Recent advances in the application of microbial diamine oxidases and other histamine-oxidizing enzymes.

The consumption of foods fraught with histamine can lead to various allergy-like symptoms if the histamine is not sufficiently degraded in the human body. The degradation occurs primarily in the small intestine, naturally catalyzed by the human diamine oxidase (DAO). An inherent or acquired deficiency in human DAO function causes the accumulation of histamine and subsequent intrusion of histamine into the bloodstream. The histamine exerts its effects acting on different histamine receptors all over the body but also directly in the intestinal lumen. The inability to degrade sufficient amounts of dietary histamine is known as the 'histamine intolerance'. It would be preferable to solve this problem initially by the production of histamine-free or -reduced foods and by the oral supplementation of exogenous DAO supporting the human DAO in the small intestine. For the latter, DAOs from mammalian, herbal and microbial sources may be applicable. Microbial DAOs seem to be the most promising choice due to their possibility of an efficient biotechnological production in suitable microbial hosts. However, their biochemical properties, such as activity and stability under process conditions and substrate selectivity, play important roles for their successful application. This review deals with the advances and challenges of DAOs and other histamine-oxidizing enzymes for their potential application as processing aids for the production of histamine-reduced foods or as orally administered adjuvants to humans who have been eating food fraught with histamine.

Production of wheat gluten hydrolysates with reduced antigenicity employing enzymatic hydrolysis combined with downstream unit operations.

BACKGROUND: Due to allergies or other health disorders a certain segment of the population is not able to safely consume some plant proteins, which are the main protein support in human nutrition. Coeliac disease is a prominent autoimmune disorder and requires a strict adherence to a gluten-free diet. The aim of this study was to identify suitable combinations of enzymatic hydrolysis and common unit operations in food processing (centrifugation, ultra-filtration) to produce gluten-free wheat gluten hydrolysates for food application. To analyse the hydrolysates, a simple and cheap competitive ELISA protocol was designed and validated in this study as well. RESULTS: The competitive ELISA was validated using gliadin spiked skim milk protein hydrolysates, due to the latter application of the assay. The limit of quantification was 4.19 mg kg(-1) , which allowed the identification of gluten-free (<20 mg kg(-1) ) hydrolysates. Enzymatic hydrolysis, including the type of peptidase, and the downstream processing greatly affected the antigenicity of the hydrolysates. CONCLUSION: Enzymatic hydrolysis and downstream processing operations, such as centrifugation and ultra-filtration, reduced the antigenicity of wheat gluten hydrolysates. Gluten-free hydrolysates were obtained with Flavourzyme after centrifugation (25 g L(-1) substrate) and after 1 kDa ultra-filtration (100 g L(-1) substrate). A multiple peptidase complex, such as Flavourzyme, seems to be required for the production of gluten-free hydrolysates. © 2015 Society of Chemical Industry.

Toward Oral Supplementation of Diamine Oxidase for the Treatment of Histamine Intolerance.

A new diamine oxidase (DAO-1) was discovered recently in the yeast Yarrowia lipolytica PO1f and investigated for its histamine degradation capability under simulated intestinal conditions. DAO-1 was formulated together with catalase as a sucrose-based tablet. The latter (9 × 7 mm; 400 mg) contained 690 nkat of DAO-1 activity, which was obtained from a bioreactor cultivation of a genetically modified Y. lipolytica with optimized downstream processing. The DAO-1 tablet was tested in a histamine bioconversion experiment under simulated intestinal conditions in the presence of food constituents, whereby about 30% of the histamine was degraded in 90 min. This amount might already be sufficient to help people with histamine intolerance. Furthermore, it was found that the stability of DAO-1 in a simulated intestinal fluid is influenced distinctively by the presence of a food matrix, indicating that the amount and type of food consumed affect the oral supplementation with DAO. This study showed for the first time that a microbial DAO could have the potential for the treatment of histamine intolerance by oral supplementation.

Production and characterization of a new diamine oxidase from Yarrowia lipolytica.

A putative diamine oxidase (DAO) from Yarrowia lipolytica PO1f (DAO-1) was homologously recombinantly integrated into the genome of Y. lipolytica PO1f using the CRISPR-Cas9 system for the subsequent DAO production in a bioreactor. Thereby, it was proven that the DAO-1 produced was indeed a functional DAO. The cultivation yielded 2343 ± 98 nkat/Lculture with a specific DAO activity of 1301 ± 54.2 nkat/gprotein, which was a 93-fold increase of specific DAO activity compared to the native Y. lipolytica PO1f DAO-1 production. The DAO-1 showed a broad substrate selectivity with tyramine, histamine, putrescine and cadaverine being the most favored substrates. It was most active at 40 °C, pH 7.2 in Tris-HCl buffer (50 mM) (with histamine as substrate), which is comparable to human and porcine DAOs. The affinity of DAO-1 towards histamine was lower compared to mammalian DAOs (Km = 2.3 ± 0.2 mM). Nevertheless, DAO-1 degraded around 75% of the histamine used in a bioconversion experiment with a food-relevant concentration of 150 mg/L. With its broad selectivity for the most relevant biogenic amines in foods, DAO-1 from Y. lipolytica PO1f is an interesting enzyme for application in the food industry for the degradation of biogenic amines.

Evaluation of porcine diamine oxidase for the conversion of histamine in food-relevant amounts.

Histamine exists in a multitude of foods and displays an emerging role within food intolerances. Our aim was to identify the activity of porcine diamine oxidase (DAO) required for the in vitro degradation of histamine amounts that are found in typical meals containing histamine (75 mg, equaled 150 mg/L). Furthermore, we investigated an actual dietary supplement that is commercially available for histamine intolerant individuals for its histamine reduction capability. Kinetic investigations of porcine DAO showed a substrate inhibition by histamine concentrations greater than 56 mg/L (0.5 mM). The stability of free porcine DAO was tested in a fed state simulated intestinal fluid and exhibited a half-life period of around 19 min. A total of 50 nanokatal (nkat) free porcine DAO, which equaled the amount of enzyme isolated from around 100 g pig kidney, were necessary for the in vitro reduction of around 90% of the histamine. The dietary supplement that contains a pig kidney extract did not show DAO activity. Instead, the used histamine (0.75 mg) was apparently reduced due to the adsorption of histamine onto a capsule component by 18.9 ± 2.3% within 5 hr. Although the capsule preparation retained its overall structure and shape for at least 90 min in simulated gastric fluid, the apparent histamine reduction was significantly reduced to 12.1 ± 2.3% (P ≤ 0.05). In conclusion, an alternative to the pig kidney DAO or an improved capsule preparation is needed to ensure an adequate supplementation for histamine-intolerant humans. PRACTICAL APPLICATION: Histamine intolerance is an emerging issue in our society and the intolerance-related physiological symptoms are currently not reliably treatable due to a lack of scientific investigation. A commercially available dietary supplement for histamine intolerance does not fulfil the requirements for a satisfactory histamine reduction in intolerant humans. The activity of the histamine degrading enzyme diamine oxidase, required for a satisfactory histamine degradation, is by far higher than the theoretical amount apparently given in the dietary supplement. With this knowledge, it is obvious that improved food supplements must be developed to help histamine intolerant humans.