Turmeric (Curcuma longa L.) products: What quality differences exist?

Background: Curcuma longa L. (root and rhizome), commonly known as turmeric, is a plant of high medicinal and economic value globally, including within the EU where it is mainly used as a spice and food supplement. Its key active ingredients have been studied extensively, but concerns remain about the composition and thus the quality of extracts and products on the market. Recently, problems of adulteration with other Curcuma species and general poor quality have been detected within crude turmeric powders and final products. This study aimed to investigate the chemical variation of turmeric finished products available in the UK and identify the quality of turmeric products obtained from specific stages of the supply chain, with a focus on quality differences in the UK. H-1-NMR spectroscopy metabolomics coupled to Principle Component Analysis (PCA) and HPTLC methods were used for the phytochemical and metabolomics investigation of 72 turmeric samples, including crude powders, intermediate products from different manufacturing stages and commercial products obtained from health food stores and the Internet. A significant variation in the chemical composition of turmeric finished products, especially in the ones containing turmeric extracts, was found. Several products were found to contain only curcumin or curcuminoids, while the other active ingredients and marker compounds of C. longa were lacking. Products obtained from different stages of the Pukka value chain presented similar chemical composition, with the intermediate products (S57-59) showing the highest amount of active ingredients. Consequently, the manufacturing practices involved in the production of turmeric food supplements are critical stages to obtain high-quality final products. Often the focus has been only on the primary material, its natural variation and forms of production. This study highlights the importance of developing well-controlled integrated systems for the quality assurance of dietary supplements throughout the supply chain from seed to final product.