Application of an indirect ELISA and a PCR technique for detection of cows’ milk in sheep's and goats’ milk cheeses

Novel and Sensitive Touchdown Polymerase Chain Reaction Assays for the Detection of Goat and Sheep Milk Adulteration with Cow Milk

Milk is the most consumed liquid food in the world due to its high nutritional value and relatively low cost, characteristics that make it vulnerable to adulteration. One of the most common types of milk adulteration involves the undeclared addition of cow's milk to milk from other mammalian species, such as goats, sheep, buffalo or donkeys. The incidence of such adulteration not only causes a crisis in terms of commercial market and consumer uncertainty but also poses a risk to public health, as allergies can be triggered by proteins in undeclared cow's milk. In this study, a specific qualitative touchdown (TD) PCR method was developed to detect the undeclared addition of cow's milk in goat and sheep milk based on the discrimination of the peak areas of the melting curves after the modification of bovine-specific primers. The developed methodology has high specificity for the DNA templates of other species, such as buffalos and donkeys, and is able to identify the presence of cow's milk down to 1%. Repeatability was tested at low bovine concentrations of 5% and 1% and resulted in %RSD values of 1.53-2.04 for the goat-cow assay and 2.49-7.16 for the sheep-cow assay, respectively. The application of this method to commercial goat milk samples indicated a high percentage of noncompliance in terms of labeling (50%), while a comparison of the results to rapid immunochromatographic and ELISA kits validated the excellent sensitivity and applicability of the proposed PCR methodology that was able to trace more adulterated samples. The developed assays offer the advantage of multiple detection in a single run, resulting in a cost- and time-efficient method. Future studies will focus on the applicability of these assays in dairy products such as cheese and yogurt.

Rapid discrimination of the identity of infant formula by triple-channel models

Infant formula is related to children's life and health. However, the existing identification methods for infant formula are time-consuming, costly and prone to environmental pollution. Therefore, a simple, efficient and less polluting identification method for infant formula is urgently needed. The aim of this study was to distinguish between goat and cow infant formula using HS-SPME-GC-MS and E-nose combined with triple-channel models. The results indicated that the main difference of them attributed to thirteen volatile compounds and three sensor variables. Based on this, the linear discriminant and partial least squares discriminant analyses were conducted, and a multilayer perceptron neural network model was constructed to identify the commercial samples. There was a high percentage of correct classifications (>90%) in samples. Together, our work demonstrated that the volatile compounds of infant formula combined with chemometric analysis were effective and rapid for detecting two infant formulas.

Development of CRISPR-Mediated Nucleic Acid Detection Technologies and Their Applications in the Livestock Industry

The rapid rate of virus transmission and pathogen mutation and evolution highlight the necessity for innovative approaches to the diagnosis and prevention of infectious diseases. Traditional technologies for pathogen detection, mostly PCR-based, involve costly/advanced equipment and skilled personnel and are therefore not feasible in resource-limited areas. Over the years, many promising methods based on clustered regularly interspaced short palindromic repeats and the associated protein systems (CRISPR/Cas), i.e., orthologues of Cas9, Cas12, Cas13 and Cas14, have been reported for nucleic acid detection. CRISPR/Cas effectors can provide one-tube reaction systems, amplification-free strategies, simultaneous multiplex pathogen detection, visual colorimetric detection, and quantitative identification as alternatives to quantitative PCR (qPCR). This review summarizes the current development of CRISPR/Cas-mediated molecular diagnostics, as well as their design software and readout methods, highlighting technical improvements for integrating CRISPR/Cas technologies into on-site applications. It further highlights recent applications of CRISPR/Cas-based nucleic acid detection in livestock industry, including emerging infectious diseases, authenticity and composition of meat/milk products, as well as sex determination of early embryos.

