A novel approach to the quantification of bovine milk in ovine cheeses using a duplex polymerase chain reaction method

Detection and quantification of adulteration in milk and dairy products: A novel and sensitive qPCR-based method

•

A novel qPCR method was able to detect and quantify cow, buffalo, goat and sheep DNA in milk and dairy products.

•

Established detection limit was 0.016 ng for the four species.

•

The limit of detection of cow DNA in buffalo, goat and sheep DNA samples was 0.1% (0.01 ng)

•

This method is able to detect and quantify adulteration between cows, buffaloes, goats and sheep dairy samples.

Species identification in dairy products has a notable importance in food traceability and adulteration control and consequently has a significant effect on the final economic value of foods. In the present study, we developed a method based on real-time quantitative PCR (qPCR) for detection and quantification of cow DNA in DNA samples from milk and dairy products from buffaloes, goats, and sheep. The qPCR reactions showed high specificity, and the amplifications only occurred to species-specific primers. The calibration curves allowed for the quantification of the amount of DNA of each species-specific primer, and the established detection limit was 0.016 ng for the four species. The detection limit of cow DNA in buffalo, goat and sheep DNA samples was 0.1% (0.01 ng). Although the present study aimed to detect and quantify cow DNA in buffalo, goat, and sheep dairy products, we believe that the qPCR assays can also be directed to differentiate and quantify goat × sheep, and/or buffalo × goat/sheep.

Animal Species Authentication in Dairy Products

Milk is one of the most important nutritious foods, widely consumed worldwide, either in its natural form or via dairy products. Currently, several economic, health and ethical issues emphasize the need for a more frequent and rigorous quality control of dairy products and the importance of detecting adulterations in these products. For this reason, several conventional and advanced techniques have been proposed, aiming at detecting and quantifying eventual adulterations, preferentially in a rapid, cost-effective, easy to implement, sensitive and specific way. They have relied mostly on electrophoretic, chromatographic and immunoenzymatic techniques. More recently, mass spectrometry, spectroscopic methods (near infrared (NIR), mid infrared (MIR), nuclear magnetic resonance (NMR) and front face fluorescence coupled to chemometrics), DNA analysis (real-time PCR, high-resolution melting analysis, next generation sequencing and droplet digital PCR) and biosensors have been advanced as innovative tools for dairy product authentication. Milk substitution from high-valued species with lower-cost bovine milk is one of the most frequent adulteration practices. Therefore, this review intends to describe the most relevant developments regarding the current and advanced analytical methodologies applied to species authentication of milk and dairy products.

Are current analytical methods suitable to verify VITAL® 2.0/3.0 allergen reference doses for EU allergens in foods?

Food allergy affects up to 6% of Europeans. Allergen identification is important for the risk assessment and management of the inadvertent presence of allergens in foods. The VITAL® initiative for voluntary incidental trace allergen labeling suggests protein reference doses, based on clinical reactivity in food challenge studies, at or below which voluntary labelling is unnecessary. Here, we investigated if current analytical methodology could verify the published VITAL® 2.0 doses, that were available during this analysis, in serving sizes between 5 and 500 g. Available data on published and commercial ELISA, PCR and mass spectrometry methods, especially for the detection of peanuts, soy, hazelnut, wheat, cow's milk and hen's egg were reviewed in detail. Limit of detection, quantitative capability, matrix compatibility, and specificity were assessed. Implications by the recently published VITAL® 3.0 doses were also considered. We conclude that available analytical methods are capable of reasonably robust detection of peanut, soy, hazelnut and wheat allergens for levels at or below the VITAL® 2.0 and also 3.0 doses, with some methods even capable of achieving this in a large 500 g serving size. Cow's milk and hen's egg are more problematic, largely due to matrix/processing incompatibility. An unmet need remains for harmonized reporting units, available reference materials, and method ring-trials to enable validation and the provision of comparable measurement results.

