Milk identification of different species: 13C-NMR spectroscopy of triacylglycerols from cows and buffaloes' milks

Regio- and Stereospecific Analysis of Triacylglycerols—A Brief Overview of the Challenges and the Achievements

The efforts to reveal, in detail, the molecular and intramolecular structures of one of the main lipid classes, namely, triacyl-sn-glycerols, which are now known to affect their specific and important role in all living organisms, are briefly overviewed. Some milestones of significance in the gradual but continuous development and improvement of the analytical methodology to identify the triacylglycerol regio- and stereoisomers in complex lipid samples are traced throughout the years: the use of chromatography based on different separation principles; the improvements in the chromatographic technique; the development and use of different detection techniques; the attempts to simplify and automatize the analysis without losing the accuracy of identification. The spectacular recent achievements of two- and multidimensional methods used as tools in lipidomics are presented.

Detection of bovine milk adulteration in caprine milk with N-acetyl carbohydrate biomarkers by using 1H nuclear magnetic resonance spectroscopy

In a return to tradition, the popularity of caprine milk is on the rise. However, particularly in countries with developed dairy industries based on bovine milk, there is the risk of adulteration with bovine milk, which is a cheaper alternative. Thus, a rapid, robust, and simple method for the detection of bovine milk added to caprine milk is necessary, and ¹H nuclear magnetic resonance spectroscopy appears to provide a solution. A matrix of 115 pure and artificially adulterated pasteurized milk samples was prepared and used to discover biomarkers of bovine milk that are independent of chemical and biological variation caused by factors such as genetics, diet, or seasonality. Principal component analysis and orthogonal projections to latent structures discriminant analysis of pure bovine milk and pure caprine milk revealed spectral features that were assigned to the resonances of 4 molecules. Of these, the peaks corresponding to protons in the N-acetylglucosamine and N-acetylgalactosamine acetyl moieties showed significant applicability for our method. Receiver operating characteristic curve analysis was used to evaluate the performance of the peak integrals as biomarkers of adulteration. This approach was able to distinguish caprine milk adulterated with 5% of bovine milk with 84.78% accuracy and with 10% of bovine milk an excellent 95.65% accuracy. This study demonstrates that N-acetyl carbohydrates could be used as biomarkers for the detection of bovine milk in caprine milk and could help in protecting caprine milk authenticity.

Quantification of Fatty Acids and their Regioisomeric Distribution in Triacylglycerols from Porcine and Bovine Sources Using 13 C NMR Spectroscopy

The uptake of specific fatty acids in humans is dependent on their position on the glycerol backbone. There is a great interest in methods that can access this information fast and accurately. By way of high-resolution NMR, we have analyzed TAG extracted from pig and beef tissues and obtained quantitative data for the composition and regioisomeric distribution of all major unsaturated fatty acids usually found in these source materials, using a combination of manual integration and deconvolution of ¹³ C NMR spectra. In addition, we have developed a method for determining composition and regioisomeric distribution of the two main saturated fatty acids found in pork (16:0, 18:0). The results are discussed in relation to species-specific genetic characteristics of fatty acid and TAG biosynthesis. The developed method could support decisions related to breeding for desired fatty acid profiles, and stimulate further methodology developments using high field NMR.

NMR Lipid Profile of Milk from Alpine Goats with Supplemented Hempseed and Linseed Diets

The supplementation of goat diets with natural products to obtain milk with nutraceutical components is a common practice. In these last years, the influence of supplementation of specifically designed diets has been studied with different analytical tools in order to explore possible beneficial effects in human consumption of animal milk and milk-derived products. In this study, the lipid fraction of milk from Alpine goats undergoing different dietary regimens was studied by ¹H-NMR spectroscopy. Alpine goats were fed with linseed or hempseed supplements, and after 14 weeks of treatment, milk was collected and analyzed. Results showed that feeding diets supplemented with seeds positively affected the fatty acid composition with a pronounced increase in unsaturated fatty acids for both diets compared to a control diet. Specifically, linolenic acid content was more than doubled for linseed diet compared with the hempseed and control groups, while linoleic acid greatly increased only upon hempseed supplementation. However, a number of conjugated linoleic acid (CLA) isomers and higher levels of fatty acids with trans configuration were found in supplemented diets, particularly in the linseed diet.

