A real-time PCR method for the detection and quantification of lupin flour in wheat flour-based matrices

Influence of Roasting Temperature on the Detectability of Potentially Allergenic Lupin by SDS-PAGE, ELISAs, LC-MS/MS, and Real-Time PCR

Seeds of "sweet lupins" have been playing an increasing role in the food industry. Lupin proteins may be used for producing a variety of foods, including pasta, bread, cookies, dairy products, and coffee substitutes. In a small percentage of the population, lupin consumption may elicit allergic reactions, either due to primary sensitization to lupin or due to cross-allergy with other legumes. Thus, lupin has to be declared on commercial food products according to EU food regulations. In this study, we investigated the influence of roasting seeds of the L. angustifolius cultivar "Boregine" on the detectability of lupin by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), ELISAs, LC-MS/MS, and real-time PCR. Seeds were roasted by fluidized bed roasting, and samples were drawn at seed surface temperatures ranging from 98 °C to 242 °C. With increasing roasting temperature, the extractability of proteins and DNA decreased. In addition, roasting resulted in lower detectability of lupin proteins by ELISAs and LC-MS/MS and lower detectability of DNA by real-time PCR. Our results suggest reduced allergenicity of roasted lupin seeds used for the production of "lupin coffee"; however, this has to be confirmed in in vivo studies.

Legumes: A Vehicle for Transition to Sustainability

Legumes are an excellent source of protein and have been used in the human diet for centuries. Consumption of legumes has been linked to several health benefits, including a lower risk of cardiovascular diseases, type 2 diabetes mellitus, and certain types of cancer, while legumes' high fiber content promotes digestive health. Aside from the positive health benefits, one of the most significant advantages of legumes is the low environmental footprint of their cultivation. They can be grown in a variety of climates and soil types, and they require less water and fertilizer than other crops, making them a sustainable option for farmers. Thanks to their nutritional and physicochemical properties, they are widely used by the food industry since the growing popularity of plant-based diets and the increasing demand for alternatives to meat offers the opportunity to develop legume-based meat substitutes. As the use of legumes as a source of protein becomes widespread, new market opportunities could be created for farmers and food industries, while the reduction in healthcare costs could have a potential economic impact. Achieving widespread adoption of legumes as a sustainable source of protein requires coordinated efforts by individuals, governments, and the private sector. The objective of this narrative review is to present the benefits coming from legume consumption in terms of health and environmental sustainability, and underline the importance of promoting their inclusion in the daily dietary pattern as well as their use as functional ingredients and plant-based alternatives to animal products.

Mechanisms and Health Aspects of Food Adulteration: A Comprehensive Review

Food adulteration refers to the alteration of food quality that takes place deliberately. It includes the addition of ingredients to modify different properties of food products for economic advantage. Color, appearance, taste, weight, volume, and shelf life are such food properties. Substitution of food or its nutritional content is also accomplished to spark the apparent quality. Substitution with species, protein content, fat content, or plant ingredients are major forms of food substitution. Origin misrepresentation of food is often practiced to increase the market demand of food. Organic and synthetic compounds are added to ensure a rapid effect on the human body. Adulterated food products are responsible for mild to severe health impacts as well as financial damage. Diarrhea, nausea, allergic reaction, diabetes, cardiovascular disease, etc., are frequently observed illnesses upon consumption of adulterated food. Some adulterants have shown carcinogenic, clastogenic, and genotoxic properties. This review article discusses different forms of food adulteration. The health impacts also have been documented in brief.

Selection of Specific Nanobodies against Lupine Allergen Lup an 1 for Immunoassay Development

The declaration of lupine supplements is mandatory to avoid lupine allergy for sensitive individuals. However, reliable detection methods against lupine allergen remain critical to prevent the unintended consumption of allergen contaminated food. In this study, we have immunized an alpaca with lupine protein extracts and retrieved nanobodies (Nbs). Nevertheless, the target antigen has been recognized as Lup an 1, which has been classified as β-conglutin, and confirmed to connect with lupine allergy. After selection of the best Nb-pair, a sandwich enzyme-linked immunosorbent assay (ELISA) has been developed providing a linear range of 0.036–4.4 μg/mL with detection limit of 1.15 ng/mL. This immunoassay was confirmed by detecting the samples with spiked allergen, and a recovery from 86.25% to 108.45% with coefficient of variation (CV) less than 4.0% has been determined. Generally, this study demonstrated the selection of Nbs against allergen with crude protein content to develop the immunoassay for lupine surveillance in foods.

