Relationship between Salinity and Histamine Accumulation in Padaek, a Salt-Fermented Freshwater Fish Paste from Laos

Padaek is a salt-fermented freshwater fish product popularly used in Laos as a shelf-stable all-purpose seasoning. For padaek production, the fish is fermented with salt and rice bran at ambient temperature. Although it is considered edible after 2 to 3 months of fermentation, 6 to 12 months is required to enhance its palatability. Its long shelf life and abundance of free amino acids, such as glutamate and lysine, are distinctive features of the product. Although commercial products are currently available, the tradition of making and consuming padaek at home continues, particularly in rural areas, to make use of indigenous freshwater fish, which provides a continuous supply of food and nutrition. Histamine can cause foodborne intoxication. Occasionally, its excessive accumulation occurs in amino acid-containing food, such as fermented fish products, because of the growth of microorganisms with histidine decarboxylase activity. We found a negative correlation between salinity and histamine content in homemade padaek products collected from rural households. Experimental padaek fermentation with initial salinity conditions of 10 and 6.5% exhibited significant histamine accumulation after 2 weeks of incubation at 30°C and exceeded 1,000 ppm within 6 months, but no histamine was detected in fermentation with an initial salinity of 18% over the same period. This indicated that salinity was a critical factor for controlling the risk of histamine accumulation during padaek fermentation. We, therefore, created and used a simplified calculation chart to help local households adjust the initial salinity to a sufficient level to reduce histamine accumulation during padaek fermentation. This producer-friendly approach for reducing the risk of histamine accumulation in this popular fermented food in Laos should be widely implemented to enhance food safety management in the country.