Sensitive ELISA and lateral flow immunoassay for the detection of walnut traces in processed food and working surfaces

Walnut represents one of the most allergenic nuts that can be found as a hidden allergen. In this study, sandwich ELISA and lateral flow immunoassay (LFIA), based on the determination of Jug r 1, were developed to detect walnut. Cross-reactivity was only found with Pecan nut among a panel of 88 food ingredients tested. ELISA and LFIA could detect 0.25 and 0.5 µg/g of walnut protein in complex food matrices spiked with walnut extract, respectively. Furthermore, walnut was detected in blended (chocolate) and incurred foods (ice cream and bread) added with ground walnut at levels of 0.5 and 1.5 µg protein/g by ELISA and LFIA, respectively. LFIA could also detect 0.1 μg of walnut protein in working surfaces. ELISA displayed acceptable precision and high recovery (71-97 %) and both tests were robust. This study shows that developed ELISA and LFIA are reliable tools to be applied in allergen control programs.

Prevalence and early-life risk factors for tree nut sensitization and allergy in young adults

BACKGROUND

Tree nut allergy may cause anaphylaxis. There are limited population-based studies on prevalence and early-life risk factors.

METHODS

We evaluated the prevalence of reported symptoms and allergic sensitization to tree nuts at age 24 years in the BAMSE population-based cohort study and assessed early-life factors associated with the development of tree nut allergy. We estimated tree nut allergy prevalence, by analysing questionnaire data on tree nut ingestion and symptoms at age 12, 16 and 24 years, and IgE sensitization at age 24 years to hazelnut, walnut, pecan, cashew, pistachio, Brazil nut, almond extracts and allergen molecules Cor a 1, 9, 14 (hazelnut), Jug r 1 (walnut) and Ana o 3 (cashew). We evaluated eczema, asthma, food allergies, inherited risk of allergy and gender as potential early-life risk factors.

RESULTS

Data were available for 2215/4089 (54%) BAMSE study participants, for estimation of the prevalence of tree nut sensitization (21.2%), tree nut allergy symptoms (9.8%) and combined sensitization and symptoms (7.9%, 2.1% for storage protein sensitization and symptoms, 4.3% for any sensitization and non-mild symptoms). Sixty-three per cent of sensitized individuals (295/470) were asymptomatic, but only 76/470 (16%) storage protein sensitized individuals. Egg allergy (OR_adj 8.50 95% CI 2.15-33.6), eczema (OR_adj 2.53 95% CI 1.21-5.32) and asthma (OR_adj 5.59 95% CI 2.35-13.3)) at pre-school age were associated with future development of tree nut symptoms and storage protein sensitization. At age 24 years, tree nut allergy was associated with current eczema and with markers of current asthma severity. Sensitization to storage proteins was more strongly associated with symptoms than sensitization to whole extract for all tree nuts evaluated.

CONCLUSIONS

In this Swedish cohort, we found tree nut whole extract sensitization is common but usually asymptomatic. Storage protein sensitization is a more reliable indicator of tree nut symptoms. Tree nut allergy is associated with early onset, persistent and severe atopic disease.

Sequence analysis of digestion-resistant peptides may be an efficient strategy for studying the linear epitopes of Jug r 1, the major walnut allergen

Jug r 1, the major allergen of walnut, triggers severe allergic reactions through epitopes. Hence, research on the efficient strategy for analyzing the linear epitopes of Jug r 1 are necessary. In this work, bioinformatics analysis was used to predict the linear epitopes of Jug r 1. Overlapping peptide synthesis was used to map linear epitopes. In vitro simulated gastrointestinal digestion and HPLC-MS/MS were used to identify digestion-resistant peptides. The results showed that six predicted linear epitopes were AA28-35, AA42-49, AA55-62, AA65-73, AA97-104, and AA109-121. AA16-30 and AA125-139 were identified by the sera of walnut allergic patients. Five digestion-resistant peptides were AA19-33, AA40-45, AA54-74, AA96-106, and AA117-137. The predicted results only included one of the linear epitopes identified by sera, while the digestion-resistant peptides covered all. Therefore, the digestion-resistant property of food allergens may be a promising direction for studying the linear epitopes of Jug r 1.