Low-histamine diets are currently used to reduce symptoms of histamine intolerance, a disorder in histamine homeostasis that increases plasma levels, mainly due to reduced diamine-oxidase (DAO) activity. These diets exclude foods, many of them of plant origin, which patients associate with the onset of the symptomatology. This study aimed to review the existing data on histamine and other biogenic amine contents in nonfermented plant-origin foods, as well as on their origin and evolution during the storage or culinary process. The only plant-origin products with significant levels of histamine were eggplant, spinach, tomato, and avocado, each showing a great variability in content. Putrescine has been found in practically all plant-origin foods, probably due to its physiological origin. The high contents of putrescine in certain products could also be related to the triggering of the symptomatology by enzymatic competition with histamine. Additionally, high spermidine contents found in some foods should also be taken into account in these diets, because it can also be metabolized by DAO, albeit with a lower affinity. It is recommended to consume plant-origin foods that are boiled or are of maximum freshness to reduce biogenic amine intake.

Diamine oxidase (DAO) is one of the key enzymes involved in the degradation of dietary histamine. An imbalance of histamine scavenging systems leads to histamine intolerance, a diet-related disorder that may be tackled by following a low-histamine diet. Recently, the supplementation with exogenous DAO enzyme of animal origin has received the green light as a novel food to enhance intestinal degradation of histamine. This work performed a screening for histamine-degrading capacity of Leguminosae species in order to explore its potential suitability as plant-derived active ingredient of enzymatic supplements. In vitro DAO activity was determined both in raw pulses and lyophilised sprouts by an enzymatic assay coupled to UHPLC-FLD and several germination and storage conditions were assessed. The sprouts of edible legumes showed an in vitro histamine-degrading capacity ranging from 36.0 to 408.3 mU g -1 , much higher than that found for the non-germinated seeds (0.14 -1.95 mU g -1 ). The germination of legume seeds for 6 days in darkness provided the maximum DAO activity. Only the freezing storage of the lyophilized sprouts kept the enzymatic activity intact for at least 12 months. These results demonstrate that certain edible legumes could be suitable for the formulation of DAO supplements for the treatment of histamine intolerance.