Objective
Fermentation of milk by lactic acid bacteria is essential for the production of cheese, yoghurt and other dairy products. The degradation of milk proteins during milk fermentations is catalysed by many different enzymes which together form the proteolytic system. The activity of this proteolytic system determines the rate and extent of the fermentation process and plays a crucial role in the development of the rheological and organoleptic properties of the final product. The components of the proteolytic systems of Lactococcus lactis, Lactobacilllus helveticus and Lactobacillus delbrückii have been studied in detail both at the biochemical and the genetic level. In this project various complementary approaches will be used to genetically modify the proteolytic properties of L.lactis. Strains will be constructed in which (i) the activity, specificity and/or stability of the proteinases PrtP has been engineered; (ii) the peptide transport activity and specificity has been engineered; (iii) the activity of one or multiple peptidases has been affected either by gene deletion or overexpression; the genes encoding 8 unique peptidases of L.lactis and at least 5 other unique enzymes from the lactobacillus species are available for these studies; (iv) combinations of these enzymes are affected. Food-grade cloning techniques, based on self-cloning, will be used to genetically engineer L.lactis which will allow the evaluation of the modified strains in cheese trials. The breakdown of caseins by these modified strains will be followed in detail by on-line HPLC-ion mass spray spectrometry measurements, which will reveal bottlenecks in the proteolytic pathway and identify the relative importance of specific peptides as nitrogen sources for the organism and/or sources of flavour compounds.
Finally, the complex (coordinated) regulation of expression of the components of the proteolytic pathway will be studied by fusing expression signals to genes encoding specific reporter proteins, and by analysing proteolysis in the cheese matrix directly with specific enzyme assays. Following the construction of the first generation of modified L.lactis strains, and their biochemical characterization, cheese slurry experiments and small scale cheese trials will be carried out with single and mixed starter cultures. The proteolysis in the cheeses will be evaluated by official cheese examiners. Based on the outcome of these studies new (second generation) strains will be constructed and selected strains (with desirable properties) will be tested further in large scale cheese trials.
Fields of science (EuroSciVoc)
CORDIS classifies projects with EuroSciVoc, a multilingual taxonomy of fields of science, through a semi-automatic process based on NLP techniques.
CORDIS classifies projects with EuroSciVoc, a multilingual taxonomy of fields of science, through a semi-automatic process based on NLP techniques.
- natural scienceschemical sciencesorganic chemistryorganic acids
- natural sciencesbiological sciencesmicrobiologybacteriology
- agricultural sciencesanimal and dairy sciencedairy
- natural sciencesbiological sciencesbiochemistrybiomoleculesproteinsenzymes
- engineering and technologyindustrial biotechnologybioprocessing technologiesfermentation
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Topic(s)
Call for proposal
Data not availableFunding Scheme
CSC - Cost-sharing contractsCoordinator
9751 NN HAREN GN
Netherlands