Sensitive detection of Piper nigrum L. adulterants by a novel screening approach based on qPCR

The spice made from the fruits of Piper nigrum L. (Piperaceae) has high economic value since the beginnings of international trade. Because its price has been increasing, adulterations with papaya seeds, cayenne pepper and maize flour were reported. These have been screened by methodologies dedicated to the detection of single adulterants lacking sensitivity and specificity. Herein we propose a specific, highly-sensitive, high-throughput and affordable qPCR-based methodology for the detection of P. nigrum contaminants (Carica papaya, Zea mays and Capsicum annuum) using plant DNA barcodes trnL and psbA-trnH. The method enables the specific detection of contaminants in a short time with low limits of detection (LOD₆ values of 1, 2 and 10 Haploid Genome Equivalents). A market survey (29 samples) revealed 41% of samples contaminated, though about ¾ at very low levels indicating accidental contamination. The proposed tool will contribute to the improvement of quality of this much traded spice.