Avian-specific real-time PCR assay for authenticity control in farm animal feeds and pet foods

A Simple and Reliable Single Tube Septuple PCR Assay for Simultaneous Identification of Seven Meat Species

Multiplex PCR methods have been frequently used for authentication of meat product adulteration. Through screening of new species-specific primers designed based on the mitochondrial DNA sequences, a septuple PCR method is ultimately developed and optimized to simultaneously detect seven species including turkey (110 bp), goose (194 bp), pig (254 bp), sheep (329 bp), beef (473 bp), chicken (612 bp) and duck (718 bp) in one reaction. The proposed method has been validated to be specific, sensitive, robust and inexpensive. Taken together, the developed septuple PCR assay is reliable and efficient, not only to authenticate animal species in commercial meat products, but also easily feasible in a general laboratory without special infrastructures.

The Quality of DNA Isolated from Processed Food and Feed via Different Extraction Procedures

The extraction of DNA is a critical step for species identification by PCR analysis in processed food and feed products. In this study, eight DNA extraction procedures were compared—DNeasy Blood and Tissue Kit, DNeasy mericon Food Kit, chemagic DNA Tissue 10 Kit, Food DNA Isolation Kit, UltraPrep Genomic DNA Food Mini Prep Kit, High Pure PCR Template Preparation Kit, phenol—chloroform extraction, and NucleoSpin Food—Using self-prepared samples from both raw and heat-processed and/or mechanically treated muscles and different types of meat products and pet food (pork, beef, and chicken). The yield, purity, and suitability of DNA for PCR amplification was evaluated. Additionally, comparisons between the effectiveness of various extraction methods were made with regard to price, and labor- and time-intensiveness. It was found that the DNeasy mericon Food Kit was the optimal choice for the extraction of DNA from raw muscle, heat-treated muscle, and homemade meat products from multiple and single species.

A Multiplex PCR Assay Mediated by Universal Primers for the Detection of Adulterated Meat in Mutton

This study aimed to establish a multiplex PCR detection system mediated by "universal primers," which would be able to determine whether mutton meat contained nonmutton ingredients from rats, foxes, and ducks. Based on the sequence variation of specific mitochondrial genes, nine different multiplex PCR primers were designed, and four kinds of meat products were rapidly identified by electrophoresis using an optimized multiplex PCR system based on the molecular weight differences of the amplified products. Multiplex PCR applications optimized for meat food source from food samples for testing was used to verify the accuracy of the identification method. The results showed that the primers in multiple PCR system mediated by universal primers could be used for the rapid identification of rat, fox, duck, and sheep meat in mutton products, and the detection sensitivity could reach 0.05 ng/μL. The identification of food samples validated the practical value of this method. Therefore, a multiplex PCR system mediated by universal primers was established, which can be used to quickly identify the origin of animal ingredients from rats, foxes, and ducks in mutton products.

Bridging legal requirements and analytical methods: a review of monitoring opportunities of animal proteins in feed

Availability and safety of food ranks among the basic requirements for human beings. The importance of the food producing sector, inclusive of feed manufacturing, demands a high level of regulation and control. This paper will present and discuss the relationships in the triangle of legislation, the background of hazards with a biological nature, and opportunities for monitoring methods, most notable for prion-based diseases as primary issue. The European Union legislation for prevention of prion-based diseases since 2000 is presented and discussed. The definitions and circumscriptions of groups of species will be analysed in the view biological classification and evolutionary relationships. The state of the art of monitoring methods is presented and discussed. Methods based on visual markers (microscopy), DNA-based methods (PCR), protein-based methods (ELISA, mass spectroscopy, proteomics), near infrared oriented methods and combinations thereof are being evaluated. It is argued that the use in legislation of non-homogeneous groups of species in a biological sense will hamper the optimal design of monitoring methods. Proper definitions are considered to act as bridges between legal demands and suitable analytical methods for effective monitoring. Definitions including specified groups of species instead of single species are more effective for monitoring in a range of cases. Besides the desire of precise circumscription of animal groups targeted by legislation, processed products need well defined definitions as well. Most notable examples are blood versus blood products, and hydrolysis of several types of material. The WISE principle for harmonising the design of legislation and of analytical methods is discussed. This principle includes the elements Witful (reasonable legal principles), Indicative (clear limits between prohibition and authorisation), Societal demands (public health, environment, economy), and Enforceable (presence of suited monitoring methods) in order to promote a balanced effort for reaching the desired level of safety in the food production chain.

