Session: Current Topics in Biological Chemistry:

The reported incidence of food allergy has increased over recent decades. Food allergies are an inappropriate immune response mediated by immunoglobin-E antibodies to otherwise harmless food proteins. Tree nuts, such as pecans, are considered to be a component of a healthy diet, but are among eight foods that commonly cause serious allergic reactions. There are three seed storage proteins that commonly act as pecan nut allergens, namely Car i 1, Car i 2, and Car i 4. Car i 1 is a 13 kDa 2S albumin; Car i 2 a 55 kDa trimeric vicilin; and Car i 4 a hexameric legumin. To better understand the accumulation of allergens during development, nuts from Sumner and Desirable pecan cultivars were analyzed by LC-MS/MS across developmental stages to determine onset of allergen peptide detection. Car i 1 and Car i 2 allergen peptides were first observed in late September (2013). The Car i 1 peptide ‘QCCQQLSQMEEQCQCEGLR’ and Car i 2 peptides ‘NFLAGQNNIINQLER’ and ‘VFSNDILVAALNTPR’ were identified as early markers. Due to low abundance, Car i 4 peptides were not reliably detected. However, an isoform of Car i 4 was identified with 82% sequence identity, the gene expression of which was previously found to be nineteen times higher after cotyledon expansion than that of the canonical Car i 4. Canonical Car i 4 peptides were detected in only 10% of pecan samples analyzed, whereas Car i 4 isoform peptides were detected in 38% of samples. Identifying reliable pecan allergen peptides by mass spectrometry is important for optimizing the detection of trace allergens in foods. The Car i 1 and 2 peptides described here are excellent candidates for overall pecan nut detection and monitoring in foods, but data also suggest the need for continued immunological study of pecan allergen isoforms.

Dr. Christopher P Mattison

USDA ARS SRRC

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