Development and Validation of a Real-Time PCR Based Assay to Detect Adulteration with Corn in Commercial Turmeric Powder Products

Turmeric, or Curcuma longa, is commonly consumed in the South East Asian countries as a medical product and as food due to its therapeutic properties. However, with increasing demand for turmeric powder, adulterated turmeric powders mixed with other cheap starch powders, such as from corn or cassava, are being distributed by food suppliers for economic benefit. Here, we developed molecular markers using quantitative real-time PCR to identify adulteration in commercial turmeric powder products. Chloroplast genes, such as matK, atpF, and ycf2, were used to design species-specific primers for C. longa and Zea mays. Of the six primer pairs designed and tested, the correlation coefficients (R-2 ) were higher than 0.99 and slopes were -3.136 to -3.498. The efficiency of the primers was between 93.14 and 108.4%. The specificity of the primers was confirmed with ten other species, which could be intentionally added to C. longa powders or used as ingredients in complex turmeric foods. In total, 20 blind samples and 10 commercial C. longa food products were tested with the designed primer sets to demonstrate the effectiveness of this approach to detect the addition of Z. mays products in turmeric powders. Taken together, the real-time PCR assay developed here has the potential to contribute to food safety and the protection of consumer's rights.