Effect of food matrix and thermal processing on the performance of a normalised quantitative real-time PCR approach for lupine (Lupinus albus) detection as a potential allergenic food

An integrated microfluidic platform for on-site qPCR analysis: food allergen detection from sample to result

Improving food safety is crucial in the context of a "One Health" approach. To guarantee product quality and safety, the food industry, which has a very high turnover rate, needs short time-to-result analyses. Therefore, user-friendly systems at the point-of-need are necessary, presenting relevant analytical information and fulfilling the current regulations. To answer these challenges, a microfluidic platform integrating sample preparation and subsequent multiplex qPCR detection has been developed for on-site testing. The system consists of a fully automated instrument driving a microfluidic cartridge dedicated to the detection of multiple allergens in complex food matrices. The first part of the microfluidic cartridge contains pumps, reservoirs, valves and a filter to achieve DNA extraction, concentration and purification. Multiplex qPCR detection is carried out in the second part of the cartridge including a negative control chamber and five chambers for target analyte detection. The in-house developed instrument contains all functions to autonomously drive the microfluidic cartridge: pneumatic control for fluid actuation, thermal control for qPCR amplification and an optical system using three fluorescent wavelengths for multiplex detection of the target analytes and controls. We demonstrate the simultaneous detection of four different allergens - gluten, sesame, soy and hazelnut - from various complex food matrices. The turn-around-time from sample to result is close to two hours and controls in place validate the obtained results. For gluten, a direct comparison with ELISA shows that the regulatory threshold of 20 ppm is comfortably fulfilled. Moreover, all results are in agreement with external laboratory analyses performed in parallel on the same samples. Our findings confirm that the system can be used safely on-site without the risk of cross contamination between the various samples being analysed. In conclusion, our microfluidic platform offers a robust method for on-site allergen management.

Replacing the animal fat in Bologna sausages using high internal phase emulsion stabilized with lentil protein isolate (Lens culinaris)

High internal phase emulsions (HIPEs) are promising techniques that can replace saturated fat in food without reducing the product's texture, sensory attributes, water-holding capacity, and cooking loss. In the current investigation, 100% pork back fat was replaced by HIPEs formed with lentil protein isolate (LPI) in Bologna sausages. HIPEs were prepared by 25% LPI dispersion (2, 4, 6, and 8%, w/w) and 75% (w/w) soybean oil. HIPEs with higher LPI concentration (4, 6, and 8%, w/w) showed lower droplet size, firmer appearance, and better rheology behavior than 2% LPI. The concentrations LPI (2%, 4%, 6%, and 8%, w/w) led to increased moisture in sausages (FH2, FH4, FH6, and FH8, respectively) compared to the FC. These LPI levels resulted in sausage values for pressed juice similar to the FC and lower energy values than sausages with soybean oil (FO) and pork back fat (FC). Besides, these LPI concentrations (4%, 6%, and 8%, w/w) resulted in a lower oil oxidation level in sausages with HIPEs (FH4, FH6, and FH8, respectively) compared to the control sausage formulation with pork back fat (FC). Bologna sausages elaborated with HIPEs showed emulsion stability values higher than 97%, without significance difference between them. The texture and sensory properties of sausages made with HIPEs were comparable to those made with pork back fat. HIPEs may improve the oxidation stability of the Bologna sausages. These results highlight the effectiveness of HIPEs structured with lentil protein in successfully substituting pork back fat in Bologna sausages with a better nutritional appeal.

Highly accurate and sensitive absolute quantification of bacterial strains in human fecal samples

BACKGROUND

Next-generation sequencing (NGS) approaches have revolutionized gut microbiome research and can provide strain-level resolution, but these techniques have limitations in that they are only semi-quantitative, suffer from high detection limits, and generate data that is compositional. The present study aimed to systematically compare quantitative PCR (qPCR) and droplet digital PCR (ddPCR) for the absolute quantification of Limosilactobacillus reuteri strains in human fecal samples and to develop an optimized protocol for the absolute quantification of bacterial strains in fecal samples.

