Beef authentication and retrospective dietary verification using stable isotope ratio analysis of bovine muscle and tail hair

Origin traceability of Cordyceps sinensis based on trace elements and stable isotope fingerprints

Cordyceps sinensis is a kind of valuable Chinese herbal medicine, and its quality and price depend on the place of origin. Building a traceability system for Cordyceps sinensis products is an effective way to protect Cordyceps sinensis geographical indication products and consumers. In this study, concentrations of 45 trace elements and stable C, N, and Pb isotopes were used to distinguish Cordyceps sinensis samples from different habitats and different varieties (natural and artificial). The results showed that there were significant differences in the isotope compositions of N and Pb and trace elements contents in the Cordyceps sinensis samples from different sources. Stepwise discriminant analysis was used to select effective traceability indicators, and three discriminant models were successfully established. A combination of Co, Sr, Cu, Tl, and Zr indexes was selected to distinguish the naturally grown samples from the artificially cultivated ones, with an overall cross-validation correctness rate of 90.0 %; while a combination of As, Cu, Rb, Tl, W, and Zr indexes was adopted to distinguish the naturally grown samples from different regions, with a corresponding 100.0 % overall cross-validation correctness rate. To simultaneously distinguish samples between natural and artificial and between different regions, a combination of As, Cu, Rb, Tl, U, W, and δ15N indexes was employed, with an overall cross-validation correctness rate of 89.3 %.

Isotope Fingerprinting as a Backup for Modern Safety and Traceability Systems in the Animal-Derived Food Chain

In recent years, due to the globalization of food trade and certified agro-food products, the authenticity and traceability of food have received increasing attention. As a result, opportunities for fraudulent practices arise, highlighting the need to protect consumers from economic and health damages. In this regard, specific analytical techniques have been optimized and implemented to support the integrity of the food chain, such as those targeting different isotopes and their ratios. This review article explores the scientific progress of the last decade in the study of the isotopic identity card of food of animal origin, provides the reader with an overview of its application, and focuses on whether the combination of isotopes with other markers increases confidence and robustness in food authenticity testing. To this purpose, a total of 135 studies analyzing fish and seafood, meat, eggs, milk, and dairy products, and aiming to examine the relation between isotopic ratios and the geographical provenance, feeding regime, production method, and seasonality were reviewed. Current trends and major research achievements in the field were discussed and commented on in detail, pointing out advantages and drawbacks typically associated with this analytical approach and arguing future improvements and changes that need to be made to recognize it as a standard and validated method for fraud mitigation and safety control in the sector of food of animal origin.

Characterization of Beef Coming from Different European Countries through Stable Isotope (H, C, N, and S) Ratio Analysis

The need to guarantee the geographical origin of food samples has become imperative in recent years due to the increasing amount of food fraud. Stable isotope ratio analysis permits the characterization and origin control of foodstuffs, thanks to its capability to discriminate between products having different geographical origins and derived from different production systems. The Framework 6 EU-project "TRACE" generated hydrogen (²H/¹H), carbon (¹³C/¹²C), nitrogen (¹⁵N/¹⁴N), and sulphur (³⁴S/³²S) isotope ratio data from 227 authentic beef samples. These samples were collected from a total of 13 sites in eight countries. The stable isotope analysis was completed by combining IRMS with a thermal conversion elemental analyzer (TC/EA) for the analysis of δ(²H) and an elemental analyzer (EA) for the determination of δ(¹³C), δ(¹⁵N), and δ(³⁴S). The results show the potential of this technique to detect clustering of samples due to specific environmental conditions in the areas where the beef cattle were reared. Stable isotope measurements highlighted statistical differences between coastal and inland regions, production sites at different latitudes, regions with different geology, and different farming systems related to the diet the animals were consuming (primarily C3- or C4-based or a mixed one).

