Microbial origin of non proteolytic aminoacyl derivatives in long ripened cheeses

Cheese ripening involves a complex series of biochemical events that contribute to the development of each cheese characteristic taste, aroma and texture. Proteolysis, which has been the subject of active research in the last decade, is the most complex of these biochemical events. However, also aminoacyl derivates of non-proteolytic origin (γ-glutamyl-amino acids and lactoyl-amino acids) with interesting sensory properties have been identified in cheeses. In the present work, an enzymatic activity producing γ-glutamyl-phenylalanine in Parmigiano-Reggiano water soluble extracts was observed. It was hypothesized that γ-glutamyl-amino acids and lactoyl-amino acids could be originated by enzymes of bacterial origin. In order to confirm this hypothesis, Lactobacillus helveticus and Lactobacillus rhamnosus were chosen as representative of starter and non starter microbiota of Parmigiano Reggiano cheese. They were used as model bacteria, in the presence of suitable precursors, to verify their ability to produce γ-glutamyl-phenylalanine and lactoyl-phenylalanine. The eventual abilities of these strains were tested both during growth and after cell lyses. While γ-glutamyl-phenylalanine was produced only by lysed cells, lactoyl-phenylalanine was produced either by growing or lysed cells in different amount depending on the species, the cells condition and the time of incubation.