A novel real-time polymerase chain reaction (PCR) method for the detection of walnuts in food

Cu2-xSe@Bi2MoO6 nanozyme-based immunoassay for the colorimetric detection of walnut allergen in foods

In the present study, we developed a nanozyme-based direct competitive immunoassay to detect walnut allergen (Jug r 4) in foods. Walnut monoclonal antibody (mAb) and Cu2-xSe@Bi2MoO6 nanocomposites were generated to form a signal probe by electrostatic adsorption. The nanocomposites had high peroxidase-like activity and could be stored at room temperature. The linear range of the optimized assay was 137.35 ± 0.14 to 3526.0 ± 4.53 μg/L with a limit of detection of 81.63 ± 0.89 μg/L. This method was validated by detecting walnut protein in bread, biscuits, and milk samples, providing recovery rates of 70.63-127.04 %. The fast and sensitive assay was suitable for the rapid detection of walnut allergen in foods.

Collaborative trial validation of a new multiplex real-time PCR to sensitively detect allergenic nuts in food

In this article, we present a multiplex real-time PCR method for a simultaneous, sensitive and specific detection and semi-quantitative estimation of the allergenic species peanut, hazelnut, walnut and cashew in food. Due to the use of multicopy target sequences, a very sensitive detection of the allergenic ingredients was possible. The method was validated in-house as well as by a collaborative trial with 12 laboratories. Within the ring trial, 0.64 mg/kg (i.e. approx. 0.1–0.2 mg of peanut and tree nut-derived protein/kg) could still be detected in a processed cookie matrix, confirmed by results of incurred, processed samples spiked at very low levels between 0.9 and 50 mg/kg of the corresponding allergenic ingredient (peanut, tree nut). In addition, the method revealed good precision data. With regard to quantitative analysis though, insufficient recovery data (bias) were determined in some cases, resulting in measurement uncertainties of more than 50%.

Reduction of bitterness in green walnuts by conventional and ultrasound-assisted maceration

The efficiency of conventional and ultrasound-assisted maceration was investigated in comparison to reduce the bitterness of green walnuts. Conventional maceration was studied at room temperature for 6, 8 and 10 days while ultrasound-assisted maceration (20 kHz, %100 of amplitude) was performed at 36 °C for 6, 8, 10, 12, and 14 h. Phenolic content and antioxidant activity of green walnuts were decreased by reduction of bitterness. Phenolic content and antioxidant activity of green walnut jams prepared from debittered green walnuts by ultrasound-assisted maceration were higher than those of conventional maceration excluding ellagic acid only. Based on findings of sensory analyses, bitterness level was similar in green walnut jams prepared by ultrasound-assisted maceration for 12 h and conventional maceration for 6 days. On the other hand, green walnut jams processed by ultrasound-assisted maceration for 12 h led to the highest general acceptance. It was concluded that ultrasound-assisted maceration may provide better nutritional and sensory quality in green walnut jam. In addition, the time required for reduction of bitterness may be shortened from days to hours by ultrasound-assisted maceration.

Application of real-time PCR for tree nut allergen detection in processed foods

Currently, food allergies are an important health concern worldwide. The presence of undeclared allergenic ingredients or the presence of traces of allergens due to accidental contamination during food processing poses a great health risk to sensitized individuals. Therefore, reliable analytical methods are required to detect and identify allergenic ingredients in food products. Real-time PCR allowed a specific and accurate amplification of allergen sequences. Some processing methods could induce the fragmentation and/or degradation of genomic DNA and some studies have been performed to analyze the effect of processing on the detection of different targets, as thermal treatment, with and without applying pressure. In this review, we give an updated overview of the applications of real-time PCR for the detection of allergens of tree nut in processed food products. The different variables that contribute to the performance of PCR methodology for allergen detection are also review and discussed.

Simultaneous detection of eight species of tree nut in foods using two tetraplex polymerase chain reaction assays

Tree nuts comprise a category of food allergens that must be included in the food labels in several countries. We developed a polymerase chain reaction (PCR) method using eight specific primer pairs to detect eight representative tree nuts (almond, Brazil nut, cashew, hazelnut, macadamia nut, pecan, pistachio, and walnut) under the same experimental conditions. The specificity of the eight primer pairs was confirmed by PCR testing against a variety of plant and animal samples. The detection limit of the method ranged from 1 fg to 1 pg DNA of individual tree nuts. The method detected tree nut DNA in processed and unprocessed food. In addition, the primer pairs could be combined into two sets of tetraplex PCR system. The developed method is specific, sensitive, and efficient, making it useful for detecting trace amounts of eight species of tree nut in foods.

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.