Sensitive identification of milk protein allergens using on-line combination of transient isotachophoresis/micellar electrokinetic chromatography and capillary isoelectric focusing in fused silica capillary with roughened part

A method for on-line concentration of milk proteins from large sample volumes using combination of transient isotachophoresis (tITP) and micellar electrokinetic chromatography (MEKC) in fused silica capillary with an inner roughened part has been developed. The method utilizes reversible dynamic adsorption of proteins onto a thin layer of PEG 4000 on the roughened surface of the capillary. In addition, the tITP/MEKC method was combined with capillary isoelectric focusing (CIEF) for on-line concentration, separation, identification and sensitive determination of proteins in skimmed milk. The method allows analysis of up to 50 μL of sample. This study has focused on the four important whey proteins, bovine serum albumin (BSA), α-lactalbumin (α-LA), and two genetic variants of β-lactoglobulin (β-LG A and β-LG B). The proteins were identified on the basis of their migration times and characteristic pI values. The pI values of BSA, α-LA, β-LG A, and β-LG B were determined as 4.7, 4.4, 5.1, and 5.2, respectively. Limits of detection for BSA, α-LA and both β-LG variants were found as 1.2, 1.0 and 1.0 pg mL^-1, respectively. The linearity of calibration curves was characterized by the R² = 0.9982. The method provided highly reproducible results as the relative standard deviations of the migration times and peak areas of the examined proteins did not exceed 1.6%.

An Inexpensive CRISPR-Based Point-of-Care Test for the Identification of Meat Species and Meat Products

The growing demand for and supply of meat and meat products has led to a proportional increase in cases of meat adulteration. Adulterated meat poses serious economic and health consequences globally. Current laboratory methods for meat species identification require specialized equipment with limited field applications. This study developed an inexpensive, point-of-care Loop-Mediated Isothermal Amplification (LAMP)-CRISPR/Cas12a colorimetric assay to detect meat species using a Texas Red-labelled single-strand (ssDNA) reporter. As low as 1.0 pg/µL of the porcine NADH4, the chicken NADH dehydrogenase subunit 2 (ND2) and the duck D-loop genes was detectable under white, blue and ultraviolet light. The test turnaround time from DNA extraction to visualization was approximately 40 min. The assay accurately detected pure and mixed-meat products in the laboratory (n = 15) and during a pilot point-of-care test (n = 8) in a food processing factory. The results are 100% reproducible using lateral flow detection strips and the real-time PCR detection instrument. This technology is fully deployable and usable in any standard room. Thus, our study demonstrates that this method is a straightforward, specific, sensitive, point-of-care test (POCT) adaptable to various outlets such as customs, quarantine units and meat import/export departments.

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.

Real Time-PCR coupled with melt curve analysis for detecting the authenticity of camel milk

The study evaluated the use of Real Time-Polymerase Chain Reaction (RT- PCR) to detect the adulteration of camel milk with goat, cow milk. DNA was isolated from camel milk, camel milk powder, camel milk soap, cow milk, and goat milk using DNA extraction kit. RT- PCR amplified a single piece of DNA into millions of copies. The camel specific primers were designed using the primer- 3 online software and quantification of the isolated DNA was carried out by RT- PCR system through DNA standard curves and cycle threshold (Ct) values. The detection limit of DNA template was in the range of 0.001-0.002%. The reaction mixture (20μL) contained 10 μL SYBR Green master mix, 0.3 μL of 10 μM of each primer and 5 μL DNA. Thermal cycling consisted of an initial denaturation at 95 °C for 1 min, followed by 40 cycles for 15 s at 95 °C and 60 °C for 30 s. The primer pairs used were confirmed for their PCR efficiency, and specific products were evaluated by melt curve analysis. Results indicated positive amplification for the camel milk, camel milk powder, and camel milk soap but negative amplification for cow and goat milk. In conclusion, the RT- PCR based identification is a low cost and appropriate method for camel milk and its products. Although, the yield of DNA from camel milk soap after isolation is low but the isolated DNA segment was easily identified.

