International trade in spices has continued to thrive over thousands of years. Present-day producers and importers need to be aware of any legal requirements relating to food safety and quality standards. In addition to pathogens and impurities, the level of metal contaminants present in spices is a further product safety issue. Spices can be contaminated with metals during the growth cycle of the plant or during processing and packaging. Food fraud is another problem, as competitive gains can be made through intentional counterfeiting, substitution, adulteration, or mislabeling/misrepresentation of ingredients within products. Many of these tricks go unnoticed by consumers and regulating government agencies due in part to the lack of standardized methods for the identification of geographic origin.
High-value foods such as wine, rice, oils, honey, fruit juices, tea, coffee, and spices that are marketed according to their provenance are susceptible to food fraud. Additional profits can be made in several ways, for example by blending good quality, authentic products with inferior and cheaper ingredients or by deliberately misbranding a low-quality product as one with a higher value.
Elemental fingerprinting can help combat fraudulent activity. Foods can be authenticated based on the pattern of their trace element content, which is characteristic of the soil composition in the region of production—one study used multi-elemental profiling of 29 tea samples through inductively coupled plasma-mass spectrometry (ICP-MS) for authentication purposes. A similar elemental profiling approach was used in this study to identify the origin of 55 spices from various countries and to differentiate between assorted spices produced in the same country.
Versatile Multi-Element Analysis
Many food testing laboratories already use ICP-MS for the quality control of their products. It is a well-established, fast, multi-element technique to determine a wide range of elements present in a sample at different concentrations. However, given the variety of food types, many foods contain a complex or variable matrix that can give rise to the formation of polyatomic interferences in the ICP-MS spectrum that can affect the accuracy of the data for some elements. A series of recent developments has enhanced the matrix tolerance of ICP-MS and control of polyatomic interferences, improving its suitability for the analysis of foods. ICP-MS equipped with an ultra-high matrix introduction system enables the plasma to tolerate samples containing up to 25 percent total dissolved solids (TDS). Octopole-based collision/reaction cell (CRC) technology removes polyatomic interferences arising from the plasma and sample matrix using kinetic energy discrimination (KED) with a single gas (helium mode), improving the data quality of foods with complex matrices.
Over 50 spices from around the world of known origin were received from a business-to-business spice supply company based in the U.S. Knowing the origin of samples is critical to the development of a reliable model that can be used to authenticate unknown samples. All spice samples were microwave digested in acid (MARS 6, CEM).
Since our lab is equipped with both ICP-optical emission spectroscopy (ICP-OES) and ICP-MS, we first used ICP-OES as a screening technique to establish the concentration levels of elements present in the spice sample digests. The same samples were then analyzed using ICP-MS. Rather than dilute the samples to bring the high-level elements (aluminum, calcium, germanium, potassium, magnesium, sodium, phosphorus, sulfur) into range, we used the ICP-OES results for these elements in the statistical analysis.
A 7900 ICP-MS and 5110 ICP-OES (Agilent Technologies) fitted with an SPS 4 autosampler (Agilent Technologies) were used to analyze various spice samples. Mass Profiler Professional (Agilent Technologies) chemometric software was used for statistical analysis of the data set.
Validating the Analytical Method
To verify the spice sample digestion process, three National Institute of Standards and Technology (NIST) standard reference materials (SRMs) were analyzed by ICP-MS and ICP-OES. The mean concentrations (ppm) of three repeat measurements of three SRM digests were in good agreement (80-120 percent) with the certified concentrations, where certified concentrations were provided.