RESULTS

Using strain-specific PCR primers for L. reuteri 17938, ddPCR showed slightly better reproducibility, but qPCR was almost as reproducible and showed comparable sensitivity (limit of detection [LOD] around 104 cells/g feces) and linearity (R2 > 0.98) when kit-based DNA isolation methods were used. qPCR further had a wider dynamic range and is cheaper and faster. Based on these findings, we conclude that qPCR has advantages over ddPCR for the absolute quantification of bacterial strains in fecal samples. We provide an optimized and easy-to-follow step-by-step protocol for the design of strain-specific qPCR assays, starting from primer design from genome sequences to the calibration of the PCR system. Validation of this protocol to design PCR assays for two L. reuteri strains, PB-W1 and DSM 20016 T, resulted in a highly accurate qPCR with a detection limit in spiked fecal samples of around 103 cells/g feces. Applying our strain-specific qPCR assays to fecal samples collected from human subjects who received live L. reuteri PB-W1 or DSM 20016 T during a human trial demonstrated a highly accurate quantification and sensitive detection of these two strains, with a much lower LOD and a broader dynamic range compared to NGS approaches (16S rRNA gene sequencing and whole metagenome sequencing).

CONCLUSIONS

Based on our analyses, we consider qPCR with kit-based DNA extraction approaches the best approach to accurately quantify gut bacteria at the strain level in fecal samples. The provided step-by-step protocol will allow scientists to design highly sensitive strain-specific PCR systems for the accurate quantification of bacterial strains of not only L. reuteri but also other bacterial taxa in a broad range of applications and sample types. Video Abstract.

Food Matrix Composition Affects the Allergenicity of Baked Egg Products

BACKGROUND

Egg allergy is common and caused by sensitization to ovomucoid and/or ovalbumin. Many egg-allergic patients are able to tolerate eggs baked into other foods, such as muffins. Although heating egg extensively reduces allergens, the effect of other food ingredients on allergenicity of eggs, or the "matrix effect," is less well studied.

OBJECTIVE

We aimed to define how food matrices impact the matrix effect in egg allergenicity.

METHODS

Enzyme-linked immunosorbent assay was used to quantify ovalbumin and ovomucoid in extracts from various baked egg products: plain baked egg without a matrix, and muffins baked using either wheat flour, rice flour, or a wheat flour/banana puree mix. Allergen-specific immunoglobulin E (IgE)-blocking enzyme-linked immunosorbent assays were performed using the egg product extracts on egg-allergic patient sera to determine whether the amount of extracted egg protein in each extract correlated with how well the extracts could bind patients' egg IgE.

RESULTS

Baking eggs in any muffin matrix led to an increase in the amount of extractable ovalbumin and a decrease in the amount of extractable ovomucoid compared with plain baked egg. Compared with wheat muffins, rice muffins had more extractable ovalbumin and wheat/banana muffins had more extractable ovalbumin and ovomucoid. The egg allergens in the extracts were able to block egg-allergic patients' egg IgE.

CONCLUSIONS

Food matrices affect egg allergen availability. Patients and families should be advised that substitutions in baked egg muffin recipes can affect the amount of egg allergens in foods and potentially affect the risk of food allergic reaction.

Lentil protein isolate (Lens culinaris) subjected to ultrasound treatment combined or not with heat-treatment: structural characterization and ability to stabilize high internal phase emulsions

