Quantification of Gly m 5.0101 in Soybean and Soy Products by Liquid Chromatography-Tandem Mass Spectrometry

Label-Free Quantification by Liquid Chromatography-Tandem Mass Spectrometry of the Kunitz Inhibitor of Trypsin KTI3 in Soy Products

The greater awareness of consumers regarding the sustainability of food chains has shifted part of the consumption from animal protein sources to vegetable sources. Among these, of relevance both for human food use and for animal feed, is soy. However, its high protein content is unfortunately accompanied by the presence of antinutritional factors, including Kunitz's trypsin inhibitor (KTI). Now there are few analytical methods available for its direct quantification, as the inhibitory activity against trypsin is generically measured, which however can be given by many other molecules and undergo numerous interferences. Therefore, in this work, a direct label-free liquid chromatography-mass spectrometry (LC-MS) method for the identification and quantification of trypsin Kunitz inhibitor KTI3 in soybean and derivative products has been developed. The method is based on the identification and quantification of a marker peptide, specific for the protein of interest. Quantification is achieved with an external calibration curve in the matrix, and the limit of detection and the limit of quantification of the method are 0.75 and 2.51 μg/g, respectively. The results of the LC-MS method were also compared with trypsin inhibition measured spectrophotometrically, highlighting the complementarity of these two different pieces of information.

Quantification of lectin in soybeans and soy products by liquid chromatography-tandem mass spectrometry

Lectin is one of the major anti-nutritional factors in soybeans and inhibits digestion of dietary protein. Here, an absolute quantification method was developed to detect lectin using synthetic peptide 183TTSWDLANNK192 as reference standard and corresponding isotope labeled peptide TTSWDLANNK (Alanine-13C3,15N) as internal standard to normalize results. After the ground soybeans and soy products were defatted with n-hexane and extracted with extraction buffer, the crude protein extract was digested on filter membrane by trypsin. Further, the enzymatic hydrolysis peptides were quantified using liquid chromatography-tandem mass spectrometry. The synthetic reference peptide showed a detection limit of 0.27 ng/mL and a linear relationship in the range of 3.2-1000 ng/mL (r2 > 0.997). Correspondingly, the detect limit of lectin in soybean samples was 35.5 μg/g. The results showed that the recoveries of the lectin in spiked samples ranged from 80.9% to 108.7% with intra-day precisions (% CV) less than 9%. The method was successfully used to evaluate lectin levels in hundreds of soybean seeds from different varieties and soy products from different soybean processing techniques. Furthermore, the method may provide a potential application as a general method for the ultrasensitive detection of various protein anti-nutritional factors in food.

A novel highly sensitive soy aptasensor for antigen β-conglycinin determination

β-Conglycinin, composed of three subunits (α', α and β), is the main allergen of soy protein which can cause severe allergic reactions, such as diarrhea, decreased growth performance and even death. Among them, the β subunit is more stable and difficult to remove, being one of the main nutritional inhibitors, which can be used to evaluate the concentration of β-conglycinin. However, there is no effective, accurate method for its β subunit rapid detection. Herein, we have successfully selected a high affinity β subunit aptamer (Kd = 6.9 nM) and developed a highly sensitive aptasensor. The aptasensor displayed high specificity and the β subunit at a concentration of 70-350 nM could be detected with a detection limit of 4.48 nM (3S/N). In addition, the recoveries of β subunit were more than 90%, demonstrating its practical properties for complicated conditions such as food quality control and disease diagnosis, without requiring expensive and sophisticated equipment.

An electrochemical molecularly imprinted polymer sensor for rapid and selective food allergen detection

Food allergies are a serious and rising public health concern. The potentially fatal consequence of food allergies makes managing them costly and anxiety-inducing. Rapid, on-site detection of allergenic ingredients in foods would greatly improve the health and quality of life of food allergy sufferers. This work demonstrates the feasibility of such a device using molecularly imprinted polymers (MIPs). The MIP sensor can detect allergenic soy markers at concentrations as low as 100 parts-per-billion, two orders of magnitude below clinically relevant thresholds, in both controlled and complex food samples. Sensor performance was qualitatively validated with commercially available soy allergen detection lateral flow devices (LFDs). The outcome of this application will address a long-standing analytical challenge to achieving fast, cost-effective, and scalable methods for direct detection of allergen tracers in food analysis.

The development of lateral flow immunoassay strip tests based on surface enhanced Raman spectroscopy coupled with gold nanoparticles for the rapid detection of soybean allergen β-conglycinin

β-Conglycinin is an important storage protein in soybean, which can potentially cause food allergies in human. In this study, a sensitive mouse monoclonal antibody (3D11 mAb) with a high affinity was prepared, and sandwich lateral flow immunochromatographic detection strips were developed for the rapid detections of the soybean allergen β-conglycinin. The 3D11 mAb was combined with a rabbit polyclonal antibody in order to establish strips. The titer of 3D11 mAb was 1:2.56 × 105. The affinity constant of the 3D11 mAb was 9.6 × 109. The lowest detection limit with the naked eye of the double antibody sandwich strips was 1 μg/mL. In addition, chemical molecules p-aminothiophenol with colloidal gold were used as Raman enhancement signals in order to achieve quantitative detections of the β-conglycinin. It was determined in this study that the practical working range of the β-conglycinin concentrations was between 160 ng/mL and 100 μg/mL with the developed assay.

Enhancing online protein isolation as intact species from soy flour samples by actively modulated two-dimensional liquid chromatography (2D-LC)

In this study, an enhanced fully automated approach is described for the protein isolation from soy flour samples by two-dimensional liquid chromatography with active modulation interface. The use of two multi-port switching valves is proposed to on-line connect the first to the second dimension column, thus overcoming the problems associated with the re-mixing effects and incompatibility of eluent composition and pH. A 5-cm long C4 analytical column installed in the interface device allows to focus the proteins coming from the first column (size exclusion chromatography), before their selective elution in the second column (reversed-phase). A trap washing step was included in the total workflow, as a desalting step to remove buffer residues from the eluent of the first column and to enhance the chromatographic performances of the second column. The experimental conditions were optimized by analyses of mixed standard solutions of bovine serum albumin, glucose oxidase, immunoglobulin A, thyroglobulin and myoglobin. Then, the optimized 2D-LC method was applied to the protein analysis in extracts of soy flour, known worldwide as one of the major food allergen sources, with the final aim to recovery sufficient protein amounts for the molecular characterization and the assessment of the pattern of allergenic components.