Detection of hazelnut (Corylus spp.) in processed foods using real-time PCR

Detection of Hazelnut and Almond Adulteration in Olive Oil: An Approach by qPCR

Virgin olive oil (VOO), characterized by its unique aroma, flavor, and health benefits, is subject to adulteration with the addition of oils obtained from other edible species. The consumption of adulterated olive oil with nut species, such as hazelnut or almond, leads to health and safety issues for consumers, due to their high allergenic potential. To detect almond and hazelnut in olive oil, several amplification systems have been analyzed by qPCR assay with a SYBR Green post-PCR melting curve analysis. The systems selected were Cora1F2/R2 and Madl, targeting the genes coding the allergenic protein Cor a 1 (hazelnut) and Pru av 1 (almond), respectively. These primers revealed adequate specificity for each of the targeted species. In addition, the result obtained demonstrated that this methodology can be used to detect olive oil adulteration with up to 5% of hazelnut or almond oil by a single qPCR assay, and with a level as low as 2.5% by a nested-qPCR assay. Thus, the present research has shown that the SYBR-based qPCR assay can be a rapid, precise, and accurate method to detect adulteration in olive oil.

Tree Nuts and Peanuts as a Source of Beneficial Compounds and a Threat for Allergic Consumers: Overview on Methods for Their Detection in Complex Food Products

Consumption of tree nuts and peanuts has considerably increased over the last decades due to their nutritional composition and the content of beneficial compounds. On the other hand, such widespread consumption worldwide has also generated a growing incidence of allergy in the sensitive population. Allergy to nuts and peanuts represents a global relevant problem, especially due to the risk of the ingestion of hidden allergens as a result of cross-contamination between production lines at industrial level occurring during food manufacturing. The present review provides insights on peanuts, almonds, and four nut allergens—namely hazelnuts, walnuts, cashew, and pistachios—that are likely to cross-contaminate different food commodities. The paper aims at covering both the biochemical aspect linked to the identified allergenic proteins for each allergen category and the different methodological approaches developed for allergens detection and identification. Attention has been also paid to mass spectrometry methods and to current efforts of the scientific community to identify a harmonized approach for allergens quantification through the detection of allergen markers.

Recent Advances in the Detection of Allergens in Foods

Food allergy is a public health issue that has significantly increased worldwide in the past decade affecting consumers' quality of life and making increasing demands on health service resources. Despite recent advances in many areas of diagnosis and treatment, our general knowledge of the basic mechanisms of the disease remained limited, i.e., not at pace with the exponential number of new cases and the explosion of the new technologies. For sensitized individuals, the only effective way to prevent allergic reactions is the strict avoidance of the offending food. For this reason, a number of regulatory bodies in several countries have recognized the importance of providing information about the presence of food allergens by enacting laws, regulations, or standards for food labeling of "priority allergens." This has resulted in the need for the development of analytical methods for protection of food-allergic consumers that should be among others highly specific, sensitive, and not influenced by the presence of the food matrix components. Several analytical approaches target either the allergen itself or a corresponding allergen marker such as peptide fragment or gene segment and have been used in the detection and quantification of allergens in food products. In this short review, some of the conventional and new methods for the detection of allergens in food are listed and briefly discussed.

Egg and Milk Proteins as Hidden Allergens in Food: 5-Year (2010 to 2014) Results of Food Allergen Monitoring in Piedmont, Italy

Cow's milk and egg allergies are two of the most common food allergies. Manufacturers of food products containing milk or eggs or their derivatives as an ingredient are required by European Union regulations to list their presence on the ingredient label. Under European Union legislation, member states are mandated to carry out food safety monitoring programs to verify compliance with food labeling requirements. Through the Regional Integrated Plan for Food Safety, the Piedmont (Italy) regional authority carries out an annual program to determine the presence of undeclared allergens in foods. In the 5-year period from 2010 to 2014, a total of 1,566 food samples were analyzed for the presence of hidden egg and milk proteins. The average positive percentage was 2.8% (3.6% egg and 2% milk proteins). Comparison between the allergen concentration and the published eliciting dose (ED) for egg proteins (0.03 mg) and for total milk proteins (0.1 mg) indicated a high risk of allergen exposure for sensitized consumers. The calculated exposure was up to 135× (for milk) the ED01 reported in the literature. Food manufacturers will need to improve their allergen control programs to reduce allergen exposure and risk.

