8 Jan 2020

XRF analysis of food products

Elemental analyses of food and drink products are undertaken to determine the level of metal and mineral content. XRF is a common analysis in many grain and dairy products, screening for contaminants and nutrients.

The food industry is constantly striving to attain improved quality and security for its products. The demands of nutritional value for the consumer and the protection of food brands against counterfeiting and adulteration1 mean that the industry needs to employ state-of-the-art analytical techniques such as multi-element analysis by XRF.
 

XRF-analysis

Nutritional analysis in the dairy industry
Milk analysis, dairy analysis, and milk powder testing for iron, phosphorus and calcium, sodium and potassium are some of the essential processes in the regulation of the dairy industry and the QA of infant formula. X-ray fluorescence analysis (XRF) of milk and dairy products is not yet widespread in dairy industry, although the method has a lot of potential, as dried samples may be analyzed directly without any chemical treatment and XRF equipment is easily available.2

XRF spectrometry is a comparative technique and it requires a set of calibration standards in order to perform its quantitative measurements and this can be a difficulty in the dairy industry because of the wide range of sample types. In a recent study2 the concentrations of minerals (Na, Mg, P, S, Cl, K, and Ca) and trace elements (Mn, Fe, Ni, Cu, Zn, Rb, Sr, and Br) in different types of milk, dairy products, and infant formulas were determined using wavelength dispersive X-ray fluorescence analysis (WDXRF).

The technique used freeze dried samples pressed as tablets of 4 g and calibrations were established using available plant and milk standard reference materials. The results demonstrated the suitability of WDXRF for the quantitative analysis of Na, Mg, P, S, Cl, K, Ca, Zn, Rb, Sr, and Br in all of the dried samples. Trace elements such as Mn, Fe, Ni, and Cu were at the limit of detection (LOD) in most samples. The main disadvantage of XRF was the high LODs for trace elements (Cd, Hg, Pb, and As).

Heavy metals in food
Heavy metals can be extremely hazardous contaminants in the human food chain which are non-biodegradable and have long biological half-lives, meaning they can accumulate in the body. According to the World Health Organization3,4 heavy metals must be strictly controlled in food sources in order to guarantee public health safety. Disproportionate concentrations of heavy metals in food is associated with the etiology of many diseases, specifically cardiovascular, renal, neural, and bone disease.4


Sea-food


A key reason to monitor the levels of toxic elements in food comes from the increased contamination of the environment in which food is grown.5,6 These metals can reach the food chain through various biochemical processes and ultimately be consumed, biomagnified and threaten human health. Heavy metals are major contaminants of food and the problem is getting increasingly serious on a global scale5 because of poor regulation, contaminated land and adulterated fertilizer. Sea fishing is essential in some areas of the world to feed the population. However, industrial contamination of heavy metals such as mercury and nickel have meant that staple fish such as tuna and particularly shellfish need to examined using methods such as XRF to check for heavy metal contamination.6

Sample preparation for the XRF analysis of food
Food samples tend to be complex matrices which are difficult to prepare well. Food stuffs must be pressed at lower tonnages to avoid extracting oils and other components locked away in grains and milk powders.
A typical maximum load would be around 4 tonnes. Although Milk powder, for example, can be safely pressed at loads even exceeding 25 tonnes, there will be a noticeable tackiness on the surface which is not observed at lower tonnages. This implies separation of the sample components and would give rise to erroneous results in the XRF analysis. Examples of these analyses are the tea and milk studies2,7 mentioned previously.

Depending on the volume of samples to be produced, it may be possible to use any of the presses in the Atlas™ range. For low volume manual preparation, the manual press can be used with a 32 mm or 40 mm die. For more repeatable control of the load at higher sample throughputs, the 8-tonne Atlas™ Autotouch T8 model is ideal. When used with an Apex™ quick release die, sample throughputs of up to a hundred samples per day can be feasibly obtained.

Atlas

To learn more about what Spectroscopy can do, check out #SpectroscopySolutions for more insights into the applications XRF and FTIR can fit.

References
  1. L. Olmsted, Fake Food Scandals - A Bad Year For Food Lovers, https://www.forbes.com/sites/larryolmsted/2016/07/11/fake-food-scandals-a-bad- year-for-food-lovers/#525b92b1e75b
  2. Galina V. Pashkova, X-ray Fluorescence Determination of Element Contents in Milk and Dairy Products Food Anal. Methods (2009) 2:303–310 
  3. Ali M, Choudhury TR, Hossain B, Ali MP. Determination of traces of molybdenum and lead in foods by x-ray fluorescence spectrometry. SpringerPlus. 2014;3:341. doi:10.1186/2193-1801-3-341.
  4. Simon Kelly, Karl Heaton, et al., Tracing the geographical origin of food: The application of multi-element and multi-isotope analysis, Trends in Food Science & Technology, Volume 16, Issue 12, December 2005, Pages 555-567
  5. Lijuan Zhao, Youping Sun, Jose A. Hernandez-Viezcas, et al., Monitoring the Environmental Effects of CeO2 and ZnO Nanoparticles Through the Life Cycle of Corn (Zea mays) Plants and in situ μ‐XRF Mapping of Nutrients in Kernels, Environ. Sci. Technol. 2015, 49, 2921−2928
  6. E. Marguí, A. De Fátima Marques, M. De Lurdes Prisal, M. Hidalgo, I. Queralt and M.L. Carvalho, “Total reflection X-ray spectrometry (TXRF) for trace elements assessment in edible clams “, Appl. Spectrosc. 68, 1241 (2014). doi: https://doi.org/10.1366/13- 07364
  7. Rajapaksha, D., Waduge, V., Padilla-Alvarez, R., Kalpage, M., Rathnayake, R. M. N. P., Migliori, A., Frew, R., Abeysinghe, S., Abrahim, A., and Amarakoon, T. (2017) XRF to support food traceability studies: Classification of Sri Lankan tea based on their region of origin. X-Ray Spectrom., 46: 220–224.