This study evaluated the effect of ultrasound treatment combined or not with heat treatment applied to lentil protein isolate (LPI) aiming to enhance its ability to stabilize high internal phase emulsions (HIPE). LPI dispersion (2%, w/w) was ultrasound-treated at 60% (UA) and 70% (UB) amplitude for 7 min; these samples were subjected to and then heat treatments at 70 °C (UAT70 and UBT70, respectively) or 80 °C (UAT80 and UBT80, respectively) for 20 min. HIPEs were produced with 25% untreated and treated LPI dispersions and 75% soybean oil using a rotor-stator (15,500 rpm/1 min). The LPI dispersions were evaluated for particle size, solubility, differential scanning calorimetry, electrophoresis, secondary structure estimation (circular dichroism and FT-IR), intrinsic fluorescence, surface hydrophobicity, and free sulfhydryl groups content. The HIPEs were evaluated for droplet size, morphology, rheology, centrifugal stability, and the Turbiscan test. Ultrasound treatment decreased LPI dispersions' particle size (∼80%) and increased solubility (∼90%). Intrinsic fluorescence and surface hydrophobicity confirmed LPI modification due to the exposure to hydrophobic patches. The combination of ultrasound and heat treatments resulted in a reduction in the free sulfhydryl group content of LPI. HIPEs produced with ultrasound-heat-treated LPI had a lower droplet size distribution mode, greater oil retention values in the HIPE structure (> 98%), lower Turbiscan stability index (< 2), and a firmer and more homogeneous appearance compared to HIPE produced with untreated LPI, indicating higher stability for the HIPEs stabilized by treated LPI. Therefore, combining ultrasound and heat treatments could be an effective method for the functional modification of lentil proteins, allowing their application as HIPE emulsifiers.

Thermo-induced changes in the structure of lentil protein isolate (Lens culinaris) to stabilize high internal phase emulsions

This study aims to assess the impact of heat treatment on the emulsifying properties of lentil protein isolate (LPI) dispersion to produce high internal phase emulsions (HIPEs). The heat-treated LPI dispersion was characterized by size, turbidity, solubility, zeta potential, free sulfhydryl group, electrophoresis, differential scanning calorimetry, circular dichroism, Fourier transforms infrared spectroscopy and intrinsic fluorescence. HIPEs were produced with 25% of LPI dispersion (2%, w/w) and soybean oil (75%) using a rotor-stator (15,500 rpm/1 min). HIPEs were evaluated for their droplet size, zeta potential, centrifugal stability, microscopy, appearance, Turbiscan stability, and rheology over 60 days (25 °C). Heat treatment reduced the size of LPI, resulting in increased turbidity, solubility, and exposure of hydrophobic groups. HIPEs produced with heat-treated LPI at 70 °C (HIPE70) and 80 °C (HIPE80) for 20 min exhibited lower droplet sizes, increased stability, reduced oil loss, and a homogeneous appearance compared to HIPE produced with untreated LPI (HIPEc). In addition, HIPE70 and HIPE80 displayed resistance to shear stress, higher apparent viscosity, and increased storage modulus than HIPEc. HIPEs produced with heat-treated LPI were stable, suggesting that the treatment was efficient for improving the functional properties of the protein and the possibility of future research focusing on fat substitutes in food applications.

Effects of different processed tomatoes on carotenoid release and microbiota composition during in vitro gastrointestinal digestion and colonic fermentation

Carotenoids in tomatoes confer significant health benefits to humans but with the disadvantage of the carotenoids from raw tomatoes not being easily absorbed for utilization. Thus, this study aimed to investigate the effects of different cooking processes on carotenoid release and human gut microbiota composition during in vitro simulated gastrointestinal digestion of tomatoes. The results showed that stir-frying significantly increased the release of lycopene and β-carotene during gastrointestinal digestion, with boiling being the second most effective treatment. The boiling-treated tomatoes enhanced the carotenoid release during in vitro fermentation. Gut microbiota analysis revealed that the digestion of the raw and boiled tomatoes promoted the growth of potentially beneficial microbiota while reducing the ratio of Firmicutes/Bacteroides, which potentially helps prevent obesity. Boiling treatment significantly reduced the growth of Peptostreptococcus and was negatively correlated with carotenoid release. Overall, the boiling-treated tomatoes were more effective than the raw or stir-fried tomatoes in terms of both colon health benefits and carotenoid release.

Towards DNA-Based Methods Analysis for Honey: An Update

Honey is a natural product widely consumed all over the world due to its relationship with healthy benefits. Additionally, environmental and ethical issues have a higher weight in the consumer's choice to buy honey as a natural product. Following the high demand of this product, several approaches have been suggested and developed aiming at the assessment of honey's quality and authenticity. Target approaches, such as pollen analysis, phenolic compounds, sugars, volatile compounds, organic acids, proteins, amino acids, minerals, and trace elements, showed an efficacy, particularly concerning the honey origin. However, a special highlight is given to DNA markers, due to their useful applicability in environmental and biodiversity studies, besides the geographical, botanical, and entomological origins. Different DNA target genes were already explored for addressing diverse sources of honey DNA, with DNA metabarcoding attaining a relevant importance. This review aims to describe the latest advances on DNA-based methods applied in honey related studies, identifying the research needs for the development of new and additional required methodologies, and to select the most adequate tools for future research projects.