Validation of a Triplex Quantitative Polymerase Chain Reaction Assay for Detection and Quantification of Traditional Protein Sources, Pisum sativum L. and Glycine max (L.) Merr., in Protein Powder Mixtures

Several botanicals have been traditionally used as protein sources, including the leguminous Pisum sativum L. and Glycine max (L.) Merr. While a rich history exists of cultivating these plants for their whole, protein-rich grain, modern use as powdered supplements present a new challenge in material authentication. The absence of clear morphological identifiers of an intact plant and the existence of long, complex supply chains behoove industry to create quick, reliable analytical tools to identify the botanical source of a protein product (many of which contain multiple sources). The utility of molecular tools for plant-based protein powder authentication is gaining traction, but few validated tools exist. Multiplex quantitative polymerase chain reaction (qPCR) can provide an economical means by which sources can be identified and relative proportions quantified. We followed established guidelines for the design, optimization, and validation of qPCR assay, and developed a triplex qPCR assay that can amplify and quantify pea and soy DNA targets, normalized by a calibrator. The assay was evaluated for analytical specificity, analytical sensitivity, efficiency, precision, dynamic range, repeatability, and reproducibility. We tested the quantitative ability of the assay using pea and soy DNA mixtures, finding exceptional quantitative linearity for both targets - 0.9983 (p < 0.0001) for soy and 0.9915 (p < 0.0001) for pea. Ratios based on mass of protein powder were also tested, resulting in non-linear patterns in data that suggested the requirement of further sample preparation optimization or algorithmic correction. Variation in fragment size within different lots of commercial protein powder samples was also analyzed, revealing low SD among lots. Ultimately, this study demonstrated the utility of qPCR in the context of protein powder mixtures and highlighted key considerations to take into account for commercial implementation.

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.

Analysis of Narrow-Leaf Lupin Proteins in Lupin-Enriched Pasta by Untargeted and Targeted Mass Spectrometry

The supplementation of different food items with grain legumes and, in particular, with lupin has been demonstrated to provide useful health benefits, especially in the area of cardiovascular disease prevention. In this work, label free quantitative untargeted and targeted approaches based on liquid chromatography−electrospray ionization−tandem mass spectrometry (LC−ESI−MS/MS) for investigating the protein profile of three pasta samples containing different percentages of narrow-leaf lupin flour were carried out. The untargeted method permitted the identification of the main acidic globulins (α-conglutin, β-conglutin, and δ-conglutin) and the comparison of their profile with raw lupin flour. The targeted method, based on High-performance liquid chromatography electrospray ionization tandem mass spectrometry HPLC-Chip-Multiple Reaction Monitoring (MRM) mode, allowed the quantification of γ-conglutin, the main hypoglycemic component of lupin protein: its concentration was around 2.25 mg/g in sample A, 2.16 mg/g in sample D, and 0.57 mg/g in sample F.

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.

Narrow-Leafed Lupin Main Allergen β-Conglutin (Lup an 1) Detection and Quantification Assessment in Natural and Processed Foods

The increasing prevalence of lupin allergy as a consequence to the functional characteristics of a growing number of sweet lupin-derived foods consumption makes the imperious necessity to develop analytical tools for the detection of allergen proteins in foodstuffs. The current study developed a new highly specific, sensitive and accurate ELISA method to detect, identify and quantify the lupin main allergen β-conglutin (Lup an 1) protein in natural and processed food. The implementation of accurate standards made with recombinant conglutin β1, and an anti-Lup an 1 antibody made from a synthetic peptide commonly shared among β-conglutin isoforms from sweet lupin species was able to detect up to 8.1250 ± 0.1701 ng (0.0406 ± 0.0009 ppm) of Lup an 1. This identified even lupin traces present in food samples which might elicit allergic reactions in sensitized consumers, such as β-conglutin proteins detection and quantification in processed (roasted, fermented, boiled, cooked, pickled, toasted, pasteurized) food, while avoiding cross-reactivity (false positive) with other legumes as peanut, chickpea, lentils, faba bean, and cereals. This study demonstrated that this new ELISA method constitutes a highly sensitive and reliable molecular tool able to detect, identify and quantify Lup an 1. This contributes to a more efficient management of allergens by the food industry, the regulatory agencies and clinicians, thus helping to keep the health safety of the consumers.

