Reference Number: 4
Health: Key Research Papers
Sourdough lactic acid bacteria were preliminarily screened for proteolytic activity by using a digest of albumin and globulin polypeptides as a substrate. Based on their hydrolysis profile patterns, Lactobacillus alimentarius 15M, Lactobacillus brevis 14G, Lactobacillus sanfranciscensis 7A, and Lactobacillus hilgardii 51B were selected and used in sourdough fermentation. A fractionated method of protein extraction and subsequent two-dimensional electrophoresis were used to estimate proteolysis in sourdoughs. Compared to a chemically acidified (pH 4.4) dough, 37 to 42 polypeptides, distributed over a wide range of pIs and molecular masses, were hydrolyzed by L. alimentarius 15M, L. brevis 14G, and L. sanfranciscensis 7A. Albumin, globulin, and gliadin fractions were hydrolyzed, while glutenins were not degraded. The concentrations of free amino acids, especially proline and glutamic and aspartic acids, also increased in sourdoughs.
Compared to the chemically acidified dough, proteolysis by lactobacilli positively influenced the softening of the dough during fermentation, as determined by rheological analyses. Enzyme preparations of the selected lactobacilli which contained proteinase or peptidase enzymes showed hydrolysis of the 31-43 fragment of A-gliadin, a toxic peptide for celiac patients. A toxic peptic-tryptic (PT) digest of gliadins was used for in vitro agglutination tests on K 562 (S) subclone cells of human myelagenous leukemia origin. The lowest concentration of PT digest that agglutinated 100% of the total cells was 0.218 g/liter. Hydrolysis of the PT digest by proteolytic enzymes of L. alimentarius 15M and L. brevis 14G completely prevented agglutination of the K 562 (S) cells by the PT digest at a concentration of 0.875 g/liter. Considerable inhibitory effects by other strains and at higher concentrations of the PT digest were also found. The mixture of peptides produced by enzyme preparations of selected lactobacilli showed a decreased agglutination of K 562 (S) cells with respect to the whole 31-43 fragment of A-gliadin.
Significance of the study to the baker
In this study, a lactic acid sourdough starter was shown to degrade gliadin-derived peptides, a protein known to trigger coeliac disease.
In those with celiac disease, gliadin-derived peptides found in gluten-containing foods stimulate an immune reaction. Over time, this can damage the villi in the small intestine leading to malabsorption and deficiencies. In this study, sourdough bread that was leavened with starters containing Lactobacillus alimentarius 15M, Lactobacillus brevis 14G, Lactobacillus sanfranciscensis 7A, and Lactobacillus hilgardii 51B were shown to degrade gliadin derived peptides. These activities could be easily improved under more suitable technological conditions and/or addressed to the production of special sourdough-type bread with low contents of gliadin toxic peptides.