The effect of seasonality on the biogenic amines, free amino acids, and physico-chemical composition of raw milk Fiore Sardo cheese produced in Sardinia (Italy)

The effect of seasonality on the content of biogenic amines (BA), compounds that could threaten food safety at a high level, were evaluated in Fiore Sardo, a typical artisanal raw sheep's milk cheese produced in Sardinia. The cheese samples collected from six farms, after four months of ripening, were manufactured from January to June. The relationship between the BA content, the free amino acid (FAA) concentration, and the physico-chemical composition (pH, aw, NaCl, humidity, and the fat and protein content) was considered. The FAA and BA contents were determined by HPLC-FL. The BA content and the other parameters analysed were significantly affected (p ≤ 0.000) by seasonality and the farm of origin. Despite the differences attributable to the producers, the seasonal variations of all the parameters considered followed the same trend. As the season changed, the level of total BA grew, reaching a mean content of 1402 ± 207 mg/kg in the samples produced in June, almost five times the mean value of those manufactured in January. The most represented biogenic amine was tyramine, followed by putrescine and cadaverine. Histamine was determined almost exclusively in some samples produced in the warmer months, while β-phenylethylamine and tryptamine were found in a low concentration or not detected. The winter products did not exceed the threshold of 900 mg/kg proposed for the total BA in food, while most of the samples manufactured in the hottest months exceeded this limit, posing a potential risk to consumers' health. The total FAA and BA content were correlated (p = 0.01), indicating that with the change of the season, proteolysis phenomena increased and made the precursor amino acids available for microbial decarboxylase activity. In addition, from January to June, the pH and fat levels grew, while those of aw, humidity and NaCl tended to decline. The study highlighted that as the season changed, the rise in temperature, probably combined with the increment of fat and decrement of NaCl content, could favour proteolysis phenomena and bacterial decarboxylase activity and, as a result, the escalation of BA production. Interventions in the production protocol to reduce the negative effect of seasonality on cheese safety are needed. In addition, in light of these results, it is possible to speculate that the rising temperature and the predicted lengthening of the warm season due to climate change, which also seems to affect the spring periods, could create the ideal conditions for the production of biogenic amines for an increasingly extended phase of the year.