Tracking the British agricultural revolution through the isotopic analysis of dated parchment

Between the sixteenth and nineteenth century, British agriculture underwent a 'revolutionary' transformation. Yet despite over a century of research and the recognised centrality of agricultural developments to industrialisation and population growth, the character or chronology of any 'revolution' during this period remains contentious. Enquiry has been hampered by the fragmented and locally specific nature of historic accounts and the broad dating of early-modern zooarchaeological assemblages. To address this, we conducted stable isotope analysis on 658 legal documents written on sheepskin parchment; a unique biological resource that records the day, month and year of use (AD 1499 to 1969). We find these provide a high temporal resolution analysis of changing agricultural practices and episodes of disease. Most significantly, they suggest that if an 'Agricultural Revolution' occurred in livestock management, it did so from the mid-nineteenth century, in the aftermath of the Napoleonic Wars.

Tracing the geographic origin of velvet antlers in China via stable isotope analyses

Multielement (H, C, N, O) stable isotope ratio analysis was used to discriminate the geographical origin of velvet antlers (VAs) of deer from ten provinces in China. Ratios of ²H/¹H, ¹³C/¹²C, ¹⁵N/¹⁴N, and ¹⁸O/¹⁶O in the VA samples were measured using isotope ratio mass spectrometry. The results showed that there were highly significant differences in the mean isotopic values and in four isotopic ratios between VA samples from the ten provinces. The most significant difference among the four isotope ratios was in δ²H ratio of VA samples; regions with a more humid climate and higher average ambient temperatures had higher δ²H ratios than those with dry climates and lower temperatures. These results demonstrate that the multiple stable isotopic ratio approach is a powerful tool to help trace the geographical origin of VAs, and could be adopted by government officials to help protect consumer interests from improper labeling in VA markets.

Multielement (H, C, N, O) stable isotope ratio analysis was used to discriminate the geographical origin of velvet antlers (VAs) of deer from ten provinces in China.

Mass spectrometry in food authentication and origin traceability

Food authentication and origin traceability are popular research topics, especially as concerns about food quality continue to increase. Mass spectrometry (MS) plays an indispensable role in food authentication and origin traceability. In this review, the applications of MS in food authentication and origin traceability by analyzing the main components and chemical fingerprints or profiles are summarized. In addition, the characteristic markers for food authentication are also reviewed, and the advantages and disadvantages of MS-based techniques for food authentication, as well as the current trends and challenges, are discussed. The fingerprinting and profiling methods, in combination with multivariate statistical analysis, are more suitable for the authentication of high-value foods, while characteristic marker-based methods are more suitable for adulteration detection. Several new techniques have been introduced to the field, such as proton transfer reaction mass spectrometry, ambient ionization mass spectrometry (AIMS), and ion mobility mass spectrometry, for the determination of food adulteration due to their fast and convenient analysis. As an important trend, the miniaturization of MS offers advantages, such as small and portable instrumentation and fast and nondestructive analysis. Moreover, many applications in food authentication are using AIMS, which can help food authentication in food inspection/field analysis. This review provides a reference and guide for food authentication and traceability based on MS.

Gas Chromatography Combustion Isotope Ratio Mass Spectrometry to Detect Differences in Four Compartments of Simmental Cows Fed on C3 and C4 Diets

Fatty acids (FAs) metabolism in animals represents an important field of study since they influence the quality and the properties of the meat. The aim of this study is to assess the possibility to discriminate the diets of cows in different animal compartments and to study the fate of dietary FAs in the bovine organism, using carbon isotopic ratios. Five FAs, both essential (linoleic and linolenic) and non-essential (palmitic, stearic, and oleic) in four compartments (feed, rumen, liver, meat) of animals fed two different diets (based on either C3 or C4 plants) were considered. For all compartments, the carbon isotopic ratio (δ13C) of all FAs (with few exceptions) resulted significantly lower in cows fed on C3 than C4 plants, figuring as a powerful tool to discriminate between different diets. Moreover, chemical reactions taking place in each animal compartment result in fraction processes affecting the δ13C values. The δ13CFAs tendentially increase from feed to meat in group C3. On the other hand, the δ13CFAs generally increase from rumen to liver in group C4, while δ13CFAs of rumen and meat are mostly not statistically different. Different trends in the δ13CFAs of the two groups suggested different FAs fates depending on the diet.

