variety of applications, being used primarily in the food industry as an acidulant and preservative and for the production of emulsifying agents (1). Other applications of lactic acid are for cosmetics, pharmaceuticals, metal etching, and textile-finishing operations and as a precursor for biodegradable polylactic acid production. Lactic acid can be obtained by either chemical or biotech- nological means. The biotechnological procedures for lactic acid production are based on the bioconversion of sugar solutions by microorganisms. Recently, efforts have been made for lactic acid production using various sugar sources such as wood (2) and wheat straw hemicellulose hydrolysate (3). Given the low productivity of batch processes for lactic acid production, recent research has focused on increasing the cell concentration in the reactor. Cell immobilization is one of the most attractive methods in maintaining high cell concentration in the reactor. Production of lactic acid with immobilized cells on alginates has been reported (4-7), showing better results than with free cells. However, gels are considered to be inconvenient because they are chemically unstable and can easily be disrupted by lactate. The use of more stable supports such as porous foam glass particles (8), ceramic beads or porous glass (9), poraver beads (10), and gluten pellets (11) hardly offered a better alternative as they are relatively expensive materials. Even though cell immobilization results in increased productivity compared to free cells, the industrialization of immobilized cells has not been achieved. This can be attributed to the fact that industrialization needs a low cost, easily handled, food-grade purity support with high operational stability. Delignified cellulosic (DC) material has been proposed as an immobilization support of yeast strains for wine-making (12), low-temperature brewing (13), and continuous and high- temperature alcoholic fermentation of whey (14, 15). DC material is a support of food-grade purity, cheap, and abundant in nature, and the immobilization technique is simple and easy and showed high operational stability and a significant increase in productivity in alcohol production. Cell immobilization of Lactobacillus breVis on DC material was carried out to determine possible advantages on lactic acid productivity and yield, similar to those observed in the alcoholic fermentation (12-16), and to compare the results with those reported by other researchers. The strategy adopted was to use L. breVis immobilized on DC material in contrast to Lactoba- cillus casei immobilized on gluten pellets (11) and to examine the behavior of the biocatalyst during glucose initially and then lactose fermentation. Finally, the aim of this study was to proceed to fermentations using whey, knowing that it is a very polluting liquid of the dairy industry with negligible cost. Results concerning glucose fermentation could be useful for glucose- containing raw materials. * Corresponding author [e-mail P.Singh@ulster.ac.uk; telephone +44 (0)2870324053; fax +44 (0)2870 324965]. ² University of Patras. § University of Ioannina. # University of Ulster.