Full Length Research Paper

Production of freeze-dried lactic acid bacteria starter culture for cassava fermentation into gari

Amenan A. Yao¹*, Carine Dortu², Moutairou Egounlety³, Cristina Pinto⁴, Vinodh A. Edward⁴, Melanie Huch (née Kostinek)⁵, Charles M. A. P. Franz⁵, Willhelm Holzapfel ⁵, Samuel Mbugua⁶, Moses Mengu⁷ and Philippe Thonart^1,2

¹Wallon Center for Industrial Biology, University of Liège, Belgium.

²Bio-Industry Unit, Gembloux Agricultural University, Belgium.

³University of Bénin, Abomey-Calavi, Bénin.

⁴Council for Scientific and Industrial Research, CSIR Biosciences, South Africa.

⁵Max Rubner Institute for Nutrition, Germany.

⁶University of Nairobi, University Way, Kenya.

⁷Botswana Technology Center, Botswana.

*Corresponding author. E-mail: amenananastasie.yao@student.ulg.ac.be.  

Tel.: +3243662861. Fax: +3243662862.

Abbreviations: a_w, Water activity; CFU, colony forming unit; DW, dry cell weight; LAB, lactic acid bacteria; N_c, CFU/g DW before freeze-drying (at the end of centrifugation); N_0, CFU/g DW at the end of freeze-drying; N_Lf, proportion of viable cells before dehydration in glycerol solution; N_Li, proportion of viable cells after dehydration in glycerol solution; P, probability; DpH, Change in pH; DLA, Change in titratable acidity.

Accepted 1 June, 2009

   Abstract

Sixteen lactic acid bacteria, eight Lactobacillus plantarum, three L. pentosus, 2 Weissella paramesenteroides, two L. fermemtum and one Leuconostoc mesenteroides ssp. mesenteroides were previously isolated from cassava fermentation and selected on the basis of their biochemical properties with a view to selecting appropriate starter cultures during cassava fermentation for gari production. In this study, the potential of these pre-selected strains as suitable freeze-dried cultures was evaluated. Their ability to tolerate the freeze-drying process was assessed by dehydration in a glycerol solution of increasing concentration, followed by staining with two fluorescent markers: rhodamine 123 and propydium iodide. Twelve strains that recovered more than 50% of their population value after visualisation on an epi-fluorescent microscope were produced in a bioreactor and freeze-dried. The technological characteristics identified after the freeze-drying process, were a high cell concentration or high survival rate. The ability of the freeze-dried strains to recover their acidification activity was evaluated through the determination of the pH, titratable acidity (% lactic acid/g Dry Weight) and cell count over 24 h on MRS broth. Ultimately, the strains L. plantarum VE36, G2/25, L. fermentum G2/10 and W. paramesenteroides LC11 were selected to be developed as freeze-dried starter cultures for gari production.

Key words: Freeze-drying, gari, lactic acid bacteria, fermentation, starter culture, cassava, developing countries, fermented food.