Metabolomic profiling to detect different forms of beef fraud using rapid evaporative ionisation mass spectrometry (REIMS)

Organic food fraud is a significant challenge in the food testing sector-high price premiums, ease of access to produce to be relabelled and difficulties in developing testing strategies that can detect such frauds make organic foods particularly attractive and thus highly vulnerable to fraud. Samples of conventional and organic cattle taken across meat plants in Ireland and the United Kingdom, consisting of the neck (supraspinatus), rump (gluteus), and shin (flexor carpi radialis) regions of the carcass were analysed using a high resolution time-of-flight based rapid evaporative ionisation mass spectrometry (REIMS) system. The resulting untargeted lipidomic data (m/z 600-1000) was used to generate PCA-LDA models for production system and for muscle type, for these models, it was found that the production system model could differentiate organic from conventional beef with an accuracy of 84%, whilst the muscle type model could identify the cut of meat with a 98% accuracy; additionally, samples can be assessed against multiple models simultaneously, reducing analysis time and sample numbers. The use of REIMS showed considerable promise in its ability to detect different forms of meat fraud; its accuracy in differentiating organic from conventional beef is superior to stable isotope ratio mass spectrometry, with the added advantages of substantially shorter analysis times and lower sample analysis costs. The ability to rapidly confirm the cut of meat also demonstrates the potential of REIMS to concurrently determine multiple aspects of beef authenticity in a close to real time analysis.

Using Bioelements Isotope Ratios and Fatty Acid Composition to Deduce Beef Origin and Zebu Feeding Regime in Cameroon

The purpose of this study was to address the lack of knowledge regarding the stable isotopic composition of beef from zebu cattle reared in tropical Africa. Sixty beef carcasses belonging to the most common zebu breeds (Goudali, white Fulani, and red Mbororo) were selected and classified according to their subcutaneous fat color (white, cream or yellow). The stable isotope ratios of five bioelements—H, O, C, N, and S—in muscle fractions and the fatty acids composition were analyzed. Zebu meat from Cameroon shows peculiar δ¹³C values, related to the almost exclusive intake of grazed tropical grasses with photosynthetic cycle C4. It also shows δ²H and δ¹⁸O values higher than those reported in other areas of the world and correlated with the isotopic composition of animal drinking water. The white subcutaneous fat (“white type”) zebu showed higher δ²H and lower δ¹³C than the “yellow type”, that is correlated with a higher content of polyunsaturated fatty acid (PUFA) and a lower amount of saturated fatty acid (SFA) and monounsaturated fatty acid (MUFA). Multielement analysis seems to provide promising results for tracing the regional origin of Cameroon beef and some aspects of the livestock system, such as the nutritional status of the animals.

Traceability of animal protein byproducts in ruminants by multivariate analysis of isotope ratio mass spectrometry to prevent transmission of prion diseases

Background

Ruminant feed containing animal byproduct proteins (ABPs) is prohibited in many countries due to its risk of transmitting prion diseases (PD). In most cases the entire herd is sacrificed, which causes great harm to the producer countries by preventing their exportation of ruminant derived-products.

Methods

We used stable isotope ratio mass spectrometry (IRMS) of carbon (¹³C/¹²C) and nitrogen (¹⁵N/¹⁴N) to trace the animal protein in the blood of 15 buffaloes (Bubalus bubalis) divided into three experimental groups: 1 - received only vegetable protein (VP) during 117 days; 2 - received animal and vegetable protein (AVP); and 3 - received animal and vegetable protein with animal protein subsequently removed (AVPR). Groups 2 and 3 received diets containing 13.7% bovine meat and bone meal (MBM) added to a vegetable diet (from days 21-117 in the AVP group and until day 47 in the AVPR group, when MBM was removed).

Results

On the 36th day, differences were detectable in the feeding profile (p <0.01) among the three experimental groups, which remained for a further 49 days (85th day). The AVPR group showed isotopic rate reversibility on the 110th day by presenting values similar to those in the control group (VP) (p> 0.05), indicating that it took 63 days to eliminate MBM in this group. Total atoms exchange (> 95%) of ¹³C and ¹⁵N was observed through incorporation of the diet into the AVP and AVPR groups.

Conclusions

IRMS is an accurate and sensitive technique for tracing the feeding profile of ruminants through blood analysis, thus enabling investigation of ABP use.