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

Lupine is widely used as an ingredient in diverse food products, but it is also a source of allergens. This work aimed at proposing a method to detect/quantify lupine as an allergen in processed foods based on a normalised real-time PCR assay targeting the Lup a 4 allergen-encoding gene of Lupinus albus. Sensitivities down to 0.0005%, 0.01% and 0.05% (w/w) of lupine in rice flour, wheat flour and bread, respectively, and 1 pg of L. albus DNA were obtained, with adequate real-time PCR performance parameters using the ΔCt method. Both food matrix and processing affected negatively the quantitative performance of the assay. The method was successfully validated with blind samples and applied to processed foods. Lupine was estimated between 4.12 and 22.9% in foods, with some results suggesting the common practice of precautionary labelling. In this work, useful and effective tools were proposed for the detection/quantification of lupine in food products.

A Classification Method for Seed Viability Assessment with Infrared Thermography

This paper presents a viability assessment method for Pisum sativum L. seeds based on the infrared thermography technique. In this work, different artificial treatments were conducted to prepare seeds samples with different viability. Thermal images and visible images were recorded every five minutes during the standard five day germination test. After the test, the root length of each sample was measured, which can be used as the viability index of that seed. Each individual seed area in the visible images was segmented with an edge detection method, and the average temperature of the corresponding area in the infrared images was calculated as the representative temperature for this seed at that time. The temperature curve of each seed during germination was plotted. Thirteen characteristic parameters extracted from the temperature curve were analyzed to show the difference of the temperature fluctuations between the seeds samples with different viability. With above parameters, support vector machine (SVM) was used to classify the seed samples into three categories: viable, aged and dead according to the root length, the classification accuracy rate was 95%. On this basis, with the temperature data of only the first three hours during the germination, another SVM model was proposed to classify the seed samples, and the accuracy rate was about 91.67%. From these experimental results, it can be seen that infrared thermography can be applied for the prediction of seed viability, based on the SVM algorithm.

Evaluation of total polyphenol content and antioxidant capacity of different verity lupin seeds

Legumes, including lupins, beans, lentil and chickpea, are one of the most important crops in the world because of their nutritional quality. Lupin seeds have been used as human food and animal feed since ancient times. It was known that antioxidant photochemical in foods have many health benefits including prevention of various diseases associated with oxidative stress such as cancer, cardiovascular disease, neuro-degeneration and diabetes. Lupin grains are rich sources of complex carbohydrates, protein, vitamins and minerals. Antioxidants can be found naturally in foods. Total polyphenols content and antioxidant activity were measured in four varieties of lupin, namely in white lupin, blue lupin, yellow lupin and Mutabilis lupin species. A majority of antioxidants naturally present in foods occur in phenolic structures and especially in flavonoid structures. The content of the total polyphenols was determined by using the Folin-Ciocalteu reagent (FCR). Antioxidant activity was measured by using a compound DPPH˙ (2.2-diphenyl-1-picrylhydrazyl). In the present experiment according to the average contents of total polyphenols (TPC) in dry matter of lupin seeds there was the following line: L. Angustifolius (blue) lupin (696.212 mg GAE.100g-1) > L. Albus (white) lupin (614.13 mg GAE.100g-1) > L. Luteus (yellow) lupin (467.78 mg GAE.100g-1) > L. Mutabilis (pearl) lupin (367.36 mg GAE.100g-1). Based on the measured values of total antioxidant capacity (TAC) of lupin samples can be classified as follows: L. Albus (white) lupin (43.44%) >L. Angustifolius (blue) lupin (38.27%) >L. Luteus (yellow) lupin (22.29%) >L. Mutabilis (Pearl) lupin (20.80%). The relationship of antioxidant capacity with total polyphenolic was discussed. According to used statistical analyzes. Correlation between the phenolic contents and antioxidant capacity was significantly positive (r = 0.88). Our results confirmed that legumes can be a good source of bioactive compounds in the human nutrition. The main objective of the present work was to evaluated the content of total polyphenols and an antioxidant capacity of four Lupine species.

