Food Safety Focus (139th Issue, February 2018) – Food Incident Highlight

Natural Toxins in Raw/Undercooked Beans

In late 2017, about 100 students/staff were hospitalised after consuming undercooked common beans (biandou) at a school canteen in Mainland China. Consumption of common beans (e.g. green beans, French beans) and other beans (e.g. red kidney beans, white kidney beans) without proper processing may cause poisoning due to the naturally present toxins lectins (e.g. phytohaemagglutinins). Acute poisoning symptoms may include vomiting, diarrhoea, and abdominal pain.

Lectins are heat-liable glycoproteins widely distributed in legumes and some oilseeds. Thorough soaking and adequate heat treatments (e.g. cooking at 100°C for 10-20 min) of beans can denature lectins. Hence, appliances that cook beans at lower temperatures for several hours (e.g. slow cookers/casseroles) may not reach sufficiently high temperatures to destroy lectins. Conversely, commercially tinned/canned beans are safe to eat without further cooking as they have been subjected to thorough heat-treatment.

Consumers are advised to soak and cook beans thoroughly to minimise exposure to lectins, and not to use raw or inadequately cooked beans in the preparation of salad dishes.