Total and Free Fatty Acids Analysis in Milk and Dairy Fat

Dairy fat is one of the most complex natural fats because of its fatty acid (FA) composition. Ruminant dairy fat contains more than 400 different FA varying in carbon chain length, and degree, position and configuration of unsaturation. The following article reviews the different methods available to analyze FA (both total and free) in milk and dairy products. The most widely used methodology for separating and analyzing dairy FA is gas chromatography, coupled to a flame ionization detector (CG-FID). Alternatively, gas chromatography coupled to a mass spectrometer (GC-MS) is also used. After lipid extraction, total FA (TFA) are commonly converted into their methyl esters (fatty acid methyl esters, FAME) prior to chromatographic analysis. In contrast, free FA (FFA) can be analyzed after conversion to FAME or directly as FFA after extraction from the product. One of the key questions when analyzing FAME from TFA is the selection of a proper column for separating them, which depends mainly on the objective of the analysis. Quantification is best achieved by the internal standard method. Recently, near-infrared spectroscopy (NIRS), Raman spectroscopy (RS) and nuclear magnetic resonance (NMR) have been reported as promising techniques to analyze FA in milk and dairy products.

Evaluation of sample preparation methods for NMR-based metabolomics of cow milk

The quality of milk metabolome analyzed by nuclear magnetic resonance (NMR) is greatly influenced by the way samples are prepared. Although this analytical method is increasingly used to study milk metabolites, a thorough examination of available sample preparation protocols for milk has not been reported yet. We evaluated the performance of eight milk preparation methods namely (1) raw milk without any processing; (2) skimmed milk; (3) ultrafiltered milk; (4) skimming followed by ultrafiltration; (5) ultracentrifuged milk; (6) methanol; (7) dichloromethane; and (8) methanol/dichloromethane, in terms of spectra quality, repeatability, signal-to-noise ratio, extraction efficiency and yield criteria. A pooled sample of milk was used for all protocols. Skimming, ultracentrifugation and unprocessed milk protocols showed poor NMR spectra quality. Protocols involving multiple steps, namely methanol/dichloromethane extraction, and skimming followed by ultrafiltration produced inadequate results for signal-to-noise ratio parameter. Methanol and skimming associated to ultrafiltration provided good repeatability results compared to the other protocols. Chemical-based sample preparation protocols, particularly methanol, showed more efficient metabolite extraction compared to physical preparation methods. When considering all evaluation parameters, the methanol extraction protocol proved to be the best method. As a proof of utility, methanol protocol was then applied to milk samples from dairy cows fed a diet with or without a feed additive, showing a clear separation between the two groups of cows.

Applications of NMR in dairy research

NMR is a robust analytical technique that has been employed to investigate the properties of many substances of agricultural relevance. NMR was first used to investigate the properties of milk in the 1950s and has since been employed in a wide range of studies; including properties analysis of specific milk proteins to metabolomics techniques used to monitor the health of dairy cows. In this brief review, we highlight the different uses of NMR in the dairy industry.

Triacylglycerol stereospecific analysis and linear discriminant analysis for milk speciation

Product authenticity is an important topic in dairy sector. Dairy products sold for public consumption must be accurately labelled in accordance with the contained milk species. Linear discriminant analysis (LDA), a common chemometric procedure, has been applied to fatty acid% composition to classify pure milk samples (cow, ewe, buffalo, donkey, goat). All original grouped cases were correctly classified, while 90% of cross-validated grouped cases were correctly classified. Another objective of this research was the characterisation of cow-ewe milk mixtures in order to reveal a common fraud in dairy field, that is the addition of cow to ewe milk. Stereospecific analysis of triacylglycerols (TAG), a method based on chemical-enzymatic procedures coupled with chromatographic techniques, has been carried out to detect fraudulent milk additions, in particular 1, 3, 5% cow milk added to ewe milk. When only TAG composition data were used for the elaboration, 75% of original grouped cases were correctly classified, while totally correct classified samples were obtained when both total and intrapositional TAG data were used. Also the results of cross validation were better when TAG stereospecific analysis data were considered as LDA variables. In particular, 100% of cross-validated grouped cases were obtained when 5% cow milk mixtures were considered.