Multiple authentications of high-value milk by centrifugal microfluidic chip-based real-time fluorescent LAMP

Adulteration of food ingredients, particularly replacement of high-value milk with low-cost milk, affects food safety. For rapid and accurate identification of the possible adulterating milk species in an unknown sample, a centrifugal microfluidic chip-based real-time fluorescent multiplex loop-mediated isothermal amplification (LAMP) assay was developed to simultaneously detect milk from cow, camel, horse, goat, and yak. Using precoated primers in different reaction wells, the centrifugal microfluidic chip markedly simplified the detection process and reduced false-positive results. The entire amplification was completed within 90 min with a genomic detection limit of 0.05 ng/µL in cow, camel, horse, and goat milk and 0.005 ng/µL in yak milk. Using simulated adulterated samples for validation, the detection limit for adulterated milk samples was 2.5%, satisfying authentication requirements, as the proportion of adulterated milk higher than 10% affects economic interests. Therefore, this simple, centrifugal, microfluidic chip-based multiplex real-time fluorescent LAMP assay can simultaneously detect common milk species in commercial products to enable accurate labeling.

Quantitative determination of mutton adulteration with single-copy nuclear genes by real-time PCR

Mitochondrial genes were generally adopted for PCR-based meat adulteration authentication due to their excellent specificity to species and numerous copies in one cell. However, the number of mitochondrial gene copies varies according to cells and tissues, which leads to quantification errors for meat adulteration. To address this problem, single-copy nuclear genes were selected to develop a quantitative method for identifying mutton adulteration in this study. Both single-copy genes specific to sheep species and single-copy reference genes show good linearity between Ct values and series diluted DNA concentrations, with the correlation coefficients of 0.9999 and 0.9993, respectively. Meanwhile, a constant (correction factor) was introduced to transform DNA concentrations into mutton proportions in adulterated meat. With this method, simulated mutton-pork, mutton-chicken and mutton-duck adulteration samples could be accurately quantified with the recovery rates of 89.56%, 107.13% and 95.20%, respectively.

Rapid detection of mozzarella and feta cheese adulteration with cow milk through a silicon photonic immunosensor

Mozzarella di Bufala Campana and Feta are two cheeses with Protected Designation of Origin the fraudulent adulteration of which with bovine milk must be routinely checked to ensure that consumers actually buy these high-end products and avoid health issues related to bovine milk allergy. Here, we employed, for the first time, a silicon-based photonic immunosensor for the detection of mozzarella and feta adulteration with bovine milk. The photonic immunosensor used relies on Mach-Zehnder interferometers monolithically integrated along with their respective light sources on a silicon chip. A rabbit polyclonal antiserum raised against bovine κ-casein was used for the development of a competitive immunoassay realized in three steps, including a reaction with the antiserum, a biotinylated anti-rabbit IgG antibody, and streptavidin. The implementation of this assay configuration significantly reduced the non-specific signal due to the cheese matrix, and allowed completion of the assay in ∼9 min. After optimization of all assay conditions, bovine cheese could be quantified in mozzarella or feta at concentrations as low as 0.5 and 0.25% (w/w), respectively; both quantification limits were below the maximum allowable content of bovine milk in mozzarella and feta (1% w/w) according to the EU regulations. Equally important, the assays were reproducible with intra- and inter-assay coefficients of variation <10%, and exhibited a wide linear dynamic range that extended up to 50 and 25% (w/w) for mozzarella and feta, respectively. Taking into account its performance, the proposed immunosensor may be transformed to a new tool against fraudulent activities in the dairy industry.

A fast and reliable polymerase chain reaction method based on short interspersed nuclear elements detection for the discrimination of buffalo, cattle, goat, and sheep species in dairy products

Objective

Aim of present study was the set up of a fast and reliable protocol using species-specific markers for the quali-quantitative analysis of DNA and the detection of ruminant biological components in dairy products. For this purpose, the promoter of the gene coding for the α-lactoalbumin (LALBA) was chosen as possible candidate for the presence of short interspersed nuclear elements (SINEs).