Quantitative Real-Time PCR for the Detection of Allergenic Species in Foods

Food allergy is an increasing challenge to public health, with widespread global distribution. With no cure for this pathology, the food-allergic individuals are forced to adopt food eviction measurements, relying on label information to avoid consuming the offending foods. To safeguard these individuals, the analytical methods based on real-time PCR approaches are currently faced as excellent tools to verify labeling compliance, aiding industry and regulatory agencies to efficiently manage food allergen control programs. Therefore, this chapter intends to describe a protocol of real-time PCR to analyze allergenic food species. For method development, the main steps to be considered are (i) in silico sequence analysis and primer/hydrolysis probe design, (ii) preparation of calibrators (model foods containing the allergenic ingredient), (iii) efficient DNA extraction from complex food matrices, (iv) amplification by real-time PCR with hydrolysis probe (90-200 bp) targeting a highly specific DNA region (allergen-encoding gene), (v) sequencing PCR products for identity confirmation, and (vi) validation and application to commercial foods. Herein, a real-time PCR approach for the detection and quantification of cashew nut as an allergenic food is described as an example protocol, including all the steps for method development and validation.

Detection of Parvalbumin Fish Allergen in Canned Tuna by Real-Time PCR Driven by Tuna Species and Can-Filling Medium

Canned tuna is considered one of the most popular and most commonly consumed products in the seafood market, globally. However, in past decades, fish allergens have been detected as the main concern regarding food safety in these seafood products and are listed as the top eight food allergies. In the group of fish allergens, parvalbumin is the most common. As a thermally stable and calcium-binding protein, parvalbumin can be easily altered with changing the food matrices. This study investigated the effect of a can-filling medium (tomato sauce, spices, and brine solutions) on the parvalbumin levels in canned tuna. The effect of pH, calcium content, and the DNA quality of canned tuna was also investigated before the parvalbumin-specific encoded gene amplification. The presence of fish allergens was determined by melting curve analyses and confirmed by agarose gel electrophoresis. The obtained results showed that the presence of parvalbumin in commercially canned tuna was driven by can-filling mediums, thermal conductivity, calcium content, and the acidity of various ingredients in food matrices. The intra-specific differences revealed a variation in fish allergens that are caused by cryptic species. This study proved that allergens encoding gene analyses by agarose electrophoresis could be used as a reliable approach for other food-borne allergens in complex food matrices.

Genus Lupinus (Fabaceae): a review of ethnobotanical, phytochemical and biological studies

OBJECTIVES

Lupinus is a large and diverse genus comprising approximately 200 species, belonging to the family Fabaceae. Lupinus plants have been used for heart stimulants, nerves, urinary tract infections, skin disorders, and psoriasis in folk medicine. This review aims to recap the traditional medicinal uses, nutritional value, phytochemical profile, and biological activities of Lupinus species.

KEY FINDINGS

From the literature survey, Lupinus is considered as a factory of various phytochemicals like flavonoids, iso-flavonoids, alkaloids, triterpenoids. The presence of proteins, essential fatty acids, and amino acids, as well as alkaloids, minerals, and dietary fibers, indicated that the plants in this genus had a high nutritional value. The Lupinus extracts displayed promising antidiabetic, anticancer, antimicrobial, antidiabetic, antihypertensive, antioxidant, anti-inflammatory, and antimicrobial activities.

CONCLUSIONS

The current review provides updated information that could drive the researchers for further studies. The in vitro and in vivo experiments have demonstrated various pharmacological properties. Some pharmacokinetic and toxicological investigations are warranted to ensure its safety and validity for human use.