Identification of milk mixtures by 1H NMR profiling

Nuclear magnetic resonance profiling, combined with a single-layer artificial neural network, is used for the evaluation of the content of mixtures of different kinds of milk. In particular, aqueous fractions of cow and sheep milk mixtures are analyzed by (1) H NMR. The spectral differences are highlighted by an analysis of the variance and a principal component analysis. The species classification problem is solved by a linear discriminant analysis. The quantification of the relative amount of the milk of two different species is then achieved by solving the appropriate multilinear problem.

Detection of cow milk in donkey milk by chemometric procedures on triacylglycerol stereospecific analysis results

Stereospecific analysis is an important tool for the characterization of lipid fraction of food matrices, and also of milk samples. The results of a chemical-enzymatic-chromatographic analytical method were elaborated by chemometric procedures such as linear discriminant analysis (LDA) and artificial neural network (ANN). According to the total composition and intrapositional fatty acid distribution in the triacylglycerol (TAG) backbone, the obtained results were able to characterize pure milk samples and milk mixtures with 1, 3, 5% cow milk added to donkey milk. The resulting score was very satisfactory. Totally correct classified samples were obtained when the TAG stereospecific results of all the considered milk mixtures (donkey-cow) were elaborated by LDA and ANN chemometric procedures.

Identification of the production chain of Asiago d'Allevo cheese by nuclear magnetic resonance spectroscopy and principal component analysis

In the present work, a rapid and simple NMR method to discriminate Asiago d'Allevo cheese samples from different production chains is described. A fast and reproducible extraction of the organic fraction was employed. By applying chemometric analysis to NMR data, it is possible to differentiate PDO Asiago cheese produced in alpine farms from that produced in lowland and mountain industrialized factories. PCA of both (1)H and (13)C NMR spectra showed a good separation of alpine farm products from the other ones, whereas the lowland and mountain industrialized cheeses are undistinguishable. The samples were differentiated on the basis of a higher content of unsaturated fatty acids, principally oleic, linoleic, linolenic, and conjugated linoleic acids for the alpine farm cheeses and a higher content of saturated fatty acids for the industrialized products. Conjugated linoleic acid and 1-pentene are also discriminating components.

Nondestructive quantification of organic compounds in whole milk without pretreatment by two-dimensional NMR spectroscopy

In this study, various organic compounds in commercial whole milk were quantified simultaneously by 1H 1D and 1H - 13C HSQC 2D NMR spectra without any pretreatment. 2D NMR spectroscopy was applied to quantification of milk compounds for the first time. Milk fat content was easily determined to be 3.6 +/- 0.1%, and the lactose content was 47.8 +/- 1.0 mg/mL by 1H NMR spectra. From 1H-13C HSQC spectra, the concentrations of citrate, N-acetylcarbohydrates, and trimethylamine were determined to be 3.2 +/- 0.2, 2.9 +/- 0.1, and 4.0 +/- 0.6 mM, respectively. The latter two compounds were quantified in milk for the first time. Butyric acid, total monounsaturated fatty acids, and total polyunsaturated fatty acids of triacylglycerols were 6.2 +/- 0.5, 9.1 +/- 0.9, and 2.9 +/- 0.3 mM, respectively. The fatty acid compositions (mol %) of triacylglycerols were then calculated and were observed to be in good agreement with reference values. The results indicated that 1H 1D and 1H-13C HSQC 2D NMR spectroscopy is useful for the rapid and nondestructive determination of various compounds in milk.

