Changes in the resistance to simulated gastric digestion in probiotic bacteria during the shelf life.

LAFFERRIERE L; BURNS P; VINDEROLA G; REINHEIMER J

Tuicuman

Simposio; III Simposio Internacional de Bacterias Lácticas.; 2009

Cerela

The maintenance of cell viability of probiotic bacteria during the shelf life of the food product used as vehicle has been historically considered the parameter of choice to monitor the effectiveness of probiotic bacteria. Recent studies showed that many characteristics of interest in probiotic bacteria (gastric acid resistance (GAR), adhesion to the gut epithelium or the immunomodulating capacity) might change during the production of the probiotic culture or the fermented dairy product used as vehicle, without being reflected by changes in the cell viability. These changes might be influenced by the carbon source used and the moment at which cells are harvested during biomass production or the storage conditions. The aim of this work was to study the resistance to simulated gastric digestion in probiotic bacteria during the cold storage in milk. One commercial strain of L. acidophilus and 3 commercial strains of L. casei were used. Overnight cultures of each strain were washed in buffer and suspended in 10% skimmed milk at pH 6 or 4.5 (acidified with 85% lactic acid). Cell suspensions were maintained for 4 weeks at 5ºC or 12ºC (simulation of the temperature commonly found in open retail display cabinets in supermarkets). At time 0, 2 and 4 weeks, the GAR was assessed. For the determination of the GAR, cell suspensions in milk were mixed (1:1) with 2x saliva buffer + pepsin (containing electrolytes found in saliva and 0.6% pepsin). Cell suspensions were gradually acidified (HCl 5 or 1M) until pH 2.2 in 90 min. Cell counts were performed at time 0, 60, 70, 75, 80, 85 and 90 min in MRS agar. L. acidophilus showed a very high GAR in fresh cultures as well as in cultures maintained at 5º or 12ºC for 4 weeks (losts in cell viability < 0.5 log orders). On the contrary, L. casei strains showed a low RAG in the model used (losts in cell viability > 8 log orders after 90 min). However, during the cold storage, mainly at 12ºC, cells were able to multiply (almost 1 log order) and even a significant increase in the GAR was observed for 2 of the strains studied. This fact could be due to an induction of tolerance to a stress factor (gastric acidity) by a long exposure to sublethal levels of another stress factor (lactic acid), in a strain dependent way. These results evidence important differences in the GAR among strains. For certain strains, the functionality might change during the cold storage due to changes in cell numbers and in the GAR. Which other functional characteristics of the strains might also change without being noticed by cell counts? This is still an open question. The possible ocurrence of this phenomenum should be taken into account at the moment of stablishing the functionality of a probiotic strains in a given food matrix during the storage of the product until consumption. &amp;amp;amp;lt;!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman";} @page Section1 {size:595.3pt 841.9pt; margin:137.5pt 99.25pt 137.5pt 99.25pt; mso-header-margin:35.45pt; mso-footer-margin:35.45pt; mso-paper-source:0;} div.Section1 {page:Section1;} --&amp;amp;amp;gt;