Detection of Lupine (Lupinus spp. L.) as a food allergen using three methods: end-point PCR, Real-Time PCR and Elisa

The aim of this work was to compare three methods for the detection and quantification of lupine as an allergen in food. The methods that were used in this work were the direct method: ELISA and the indirect methods: end-point PCR and real-time PCR. We examined the detection limit (the sensitivity with which we can detect the presence of the allergen in a sample) and the reliability for performing an analysis. We used 17 samples of plant species from a processing plant for dehydrated soups production and lupine samples from lupine processing companies. Its practical use is wide and it is used mainly in the bakery industry, in the manufacture of confectionery, pasta, sauces, as a substitute for soy and also in the production of gluten-free food, because it does not contain gluten. Lupine, however, is also included in the list of 14 allergenic substances, which in accordance with the EU legislation must be listed on food labels. The high risk group, which suffers from primary sensitization or cross-reaction with peanuts, are allergic patients. In the EU, people who are allergic to peanuts range from 0.7 to 1.5%. In experiment 1, we detected the presence of lupine using primers for the detection of α- and δ-conglutine in the samples, using the end-point PCR method and the detection limit of this reaction was at the level of 100 ppm. For the vizualization of the DNA fragments, we used a 2% agarose gel and UV visualizer. In experiment 2 we detected lupine using the TaqMan real-time PCR reaction and primers for the detection of α and δ-conglutine at the level of 10 ppm of lupine in sample. The CP values of lupine using primers for the detection of α-conglutine was 24.85 ± 0.12 and the reliability equation was R2 = 0.9767. The CP lupine values using primers for the detection of δ-conglutine was 22.52 ± 0.17 and the reliability equation was R2 = 0.9925. In experiment 3, we used a sandwich ELISA method for the detection of lupine and the detection limit was within the range of 2-30 ppm and the reliability of the method according to the reliability equation was R2 = 0.9975. The high sensitivity and equation of reliability justify the use of these methods for the detection and quantification of lupine in practice. The most sensitive indirect method for the detection of lupine in our study was the method of real-time TaqMan PCR with a detection limit  10 000-10 ppm of lupine. The most sensitive direct methot was ELISA with detection limit 2-30 ppm of lupine.

Detectability of lupine seeds by ELISA and PCR may be strongly influenced by potential differences between cultivars

Accurate methods for allergen detection are needed for the verification of allergen labeling and the avoidance of hidden allergens. But systematic data on the influence of different cultivars of allergenic crop species on their detectability in enzyme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR) are lacking. As one example, seeds of 14 different cultivars of lupine (Lupinus albus, Lupinus angustifolius, Lupinus luteus) were investigated for total protein according to a Kjeldahl method, and for their relative quantitative detectability in three commercial lupine-specific ELISA tests and four lupine-specific PCR methods. Total Kjeldahl nitrogen allowed an accurate quantification of total protein. Relative differences in quantitative response between cultivars of 390-5050% and 480-13,600% were observed between ELISA kits and PCR methods, respectively. Hence, quantitative results of selected ELISA and PCR methods may be strongly influenced by the examined lupine cultivar.

Effect of lactic acid fermentation of lupine wholemeal on acrylamide content and quality characteristics of wheat-lupine bread

The effect of supplementing wheat flour at a level of 15% with lupine (Lupinus angustifolius L.) wholemeal fermented by different lactic acid bacteria on acrylamide content in bread crumb as well as on bread texture and sensory characteristics was analysed. The use of fermented lupine resulted in a lower specific volume and crumb porosity of bread on an average by 14.1% and 10.5%, respectively, while untreated lupine lowered the latter parameters at a higher level (30.8% and 20.7%, respectively). The addition of lupine resulted in a higher by 43.3% acrylamide content compared to wheat bread (19.4 µg/kg dry weight (d.w.)). Results showed that acrylamide was significantly reduced using proteolytic Lactobacillus sakei and Pediococcus pentosaceus 10 strains for lupine fermentation. Although the bread supplemented with lupine spontaneous sourdough had the lowest level of acrylamide (15.6 µg/kg d.w.), it had the malodorous flavour and was unacceptable to the consumers. The lactofermentation could increase the potential use of lupine as a food ingredient while reducing acrylamide formation and enriching bread with high quality proteins.

