trace elements (6)

9599079487?profile=RESIZE_400x This article in the Guardian newspaper gives some examples of where the determination of geological and ground water isotopes, and trace elements linked to the soil and geography where the food originates, is able to check claims of the origin of the food or crop. Examples are given about fraudulent claims of Egyptian cotton, New Zealand beef, and chocolate from beans sourced in Venezuela/Ivory Coast. It also describes the science behind identifying the country where "Adam" the torso of a young boy found in the water under Tower Bridge in London twenty years ago, spent his life before being taken to England. 

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6520790083?profile=RESIZE_584xThe season when tea is harvested, as well as the age of the tea can affect its quality, hence authenticating the season/age of high cost teas can be desirable. Chinese researchers have used trace elements and stable isotopes with chemometrics to characterise Pu'er tea according to its production year. Pu'er tea is prepared by drying green Chinese tea, then subjecting it to a microbiological fermentation by naturally occurring moulds, bacteria and yeasts. The tea is then pressed into a variety of shapes.

A total of 86 mineral elements and stable isotope compositions were determined from the Xiangzhujing Pu'er tea in five different production years. Different chemometric techniques were applied to find the best models to predict the production year.  Mn,68Zn, and 203Tl were the best authenticity markers for enabling the successful authentication of Pu'er tea with different production years. 

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4340822886?profile=RESIZE_710xDetermining the geographic origin of coffee beans is more challenging with roasted coffee beans, and is useful if it can be performed on the product available to the consumer. US researchers analysed the concentrations of 44 trace elements in 53 samples of roasted Arabica coffee beans (Coffea arabica) from 21 different countries. Although trace elements are not volatilised at roasting temperatures, the absolute elemental concentrations of coffee beans vary through different degrees of roasting (from green through dark roasts). The study analysed trace element ratios to evaluate concentration-related differences among beans from different origins. By comparing the distributions of 1892 element ratios for each of the  countries, the study demonstrated that many of the world’s coffee-producing regions can be distinguished from other regions of the world on the basis of element ratios.

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4273790207?profile=RESIZE_710xThis pilot study used SIRA (stable isotope ration analysis) and trace element analysis to verify the organic status of pork purchased in the markets from four different regions of China. Four stable isotope ratios (δ13C, δ15N, δ2H and δ18O) and the concentrations of seven elements (K, Na, Mg, Ca, Fe, Cu and Se) were determined in organic and conventional pork samples from the four locations of China. Principal component analysis (PCA) and orthogonal partial least squares discriminant analysis (OPLS-DA) were used to analyse stable isotope ratios and multi-element concentrations in pork. Discrimination between the organic and conventionally reared pigs was based mainly on δ15N as the marker for organic feedstuffs. Using the limited database of analytical values, the methodology would potentially be able to confirm whether a sample of pork came from the region and organic status it claimed. 

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Honey is the third most adulterated food globally. This study by Australian researchers examined 100 honey samples from Australia (mainland and Tasmania) along with 18 other countries covering Africa, Asia, Europe, North America and Oceania. Carbon isotopic analyses of honey and protein showed that 27% of commercial honey samples tested were of questionable authenticity. The remaining 69 authentic samples were subject to trace element analysis for geographic determination, and were analysed chemometrically. The trace elements Sr, P, Mn and K were the most useful ones to differentiate honey according to its geographic origin. The findings show the common and prevalent issues of honey authenticity and the mislabelling of its geographic origin can be identified using a combination of stable carbon isotopes and trace element concentrations.

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A method using the q-ICP-MS analysis of 19 elements has been developed to differentiate organic and conventional Brazilian rice samples. 17 certified organic samples and 33 conventionally grown rice samples from 5 different regions in Brazil were analysed, and using 19 elements it was possible to predict with 98% confidence the authenticity of the rice samples. Just using calcium and cadmium, it was possible to predict the authenticity with 96% confidence.

Read the full preliminary unedited pdf paper at:

http://www.sciencedirect.com/science/article/pii/S0889157515002008 

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