Proteomic analysis of Algerian apricot sweet kernels using combinatorial peptide ligand libraries and LC-MS/MS

Apricot (Prunus armeniaca L.), a plant famous for its delicious fruits, is widely cultivated in the Mediterranean area. Italy and Algeria are important producers, since in 2012 the yields have been 247,146 and 269,308 tonnes, respectively (http://faostat.fao.org). Although in most varieties the kernel is not edible owing to the presence of amygdalin, a toxic cyanogenic glycoside, there are some selected sweet kernel varieties. In this case, kernels are consumed alone as snacks or in combination with almond in traditional recipes. This kernel is nutritionally interesting, since it is a rich source of dietary protein, oil and fiber, as well as polyphenols, phytosterols, carotenoids, and volatile compounds.1 If it would not be discarded by food processing industry, its use would help to maximize available resources and result in generating innovative foods. Interestingly, folk medicine has employed it as a remedy for various diseases. The beneficial effects are primarily attributed to unsaturated fatty acids.2 An accurate knowledge of the protein composition would be useful for a better exploitation of apricot kernel in human nutrition, including the identification of potential allergens. We have therefore undertaken a proteomic investigation on the sweet kernel of an Algerian apricot variety, in the framework of an international collaboration, with the goal to update the P. armeniaca data bank including also minor protein components. A proteomic approach based on combinatorial peptide ligand library technology coupled to mass spectrometry has permitted to obtain an extensive proteomic map of apricot kernel, identifying 178 gene-products. Bioinformatics analysis using Gene Ontology (GO) allowed a classification of their biological functions. A preliminary investigation using the open-access tool BIOPEP suggested that tetra and tripeptides encrypted in the two most abundantly expressed proteins, i.e. Prunin1 and Prunin2, may potentially function as inhibitors of angiotensin converting enzyme (ACE), antioxidants, and stimulators of the vasoactive substance release.