Validation and comparison of a sandwich ELISA, two competitive ELISAs and a real-time PCR method for the detection of lupine in food

Methods applied in food allergen analysis should be specific, sensitive and applicable to both raw and highly processed foods. The performance of the most commonly used methods, ELISA and real-time PCR, may, however, be influenced by food processing steps, e.g., heat treatment. The present study compares the applicability of four in-house developed methods, one sandwich ELISA, two competitive ELISAs and a real-time PCR method, for the detection of lupine in four different food matrices, comprising bread, biscuits, rice patties and noodles. In order to investigate the influence of food processing on the detectability, not only the heat treated model foods but also the corresponding doughs were analysed. The sandwich ELISA proved to be the most sensitive method. The LOD was found to be 10 ppm lupine, independent from the food matrix and independent if the dough or the heat treated food was analysed. In addition, the methods were applied to the analysis of commercial foodstuffs differing in their labelling.

Extraction, isolation, and characterization of globulin proteins from Lupinus albus

Lupin has recently been added to the list of allergens requiring mandatory advisory labeling on foodstuffs sold in the European Union, and since December 2008, all products containing even trace amounts of lupin must be labeled correctly. Lupin globulins consist of two major globulins called α-conglutin (11S and "legumin-like") and β-conglutin (7S and "vicilin-like") and another additional two globulins, γ-conglutin and δ-conglutin, which are present in lower amounts. We report on a methodology to facilitate the extraction of each of these proteins using centrifugation and isolation by anion-exchange chromatography followed by size-exclusion chromatography. The isolated subunits were characterized using reducing and non-reducing polyacrylamide gel electrophoresis, western blotting, and peptide mass fingerprinting, all of which revealed that the individual protein subunits are highly pure and can be used as immunogens for the production of antibodies specific for each of the conglutin fractions, as well as standards, and the extraction protocol can be used for the selective extraction of each of the subunits from foodstuffs, thus facilitating a highly accurate determination of the lupin concentration. Furthermore, the subunits can be used to elucidate information regarding the toxicity of each of the subunits, by looking at their interaction with the IgE antibodies found in the serum of individuals allergic to lupin, providing critical information for the definition of the requirements of analytical assays for the detection of lupin in foodstuffs.

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.

gamma-Conglutin, the Lupinus albus XEGIP-like protein, whose expression is elicited by chitosan, lacks of the typical inhibitory activity against GH12 endo-glucanases

gamma-Conglutin, a glycoprotein from Lupinus albus seed, has been characterized at molecular level but its physiological function is still unknown. gamma-Conglutin shares a high structural similarity with xyloglucan-specific endo-beta-1,4-glucanase inhibitor proteins (XEGIPs) and Triticum aestivum xylanase inhibitor (TAXI-I), which act specifically against fungal glycosyl hydrolase belonging to families 12 and 11, respectively. To assess the possible involvement of gamma-conglutin in plant defense, germinating lupin seeds were incubated with chitosan. The relative quantification of gamma-conglutin mRNA extracted from cotyledons was then carried out by RT-qPCR and indicated that chitosan strongly elicited the expression of gamma-conglutin. Moreover, biochemical trials aimed to test the inhibitory capacity of the protein have been also carried out. gamma-Conglutin failed to inhibit representative fungal endo-glucanases and other cell wall-degrading enzymes. To explain the lack of inhibitory capacity we investigated the possible structural differences between gamma-conglutin and XEGIPs and TAXI-I, including the construction of a predictive 3D model of the protein. Bioinformatic analysis suggests that the lack of inhibitory activity of gamma-conglutin can be attributed to sequence differences in the inhibitor interaction domains, and in particular to a sequence deletion in one of the functional loops.