Real-time TaqMan polymerase chain reaction detection and quantification of cow DNA in pure water buffalo mozzarella cheese: method validation and its application on commercial samples

Mozzarella cheese obtained from buffalo (Bubalus bubalis) milk is a typical Italian product certificated by means of the European Protected Designation of Origin (PDO). Mozzarella cheese can also be obtained from bovine milk or bovine/buffalo milk mixtures, but in this case, it cannot be sold as PDO product, and its label must report the actual ingredients. However, bovine milk in PDO products was frequently detected in the past, suggesting fraudulent addition or accidental contamination. Several methods based on end-point polymerase chain reaction (PCR) have been profitably applied in a large number of tests to detect the presence of undeclared ingredients, also in dairy products. In the present study we report a real-time PCR method able to quantify bovine milk addition to pure buffalo cheese products. We validated a normalized procedure based on two targets: bovine mitochondrial cytochrome b (cyt b) to detect and quantify the bovine DNA and nuclear growth hormone (GH) gene used as a universal reference marker. With the use of this real-time PCR assay, 64 commercial mozzarella di bufala cheese samples purchased at local supermarkets, dairy shops, or directly from cheese manufacturers were analyzed. The results obtained demonstrate that most of the commercial samples were contaminated with bovine milk. Therefore, this assay could be conveniently employed to carry out routine and accurate controls aimed not only to discourage any fraudulent behavior but also to reduce risks for consumer health.

Implementation of Quality Control Methods in Conjunction with Chemometrics Toward Authentication of Dairy Products

The implementation of novel and accurate quality and safety control methods in conjunction with chemometrics in various fields of science, particularly in food science, showed that this combination stands for a very powerful tool for detecting food authenticity. The latter reflects both geographic origin and variety. Dairy products, in particular, have repeatedly worried the public authorities in terms of authentication regarding origin and in view of the many illnesses occasionally due to products of specific origin. Therefore, the development of a robust and reliable system endowed with this discriminatory power (varietal and/or geographic) is of great importance, both in terms of public health and consumer protection.

Nondestructive observation of bovine milk by NMR spectroscopy: analysis of existing States of compounds and detection of new compounds

In this study were successfully observed the one- (1H, 13C) and two-dimensional (1H-13C, 1H-15N, 1H-31P) NMR spectra of milk directly without any pretreatment. The signals of each NMR spectrum were assigned, and their existing states were also analyzed. Lactose existed in a free state in milk. The signals due to the butyric acid chain can be assigned among the other fatty acid chains. Monounsaturated fatty acid (oleic acid chains) and polyunsaturated fatty acid chains (linoleic and linolenic acid) were assigned by their characteristic signals. The signals from citrate, N-acetylcarbohydrates, and lecithin could be observed directly in the 1H-13C HSQC NMR spectra; the assignment of their signals was made through the 1H-13C, 1H-15N, and 1H-31P HMBC spectra of extracted milk. Signals from creatine and N-acetylcarbohydrates were detected for the first time.

Natural abundance 13C-NMR spectroscopy for the quantitative determination of fecal fat

OBJECTIVE

To evaluate 13C-NMR spectroscopy as a method for fat quantitation in human feces without time consuming or unpleasant preparation steps.

DESIGN AND METHODS

Stool samples of seven healthy subjects were collected for 18 days before and during oral intake of the inhibitor of gastrointestinal lipases Orlistat. Fecal lipid content was determined first using 13C-NMR, then by conventional gravimetry after homogenization and Bligh & Dyer lipid extraction.

RESULTS

The correlation between gravimetry and 13C-NMR was excellent (R2 = 0.91). In repeated measurements, the mean percentage error was 2.8%. On average, 13C-NMR yielded 1.27 g less fat than gravimetry. Orlistat efficacy for fat excretion assessed by 13C-NMR and by gravimetry was 34.3% and 33.9%, respectively.

CONCLUSIONS

With a total measurement time of three minutes, 13C-NMR spectroscopy of unprocessed whole stool provides an accurate alternative to gravimetry for assessing total fecal fat excretion. 13C-NMR is superior with regard to practicability and speed.