Authentication of Argan (Argania spinosa L.) Oil Using Novel DNA-Based Approaches: Detection of Olive and Soybean Oils as Potential Adulterants

Argan oil is a traditional product obtained from the fruits of the argan tree (Argania spinosa L.), which is endemic only to Morocco. It is commercialized worldwide as cosmetic and food-grade argan oil, attaining very high prices in the international market. Therefore, argan oil is very prone to adulteration with cheaper vegetable oils. The present work aims at developing novel real-time PCR approaches to detect olive and soybean oils as potential adulterants, as well as ascertain the presence of argan oil. The ITS region, matK and lectin genes were the targeted markers, allowing to detect argan, olive and soybean DNA down to 0.01 pg, 0.1 pg and 3.2 pg, respectively, with real-time PCR. Moreover, to propose practical quantitative methods, two calibrant models were developed using the normalized ΔCq method to estimate potential adulterations of argan oil with olive or soybean oils. The results allowed for the detection and quantification of olive and soybean oils within 50–1% and 25–1%, respectively, both in argan oil. Both approaches provided acceptable performance parameters and accurate determinations, as proven by their applicability to blind mixtures. Herein, new qualitative and quantitative PCR assays are proposed for the first time as reliable and high-throughput tools to authenticate and valorize argan oil.

Single-tube nested real-time PCR versus normalised real-time PCR for the quantification of allergenic cashew nut in foods: Impact of thermal processing and matrix

In this work, three allergen-encoding genes (Ana o 1, Ana o 2, Ana o 3) were investigated for the detection of cashew nut as an allergenic food. Normalised and single-tube nested real-time PCR approaches targeting the Ana o 2 or Ana o 3 genes are proposed and compared. Normalised real-time PCR detected 10 pg, while single-tube nested real-time PCR achieved 1 pg of cashew nut DNA. Single-tube nested real-time PCR targeting Ana o 3 allowed the best relative sensitivities (10 mg/kg cashew nut in dough/biscuit), being successfully validated regarding precision/accuracy. The normalised real-time PCR did not show acceptable accuracy for both targets. Sensitivity of single-tube nested real-time PCR was affected by the matrix (pasta), but not by thermal processing (dough/biscuit). Herein, two highly sensitive and specific single-tube nested real-time PCR targeting allergen-encoding genes are proposed for the first time as quantitative/validated tools for cashew nut analysis as an allergenic food.

Detection of Allergenic Proteins in Foodstuffs: Advantages of the Innovative Multiplex Allergen Microarray-Based Immunoassay Compared to Conventional Methods

Several factors can affect the allergen content and profile of a specific food, including processing procedures often leading to a decrease in allergenicity, although no change, or even an increase, have also been reported. Evaluation of the effectiveness of a processing procedure requires the availability of reliable methodologies to assess the variation in molecules able to induce allergic reactions in the analyzed food. Conventional and innovative strategies and methodologies can be exploited to identify allergenic proteins in foodstuffs. However, depending on the specific purposes, different methods can be used. In this review, we have critically reviewed the advantages of an innovative method, the multiplex allergen microarray-based immunoassay, in the detection of allergens in foodstuffs. In particular, we have analyzed some studies reporting the exploitation of an IgE-binding inhibition assay on multiplex allergen biochips, which has not yet been reviewed in the available literature. Unlike the others, this methodology enables the identification of many allergenic proteins, some of which are still unknown, which are recognized by IgE from allergic patients, with a single test. The examined literature suggests that the inhibition test associated with the multiplex allergen immunoassay is a promising methodology exploitable for the detection of IgE-binding proteins in food samples.

The impact of food matrices on egg allergenicity

Background

Although many studies show the impact of high and prolonged heating on allergenicity, scarce research exists that examined the impact of the food matrix effect. We presented a case that demonstrates the need for further investigation into this field.

