Almond (Prunus amygdalus subsp. dulcis) is a stone fruit and a major cause of food allergies. Almond is distinguished from other species in Prunus by the corrugated shell surrounding the seed (Chen et al., 2008). However, almond kernel is very similar to apri- cot kernel (P. armeniaca) not only in appearance but also in taste. Moreover, almond kernel is generally cheaper than apricot kernel in the market. Related food product labels often contain mixed messages regarding the real raw material of the products, inten- tionally or unintentionally. Although almond and apricot kernel products are widely consumed, labeling inaccuracy still leads to numerous lawsuits on retailers and manufacturers. China is the largest foreign consumer of California almonds and imports approximately 240 million pounds per year. Almond and its prod- ucts from the USA are consistently mislabeled as ‘American apricot kernel’. In 2013, this unknown practice was disclosed by the media and greatly damaged almond trading. Therefore, a method must be developed that can distinguish between almond and apricot kernel in heat-processed products.
Costa, Mafra, and Oliveira (2012) reported a real-time PCR assay that involved targeting the gene encoding the Pru du 5 allergen (Allergome code 3605) in almond with fluorescent EvaGreen dye combined with high-resolution melting analysis. However, their method is complicated, time-consuming and did not exhibit enough specificity to distinguish heat-treated apricot kernel from the almond samples. We previously used this method to detect laboratory-made apricot kernel milk and almond milk and obtained few incorrect results.
Prior studies revealed that many proteins play important indicative roles for species and are thermotolerant in heat- processed foods (Surojanametakul et al., 2011; Zhang et al., 2012). Two-dimensional electrophoresis (2-DE) combined with MALDI-TOF–TOF/MS analysis are common methods for searching specific proteins. As of this writing, no study has focused on the proteome of apricot kernel, despite that apricot kernel is a major allergen like almond. In the present study, 2-DE was used to deter- mine the proteomic differences between almond and apricot ker- nel. This differentiating protein was used as antigen to prepare a monoclonal antibody. We developed specific enzyme-linked immunosorbent assay (ELISA) methods for almond in heat-processed food based on this antibody.