Dr Yoko Nitta from the Department of Nutritional Science at Okayama Prefectural University and Dr Hiroe Kikuzaki from the Department of Food Science and Nutrition at Nara Women's University are studying a possible solution to address histamines before they enter our bodies. Both researchers have been examining how these histamines in fish, which cause food poisoning, are accumulated and how they might be neutralised when submerged in plant extracts. Nitta points out that disabling histamines in fish is more complicated than meets the eye. In order to kill any aspect of our foods that could hurt our bodies, our first reaction is normally to cook it. In many cases, this is helpful; however, in the case of histamines, cooking is not the answer. In fact, histamines cannot be reduced by heat and have no smell to indicate their harmful properties. "Once histamines are accumulated in fish, there is a risk of food poisoning before or after you have prepared your meal," she says. The main offender generating histamines in fish is histidine decarboxylase (HDC). HDC is an enzyme that catalyses synthesis of histamines. In order to prevent histamines gathering in fish products, HDC must be inhibited. According to Nitta and Kikuzaki's research, phytochemicals present in certain plants can do the job. In a sweeping review, they screened 21 spices and 122 medicinal plants to assess if they had properties capable of considerably inhibiting HDC and the production of histamines. "Of the spices we studied, cinnamon, clove, allspice and Japanese pepper showed the most inhibitory activity, inhibiting human-derived HDC by over 50 per cent," observes Nitta. "However, it was the medicinal plants that had the most significant impact, especially those from the rose family." Of the 122 specimens, Artocarpus lakoocha, amla and meadowsweet, or Filipendula ulumaria, were able to inhibit HDC by more than 90 per cent. Some of the compounds responsible for so potently inhibiting HDC were flavonoid glucoside present in the spices and ellagitannin present in meadowsweet. Amazingly, ellagitannin is 10 times more potent than previously discovered inhibitors. "Our results suggested that powerful and useful inhibitors of HDC likely exist in many different plants and investigating further to discover more potential preventers of food poisoning would be a fruitful activity," explains Kikuzaki. After conducting this extensive assessment, Nitta and Kikuzaki moved to test their findings on the bacterial HDC found in fish meat rather than merely through chemical evaluation of human-derived HDC.