Abstract
Oregano (Origanum vulgare L.) is a flowering plant that belongs to the mint family (Lamiaceae). It is used as a culinary herb and is often commercialized as a fine powder or a mixture of small fragments of dried leaves, which makes morphological recognition difficult. Like other commercial preparations of drugs and spices, the contamination of oregano mixtures with vegetable matter of lower quality, or the use of generic misleading names, are frequent and stress the need to develop a molecular traceability system to easily, quickly, and cheaply unveil these scams. The DNA-based analytical approach known as cpDNA barcoding is particularly suited for fraud identification in crop plant species (fresh products and food derivatives), and it represents a promising traceability tool as an alternative or complement to traditional detection methods. In the present study, we used a combined approach based on both qualitative and quantitative cpDNA barcoding with end-point and real-time polymerase chain reaction (PCR) analyses to assess the type and degree of contamination in commercial batches of common oregano. In a preliminary qualitative screening, we amplified, cloned, and sequenced a number of universal trnH-psbA- and trnL-barcoded regions, to identify the main contaminants in the samples under investigation. On the basis of these findings, we then developed and validated a species-specific and sequence-targeted method of testing for the quantitative assessment of contaminants, using trnL gene intron assays. Surprisingly, the results obtained in our case study indicated an almost total absence of O. vulgare in the commercial batches analyzed, but a high presence of group I contaminants (Satureja pilosa Velen.), and a moderate presence of group II contaminants (Cistus lanidifer L./Cistus albidus).
Highlights
Frequent contaminations of food matrices with vegetable matter of lower quality, combined with the use of generic names used for labeling commercial preparations, stress the need to develop and implement molecular traceability systems for foods of vegetal origin
Traceability studies on spices where frauds have been described were conducted on a limited number of species including Tymus spp. [5], Crocus sativus [6], Cinnamomun spp. [7], Salvia spp. [8], and Origanum spp
The polymerase chain reaction (PCR) products obtained by amplification of the trnH-psbA and trnL regions using universal primers and DNA templates from “unknown samples” were potentially composed by a pool of sequences representing the two barcodes in the different species potentially contained in each of the sample
Summary
Frequent contaminations of food matrices with vegetable matter of lower quality, combined with the use of generic names used for labeling commercial preparations, stress the need to develop and implement molecular traceability systems for foods of vegetal origin. Minor agricultural species include plant varieties that are cultivated for food, pharmaceutical, cosmetic, and ornamental purposes, with a modest production in terms of the cultivated areas and the quantity of the final product. For most of these species, the absence of Diversity 2018, 10, 98; doi:10.3390/d10030098 www.mdpi.com/journal/diversity. Traceability studies on spices where frauds have been described were conducted on a limited number of species including Tymus spp. For most of these spices, molecular tools used in species identification were based on a DNA barcoding approach, whereas in the specific case of Oregano (Oregano vulgare L.), a RAPD fingerprinting approach was utilized [9]
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