Cross-contamination in canine and feline dietetic limited-antigen wet diets

Background

Adverse food reactions (AFRs) are defined as abnormal responses to an ingested food or food additive. Diagnosis and treatment of AFRs consist of the complete elimination of these ingredients in the dietary trial. Previous studies have demonstrated the presence of undeclared ingredients in commercial limited-antigen dry food diets that can compromise the results and efficacy of dietary elimination trails. The aim of this study was to assess a selection of commercial canine and feline dietetic limited-antigen wet foods for the potential cross-contamination of animal proteins from origins not mentioned on the label.

Results

Eleven canine and feline dietetic limited-antigen wet foods (9 novel animal protein foods, 1 vegetarian and 1 hydrolyzed) were analyzed by polymerase chain reaction (PCR) to detect the presence DNA of animal and vegetal origins. PCR analysis confirmed the contamination of 6 of the 11 (54.5%) limited-antigen wet diets with undeclared animal protein. One of these 6 diets was solely composed of animal protein sources completely unrelated to those declared on the label. None of the foods containing horse meat or fish were contaminated, and neither were the vegetarian or the hydrolyzed food products. Moreover, the results show that had zoological class primers only been used to check for cross-class contaminations, as are generally used in the pet food industry for in-house checks, the apparent contamination rate would have been significantly underestimated: less than 20% (3/11), instead of the actual rate of 54.7% using species-specific primers.

Conclusion

This study reveals a high rate of cross-contamination in dietetic limited-antigen wet canine and feline foods, as previously described for dietetic dry limited-antigen foods (reported to be more than 80%). These results add new fuel to the discussion about the potential causes underlying the failure of elimination diets, since animal protein contaminants may actually be present in the commercial dietetic limited-antigen diets. AFRs may therefore occur as a result of inadequate practices in the pet food industry.

Qualitative and quantitative detection of chicken deoxyribonucleic acid (DNA) in dry dog foods

Chicken is a common protein source in pet foods and is concurrently listed among food allergens. Commercial over-the-counter (OTC) diets with an alternative animal protein source are considered suitable for dietary elimination trials by pet owners. The potential presence of undeclared chicken-derived ingredients in these diets can compromise the outcome of the trial during the diagnosis of adverse food reactions. The aim of this study was to selectively verify the absence or presence of chicken DNA in 10 OTC dry canine foods, using qualitative and quantitative approaches. The method of identification of chicken-derived protein was elaborated with the polymerase chain reaction (PCR) technology, whereas quantitative real-time PCR was used for the quantitative assessment. In most of the analysed samples, the chicken DNA was detectable; however, the quantified amounts were predominantly low, although differences between batches were observed.

Critically appraised topic on adverse food reactions of companion animals (5): discrepancies between ingredients and labeling in commercial pet foods

Background

Elimination dietary trials for the diagnosis of adverse food reactions (food allergies) in dogs and cats are often conducted with commercial pet foods while relying on their label to select those not containing previously-eaten ingredients. There are concerns that industrial pet foods might contain unlisted food sources that could negate the usefulness of performing food trials. Furthermore, unidentified ingredients might cause clinical reactions in patients hypersensitive to such items.

Results

We searched two article databases on July 7, 2017 and January 12, 2018 for relevant articles, and we screened abstracts from the leading international veterinary dermatology congresses for suitable material. Additional citations were found in the selected papers. In all, we extracted data from 17 articles and one abstract. The studies varied both in the number of pet foods tested (median: 15; range: 1 to 210) and that of ingredients specifically evaluated (median: 4; range: 1 to 11). Studies most often employed either PCR to detect DNA or ELISA to identify proteins from one or more vegetal or animal species; two studies used mass spectrometry to increase the number of detectable proteins. The various methods found ingredients that were not on the label in 0 to 83% (median: 45%) of tested diets; this percentage varied between 33 and 83% in pet foods with “novel/limited” ingredients proposed for elimination diets. Similarly, ingredients were found to be missing from the label in 0 to 38% (median: 1%) of tested foods. Finally, six studies evaluated, among others, several hydrolysate-containing pet foods: mislabeling with unlabeled or missing ingredients was found only in one diet.

Conclusions

The mislabeling of pet foods appears rather common, even in those with “novel” or “limited” ingredients proposed for elimination diets. Unexpected added ingredients are more frequently detected than those missing from the label. There is insufficient information to determine if the presence of a contaminating component will lead to a clinical reaction in a patient allergic to it, as challenges with the mislabeled foods were not performed in dogs or cats allergic to such ingredients. The testing of hydrolysate-containing pet foods found only one instance of possible mislabeling.

Electronic supplementary material

The online version of this article (10.1186/s12917-018-1346-y) contains supplementary material, which is available to authorized users.