Using Real-Time PCR as a tool for monitoring the authenticity of commercial coffees

Coffee is one of the main food products commercialized in the world. Its considerable market value among food products makes it susceptible to adulteration, especially with cereals. Therefore, the objective of this study was to develop a method based on Real-Time Polymerase Chain Reaction (PCR) for detection of cereals in commercial ground roast and soluble coffees. After comparison with standard curves obtained by serial dilution of DNA extracted from barley, corn and rice, the method was sensitive and specific to quantify down to 0.6 pg, 14 pg and 16 pg of barley, corn and rice DNA, respectively. To verify the applicability of the method, 30 commercial samples obtained in different countries were evaluated and those classified as gourmets or superior did not present the tested cereals DNA. However, barley was detected in various traditional (cheaper) samples from South America. In addition, corn and rice were also detected in different samples. Real-Time PCR showed to be suitable for detection of food adulterants in commercial ground roast and soluble coffees.

Simultaneous detection of peanut and hazelnut allergens in food matrices using multiplex PCR method

Multiplex PCR analysis for the detection of two targeting segments of genes coding major food protein allergens as peanut (Arachis hypogaea) Ara h 1 gene and hazelnut (Corylus avellana) Cor a 1 gene was developed. Two sets of primers were designed and tested to their specificity on a broad range of ingredients. The identity of amplicons (Ara h 1- 180 bp, Cor a 1 – 258 bp) by sequencing and alignment of sequences with sequences deposited in Genbank was confirmed. When testing the specificity of designed primer pairs on a spectrum of food ingredients, no cross reactions were detected. A potential inhibition of PCR reaction was eliminated using the universal plant primers of chloroplast gene 124 bp for the plant matrices confirmation. The intrinsic detection limit was 10 pg·ml-1 and the practical detection limit was 0.001% w/w (10 mg·kg-1) for both peanuts and hazelnuts. The method was applied to the investigation of 60 commercial food samples. The developed multiplex PCR method is cheap, specific and sensitive enough and can be used as a simple, one day procedure for the checking of undeclared peanut and hazelnut major allergens in food.

A highly sensitive and specific tetraplex PCR assay for soybean, poultry, horse and pork species identification in sausages: development and validation

A tetraplex PCR assay was developed for a rapid and reliable identification of horse, soybean, poultry, and pork species in sausages simultaneously. The method merges the use of horse (Equus caballus), soybean (Glycine max), poultry (Gallus gallus), and pork (Sus scrofa) specific primers that amplify small fragments (horse; 85bp, soybean; 100bp, poultry; 183bp and pork; 212bp) of the mitochondrial cyt b, lectin, 12S rRNA and ATPase subunit 6 genes respectively. Good quality DNA was isolated from reference sausage to optimize the assay. Tetraplex analysis of the reference sausage samples showed that the detection limit of the assay was 0.01% for each species. Taken together, all data indicated that this tetraplex PCR assay was a simple, rapid, sensitive, specific, and cost-effective detection method for horse, soybean, poultry, and pork species in commercial sausages.

