MIXED STARTER CULTURES FROM AUTOCHTHONOUS STRAINS IN FERMENTED MEAT PRODUCT MODEL SYSTEMS

N.Z. PALAVECINO; RIVAS, FRANCO P.; CASTRO M.; GARRO O.A.; VIGNOLO G.M.

S.M. de Tucumán

Simposio; IV Simposio Internacional de Bacterias Lácticas; 2013

CERELA-CONICET

The introduction of starter cultures designed using autochthonous microflora can enhance safety of fermented meat products while preserving their sensory qualities. The selection of potential starter strains is based on their technological and safety characteristics. Each of the strains of a mixed culture meant to be added to a meat product should be compatible. A first approach to this situation can be simulated in model systems where assessments compiled in vitro can be checked. Hence, the aim of this study was to evaluate the behavior of pre-selected autochthonous strains, as mixed cultures, in meat model systems. From a compatibility trial, carried out by means of the agar well diffusion method, comprising seven strains of Lactobacillus sakei and three strains of coagulase negative cocci (CNC) (Staphylococcus vitulus and two S. xylosus strains), two pairs of strains were selected. Culture A: L. sakei 487 and S. vitulinus; culture B: L.sakei 442 and S xylosus C8. The meat model contained: minced beef and pork meat (70:30), NaCl, milk powder, sugar, spices and KNO3. The ingredients were thoroughly mixed and placed in a beaker. The meat matrix was separated into three batches, which were then subdivided into six batches to create the corresponding duplicates. Batches A and B corresponded to the aforementioned mixed cultures and the third one corresponded to the control system, with the addition of sodium azide and no added cultures. The batches were incubated at 20°C and samples were withdrawn at the beginning of the trial, one and seven days after inoculation. Microbial counts were assessed on MRS agar and mannitol salt agar (AMS). Total protein content on sarcoplasmic fraction was determined by means of the bicinchoninic acid method and free aminoacid concentration was determined by the OPA method. pH measurements were also registered. Both mixed cultures adapted well to the meat environment; LAB final counts reached values of 8.6 and 8.8 log colony forming units per gram (cfu/g) and CNC final counts were 7.4 and 8.3 log (cfu/g)  in batch A and B, respectively. Regarding pH values, they diminished from 5.54 (initial time) to 4.66 (A) and 4.68 (B) at the end of the trial, while the control system did not show pH variations. Final pH values from both batches are similar to those found in local dry sausages at the end of the ripening stage. Total protein content reduction was 16% (control), 77.9% (A) and 78.4% (B) indicating a strong metabolic activity of both mixed cultures. Besides, the release of soluble aminoacids started being 0.98 mMl, showed a peak of 3.11 mM (A) and 2.43 mM (B) at 24 h, followed by a reduction (1.99 mM) in both batches. Protein fraction released at 24 h may have contributed to aminoacid supply for bacterial growth. The acidogenic capacity and the hydrolysis of meat proteins observed in batches A and B highlight the potential contribution of both mixed cultures to meat fermentation.