Walnut allergens: molecular characterization, detection and clinical relevance

Food-induced allergies have been regarded as an emergent problem of public health. Classified as important allergenic ingredients, the presence of walnut and other nuts as hidden allergens in processed foods constitutes a risk for sensitized individuals, being a real problem of allergen management. Attending to the increasing importance dedicated to walnut allergy, this review intends to provide the relevant and up-to-date information on main issues such as the prevalence of walnut allergy, the clinical threshold levels, the molecular characterization of walnut allergens and their clinical relevance, as well as the methodologies for walnut allergen detection in foods. As the walnut used in human diet comes from Juglans regia and Juglans nigra, the molecular characterization of the allergens from both species included in the prolamins (Jug r 1, Jug n 1 and Jug r 3), cupins (Jug r 2, Jug n 2 and Jug r 4) and profilins (Jug r 5), together with respective clinical relevance, were compiled in this review. The most recent progresses on walnut allergen detection techniques (protein- and DNA-based) are described and critically compared, including the emergent multitarget approaches.

Detection of Walnut Residues in Processed Foods by Polymerase Chain Reaction

A sensitive qualitative detection method for walnut (Juglans regia) using polymerase chain reaction (PCR) was developed. For detection of walnuts with high specificity, the primer pair WAL-F/WAL-R was designed based on walnut matK genes. Trace amounts of walnuts in commercial food products can be qualitatively detected using this method.

Development of an indirect competitive immunoassay for walnut protein component in food

Among food allergens, walnut is a frequent cause of adverse food reactions in allergic patients. In this study, the walnut allergen protein 2S albumin precursor (Jug r 1) cDNA was synthesised and cloned into the pGEX-6P-1 expression vector. The recombinant plasmids were transformed into Escherichia coli (E. coli) BL21(DE3) pLys for expression of protein Jug r 1. Polyclonal antibodies were prepared against the expressed purified Jug r 1 protein. An indirect competitive enzyme-linked immunosorbent assay (ELISA) for the detection and quantification of walnut soluble proteins in processed foods was developed using the prepared polyclonal antibodies. The developed ELISA had a high specificity, walnut protein standard solution at 2.2 ng/mL [inhibition concentration (IC80) of the competitive test] was clearly identified by the ELISA. The mean recoveries ranged from 86% to 112%. The coefficient of variation (CV) for the 4 model foods was 6.4-8.7%.

Almond allergens: molecular characterization, detection, and clinical relevance

Almond ( Prunus dulcis ) has been widely used in all sorts of food products (bakery, pastry, snacks), mostly due to its pleasant flavor and health benefits. However, it is also classified as a potential allergenic seed known to be responsible for triggering several mild to life-threatening immune reactions in sensitized and allergic individuals. Presently, eight groups of allergenic proteins have been identified and characterized in almond, namely, PR-10 (Pru du 1), TLP (Pru du 2), prolamins (Pru du 2S albumin, Pru du 3), profilins (Pru du 4), 60sRP (Pru du 5), and cupin (Pru du 6, Pru du γ-conglutin), although only a few of them have been tested for reactivity with almond-allergic sera. To protect sensitized individuals, labeling regulations have been implemented for foods containing potential allergenic ingredients, impelling the development of adequate analytical methods. This work aims to present an updated and critical overview of the molecular characterization and clinical relevance of almond allergens, as well as review the main methodologies used to detect and quantitate food allergens with special emphasis on almond.

Detection of allergen walnut component in food by an improved real-time PCR method

A real-time PCR method aimed at the gene sequence of the walnut vicilin-like seed storage protein was established for the detection of the allergen walnut in food. The primers and probe were designed based on published methods. The method provided positive results for walnut and negative results for other tested agricultural plant materials including pecan. The intrinsic detection limit of the method was 0.00125 ng of walnut DNA, and the practical detection limit was 0.001% (wt/wt) walnut content in wheat; both of these values are lower than that of previously published methods. Therefore, this real-time PCR method is sufficiently specific and sensitive for the detection of walnut component in food.

Identification of European Hake species (Merluccius merluccius) using real-time PCR

A rapid and precise method for identifying European hake (Merluccius merluccius) based on TaqMan technology is presented. The method can be applied to fresh, frozen, and processed fish products to detect the fraudulent or unintentional mislabeling of this species. Specific primers and a minor groove binding (MGB) TaqMan probe were designed for this purpose based on partial sequences of the mitochondrial DNA control region. Combinations of primers and probe concentrations that gave the lowest Ct value and the highest final fluorescence value were selected to carry out efficiency, specificity, and cross-reactivity assays. The method was successfully tested on 31 commercial hake samples. A Ct value of about 16 was obtained when Merluccius merluccius was present; however, the fluorescence signal was not detected most of the time (Ct value 40) or presented significantly higher Ct values (38.2 +/- 0.96) for the nonhake species.

Reliable enzyme-linked immunosorbent assay for the determination of walnut proteins in processed foods

Among food allergens of tree nuts, walnuts are a frequent cause of adverse food reactions in allergic patients. A novel sandwich enzyme-linked immunosorbent assay (ELISA) for the detection and quantification of walnut soluble proteins in processed foods was developed. The sandwich ELISA is highly specific for walnut soluble proteins. The recovery ranged from 83.4 to 123%, whereas the intra- and interassay coefficients of variation were less than 8.8 and 7.2%, respectively. This study showed that the proposed method is a reliable tool for detection in the presence of hidden walnut proteins in processed foods.

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).