Seasonal Variation in Stable Isotope Ratios of Cow Milk in Vilnius Region, Lithuania

Various studies have shown that stable isotope analysis has the potential to verify the geographic origin of foods and drinks. However, stable isotope composition is not always constant in the environment and can even change in the same area. Dairy products are of particular interest as a group of foods that play an important role in feeding the population. The composition of milk is fundamentally dependent on the feeding of the cows, and thereby on a particular environment. To better understand the amount of variation in δ18O, δ13C, and δ15N values in the milk from the same area, we measured stable isotope ratios in cow milk water, artesian water, and precipitation (δ18O) as well as in bulk milk samples (δ13C and δ15N) collected in 2014⁻2016. Different water and food sources were available during the winter (artesian water only and dry grass) and summer (artesian water and fresh grass), and spring and autumn seasons reflected transitional periods. Oxygen stable isotope ratios in milk water were relatively lower in winter and transitional seasons and higher in summer, showing the dependence on the main water source. δ13C values reflected particular food sources. This study shows the applicability of the stable isotope ratio method in linking cow milk to specific environments and reveals the amount of variation in stable isotope ratios in the same area. These results could be valuable for other studies on geographical origin determination of dairy products.

Fatty Acid- and Amino Acid-Specific Isotope Analysis for Accurate Authentication and Traceability in Organic Milk

The present study describes compound-specific δ¹³C and δ¹⁵N analyses of fatty acids and amino acids for improving the accurate authentication of organic milk (OM) against conventional milk (CM) collected in Korea. Most δ¹³C_fatty-acid and δ¹³C_amino-acid values were lower in OM than in CM ( P < 0.05); however, most δ¹⁵N_amino-acid values displayed weak discriminative power for OM authentication. Higher isotopic fractionation was observed in δ¹³C_fatty-acid than in δ¹³C_amino-acid and δ¹⁵N_amino-acid, with fractionation trends differing with individual amino acids. In particular, δ¹³C_{linoleic-acid} of -33.5‰ and δ¹³C_{myristic-acid} of -28‰ were determined to be promising year-round threshold values for Korean OM authentication. The δ¹³C_bulk was highly correlated with δ¹³C_Ala ( r = 0.92) and δ¹³C_{oleic-acid, trans} ( r = 0.77), and strong positive correlations were observed between δ¹³C_Val and δ¹³C_Ile ( r = 0.98) and between δ¹⁵N_Thr and δ¹⁵N_Ser ( r = 0.90). Chemometric modeling for OM authentication produced a high quality model ( R² X = 0.547, R² Y = 0.865, and Q² = 0.689) with reliable chemical markers, notably δ¹³C_{myristic-acid}, δ¹³C_{linoleic-acid}, and δ¹³C_stearic-acid. Furthermore, the models developed for seasonal separation in OM ( Q² = 0.954) and CM ( Q² = 0.791) were of good quality. Our findings, based on compound-specific isotope data, improve the reliability of OM authentication in cases where bulk stable isotope ratio analysis alone is insufficient. They also provide valuable insight into the control of fraudulent OM labeling in Korea, with potential application in other countries.

Distinguishing glutamic acid in foodstuffs and monosodium glutamate used as seasoning by stable carbon and nitrogen isotope ratios

Recently, a number of consumers have begun to appreciate more natural ingredients and have become less willing to consume monosodium glutamate (MSG) as a seasoning. By measuring stable isotope ratios (δ13C and δ15N) of glutamic acid contained in foodstuffs and MSG used as seasoning, we attempted to distinguish between both using elemental analyzer-isotope-ratio mass spectrometry (EA/IRMS) and gas chromatography/combustion/IRMS (GC/C/IRMS). As a result, seasoning MSG was observed to have a lower δ15N value than glutamic acid in foodstuffs. We statistically analyzed the stable isotope ratio data using canonical discriminant analysis, thereby differentiating seasoning MSG from foodstuff-derived glutamic acid at an accuracy of 96.7%. This method is effective for distinguishing glutamic acid in foodstuffs from seasoning MSG.