Identification and Detection of Bioactive Peptides in Milk and Dairy Products: Remarks about Agro-Foods

Food-based components represent major sources of functional bioactive compounds. Milk is a rich source of multiple bioactive peptides that not only help to fulfill consumers 'nutritional requirements but also play a significant role in preventing several health disorders. Understanding the chemical composition of milk and its products is critical for producing consistent and high-quality dairy products and functional dairy ingredients. Over the last two decades, peptides have gained significant attention by scientific evidence for its beneficial health impacts besides their established nutrient value. Increasing awareness of essential milk proteins has facilitated the development of novel milk protein products that are progressively required for nutritional benefits. The need to better understand the beneficial effects of milk-protein derived peptides has, therefore, led to the development of analytical approaches for the isolation, separation and identification of bioactive peptides in complex dairy products. Continuous emphasis is on the biological function and nutritional characteristics of milk constituents using several powerful techniques, namely omics, model cell lines, gut microbiome analysis and imaging techniques. This review briefly describes the state-of-the-art approach of peptidomics and lipidomics profiling approaches for the identification and detection of milk-derived bioactive peptides while taking into account recent progress in their analysis and emphasizing the difficulty of analysis of these functional and endogenous peptides.

Verification of cheeses authenticity by mass spectrometry

Cheeses are a group of fermented dairy products that are produced all over the world in various forms and flavours. Milk, especially sheep or goat milk, is still regarded as an expensive raw material in the world, which makes milk and milk products highly attractive as a fraud target. Most often, such fraud includes partial or complete substitution with cheaper sorts of milk (e.g. bovine milk). The aim of this work was to verify the authenticity of 27 cheeses commonly emerging on the Czech food market. The cheeses were distinguished on the basis of milk animal species origin. For this purpose, two mass spectrometry techniques were used: matrix-assisted laser desorption/ionization with time of flight mass spectrometry together with principal component analysis method and liquid chromatography coupled with electrospray ionization and quadrupole time-of-flight mass spectrometry. The results were a partial success, because the cheeses could only be partially distinguished with the first mass spectrometry technique probably because of the influence of some protein additive materials in cheeses. The second technique allowed for collecting higher quality results and thus appears to be highly suitable for the research task.

Species adulteration in raw milk samples using polymerase chain reaction-restriction fragment length polymorphism

Background and Aim:

Milk adulteration is pivotal because it leads to worse effects in public health as human adverse reactions with clinical signs ranged from gastrointestinal signs to anaphylactic shock. This study was carried out to estimate the prevalence of adulteration in buffalo’s milk sold in Assiut City, Egypt.

Materials and Methods:

A total of 50 raw buffalo’s milk samples were collected and examined for adulteration by addition of cow’s milk. The examination carried out by applying polymerase chain reaction-restriction fragment length polymorphism technique using cytochrome b (cyt b) gene primers and Hinf I enzymes. The size of target gene was 360 bp in both animal species and amplicon can be digested using Hinf I enzyme, this restriction enzyme divided the essential band to clear three bands at 360, 210, and 150 bp in cows’ milk, while, the enzyme could not be cleaved the amplicon in buffalo’s samples.

Results:

The obtained results cleared that the incidence of adulteration of buffalo’s milk very high percentage reaches 90%.

Conclusion:

It could be concluded that the raw buffalo’s milk sold in Assiut City subject to fraudulent practice and thus can lead to public health hazards.

Leverage principle of retardation signal in titration of double protein via chip moving reaction boundary electrophoresis

In the present work we address a simple, rapid and quantitative analytical method for detection of different proteins present in biological samples. For this, we proposed the model of titration of double protein (TDP) and its relevant leverage theory relied on the retardation signal of chip moving reaction boundary electrophoresis (MRBE). The leverage principle showed that the product of the first protein content and its absolute retardation signal is equal to that of the second protein content and its absolute one. To manifest the model, we achieved theoretical self-evidence for the demonstration of the leverage principle at first. Then relevant experiments were conducted on the TDP-MRBE chip. The results revealed that (i) there was a leverage principle of retardation signal within the TDP of two pure proteins, and (ii) a lever also existed within these two complex protein samples, evidently demonstrating the validity of TDP model and leverage theory in MRBE chip. It was also showed that the proposed technique could provide a rapid and simple quantitative analysis of two protein samples in a mixture. Finally, we successfully applied the developed technique for the quantification of soymilk in adulterated infant formula. The TDP-MRBE opens up a new window for the detection of adulteration ratio of the poor food (milk) in blended high quality one.

