ROMANO Nelson GastÓn
congresos y reuniones científicas
"Effect of ethanol pretreatment and fructo-oligosaccharides on the growth of bacterial strains isolated from agave must in a synthetic mezcal medium
Simposio; IVSimposio Internacional de Bacterias Lácticas (SIBAL). Alimentos, Salud y Aplicaciones; 2013
Institución organizadora:
Centro de Referencia para Lactobacilos (CERELA)
Mezcal, a traditional beverage from Mexico, is obtained by distillation of the fermented must obtained from the "cores" (leaf bases and stems) of Agave salmiana and Agave americana. Agave cores are rich in inulin, and after thermal hydrolysis and pressing they release a juice rich in fructose that is then fermented by many different micro-organisms present in the environment. Unlike tequila, the distillate of Agave tequilana fermented must, mezcal is mainly a homemade product. Therefore, the fermentation conditions and the use of starter microorganisms, among other aspects of the process, are mostly not controlled variables. Thus, the identification and characterization of the microorganisms involved in the fermentation and their growth properties are relevant to optimize the production process. Along the fermentation process, microorganisms have to overcome stress conditions such as low pH and increasing ethanol concentrations. Fructo-oligosaccharides (FOS) are widely known prebiotics and, due to their hydroxylated nature, may act as membrane protectants under such stress conditions. The CIDCA collection has more than 50 isolates of bacteria from mezcal must, and several of them are Gram (+), catalase (-) bacilli. In the present work we evaluated the ability of 9 of these isolates to grow in an artificial medium with a composition resembling that of the late fermented must (named SMM from synthetic mezcal medium), and the effect of acclimatization with ethanol and the FOS supplementation. To determine the ethanol tolerance the isolates were pretreated as follows: 1) shock: 30 min incubation at high ethanol concentrations (12 or 25 % v/v in saline solution), or 2) acclimatization: 48 h incubation in modified MRS with sub lethal ethanol concentrations (6 or 8 % v/v). In both cases, after treatment the cells were inoculated into SMM (ethanol 12 % v/v and pH 3.5). To analyze the protective effect of FOS, the synthetic mezcal medium was supplemented with increasing concentrations (0 to 5 % w/v) of FOS (Orafti p95). Growth kinetics at 30 °C were followed by recording the optical density values (OD) at 590 nm. The lag phase extension and the final OD of the cultures were considered as the response parameters. After a shock with 12 % v/v ethanol, the lag time and final OD did not change with respect to the control. No growth in SMM was detected for any of the isolates after the exposure to 25 % v/v ethanol for 30 min. The acclimatization with 6 or 8 % v/v ethanol increased the tolerance of some strains to the stress conditions in SMM, as shown by the shorter lag phases and higher final OD. The addition of FOS to the SMM positively affected bacterial growth, showing shorter lag phase and higher final OD than those observed in pretreated or untreated cells. This growth promoting effect was increased at higher FOS concentrations and might act in a synergistic way with the acclimatization.