Case

An 8-month-old breast-fed girl with a history of moderate eczema presented with concern for food allergy. At 7 months old, she seemed to have difficulty with nursing after consumption of peanut butter, and her pediatrician recommended further avoidance. On presentation to allergy, she had not yet consumed eggs; therefore, skin testing was obtained for both peanut and egg. Her skin testing result to peanut was negative, whereas to egg was elevated at 5/20 mm. To further support clinical decision-making, blood work was obtained, and the egg white specific immunoglobulin E (IgE) value was elevated to 1.33 kU/L. It was recommended to the family to pursue home introduction of peanut and return for oral challenge to baked egg. At 14 months old, the patient returned for oral challenge and successfully tolerated one-half of a muffin. She was discharged with instructions to continue consumption of one-half of a muffin ideally three or more times a week, which the parents reported she continued to tolerate.

Conclusion

When the patient was 24 months old, the mother decided, without consultation, to introduce banana-chocolate chip muffins. With the first two ingestions, she developed immediate urticaria. On the third consumption, she developed anaphylaxis, which required epinephrine, with rapid improvement. The patient subsequently returned to regular consumption of standard egg muffins (as well as bananas and chocolate individually), which she continued to tolerate. Based on our patient's ability to tolerate baked egg muffins without banana but significant reaction to baked egg muffins with banana, a potential explanation is that the addition of banana disrupted the egg-wheat matrix. This report points toward a continued need to investigate the role food matrices play on the allergenicity of foods. Furthermore, this case demonstrated the importance of adhering to allergist-prescribed recipes to prevent allergic reactions.

Detection of Peanut Allergen by Real-Time PCR: Looking for a Suitable Detection Marker as Affected by Processing

Peanut (Arachis hypogaea) contains allergenic proteins, which make it harmful to the sensitised population. The presence of peanut in foods must be indicated on label, to prevent accidental consumption by allergic population. In this work, we use chloroplast markers for specific detection of peanut by real-time PCR (Polymerase Chain Reaction), in order to increase the assay sensitivity. Binary mixtures of raw and processed peanut flour in wheat were performed at concentrations ranging from 100,000 to 0.1 mg/kg. DNA isolation from peanut, mixtures, and other legumes was carried out following three protocols for obtaining genomic and chloroplast-enrich DNA. Quantity and quality of DNA were evaluated, obtaining better results for protocol 2. Specificity and sensitivity of the method has been assayed with specific primers for three chloroplast markers (mat k, rpl16, and trnH-psbA) and Ara h 6 peanut allergen-coding region was selected as nuclear low-copy target and TaqMan probes. Efficiency and linear correlation of calibration curves were within the adequate ranges. Mat k chloroplast marker yielded the most sensitive and efficient detection for peanut. Moreover, detection of mat K in binary mixtures of processed samples was possible for up to 10 mg/kg even after boiling, and autoclave 121 °C 15 min, with acceptable efficiency and linear correlation. Applicability of the method has been assayed in several commercial food products.

Lupine allergens: Clinical relevance, molecular characterization, cross-reactivity, and detection strategies

Lupine is commonly utilized as a technological food and ingredient in a great variety of processed products (snacks, bakery, meat, and dairy products) principally owing to its nutritional value and technological properties. However, its ingestion, even at trace amounts (in the range of mg protein per kg of food), can lead to severe adverse reactions in allergic individuals. Lupine belongs to the Leguminosae family, having the conglutins (α-, β-, δ-, and γ-) as allergens, among other proteins. Cross-sensitization of lupine-sensitized individuals with other legume species, mainly peanut, can occur, but the associated clinical reactivity is still unclear. The protection of the sensitized individuals should depend on an avoidance diet, which should rely on the compliance of food labeling and, as such, on their verification by analytical methods. Food processing, such as heat treatments, has an important influence on the structural properties of lupine proteins, altering their detectability and allergenicity. In this review, different aspects related with lupine allergy are described, namely, the overall prevalence, clinical relevance, diagnosis, and treatment. The characterization of lupine allergens and their potential cross-reactivity with other legumes are critically discussed. The effects of food matrix, processing, and digestibility on lupine proteins, as well as the available analytical tools for detecting lupine at trace levels in foods, are also herein emphasized.

