Tracing tiger nut (C. esculentus L.): functional food from the colossal Cyperus genus

Tiger nuts (also called earth almonds or chufa) are the stolons of the sedge Cyperus esculentus L. and have been traditionally used as food or as an additive to drinks such as horchata de chufa. Recently, chufa experienced a hype as functional food because of its richness in dietary fiber and as a source of unsaturated fatty acids. Its close relative, nutgrass (Cyperus rotundus L.) has similarly long history of human use, but rather for medical purposes, due to a high content of secondary compounds. Both species are invasive weeds responsible for high yield losses in crop plants, especially in Southeast Asia, Africa, and subtropical America. They are not easily discerned, occur together, and are both traded under similar or identical vernacular names. For the purpose of consumer protection, it is important to discriminate them in commercial samples, which is not trivial by morphological markers and often impossible since they are mostly used in highly processed form. Therefore, a molecular authentication assay was developed using taxonomically authenticated plants as reference material. The plastidic marker psbA-trnH igs (intergenic spacer) and the nuclear marker Internally Transcribed Spacer were used for barcoding. To develop a sequencing-free fingerprinting assay, a single-nucleotide polymorphism in the ITS2 region could be employed to discriminate C. esculentus from its possible adulterant C. rotundus by a tailored Amplificatory Refractory Mutation System PCR. This approach was successful both, in reference to plants, as well as in highly processed commercial products such as tiger nut flour. We show that by a single PCR we can detect surrogation by nutgrass down to a threshold of 10% in tiger nuts as contribution to safeguard product authenticity against possible adulterations in a growing global market.