Variability of Corylus avellana, L. CorA and profilin pollen allergens expression

Corylus avellana is the source of inhalant allergies induced by hazel pollen as well as food allergies induced after ingestion of hazelnuts. In this study, real-time PCR approach was used to analyse expression of hazel pollen allergens on the molecular level. Relative quantity of hazelnut allergens Corylus avellana, L. CorA and Corylus avellana, L. pollen profiling in samples from different Ukraine areas were determining and comparing. Differences among the levels of both analysed allergen transcripts were found for hazel CorA and profillin. In both cases, the expression within the urbanized growth conditions was higher when compared to the sample from village area. The average expression for CorA was 0.84 times higher than for profilin and the results are very variable depending on the place of growth. Expression levels here were within the range of 2.957 up to the 52.936. Profilin expression was the highest in the sample from the polluted place of growth-cement plant area with the value of 52 times higher when compared to the sample from the village area. In this study, comparison of expression levels of hazel CorA and profiling pollen allergens was performed for the first time. Real-time PCR assay developed in this study proved the sensitivity for detection of the changes of the hazel pollen allergens expression levels and could benefit labs by fast and reproducible detection method of these allergens.

Changes in expression of BetV1 allergen of silver birch pollen in urbanized area of Ukraine

The aim of the study was to determinate the level of expression of silver birch allergen Betv1 in pollen samples from different Ukraine areas by RT-qPCR SYBR Green assay. Protocol for quantifying the expression of Betv1 allergen was developed when testing of three housekeeping genes-cyclophylin, alpha-tubulin and transcription factor CBF1. Samples from urbanized area was analysed by real-time PCR when a sample from forest growth conditions was used as a calibrator. Real-time PCR based quantifying of Betv1 provides a useful method for rapid and sensitive analyses of this silver birch allergen. Our results show higher expression levels in samples from central parts of urbanized area as housing estates when compared to the samples from borders of the urbanized area.

Multiplex DNA detection of food allergens on a digital versatile disk

The development of a DNA microarray method on a digital versatile disk (DVD) is described for the simultaneous detection of traces of hazelnut ( Corylus avellana L.), peanut ( Arachis hypogaea ), and soybean ( Glycine max ) in foods. After DNA extraction, multiplex PCR was set up using 5'-labeled specific primers for Cor a 1, Ar h 2, and Le genes, respectively. Digoxin-labeled PCR products were detected by hybridization with 5'-biotinylated probes immobilized on a streptavidin-modified DVD surface. The reaction product attenuates the signal intensity of the laser that reached the DVD drive used as detector, correlating well with the amount of amplified sequence. Analytical performances showed a detection limit of 1 μg/g and good assay reproducibility (RSD 8%), suitable for the simultaneous detection of the three targeted allergens. The developed methodology was tested with several commercially available foodstuffs, demonstrating its applicability. The results were in good agreement, in terms of sensitivity and reproducibility, with those obtained with ELISA, PCR-gel agarose electrophoresis, and RT-PCR.

Simultaneous detection of DNA from 10 food allergens by ligation-dependent probe amplification

The simultaneous detection of DNA from different allergenic food ingredients by a ligation-dependent probe amplification (LPA) system is described. The approach allows detection of several targets in a one-tube assay. Synthetic oligonucleotides were designed to detect DNA from peanuts, cashews, pecans, pistachios, hazelnuts, sesame seeds, macadamia nuts, almonds, walnuts and brazil nuts. The specificity of the system was tested with DNA from more than 50 plant and animal species. The sensitivity of the method was suitable to detect allergenic ingredients in the low mg kg(-1) range. The limit of detection (LOD) for single allergens in different food matrices was 5 mg kg(-1). The novel analytical strategy represents a useful tool for the surveillance of established legislation on food allergens within the European Union.

