Histamine and histamine-producing bacteria in retail Swiss and low-salt cheeses

Abstract

Seventeen low-sodium and low-salt cheeses and 50 Swiss cheeses were surveyed for histamine and histamine-producing organisms. Two of the low-salt cheeses and nine of the Swiss cheese samples contained greater than 45 mg histamine per 100 g of cheese, as determined by the AOAC method. Over 800 total colonies were randomly chosen and screened for histamine production by the leucocrystal violet detection method following their initial isolation from MRS media. However, none of the leucocrystal violet-positive isolates from the low-salt cheese and only five from the Swiss cheese were found to produce histamine in MRS broth supplemented with L-histidine. Proteolysis (determined by the trinitrobenzene-sulfonic acid assay) was also measured in the low-salt cheeses in an attempt to further understand the role of free histidine as a substrate with respect to histamine content. In general, the cheese samples with high histamine levels also had the high values for trichloroacteic acid-soluble nitrogen. However, the highest proteolysis values did not necessarily correlate with the highest histamine values. Two samples of low-salt Swiss cheese that had high trichloroacetic acid-soluble nitrogen (greater than 200 μmoles glycine equivalents per g of cheese) contained less than 15 mg histamine per 100 g cheese.