Meat provenance: Authentication of geographical origin and dietary background of meat

The authenticity of meat is now an important consideration in the multi-step food chain from production of animals on farm to consumer consumption of the final meat product. A range of techniques, involving analysis of elemental and molecular constituents of meat, fingerprint profiling and multivariate statistical analysis exists and these techniques are evolving in the quest to provide robust methods of establishing the dietary background of animals and the geographical origin of the meat derived from them. The potential application to meat authentication of techniques such as stable isotope ratio analysis applied to different animal tissues, measurement in meat of compounds directly derived from the diet of animals, such as fatty acids and fat soluble vitamins, and spectroscopy is explored. Challenges pertaining to the interpretation of data, as they relate to assignment of dietary background or geographical origin, are discussed.

Using 13C in cattle hair to trace back the maize level in the feeding regime-A field test

Sections from cattle hair serve as an isotopic archive-they contain information on the cattle diet from different time periods. We tested the reliability of 13C signatures (δ13C) in cattle tail switch hair to retrospectively trace back the annual dietary proportion of maize of different production systems without having to sample and analyze the feed. Furthermore, we investigated if differences in dietary proportion of maize during summer and winter feeding can be detected in a single tail switch hair by sampling hair only once a year. We sampled hair and obtained information on management and annual composition of diets on 23 cattle farms in northern Germany. Farms differed in dietary proportions of maize, grass and concentrates as well as in grazing regime (year-round grazing, summer grazing, no grazing). We found that the annual mean δ13C values (δ13CY) of two hair sections that contain the isotopic information of summer and winter feeding is a robust indicator for the annual proportion of maize in cattle diet on a farm. The grazing regimes could clearly be distinguished by analyzing seasonal mean δ13C values (δ13CS). We could also demonstrate short term changes in the diet changes by means of δ13CS. We conclude that the method can be used in different cattle production systems to check on dietary proportions of maize for a period of one year before sampling of hair.

Detecting animal by-product intake using stable isotope ratio mass spectrometry (IRMS)

Sheep are used in many countries as food and for manufacturing bioproducts. However, when these animals consume animal by-products (ABP), which is widely prohibited, there is a risk of transmitting scrapie - a fatal prion disease in human beings. Therefore, it is essential to develop sensitive methods to detect previous ABP intake to select safe animals for producing biopharmaceuticals. We used stable isotope ratio mass spectrometry (IRMS) for ¹³C and ¹⁵N to trace animal proteins in the serum of three groups of sheep: 1 - received only vegetable protein (VP) for 89 days; 2 - received animal and vegetable protein (AVP); and 3 - received animal and vegetable protein with animal protein subsequently removed (AVPR). Groups 2 and 3 received diets with 30% bovine meat and bone meal (MBM) added to a vegetable diet (from days 16-89 in the AVP group and until day 49 in the AVPR group, when MBM was removed). The AVPR group showed ¹⁵N equilibrium 5 days after MBM removal (54th day). Conversely, ¹⁵N equilibrium in the AVP group occurred 22 days later (76th day). The half-life differed between these groups by 3.55 days. In the AVPR group, ¹⁵N elimination required 53 days, which was similar to this isotope's incorporation time. Turnover was determined based on natural ¹⁵N signatures. IRMS followed by turnover calculations was used to evaluate the time period for the incorporation and elimination of animal protein in sheep serum. The δ¹³C and δ¹⁵N values were used to track animal protein in the diet. This method is biologically and economically relevant for the veterinary field because it can track protein over time or make a point assessment of animal feed with high sensitivity and resolution, providing a low-cost analysis coupled with fast detection. Isotopic profiles could be measured throughout the experimental period, demonstrating the potential to use the method for traceability and certification assessments.

Stable carbon and nitrogen isotopes as a potential tool to differentiate pork from organic and conventional systems

BACKGROUND

Isotopic discrimination, dietary composition and feeding regime determine the carbon and nitrogen stable isotope ratios of animals. Accordingly, measurement of the stable isotope ratios of carbon and nitrogen can be a potential method to identify patterns of pork production.