Determination of mammalian deoxyribonucleic acid (DNA) in commercial vegetarian and vegan diets for dogs and cats

The determination of undeclared ingredients in pet food using different analytical methods has been reported in recent years, raising concerns regarding adequate quality control, dietary efficacy and the potential for purposeful adulteration. The objective of this study was to determine the presence or absence of mammalian DNA using multiplex polymerase chain reaction (PCR) on diets marketed as vegetarian or vegan for dogs and cats. The diets were tested in duplicate; two samples were purchased approximately 3 to 4 months apart with different lot numbers. Multiplex PCR-targeted mitochondrial DNA with two species-specific primers was used to amplify and sequence two sections of the cytochrome b gene for each of the 11 mammalian species. Half of the diets assessed (7/14) were positive for one or more undeclared mammalian DNA source (bovine, porcine, or ovine), and the result was repeatable for one or more species in six diets. While most of the detected DNA was found at both time points, in some cases, the result was positive only at one time point, suggesting the presence may have been due to unintentional cross-contact with animal-sourced ingredients. DNA from feline, cervine, canine, caprine, equine, murine (mouse and rat) and leporine was not identified in any samples. However, evidence of mammalian DNA does not confirm adulteration by the manufacturer nor elucidate its clinical significance when consumed by animals that may benefit from a vegetarian or vegan diet.

The development of a hexaplex-conventional PCR for identification of six animal and plant species in foodstuffs

A hexaplex-conventional PCR assay was developed for identification of five meat and one plant species origins in foodstuffs simultaneously. The method merges the use of horse (Equus caballus), soybean (Glycine max), sheep (Ovis aries), poultry (Meleagris meleagris), pork (Sus scrofa), and cow (Bos taurus) specific primers that amplify fragments (horse; 85 bp, soybean; 100 bp, sheep; 119 bp, poultry; 183 bp, pork; 212 bp and cow; 271 bp) of the mitochondrial cyt b, lectin, 12S rRNA, 12S rRNA, ATPase subunit 6 genes and ATPase subunit 8 genes respectively, and a universal 18S rRNA primers that amplifies a 141 bp. Multiplex analysis of the reference food samples showed that detection limit of the hexaplex assay was 0.01% for each species. Taken together, all data indicated that this hexaplex PCR assay was a simple, fast, sensitive, specific, and cost-effective detection method for horse, soybean, sheep, poultry, pork and cow species in foodstuffs.

Rapid bovine and caprine species identification in ruminant feeds by duplex real-time PCR melting curve analysis using EvaGreen fluorescence dye

A duplex real-time PCR assay with melting curve analysis, using the EvaGreen fluorescence dye, was developed for rapid and reliable identification of bovine and caprine in ruminant feeds. The method merges the use of bovine (Bos taurus) and caprine (Capra hircus) specific primers that amplify small fragments (bovine 96 bp and caprine 142 bp) of the mitochondrial 16S rRNA and 12S rRNA genes, respectively. DNA was isolated from heat-treated meats (133 °C/3 bar for 20 min) mixtures of bovine and caprine and was used to optimize the assay. Gene products of caprine and bovine produced two distinct melting peaks simultaneously at 82 and 86.8 °C, respectively. Duplex analysis of the reference samples showed that the detection limit of the assay was 0.003 % for bovine and 0.005 % for caprine species. The aim of this study was to develop a duplex real-time PCR assay followed by a melt curve step for sensitive, rapid, specific, and cost-effective detection of bovine and caprine species based on the amplicon melting peak in ruminant feeds to prevent Transmissible Spongiform Encephalopathies.

A higher sensitivity and efficiency of common primer multiplex PCR assay in identification of meat origin using NADH dehydrogenase subunit 4 gene

A Common Primer Multiplex PCR (CP-M-PCR) was developed to detect meat origin of four groups of animal (pig, ruminant, avian and rabbit). This method demonstrated higher sensitivity and efficiency than the conventional multiplex PCR. In this approach, a common forward primer was designed in the 5' end of a homologous region of mitochondrial NADH dehyrogenase subunit 4 (Nad 4) gene sequences of all the animal groups. Specific adapter reverse primers were designed by adding an adapter sequence at the 5' end. The same adapter sequence was used as the common adapter reverse primer. The primers generated specific fragments of 267, 370, 504, and 548 bp lengths for pig, ruminant, avian and rabbit meats, respectively. The use of adapter sequence at the 5' end of the common adapter reverse primers increased the efficiency of the amplification and the application of a common forward primer solved the complexity in multiplex PCR system. Bands of specific amplification can be detected in the PCR assays containing as low as 10(-6) μM of adapter reverse primer. This result indicated that the sensitivity was tremendously increased as compared to the conventional multiplex PCR (10(-3) μM). CP-M-PCR detection limit of the DNA samples was 0.1 ng for the four groups of meats. CP-M-PCR has greatly improved the sensitivity and efficiency of the PCR system for a more reliable and accurate outcome than conventional multiplex PCR system.