Histamine production by Raoultella ornithinolytica in mahi-mahi meat at various storage temperatures

Mahi-mahi meat was inoculated with Raoultella ornithinolytica at 5.0 log CFU/g and stored at −20°C, 4°C, 15°C, 25°C, or 37°C to investigate bacterial growth and formation of total volatile base nitrogen and histamine in mahi-mahi meat. R. ornithinolytica grew rapidly in samples stored at temperature above 15°C. The histamine contents quickly increased to higher than 50 mg/100 g in samples stored at 25°C and 37°C within 12 hours as well as those stored at 15°C within 48 hours. The total volatile base nitrogen contents increased to higher than the index level (30 mg/100 g) for fish decomposition at 25°C within 48 hours and 37°C within 24 hours. However, bacterial growth and histamine formation were controlled by cold storage of the samples at 4°C or below. Once the frozen mahi-mahi samples stored at −20°C for 2 months were thawed and stored at 25°C after 24 hours, histamine started to accumulate rapidly (>50 mg/100 g of fish).