Duplex digital droplet PCR for the determination of apricot kernels in marzipan

Marzipan is a mixture of almonds, sugar, and water. Almonds can be replaced by apricot kernels, which results in a similar product called persipan. Depending on the prices of almonds, profit can be maximized using apricot kernels instead of almonds. If not specified on the product, this kind of substitution is illegal and is prosecuted by official food control authorities. Likewise, also commercial buyers would like to know which product they bought. Real-time PCR systems for the determination of apricot DNA are already available, however, real-time PCR requires the use of external standards, which have a direct impact on the accuracy of the measurement. Currently, such standards are not available. In contrast to real-time PCR, digital PCR does not require external standards and exhibits a smaller measurement uncertainty as shown in recent publications. Therefore, we developed a duplex droplet digital PCR system to measure the proportion of apricot in marzipan without the use of external standards. We present validation data and results of an international proficiency test, underlining the applicability of this system.