RESULTS

In the current study, we investigated the carbon and nitrogen isotopic ratio in pork from organic and conventional systems. The average carbon and nitrogen isotope ratios for various organic tissues, including hair, blood and defatted meat, were higher than those of conventionally raised ones. The discriminant analysis results based on the combination of carbon and nitrogen isotopic ratios in defatted meat reached a 100% correct classification. Furthermore, the variation in carbon and nitrogen stable isotope ratios of retail organic and conventional pork has been studied over 1 year. The results suggested that organic pork had a higher δ(13) C value than that of the conventional pork in all but three fortnights. Grouping of the δ(15) N data showed that the δ(15) N value in organic pork was higher than that of the conventional one throughout the whole year.

CONCLUSION

The method established in the present study provides a potential detection that can be highly valuable to prevent fraudulent labelling of organic pork. © 2015 Society of Chemical Industry.

Stable Isotope Ratio Analysis for Assessing the Authenticity of Food of Animal Origin

The main elemental constituents (H, C, N, O, and S) of bio-organic material have different stable isotopes (² H, ¹ H; ¹³ C,¹² C; ¹⁵ N,¹⁴ N; ¹⁸ O,¹⁷ O,¹⁶ O; ³⁶ S, ³⁴ S, ³³ S, and ³² S). Isotopic ratios can be measured precisely and accurately using dedicated analytical techniques such as isotope ratio mass spectrometry (IRMS). Analysis of these ratios shows potential for assessing the authenticity of food of animal origin. In this review, IRMS analysis of food of animal origin and variability factors related to stable isotope ratios in animals are described. The study also lists examples of application of stable isotope ratio analysis to meat, dairy products, fish, and shellfish and emphasizes the strengths and weaknesses of the technique. Geographical, climatic, pedological, geological, botanical, and agricultural factors affect the stable isotope ratios (SIR) of bio-elements, and SIR variations are ultimately incorporated into animal tissue through eating, drinking, breathing, and exchange with the environment, being recorded in the resulting foods. SIR analysis was capable of determining geographical origin, animal diet, and the production system (such as organic/conventional or wild/farmed) for pork, beef, lamb, poultry, milk, butter, cheese, fish, and shellfish. In the case of the hard PDO (protected designations of origin) cheeses Grana Padano and Parmigiano Reggiano it is also used in real-life situations to assess the authenticity of grated and shredded cheese on the market.

Geographical variability in northern European sheep wool isotopic composition (δ(13) C, δ(15) N, δ(2) H values)

RATIONALE

Light stable isotopic analysis of herbivore proteinaceous tissues (hair, muscle, milk) is critical for authenticating the point of origin of finished agricultural or industrial products in both ancient and modern economies. This study examined the distribution of light stable isotopes in herbivores in northern Europe (Iceland to Finland), which is expected to depend on regional-level environmental inputs (precipitation, temperature) and local variables (vegetation type, fodder type, soil type).

METHODS

Sheep wool was obtained from animals managed using traditional methods and located across a gradient of northern European environments. Defatted whole-year samples were analysed by isotope ratio mass spectrometry (IRMS) for carbon (δ(13) C values), nitrogen (δ(15) N values) and un-exchangeable hydrogen (δ(2) H values) isotopic composition.

RESULTS

Wool δ(13) C, δ(15) N and δ(2) H values showed the same correlations to local mean annual precipitation and temperature as were expected for graze plants. Wool δ(2) H values were correlated with local modelled meteoric water δ(2) H values, mediated by plant solid tissue and leaf water fractionations. Cluster analysis distinguished wool from Sweden and the Baltic region from more western material. Local variation in vegetation or soil type did not disrupt dependence on climatic variables but did affect geospatial discrimination.

CONCLUSIONS

Wool isotopic composition in northern Europe is controlled by the effects of local precipitation and temperature on graze plant inputs, and is only weakly affected by pasture type. Copyright © 2016 John Wiley & Sons, Ltd.

