Recent advances in cheese microbiology

Microorganisms are an essential component of all natural cheese varieties a nd play important roles during both cheese manufacture and ripening. They c an be divided into two main groups; starters and secondary flora. The start er flora, Lactococcus lactis. Streptococcus thermophilus, Lactobacillus hel veticus and Lactobacillus delbrueckii used either individually or in variou s combinations depending on the cheese variety, are responsible for acid de velopment during cheese production. Starters may be either blends of define d strains or, as in the case of many cheeses manufactured by traditional me thods, composed of undefined mixtures of strains which are either added at the beginning of manufacture or are naturally present in the cheese milk. D uring cheese ripening, the starter culture, along with the secondary flora promote a complex series of biochemical reactions which are vital for prope r development of both flavour and texture. The secondary flora is composed of complex mixtures of bacteria, yeasts and moulds, and is generally specif ically associated with particular cheese varieties. In many cheese varietie s, the action of the secondary flora contributes significantly to the speci fic characteristics of that particular variety. The secondary flora may be added in the form of defined cultures, but in many situations is composed o f adventitious microorganisms gaining access to the cheese either from ingr edients or the environment. During cheese manufacture and ripening, complex interactions occur between individual components of the cheese flora. Envi ronmental factors within the cheese also contribute to these interactions. Elucidation of such interactions would greatly add to our understanding of the cheese ripening process and would enable a more targeted approach to st arter/adjunct selection for cheese quality improvement. In the past, resear ch in this area was dependent on classical microbiological techniques, whic h are very time consuming, not suitable for handling large numbers of isola tes and generally not suitable to studies at sub species levels, However, d evelopments in this area have recently undergone a major revolution through the development of a range of molecular techniques, which enable rapid ide ntification of individual isolates to species and strain level. Application of such techniques to the study of cheese microbiology should lead to majo r advances in understanding this complex microbial ecosystem and its impact on cheese ripening and quality in the coming years. (C) 2001 Elsevier Scie nce Ltd. All rights reserved.