Methods

DNA was isolated from somatic cells of 120 individual milk samples of cattle (30), Mediterranean river buffalo (30), goat (30), and sheep (30) and the gene promoter region (about 600/700 bp) of LALBA (from about 600 bp upstream of exon 1) has been sequenced. For the development of a single polymerase chain reaction (PCR) protocol that allows the simultaneous identification of DNA from the four species of ruminants, the following internal primers pair were used: 5′-CACTGATCTTAAAGCTCAGGTT-3′ (forward) and 5′-TCAGA GTAGGCCACAGAAG-3′ (reverse).

Results

Sequencing results of LALBA gene promoter region confirmed the presence of SINEs as monomorphic “within” and variable in size “among” the selected species. Amplicon lengths were 582 bp in cattle, 592 bp in buffalo, 655 in goat and 729 bp in sheep. PCR specificity was demonstrated by the detection of trace amounts of species-specific DNA from mixed sources (0.25 ng/μL).

Conclusion

We developed a rapid PCR protocol for the quali-quantitative analysis of DNA and the traceability of dairy products using a species-specific marker with only one pair of primers. Our results validate the proposed technique as a suitable tool for a simple and inexpensive (economic) detection of animal origin components in foodstuffs.

Rapid capillary electrophoresis approach for the quantification of ewe milk adulteration with cow milk

The substitution of ewe milk with more economic cow milk is a common fraud. Here we present a capillary electrophoresis method for the quantification of ewe milk in ovine/bovine milk mixtures, which allows for the rapid and inexpensive recognition of ewe milk adulteration with cow milk. We utilized a routine CE method for human blood and urine proteins analysis, which fulfilled the separation of skimmed milk proteins in alkaline buffer. Under this condition, ovine and bovine milk exhibited a recognizable and distinct CE protein profiles, with a specific ewe peak showing a reproducible migration zone in ovine/bovine mixtures. Based on ewe specific CE peak, we developed a method for ewe milk quantification in ovine/bovine skimmed milk mixtures, which showed good linearity, precision and accuracy, and a minimum amount of detectable fraudulent cow milk equal to 5%.

Detection of ovine milk adulteration using taqman real-time pcr assay

Food safety, quality and composition have become the subjects of increasing public concern. To prevent fraud and enhance quality assurance, credible analysis of dairy products is crucial. Bovine milk is more widely available and cheaper than milk of sheep and goat. Bovine milk is also processed in large quantities to produce a range of dairy produce. DNA-based methods have proven to be more reliable, because of the stability of DNA under the conditions of high temperature, high pressure, and chemical treatment used during the processing of some food products. The commercial InnuDETECT cheese assay based on the principle TaqMan real-time PCR systems have been tested for the identification and quantification of bovine DNA in ovine milk samples. DNA was extracted using the InnuPREP DNA Mini Kit and quantified by the QuantiFluor dsDNA system. The assay showed good linearity, with correlation coefficient of R2 = 0.983 and efficiency of 86%. The internal control amplified fragment from different mammalian species (cow, sheep and goat), with similar CT values. Detection of bovine DNA in milk mixtures was achieved even in samples containing 0.5% of bovine milk. The InnuDETECT cheese assay has been successfully used to measure bovine DNA in ovine milk, and will prove useful for bovine species identification and quantitative authentication of animal-derived products.

Validation of a fast real-time PCR method to detect fraud and mislabeling in milk and dairy products

Fast real-time PCR TaqMan assays were developed and validated for species identification in dairy products. Based on the amplification of 12S rRNA and cytB partial genes of mitochondrial DNA, the methods were demonstrated to be sensitive, fast, and species-specific for Bos taurus, Ovis aries, Bubalus bubalis, and Capra hircus. The limit of detection calculated was lower than 1%, and the efficiency was reported to be higher than 96% in every assay. An internal amplification control was used to detect possible false negatives. The method was validated by means of laboratory-prepared samples mixing different species. Moreover, 18 commercial dairy samples were analyzed by both real-time PCR and isoelectric focusing, the official European Union reference method. The 4 TaqMan assays were confirmed to be a useful tool for milk and dairy product authentication.

