<i>In silico</i> prediction and IgE serum screening for potential allergenicity of novel foods-a case of fungal biomass Fermotein®

The fungus <i>Rhizomucor pusillus</i> CBS 143028 is the source of a novel food called Fermotein®, a whole fungal biomass rich in proteins, fibres, and micronutrients. To enable Fermotein® to enter the food market, the safety of the microorganism needs to be carefully assessed, including studying the allergenicity potential of proteins encoded by its genome. An <i>in silico</i> allergen database screening identified 23 proteins with more than 50% sequence identity over their full sequence, with proteins from food origin requiring allergen labelling in the European Union. These proteins are present in fish, crustaceans (e.g., shrimp, crab), peanuts, pistachio nuts, sesame seeds, and wheat. To unequivocally establish the likelihood of potential cross-reactivity of the proteins present in the novel food with those established allergens, sera of patients with doctor-diagnosed allergies to these six food categories were screened using ImmunoCAP technology. Of the 106 sera samples tested, 16 showed low IgE binding to Fermotein®. In 11 out of the 16 sera, it was demonstrated by IgE inhibition assays with Proteinase K-digested Fermotein® that all reactivity was directed to fungal carbohydrate moieties. For the remaining five sera, ImmunoCAP inhibition assays with the relevant allergen extracts and with purified human proteins highly homologous to the implicated allergen molecules demonstrated that there was no evidence to support significant cross-reactivity with the potential allergens identified in the bioinformatics <i>in silico</i> search. It is clear that IgE recognition of Fermotein® is dominated by clinically irrelevant carbohydrates. Based on these analyses, it is safe to conclude that Fermotein® presents a negligible allergenicity risk for food-allergic patients because the observed bioinformatics hits did not translate into IgE cross-reactivity.