Natural (15)N Abundance in Key Amino Acids from Lamb Muscle: Exploring a New Horizon in Diet Authentication and Assessment of Feed Efficiency in Ruminants

Natural (15)N abundance (δ(15)N) varies between individual amino acids (AAs). We hypothesized that δ(15)N of nontransaminating and essential AAs ("source" AAs, such as phenylalanine) present in animal tissues could be used as a marker of dietary origin, whereas δ(15)N of transaminating AAs ("trophic" AAs, such as glutamic acid) could give more detailed insights into animal feed efficiency. Two diets based on dehydrated Lucerne pellets were tested in growing lambs, which promoted different feed efficiencies. No dietary effects were noted on δ(15)N of any AAs analyzed in lamb muscle. In addition, δ(15)N of phenylalanine was unexpectedly similar to that of glutamic acid, suggesting that δ(15)N of AAs is significantly derived from the metabolism of the rumen microbiota and, thus, are not suited for diet authentication in ruminants. In contrast, the δ(15)N of transaminating AAs facilitates an improved prediction of animal feed efficiency compared to the classical isotopic bulk N analysis.

Isotopic composition of sheep wool records seasonality of climate and diet

RATIONALE

Hair keratin is a very important material in ecological and archaeological studies because it grows continuously, can be obtained non-invasively, does not require extensive processing prior to analysis and can be found in archaeological sites. Only a few studies have examined seasonal variations in hair isotope values, and there is no published dataset examining the isotope variability recorded in the keratinous tissues of stationary (i.e., non-migrating) domestic mammals.

METHODS

Thirty-six Irish sheep were sampled in eight farms every three months between September 2006 and June 2007. A shearing strategy was adopted to sample only the most recently grown wool in order to represent an average of the summer, autumn, winter and spring conditions. The stable isotope ratios of the ground samples were measured using two different stable isotope mass spectrometers operated in dual-inlet (C, N) and continuous-flow (O, H) mode.

RESULTS

Wool O isotope ratios are a good proxy for seasonal variability in climate and can be used to anchor a chronology independently of other isotope records (C, N) that are influenced by diet or physiology. By contrast, interpretation of seasonal variations in hair H isotope composition in terms of climate is more complex probably due to the influence of dietary H. The C and N isotope values of grass-fed animals varied seasonally, probably reflecting the annual cycle of seasonal variation in grass isotope values. The highest δ(13) C values were measured in summer-grown wool, while the highest δ(15) N values were measured in winter-grown wool. Supplementation of the sheep diet with concentrates was detected easily and was marked by an increase in δ(13) C values and a decrease in δ(15) N values in winter-grown wool.

CONCLUSIONS

The present study demonstrates that time-resolved sampling and stable isotope ratio analysis of sheep wool can be used to identify short-term changes in diet and climate and therefore offer a tool to examine a wide variety of present and past husbandry practices.

Transamination governs nitrogen isotope heterogeneity of amino acids in rats

The nitrogen isotope composition (δ¹⁵N) of different amino acids carries different dietary information. We hypothesized that transamination and de novo synthesis create three groups that largely explain their dietary information. Rats were fed with ¹⁵N-labeled amino acids. The redistribution of the dietary ¹⁵N labels among the muscular amino acids was analyzed. Subsequently, the labeling was changed and the nitrogen isotope turnover was analyzed. The amino acids had a common nitrogen half-life of ∼20 d, but differed in δ¹⁵N. Nontransaminating and essential amino acids largely conserved the δ¹⁵N of the source and, hence, trace the origin in heterogeneous diets. Nonessential and nontransaminating amino acids showed a nitrogen isotope composition between their dietary composition and that of their de novo synthesis pool, likely indicating their fraction of de novo synthesis. The bulk of amino acids, which are transaminating, derived their N from a common N pool and hence their δ¹⁵N was similar.

Tracing the geographic origin of beef in China on the basis of the combination of stable isotopes and multielement analysis

The potential for classifying beef samples on the basis of their geographical origin was investigated by stable isotope and multielement analysis using samples from various provinces in China. C and N isotope composition and the concentrations of 23 elements of the defatted beef samples were determined. It was shown that as compared to the Tibet beef fed predominantly on C3 pasture, maize-fed beef produced in Shandong and Heilongjiang province gave rise to a significant difference in (13)C content. Significant differences were also observed in 18 elements among the defatted beef samples. Stable isotope data and multielement concentrations determined in the beef were subjected to multivariate analysis, including principal component analysis (PCA) and discriminant analysis (DA). Eight key variables were identified as providing maximum discrimination among samples. DA gave an overall correct classification rate of 100% and a cross-validation rate of 100%. This research has proved that the geographical origin of beef in China can be identified by a combination of stable isotopes and multielement analysis.