A duplex polymerase chain reaction assay for the identification of goat cashmere and sheep wool

In this article attempts were made to establish one-step duplex PCR assay for the identification of goat cashmere and sheep wool. Primers were selected from published papers or designed in the well-conserved region of mitochondrial D-loop genes after alignment of the available sequences in the GenBank database. A fragment of 294 bp from cashmere goat was amplified and three PCR fragments including a bright main band of approximately 404 bp in length were obtained from sheep. The duplex PCR was found to be effective in detecting mixed samples precisely when sheep wool was mixed to goat cashmere with the relative proportion of over 9.09%. The duplex PCR could be considered as a simple and promising method in identification of goat cashmere and sheep wool.

New method for the simultaneous identification of cow, sheep, goat, and water buffalo in dairy products by analysis of short species-specific mitochondrial DNA targets

A novel method is presented here as an analytical tool for food control and authentication of dairy products manufactured from the milk of cow, sheep, goat, and buffalo. The method is based on multiplex polymerase chain reaction (PCR) of species-specific mitochondrial DNA (mtDNA) targets followed by fragment size analysis by capillary electrophoresis. The method includes (a) simultaneous detection of four species, (b) internal control for DNA extraction and PCR, (c) mtDNA as a target for PCR, (d) amplicons of <200 bp, and (e) flexibility in the electrophoresis and fragment size detection method. Species identification proved to be straightforward, efficient, sensitive, and robust. The method is sensitive to an at least 1% (v/v) relative proportion of milk in binary mixtures. A survey of commercial products showed that 12.5% failed to conform to the description of the contents, by either the introduction or absence of listed species, thus demonstrating the relevance of this type of testing.

Extração de DNA e avaliação da composição espécie-específica de queijos

Foram testados três métodos de extração de DNA em amostras de queijo, com o objetivo de identificar uma técnica eficiente para extração de DNA em amostras com várias limitações, como alto teor de gordura, alto grau de degradação do DNA e grande concentração de impurezas. A técnica que faz uso do tiocianato de guanidina mostrou-se mais adequada para identificação de adição intencional não declarada de leite bovino em queijos bubalinos, podendo ser empregada para certificação de produto específico (selo de Identidade de Espécie).

Identification of hare meat by a species-specific marker of mitochondrial origin

Meat species identification in food has gained increasing interest in recent years due to public health, economic and legal concerns. Following the consumer trend towards high quality products, game meat has earned much attention. The aim of the present work was to develop a DNA-based technique able to identify hare meat. Mitochondrial cytochrome b gene was used to design species-specific primers for hare detection. The new primers proved to be highly specific to Lepus species, allowing the detection of 0.01% of hare meat in pork meat by polymerase chain reaction (PCR). A real-time PCR assay with the new intercalating EvaGreen dye was further proposed as a specific and fast tool for hare identification with increased sensitivity (1pg) compared to end-point PCR (10pg). It can be concluded that the proposed new primers can be used by both species-specific end-point PCR or real-time PCR to accurately authenticate hare meat.

Rapid detection of bovine milk in yak milk using a polymerase chain reaction technique

Yak milk contains a greater percentage of protein and has better quality than bovine milk. There has been an increasing focus on yak milk and milk products during the last few years. In the present study, a PCR-based assay was developed for the specific identification of bovine milk in yak milk by designing 3 primers targeting the mitochondrial ND1 gene. The use of 3 primers in a single PCR reaction set yielded 2 amplification fragments of 293 and 190 bp from bovine milk DNA, whereas only 1 amplification fragment of 293 bp was obtained in yak milk DNA. The technique was applied to raw and heat-treated binary mixtures of yak and bovine milks and enabled the specific detection of bovine milk with a detection limit of 0.1%. The assay developed is sensitive, fast, and straightforward, and it might be useful in the quality control of yak milk and milk products.

