Md Foods Amba

The surface of smear ripened cheese varieties, like the well known Tilsit, Danbo, Limburger, Appenzeller and other cheeses is smeared repeatedly with salt water containing microorganisms during the ripening period of several weeks. The surface microflora developing on the cheese surface is called 'Red-Smear' and is responsible for the typical red-brown color and the unique aroma of smear cheeses. Critical for the ripening process is the initial phase when the cheese surface is still bare and not covered by the appropriate microflora. Traditionally, growth is started with the help of mature cheeses which are smeared first (old-young smearing). Thus, all necessary microorganisms have been transferred to the smear tank when smearing of young cheeses is started. Disadvantage of this approach is that, if present, undesirable contaminants like the pathogenic Listeria monocytogenes will be spread to all cheeses via the smear machines. Therefore, ripening hygiene of these cheese varieties is widely criticized. Since the microbial ecology of the smear cheese surface is still not understood in detail, no surface starter culture is commercially available. A change to more hygienic ripening conditions in the cheese industry is therefore still not possible. The use of a defined surface starter will replace 'old-young' smearing and should minimize the risk of food poisoning by pathogenic bacteria like L. Monocytogenes. The aim of the project is to design a SURFACE starter culture consisting of a defined strain mix (bacteria and yeasts) which shows fast growth on cheese, as well as appropriate flavour and color production and can be used economically by cheese producers. Based on the expertise of the 6 participants, studies in the fields of determinative bacteriology, microbial ecology and physiology, as well as ripening biochemistry is proposed: (1 ) The project will start with the isolation and classification of new surface bacteria from commercial smear cheeses. (2) Suitable strains in various combinations will be screened for growth, aroma-1 and color development in model systems. Interactions between species will be studied for a better understanding of the ecology of the surface microflora of smear cheeses. (3) Starters will be produced from selected mixed cultures and experimental cheeses will be ripened on laboratory and pilot scale. (4) Several ripening indices of experimental cheese will be determined, such as protein degradation7 amino acids, and biogenic amines. Special emphasis will be put on the analysis of volatile flavour compounds which are responsible for the unique aroma of sme cheeses. (5) Enzyme activities important for ripening will be quantified, new enzymes not found in lactic acid bacteria will be purified.