Beef authentication using dietary markers: chemometric selection and modelling of significant beef biomarkers using concatenated data from multiple analytical methods

This work aimed to identify a combination of isotopic and molecular biomarkers in bovine muscle and adipose tissue for authentication of the diet of beef cattle. Muscle and adipose tissue samples were collected from animals one of four dietary treatments fed over a 1 year period : pasture (P), barley-based concentrate (C), silage followed by pasture (SiP) or silage followed by pasture with concentrate (SiPC). In total, 83 variables were studied including volatile compounds, colour and reflectance measurements, stable isotope ratios, fatty acids, β-carotene, lutein and α-tocopherol. Chemometric models were created for each dietary treatment using the entire and an attenuated variable set. Meat from each dietary treatment was identified with a high level of accuracy (correct classification between 90.8% and 100%) using a discriminant approach. After elimination of insignificant variables, accuracy was maintained or marginally improved. SIMCA class-modelling performed moderately well, especially with the reduced variable set (76.1-100% correct classification).

Critique: measuring hydrogen stable isotope abundance of proteins to infer origins of wildlife, food and people

Measurement of the relative abundance of 2H (expressed in δ 2H values) in tissues of plants, wildlife and people has evolved into a powerful forensic tool. The approach is based on the strong linkage between spatial patterns of δ 2H values in precipitation at local and continental scales, and the tissues of plants and animals produced on these ‘isoscapes’. Unfortunately, despite this exciting potential, difficulties inherent in the measurement of δ 2H values in complex organic materials such as proteins, as well as the accuracy of such measurements, and a reluctance to adopt strict quality assurance/QC approaches to address challenges associated with these measurements, has clearly limited this potential. These challenges are entirely avoidable and techniques now exist for the routine reliable measurement of δ 2H values in materials of forensic interest that will allow completely comparable data among laboratories.

Does natural weathering change the stable isotope composition (²H, ¹³C, ¹⁵N, ¹⁸O and ³⁴S) of cattle hair?

Stable isotope analysis of hair has found applications in many fields of science because it provides a temporally resolved, fairly stable isotopic archive of mammalian individuals. We investigated whether this hair archive is modified by natural weathering while attached to a living animal. We analyzed the tail switch hairs of one suckler cow, sampled seven times over a period of four annual summer pasture-winter stall feeding cycles. We compared relative isotope ratios (δ²H, δ¹³C, δ¹⁵N, δ¹⁸O and δ³⁴S) of sections of hair that grew simultaneously but were exposed to natural weathering conditions over different periods of time. Natural wear caused a loss of mass of approx. 0.13% day⁻¹, with no apparent effect of environmental conditions. Changes in δ²H, δ¹³C, δ¹⁵N and δ¹⁸O were below the detection limit, indicating that hair is a reliable archive for the isotopes of these elements. In contrast, δ³⁴S values increased during the grazing period by about 1‰, with exposure to UV radiation appearing to have a major influence on this result. The δ³⁴S values decreased during the subsequent stall period, probably due to abrasion. Seasonal variation in δ³⁴S may indicate alternating environments that differ in their weathering conditions.

Multielement isotope analysis of bovine muscle for determination of international geographical origin of meat

Multielemental (C, N, H, S) stable isotope ratio analysis was used as an analytical tool to verify the geographical origin of beef from several European and non-European countries. Beef samples were collected from nine different countries, and the (13)C/(12)C, (15)N/(14)N, (2)H/(1)H, and (34)S/(32)S ratios of defatted beef were measured using isotope ratio mass spectrometry (IRMS). There were highly significant differences in the mean isotopic values of the beef from different countries. The results of discriminant analysis showed that the four isotope ratios were significant for the discrimination of geographical origin and that 84.9% of the samples were correctly assigned to the country of origin (82.2% when cross-validated). Beef was also classified according to geographical origin when additional information on different feeding regimens used in Ireland was included, with 85.0% of the samples correctly allocated and 82.9% cross-validated using the isotopic signatures. All of the Irish beef samples verifiable as pasture-fed beef were correctly classified and then cross-validated.