Effect of Ripening Temperature on Microbial Safety and Biogenic Amine Levels in Rennet Cheeses Produced from Raw Cow Milk

Abstract

Europe is the largest producer and consumer of cheese, with growing interest in raw milk cheeses due to their natural qualities and unique flavor. However, the absence of pasteurization increases the risk of pathogens and biogenic amines (BAs), which can cause foodborne illnesses. This study examined the effect of two ripening temperatures (5 °C and 12 °C) on microbial quality and BAs in rennet cheeses made from unpasteurized cow’s milk over 63 days. Microbial counts and BAs were analyzed at nine ripening stages (0, 7, 14, 21, 28, 35, 42, 50, and 63 days). BAs, including histamine, tyramine, tryptamine, and putrescine, were quantified using high-performance liquid chromatography (HPLC) with a UV/VIS DAD detector. Microbiological tests followed ISO standards, assessing total microorganisms, lactic acid bacteria, molds, yeasts, E. coli, Enterobacteriaceae, coagulase-positive staphylococci, Salmonella spp., L. monocytogenes, and Campylobacter spp. Data were analyzed using ANOVA with Bonferroni correction (P < 0.05). Although raw milk samples did not meet hygiene standards, neither the milk nor cheese contained Salmonella spp., L. monocytogenes, or Campylobacter spp. Ripening temperature significantly affected BA levels, with cheeses ripened at 12 °C showing higher total BAs (464.08 mg/kg) than those at 5 °C (296.63 mg/kg), with tyramine being most prevalent. A positive correlation was found between raw milk use and increased tyramine levels, further elevated by higher ripening temperatures. The presence of hygiene indicator microorganisms (molds, yeasts, staphylococci, E. coli, Enterobacteriaceae) and elevated BA levels highlight the need for strict control measures to ensure cheese safety.