Detection of allergenic ingredients using real-time PCR: a case study on hazelnut (Corylus avellena) and soy (Glycine max)

Compliance with the European allergen labeling legislation (Directive 2007/68/EC) is only possible when coupled with appropriate methods to detect allergens in food. The aim of the current study was to develop new real-time PCR assays for the detection of hazelnut and soy and evaluate these assays via comparison with commercially available kits. Although the new assays were not as sensitive as the commercial qualitative assays, they proved to be more specific. Moreover, the cross-reactivity study indicated contamination of some of the food products used with either hazelnut or soy, which presents a risk for the allergic consumer. The assays were able to quantify as few as 5-15 genome copies. This unit, used to express analytical results for allergen detection by means of PCR, needs to be converted to a unit expressing the amount of allergenic ingredient in order to be informative. This study emphasizes that the use of real-time PCR for allergen quantification is complicated by the lack of appropriate reference materials for allergens.

Multiplex, quantitative, ligation-dependent probe amplification for determination of allergens in food

Legislation requires labeling of foods containing allergenic ingredients. Here, we present a robust 10-plex quantitative and sensitive ligation-dependent probe amplification method, the allergen-multiplex ligation-dependent probe amplification (MLPA) method, for specific detection of eight allergens: sesame, soy, hazelnut, peanut, lupine, gluten, mustard, and celery. Ligated probes were amplified by polymerase chain reaction (PCR), and amplicons were detected using capillary electrophoresis. Quantitative results were obtained by comparing signals with an internal positive control. The limit of detection varied from approximately 5 to 400 gene copies, depending on the allergen. The method was tested using different foods spiked with mustard, celery, soy, or lupine flour in the 1-0.001% range. Depending on the allergen, sensitivities were similar or better than those obtained with qPCR. The allergen-MLPA method is modular and can be adapted by adding probe pairs for other allergens. The DNA-based allergen-MLPA method will constitute a complementary method to the traditional protein-based methods.

Biomolecular identification of allergenic pollen: a new perspective for aerobiological monitoring?

BACKGROUND

Accurate and updated information on airborne pollen in specific areas can help allergic patients. Current monitoring systems are based on a morphologic identification approach, a time-consuming method that may represent a limiting factor for sampling network enhancement.

OBJECTIVE

To verify the feasibility of developing a real-time polymerase chain reaction (PCR) approach, an alternative to optical analysis, as a rapid, accurate, and automated tool for the detection and quantification of airborne allergenic pollen taxa.

METHODS

The traditional cetyl trimethyl ammonium bromide-based method was modified for DNA isolation from pollen. Taxon-specific DNA sequences were identified via bioinformatics or literature searches and were PCR amplified from the matching allergenic taxa; based on the sequences of PCR products, complementary or degenerate TaqMan probes were developed. The accuracy of the quantitative real-time PCR assay was tested on 3 plant species.

RESULTS

The setup of a modified DNA extraction protocol allowed us to achieve good-quality pollen DNA. Taxon-specific nuclear gene fragments were identified and sequenced. Designed primer pairs and probes identified selected pollen taxa, mostly at the required classification level. Pollen was properly identified even when collected on routine aerobiological tape. Preliminary quantification assays on pollen grains were successfully performed on test species and in mixes.

CONCLUSIONS

The real-time PCR approach revealed promising results in pollen identification and quantification, even when analyzing pollen mixes. Future perspectives could concern the development of multiplex real-time PCR for the simultaneous detection of different taxa in the same reaction tube and the application of high-throughput molecular methods.

Development and validation of an indirect competitive enzyme linked-immunosorbent assay for the determination of potentially allergenic sesame (Sesamum indicum) in food

This study was designed to develop an indirect competitive enzyme linked-immunosorbent assay (ELISA) to detect traces of sesame in food. Antibodies against sesame were prepared by immunizing a hen with a protein extract of white, peeled sesame. The ELISA did not show any cross-reactivity with 12 of 13 food ingredients tested, only for chocolate was a low cross-reactivity of 0.7% observed. To eliminate matrix effects, sesame protein standard solutions were prepared by diluting the sesame extract with blank food matrix (1:20 diluted with PBS). Recovery of sesame protein in food samples (crisp toasts, snacks, and rolls) spiked with different sesame protein concentrations ranged from 85% to 120%, with the exception of multigrain crisp toast, resulting in too high recoveries (117%-160%) and whole grain bread, yielding too low recoveries (70%-85%). In crisp bread, cracker, cereals, and snacks the limit of detection (LOD) was found to be 5 microg of sesame protein/g of food, in fresh breads and rolls, the LOD was 11 microg of sesame protein/g of food.