Authentication of Ginkgo biloba Herbal Products by a Novel Quantitative Real-Time PCR Approach

Ginkgo biloba is a widely used medicinal plant. Due to its potential therapeutic effects, it is an ingredient in several herbal products, such as plant infusions and plant food supplements (PFS). Currently, ginkgo is one of the most popular botanicals used in PFS. Due to their popularity and high cost, ginkgo-containing products are prone to be fraudulently substituted by other plant species. Therefore, this work aimed at developing a method for G. biloba detection and quantification. A new internal transcribe spacer (ITS) marker was identified, allowing the development of a ginkgo-specific real-time polymerase chain reaction (PCR) assay targeting the ITS region, with high specificity and sensitivity, down to 0.02 pg of DNA. Additionally, a normalized real-time PCR approach using the delta cycle quantification (ΔCq) method was proposed for the effective quantification of ginkgo in plant mixtures. The method exhibited high performance parameters, namely PCR efficiency, coefficient of correlation and covered dynamic range (50-0.01%), achieving limits of detection and quantification of 0.01% (w/w) of ginkgo in tea plant (Camellia sinensis). The quantitative approach was successfully validated with blind mixtures and further applied to commercial ginkgo-containing herbal infusions. The estimated ginkgo contents of plant mixture samples suggest adulterations due to reduction or almost elimination of ginkgo. In this work, useful and robust tools were proposed to detect/quantify ginkgo in herbal products, which suggests the need for a more effective and stricter control of such products.

Effect of Instant Controlled Pressure Drop (DIC) Treatment on the Detection of Nut Allergens by Real Time PCR

Tree nuts show nutritional properties and human health benefits. However, they contain allergenic proteins, which make them harmful to the sensitised population. The presence of tree nuts on food labelling is mandatory and, consequently, the development of suitable analytical methodologies to detect nuts in processed foods is advisable. Real-Time PCR allowed a specific and accurate amplification of allergen sequences. Some food processing methods could induce structural and/or conformational changes in proteins by altering their allergenic capacity, as well as produce the fragmentation and/or degradation of genomic DNA. In this work, we analysed by means of Real-Time PCR, the influence of pressure and thermal processing through Instant Controlled Pressure Drop (DIC) on the detectability of hazelnut, pistachio and cashew allergens. The detection of targets in hazelnut, pistachio and cashew (Cor a 9, Pis v 1 and Ana o 1, respectively) is affected by the treatment to different extents depending on the tree nut. Results are compared to those previously obtained by our group in the analysis of different treatments on the amplificability of the same targets. Reduction in amplificability is similar to that reported for some autoclave conditions. Our assays might allow for the detection of up to 1000 mg/kg of hazelnut, pistachio and cashew flours after being submitted to DIC treatment in food matrices.

Method for the Identification of Plant DNA in Food Using Alignment-Free Analysis of Sequencing Reads: A Case Study on Lupin

Fast and reliable analytical methods for the identification of plants from metagenomic samples play an important role in identifying the components of complex mixtures of processed biological materials, including food, herbal products, gut contents or environmental samples. Different PCR-based methods that are commonly used for plant identification from metagenomic samples are often inapplicable due to DNA degradation, a low level of successful amplification or a lack of detection power. We introduce a method that combines metagenomic sequencing and an alignment-free k-mer based approach for the identification of plant DNA in processed metagenomic samples. Our method identifies plant DNA directly from metagenomic sequencing reads and does not require mapping or assembly of the reads. We identified more than 31,000 Lupinus-specific 32-mers from assembled chloroplast genome sequences. We demonstrate that lupin DNA can be detected from controlled mixtures of sequences from target species (different Lupinus species) and closely related non-target species (Arachis hypogaea, Glycine max, Pisum sativum, Vicia faba, Phaseolus vulgaris, Lens culinaris, and Cicer arietinum). Moreover, these 32-mers are detectable in the following processed samples: lupin flour, conserved seeds and baked cookies containing different amounts of lupin flour. Under controlled conditions, lupin-specific components are detectable in baked cookies containing a minimum of 0.05% of lupin flour in wheat flour.

