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Potential of cheese microorganisms ecosystems for the production of bioactive peptides, and effect of the dairy matrices in the survival of dairy microorganisms through digestion

Abstract : This thesis was realized to respond to two particular objectives a) to determine the presence of bioactive peptides with activities as antioxidants and inhibitors of the angiotensin converting enzyme (ACE) in Mexican cheeses; and b), to observe the effect of composition and structure of dairy matrices in survival of dairy microorganism through digestion. Two Mexican cheeses were analyzed separately: Cotija cheeses ripened 6 months; and Fresh goat cheese (unripened) produced from raw and pasteurized milk. Studied cheeses had important antioxidant activity that was higher in fractions with smaller peptides. Young Cotija cheese had similar values than Fresh goat cheese. But activity increased throughout ripening (because of the production of soluble peptides). Milk pasteurization (Fresh goat cheeses) did not affect the antioxidant activity. This activity was correlated with the hydrophilic peptides. Also, both cheeses possess ACE inhibitor activity that was higher in Fresh goat cheese than in young Cotija cheese. This inhibitor activity was more correlated with the hydrophobic peptides. Pasteurization of Fresh goat cheeses increased the production of hydrophobic peptides. The release of bioactive peptides in cheeses has always been considered as dependent of the proteolysis caused by cheese microbiota. Some of these microorganisms are capable to survive digestion. It has been hypothesized that the presence of a food matrix could enhance their resistance through digestion.We measured the viability of three dairy microorganisms; Streptococcus thermophilus, Brevibacterium aurantiacum and Hafnia alvei during (in vitro and in vivo) digestion. Microorganisms were included in liquid and gel dairy matrices with and without fat: Skim milk (SM), whole milk (WM), rennet gel of skim milk (GSM) and rennet gel of whole milk (GWM). In vitro digestion was carried on with a dynamic digester (DIDGI) that simulated the stomach, duodenum and small intestine. Parameters of digestion were the same for all the matrices tested. The degradation of the dairy matrices through in vitro digestion was analyzed by electrophoreses and GC-Mass. Confocal laser scanning microscopy (CLSM) was performed to observe matrix microstructure.During in vitro digestion, the microorganisms had different survival rates; S. thermophilus was highly sensitive to gastric stress, and was not found in the duodenal compartment. B. auranticum was moderately sensitive to gastric stress but resistant to duodenal stress. H. alvei was highly resistant to both stresses. Despite its buffer capacity, we did not observe any effect of the dairy matrices on microorganisms survival. CLSM images, probed the effect of low pH on microorganisms survival. However our in vivo analyses failed to confirm in vitro observations and tested microorganisms were not detected.
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Leticia Hernández Galán. Potential of cheese microorganisms ecosystems for the production of bioactive peptides, and effect of the dairy matrices in the survival of dairy microorganisms through digestion. Food engineering. Université Paris Saclay (COmUE); Instituto tecnólogico y de estudios superiores (Monterrey, Mexique), 2016. English. ⟨NNT : 2016SACLA015⟩. ⟨tel-02924690⟩

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