Interactions between non-starter microorganisms during cheese manufacture and repening

Abstract

The prerequisites for any organism to be able to contribute to the secondary ripening processes in cheese are the availability of substrate(s), appropriate conditions for growth and enzyme activity (especially pH, salt concentration and temperature), and sufficient time to allow the biochemical reactions to take place. The role of deliberately added secondary microorganisms in the ripening of some varieties (e.g. the mould-ripened cheeses and the Emmental-type cheeses) is relatively clear. However, in many other varieties the contribution of secondary microorganisms to the development of cheese flavour during ripening remains a contentious topic. These secondary organisms may include both cultures added deliberately as adjuncts to blends of the primary acid-producing starter cultures and adventitious non-starter lactic acid bacteria (NSLAB) present as contaminants in the cheese. Results from a range of experimental cheeses made using defined-strain lactic starters together with the addition of a number of other cultures (leuconostocs, lactobacilli and pediococci) suggest that a range of interactions are possible between such added cultures and adventitious NSLAB during cheese ripening. Although these added cultures may contribute directly to flavour development in the cheese, their more important contribution may be indirect by inhibiting undesirable adventitious NSLAB responsible for off-flavour production. This inhibition may be direct, or indirect with the added cultures competing with the adventitious flora for a limited pool of substrates and growth factors present in the cheese. The key role of the pasteuriser in controlling entry of undesirable adventitious NSLAB into the commercial cheesemaking process is discussed, and the recommendation made for measuring pasteurisation efficiency by comparison of bacterial counts rather than reliance on the alkaline phosphatase test. As adventitious NSLAB are always likely to be able to gain access to the cheesemaking process in commercial factories, it is suggested that, as the interactions of the total microflora of cheese become better understood, the deliberate addition of selected ‘adjunct’ cultures along with the normal lactic starter may become a practical means of controlling cheese flavour development.