Immunoreactivity of Lupine and Soybean Allergens in Foods as Affected by Thermal Processing

Lupine and soybean are important technological aids for the food industry. However, they are also capable of inducing severe allergic reactions in food-sensitized/allergic individuals. In this context, this work intended to study the combined effects of thermal processing and food matrix on the immunoreactivity of lupine and soybean proteins used as ingredients in bakery and meat products, respectively. For this purpose, the effects of baking, mild oven cooking, and autoclaving on the protein profiles were evaluated, using model mixtures simulating the production of lupine-containing breads and soybean-containing cooked hams/sausages, by native- and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and immunoblotting using specific antibodies. The results showed that lupine gamma-conglutin immunoreactivity was slightly decreased in wheat flour mixtures compared to rice, but it was more pronounced in baked products. In meat mixtures, substantial protein fragmentation was noted after autoclaving, with decreased immunoreactivity of soybean trypsin inhibitor. The analysis of 22 commercial products enabled the identification of lupine gamma-conglutin in four bakery samples and soybean trypsin-inhibitor in five sausages, and further differentiated autoclaved from other milder thermally treated products. Generally, the immunoreactivity of target proteins was reduced by all the tested thermal treatments, though at a higher extent after autoclaving, being slightly altered by the food matrix.

Detection and Quantification of Milk Ingredients as Hidden Allergens in Meat Products by a Novel Specific Real-Time PCR Method

Milk ingredients are often included in a wide range of meat products, such as cooked hams and sausages, to improve technological characteristics. However, milk proteins are also important food allergens. The aim of this study was the development of a highly sensitive and specific real-time PCR system targeting the 12S rRNA gene of Bos domesticus for the detection and quantification of milk as an allergenic ingredient in processed meat products. The method was able to achieve an absolute limit of detection (LOD) of 6 fg of milk DNA. Using a normalized approach (∆Ct method) for the detection of milk protein concentrate (MPC), it was possible to obtain sensitivities down to 0.01% (w/w) of MPC in model hams (raw and cooked) and autoclaved sausages, and 0.005% in raw sausage mixtures. The developed systems generally presented acceptable PCR performance parameters, being successfully validated with blind samples, applied to commercial samples, and further compared with an immunochemical assay. Trace amounts of milk material were quantified in two out of 13 samples, but the results mostly infer the excessive practice of the precautionary labeling.

A critical review of the specifications and performance of antibody and DNA-based methods for detection and quantification of allergens in foods

Despite the availability of a large number of antibody and DNA based methods for detection and quantification of allergens in food there remain significant difficulties in selecting the optimum technique to employ. Published methods from research groups mostly contain sufficient detail concerning target antigen, calibration procedures and method performance to allow replication by others. However, routine allergen testing by the food industry relies upon commercialised test kits and frequently the suppliers provide disappointingly little specification detail on the grounds that this is proprietary information. In this review we have made a critical assessment of the published literature describing the performance of both commercial and non-commercial test kits for food allergens over the period 2008-2018. Mass spectrometric methods, which have the potential to become reference methods for allergens, are not covered in this review. Available information on the specifications of commercial ELISA and LFD test kits are tabulated for milk, egg and peanut allergens, where possible linking to publications concerning collaborative studies and proficiency testing. For a number of commercial PCR test kits, specifications provided by manufacturers for detection of a small selection of allergen are tabulated. In conclusion we support the views of others of the critical need for allergen reference materials as the way forward to improve the comparability of different testing strategies in foods.

The role of incurred materials in method development and validation to account for food processing effects in food allergen analysis

The issue of undeclared allergens represents a matter of great concern, being the subject of many alert notifications by the Rapid Alert System for Food and Feed portal of the European Commission, often leading to food recalls. The availability of reliable analytical approaches able to detect and quantify hidden allergens in processed foods is increasingly requested by the food industry, food safety authorities and regulatory bodies to protect sensitive consumers' health. The present review discusses the fundamental role of incurred materials for method development and analytical performance assessment in a metrology perspective on testing for undeclared allergens in processed foodstuffs. Due to the nature of the analytes and their susceptibility to various processing effects, reliability and comparability of results have posed a great challenge. In this context, the use of incurred samples as reference materials permits simulation of the effects of food processing on target analyte structure affecting analyte extractability and detectability. Graphical abstract ᅟ.

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.