tyramine production of the lactic acid bacteria Lactobacillus brevis CECT

1 2 A Central Composite Face design was used to study growth and tyramine production 3 by two strains of lactic acid bacteria, Lactobacillus brevis CECT 4669 and Enterococcus 4 faecium BIFI-58. The effects of five physicochemical factors (incubation temperature and 5 time, environmental pH, added tyrosine concentration, and pyridoxal-5-phosphate (PLP) 6 supplementation) on cell growth and tyramine production were analysed under aerobic or 7 anaerobic conditions. The parameters of the quadratic model, for each response variable, were 8 estimated by Multiple Linear Regression (MLR), and the statistical analysis of the results 9 allowed the elucidation of mathematical models capable of predicting the behaviour of the 10 responses as a function of the main variables involved in the process. Incubation time was 11 found to be the most important variable influencing growth in L. brevis while pH showed the 12 highest contribution in E. faecium. The production of tyramine was dependent on the added 13 tyrosine concentration and incubation time. The proposed MLR model predicted the optimum 14 conditions that gave maximum responses for L. brevis and E. faecium growth and tyramine 15 production. This model predicted in both strains that anaerobic condition at acidic pH (4.4) 16 favours tyramine production. Thus, a similar behavior was predicted for the two tyramine17 producing strains of lactic acid bacteria in relation to tyramine production. 18