Role of Streptococcus thermophilus PRI60 in histamine accumulation in cheese

The contribution of Streptococcus thermophilus to histamine formation during cheese ripening was evaluated. Cheeses were produced using, as starter cultures, histamine-producing or non-producing S. thermophilus strains (PRI60 and PRI40, respectively), in combination with a decarboxylase-negative Lactobacillus helveticus strain. Cheeses inoculated with the strain PRI40 and with cell-free extracts of PRI60 added were also produced. The different combinations of starter cultures were responsible for different proteolytic patterns as demonstrated by the behaviour of water-soluble, trichloroacetic soluble, and phosphotungstic acid soluble nitrogen. A single histaminogenic strain, present during fermentation and ripening, also in the form of a cell lysate, produced histamine up to 180 mg/kg in cheese. Histamine was found at a higher level in cheeses manufactured with PRI60 starter, but was also detected in cheese containing the cell-free HdcA enzyme. The problem of histamine formation by S. thermophilus in artisanal cheeses must not be overlooked, especially during typical production practices.