End of Project Report The objectives of this project were to isolate and identify the non-starter lactobacilli in mature Cheddar cheese, identify strains which impart mature flavours to cheese and determine their role in developing cheese flavour. The main conclusions were as follows: Based on an analysis of 18 mature Cheddar cheeses, selected from 7 commercial manufacturers, non-starter lactic acid bacteria typically numbered, as expected, 106-108 per gram and were dominated (97 percent) by Lactobacillus paracasei. Although a small number of strains (typically 1 to 4) was found in each cheese there was considerable strain diversity in cheeses within as well as between manufacturing plants. When selected strains were investigated for survival and flavour enhancement when added (as starter adjuncts) with the normal starter cultures in Cheddar cheese manufacture, it was found that they remained dominant for up to 3 months of ripening. Commercial grading of these cheeses at 3 and 6 months confirmed that the added strains did modify flavour development and one (DPC 4103), in particular, had a beneficial effect. It was confirmed that two selected strains of non-starter lactobacilli were capable of metabolising citrate under the conditions of Cheddar cheese ripening and, consequently, if present in sufficient numbers, would influence flavour development. The work was greatly facilitated by the successful and novel adaptation of a modern rapid molecular technique (RAPD) for species and strain classification. In summary these studies found that one species of lactobacilli (Lb. paracasei) was the dominant non-starter lactic acid bacteria in mature Cheddar cheese. Although a wide variety of strains were identified, only a few were found in any particular cheese, suggesting their likely role in cheese flavour diversity even within the same manufacturing plant. This suggests the potential for flavour control or enhancement through the selective and controlled use of non-starter lactic acid bacteria. Preliminary investigations of the metabolism of those organisms supports this view and a follow-up study now in progress should provide greater clarity on this matter. Department of Agriculture, Food and the Marine