Development and validation of a duplex real-time PCR method to simultaneously detect potentially allergenic sesame and hazelnut in food

The paper describes the development and validation of a duplex real-time PCR method allowing the simultaneous detection of traces of potentially allergenic sesame and hazelnut in food. For the detection of sesame and hazelnut, the genes coding for two major allergenic proteins, Ses i 1 and Cor a 1, were selected. The duplex real-time PCR assay did not show any cross-reactivity with 25 common food ingredients from sesame and/or hazelnut containing foods. Analysis of serially diluted sesame/hazelnut DNA resulted in good linearity up to a dilution of 1:10000 (corresponding to 10 pg microL(-1) or 50 pg). Sesame and hazelnut could be detected in blank whole meal cookies which had been spiked with 0.005% sesame and 0.005% hazelnut. The applicability of the real-time PCR assay for determining sesame and hazelnut in different food matrices was investigated by analyzing 30 commercial foodstuffs comprising salty snacks, cookies, chocolates, creams, mueslis and muesli bars.

Disposable electrochemical DNA-array for PCR amplified detection of hazelnut allergens in foodstuffs

An electrochemical low-density DNA-array has been designed and implemented to be used in combination with polymerase chain reaction (PCR) in order to investigate the presence of hazelnut major allergens (Cor a 1.04, Cor a 1.03) in foodstuff. Unmodified PCR products were captured at the sensor interface via sandwich hybridization with surface-tethered probes and biotinylated signalling probes. The resulting biotinylated hybrids were coupled with a streptavidin-alkaline phosphatase conjugate and then exposed to a alpha-naphthyl phosphate solution. Differential pulse voltammetry was finally used to detect the alpha-naphthol signal. The detection limits for Cor a 1.03 and Cor a 1.04 were 0.3 and 0.1 nmol L(-1), respectively (R.S.D. 10%). The optimized conditions were used to test several commercially available foodstuffs, claiming to contain or not the targeted nuts. The results were compared with those obtained with classical ELISA tests.

Development of a real-time PCR method to detect potentially allergenic sesame (Sesamum indicum) in food

Recent papers indicate that the prevalence of allergic reactions to sesame (Sesamum indicum) is increasing in European countries. This paper describes the development of a selective real-time PCR method for the detection of sesame in food. The assay did not show any cross-reactivity with 17 common food ingredients. The real-time PCR method was applied to determine sesame in several crackers, salty snacks, biscuits, tahina sesame paste and sesame oil. With the exception of sesame oil, in all of the samples where sesame was declared, sesame was detected by the real-time PCR assay (Ct value<35). In the samples which might contain sesame or where sesame was not listed, sesame could not be detected (Ct value>35).

Quantitative determination of soybean meal content in compound feeds: comparison of near-infrared spectroscopy and real-time PCR

Standard methods for determining the raw material content of compound feed are little exploited, except for the identification of meat and bone meal in feeds. In this work, near-infrared (NIR) spectroscopy and real-time polymerase chain reaction (PCR) were applied in order to establish new and fast methods for quantification of soybean meal content in compound feeds. The best prediction quality was achieved by using a model based on NIR spectroscopy (R2 = 0.9857, standard error of cross-validation 1.1065). Furthermore, a sensitive qualitative detection method by using the real-time PCR was developed (R2 = 0.976, slope -3.7599). Finally, the differences between the real-time PCR result and the NIR spectroscopy result for a given sample were also treated, and we found that the NIR spectroscopy method provided quite accurate results which approach closely those of the real-time PCR method.