A novel method for species identification in milk and milk-based products

This study describes a method for species-specific detection of animal DNA from different species (cattle, sheep, goat, water buffalo) in milk and dairy products. A primer set was designed in conserved region on the basis of the alignment of the sequence codifying the genomic κ-casein gene in order to amplify all four species with a single primer pair. Polymorphisms were detected via minisequencing with extension primers designed in conserved sequences for haplotype determination that allow unambiguous assignment to each species. The method was successfully applied to the detection of raw and pasteurized milk from the four different species considered as well as to cheese products from the retail trade. Estimation of the limit of detection was carried out using a progression of dilutions of genomic DNA as well as DNA isolated from milk of a known number of somatic cells from different species in order to be able to achieve detection rates as low as 0·1% bovine milk mixed with buffalo 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.

Conventional and real-time PCR-based approaches for molecular detection and quantitation of bovine species material in edible gelatin

The majority of edible gelatin in Europe is derived from pigskin, but a significant portion is extracted from bovine tissue. Because of the bovine spongiform encephalopathy crisis, consumers might be concerned about the gelatin used in various products. To assure consumers of the quality and safety of edible gelatin, European Union directive 1999/724/EC described general guidelines for gelatin production, including requirements for documentary proof confirming that raw materials are from animals fit for human consumption. Analytical methods to confirm gelatin documentation or raw material animal species source in the finished product are lacking. In this study, several published species-specific PCR systems were evaluated as potential molecular methods for determining the origin of the raw material used in making gelatin. A recently validated bovine species-specific PCR primer set targeting the ATPase 8 subunit gene in bovine mitochondrial DNA was suitable for detection of bovine material in gelatin. This PCR primer set was optimized using conventional and real-time PCR approaches. An evaluation of these two PCR methods confirmed the high specificity for the adopted primer set in various gelatin matrices of known origin. The inclusion of bovine gelatin in pork or fish gelatin can be detected at 0.1 to 0.001%. These PCR assays are potential molecular detection tools that can be used to routinely detect bovine gelatin either alone or as an inclusion in gelatin made from other species.

High-performance liquid chromatography of governing liquid to detect illegal bovine milk's addition in water buffalo Mozzarella: Comparison with results from raw milk and cheese matrix

A method to detect fraudulent addition of bovine milk in water buffalo Mozzarella cheese by gradient high-performance liquid chromatography (RP-HPLC), relying on the measurement of quantity ratios within beta-lactoglobulin protein family, is described. Analyses were performed on raw milk, cheese matrix and cheese governing liquid using a C4 column and UV detection. This work demonstrated that bovine milk addition during cheesemaking can be detected in governing liquid of Mozzarella down to the EU law limit of 1% as well as in raw milk and cheese matrix. A significant lowering of peaks' areas and heights was observed in cheese matrix and governing liquid samples in comparison with the corresponding milk ones, possibly due to proteins' degradation during the cheesemaking process. The results show that, unlike previous works reported, the use of a matrix-specific calibration curve is essential in order to achieve a proper quantitation of beta-lactoglobulin proteins, thus allowing a reliable estimation of bovine milk addition.

Application of Polymerase Chain Reaction to Detect Adulteration of Sheep's Milk with Goats’ Milk

The polymerase chain reaction has been applied for the specific detection of goats' milk in sheep's milk using primers targeting the mitochondrial 12S ribosomal RNA gene. The use of goat-specific primers yielded a 122-bp fragment from goats' milk DNA, whereas no amplification signal was obtained in sheep's, cows', and water buffaloes' milk DNA. Polymerase chain reaction analysis of raw and heat-treated milk binary mixtures of sheep/goat enabled the specific detection of goats' milk with a sensitivity threshold of 0.1%. This study demonstrates the usefulness of the proposed polymerase chain reaction assay for authentication of milk products in routine analysis.