Development of a real-time quantitative PCR assay using a TaqMan minor groove binder probe for the detection of α-lactalbumin in food

Here, we report the development of a real-time PCR assay using a TaqMan minor groove binder (MGB, Genecore, NCBI: AF249896.1, 806-820) probe and primer sets designed to recognize the α-lactalbumin gene from the cow (Bos taurus). We evaluated the efficacy of this assay for detecting and quantifying cow α-lactalbumin in commercial foods. Our results demonstrated that the developed method was highly sensitive and showed high specificity for cow milk, with consistent detection of 0.05 ng of bovine DNA. We tested 42 commercial food samples with or without cow milk listed as an ingredient by using the developed assay. Among the 42 samples, 26 products that listed milk as an ingredient and 3 products might contain milk showed positive signals, whereas the other 9 products that did not contain milk and 4 products that might contain milk tested negative. Therefore, this method could be widely used for the detection of cow milk allergens in food.

Assessment of goat milk adulteration with a label-free monolithically integrated optoelectronic biosensor

The label-free detection of bovine milk in goat milk through a miniaturized optical biosensor is presented. The biosensor consists of ten planar silicon nitride waveguide Broad-Band Mach-Zehnder interferometers (BB-MZIs) monolithically integrated and self-aligned with their respective silicon LEDs on the same Si chip. The BB-MZIs were transformed to biosensing transducers by functionalizing their sensing arm with bovine k-casein. Measurements were performed by continuously recording the transmission spectra of each interferometer through an external spectrometer. The amount of bovine milk in goat milk was determined through a competitive immunoassay by passing over the sensor mixtures of anti-k-casein antibodies with the calibrators or the samples. The output spectra of each BB-MZI recorded during the reaction were subjected to Discrete Fourier Transform in order to convert the observed spectral shifts to phase shifts in the wavenumber domain. The method had a detection limit of 0.04 % (v/v) bovine milk in goat milk, dynamic range 0.1-1.0 % (v/v), recoveries 93-110 %, and intra- and inter-assay coefficients of variation less than 12 and 15 %, respectively. The proposed biosensor compared well in terms of analytical performance with a competitive ELISA developed using the same monoclonal antibodies. Nevertheless, the duration of the biosensor assay was 10 min whereas the ELISA required 2 h. Thus, the fast and sensitive determinations along with the small size of the sensor make it ideal for incorporation into portable devices for assessment of goat or ewe's milk adulteration with bovine milk at the point-of-need.

Quantification of cow's milk percentage in dairy products - a myth?

The substitution of ewe's and goat's milk for cheaper cow's milk is still a fraudulent practice in the dairy industry. Moreover, soy-based products (e.g., soy milk, yoghurt) have to be checked for cow's milk as they are an alternative for people suffering from an allergy against bovine milk proteins. This work reports the evaluation of different protein-based electrophoretic methods and DNA-based techniques for the qualitative detection as well as the quantitative determination of cow's milk percentage in dairy and soy milk products. Isoelectric focusing (IEF) of γ-caseins using an optimized pH gradient was appropriate not only for the detection of cow's milk, but also for an estimation of cow's milk percentage in mixed-milk cheese varieties. Urea-polyacrylamide gel electrophoresis (PAGE) proved the method of choice to detect cow's milk in soy milk products, whereas IEF and SDS-PAGE of proteins were not applicable due to false-positive results. Polymerase chain reaction (PCR) analysis was used to confirm the results of protein-based electrophoretic methods. Problems inherent in quantitative analysis of cow's milk percentage using protein-based techniques and even more using DNA-based methods were emphasized. Applicability of quantitative real-time PCR for the determination of cow's milk percentage in mixed-milk cheese was shown to be hampered by several factors (e.g., somatic cell count of milk; technological parameters influencing the final DNA concentration in ripened commercial cheese samples). The implementation of certified reference standards (of major relevant cheese groups) containing 50% cow's milk was urgently recommended to enable at least a yes/no decision in commercial mixed-milk cheese samples.