Leuconostoc IN FOOD INDUSTRY: PERFORMANCE AGAINST TECHNOLOGICAL STRESS CONDITIONS

D'ANGELO, L. ; GUGLIELMOTTI, D. M.; MERCANTI, D.J.; QUIBERON, A.; SUÁREZ, V. B.

San Miguel de Tucumán

Simposio; V International Symposium on Lactic Acid Bacteria; 2016

CERELA - CONICET

Leuconostoc is a lactic acid bacteria (LAB) used as starter in several fermentative food processes, being also present in traditional cheeses as autochthonous non-starter lactic acid bacteria (NSLAB). High intrinsic capacity of strains to survive and grow in adverse technological conditions (during storage or fermentative process) is essential to assure high number of viable cells and adequate performance during fermentation. On the other hand, cells subjected to sub-lethal stress conditions (adaptation) could improve their resistance to the specific factor of adaptation and/or to other stress factors. In a previous work, 12 out of 29 strains, which showed good resistance against thermal, acidic, alkaline, osmotic and oxidative shocks, were selected for this study. Growth performance of these strains was evaluated in diverse stress conditions: i) MRS broth, 24 h ? 30º C (control); ii) MRS broth at pH 5.0 and 5.5, incubating at 30º C - 24 h (acidic stress); iii) MRS broth at pH 8, incubating at 30º C - 24 h (alkaline stress); iv) MRS broth added of NaCl 4 % (w/v), incubating at 30º C - 24 h (osmotic stress) and v) MRS broth incubating at 10º C - 24 and 48 h (cold stress). Growth rates (GR, %) defined as O.D.s / O.D.c x 100 (O.D.s= optical density of strain under stress condition and O.D.c= optical density of control cells, both measured at the end of the experience), were calculated. Six (6) strains, (Ln N6, Ln N19, Ln N12, Ln D2, Ln D11 and Ln MB7 in decreasing order) showed the better average growth rate values. Thermal adaptation (40º C ? 30 min, MRS broth) on four (4) out of these six (6) strains (Ln N19, Ln N12, Ln D2 and Ln D11) was performed. After heat adaptation, cells were subjected to thermal (55º C ? 15 min), acidic (pH 4, 30 min - 30º C) and oxidative (H2O2 0.3 % (p/v), 30 min - 30º C) shock conditions. Afterwards, new GR (%) under the stress conditions previously described, were calculated. Strains Ln N12, Ln D2 and Ln D11 improved their shock resistance in 1.43 - 1.84 (thermal) and 2.79 - 4.85 (acidic) log orders, while no changes were observed for Ln N19. Regarding oxidative shock, all strains diminished their resistance between 1.30 and 3.05 log orders. Growth rate values (%) increased for all strains with thermal adaptation, with variable values according to the strain and the stress factor considered (between 3.17 % and 53.2 %). In general, strain Ln N19 showed the highest increases in GR values after adaptation. Based on these results, Ln N6 (Leuconostoc lactis) and Ln N12 (Leuconostoc mesenteroides) were selected as the most suitable strains to resist conservation processes and growth technological stress conditions commonly applied in the fermentative food industry.