Reduced β-lactoglobulin IgE binding upon in vitro digestion as a result of the interaction of the protein with casein glycomacropeptide

Exploration of Specific Nanobodies As Immunological Reagents to Detect Milk Allergen of β-Lactoglobulin without Interference of Hydrolytic Peptides

Milk proteins are widely used for food supplementation, despite the potential risk of food allergy, especially against β-lactoglobulin (BLG), which makes BLG surveillance critical. Possible interaction of detecting antibodies with BLG-derived peptides will result in unprecise inspection. Thus, in this study, it was proposed to generate nanobodies (Nbs) and validate the immunological detection of intact BLG rather than hydrolytic peptides. Nbs were successfully retrieved and characterized with high stability and target specificity. A competitive enzyme-linked immunosorbent assay (cELISA) was developed with a linear range from 39 to 10,000 ng/mL and a detection limit (LOD) of 4.55 ng/mL, with a recovery of 86.30%-95.09% revealed by analysis of spiked samples. Meanwhile, a sandwich ELISA (sELISA) was established with Nb82 and BLG polyclonal antibody (pAb-BLG) providing a linear range from 29.7 to 1250 ng/mL and an LOD of 13.82 ng/mL with a recovery of 87.82%-103.97%. The interaction of selected Nbs with BLG-derived peptides was investigated by Nb structure modeling and BLG docking. No binding on hydrolytic peptides was revealed, confirming the precision of Nb-mediated immunoassays. In summary, this study successfully identified BLG-specific Nbs for immunoassay development and guaranteed the monitoring of intact BLG without interference of hydrolytic peptides, providing experimental evidence that our Nbs recognize intact food allergen.

Immunomodulatory Role of BLG-Derived Peptides Based on Simulated Gastrointestinal Digestion and DC-T Cell from Mice Allergic to Cow's Milk

Peptides, but not whole protein, elicit an allergic reaction since food allergens should be consumed by digestion. In this study, we explored the remaining peptides after simulated digestion of cow’s milk in order to search for β-lactoglobulin (BLG)-derived peptides that could play an immunomodulatory role. As a major allergen in milk, BLG-derived peptides, 109 in total, were identified both from simulated infant and adult digestion in vitro. These peptides were mainly located in four regions, and they were synthesized as five peptides, namely, BLG_1–14, BLG_24–35, BLG_40–60, BLG_82–101, and BLG_123–139. Then, the effect of peptides on the Caco-2 cell’s transport absorption, the co-stimulatory molecules of DC, and the T-cell phenotype was explored. The results suggested all peptides showed better transport absorption capacity with the apparent permeability coefficient higher than 2 × 10⁻⁶ cm·s⁻¹. The ability of BLG_40–60 for promoting lamina propria-derived DC cell (LPDC) maturation was observed by the increase in MHC II. Moreover, BLG_1–14 and BLG_40–60 directed activation of T lymphocytes towards a Th1 phenotype. This is the first report of the immunomodulatory potential of peptides in the sensitization of allergic reaction, and one peptide, BLG_40–60, was regarded as an immunomodulatory peptide, one that should be further explored in an animal model in depth.

Mechanism of the Reduced IgG/IgE Binding Abilities of Glycated β-Lactoglobulin and Its Digests through High-Resolution Mass Spectrometry

Glycation between proteins and reducing sugars is the common chemical modification in food protein, and many studies have focused on the allergenicity of the glycated protein. However, a systemic study on the allergenicity change of its digests is lacking. In this work, we explored the change rule of the digestibility and allergenicity of glycated β-Lg during in vitro gastrointestinal digestion and interpreted the mechanism using high-resolution mass spectrometry. Glycation with arabinose increased the resistance of β-Lg to digestive enzyme, with a low hydrolysis value. Indirect competitive ELISA showed that the IgG/IgE binding rates of β-Lg were reduced after glycation and further reduced after digestion, in comparison with the digests of unglycated β-Lg. There are two reasons for this phenomenon. On the one hand, 11 glycated sites were determined in the lowest allergenicity arabinose-β-Lg conjugation (Ara-β-Lg), which was distributed in the IgG and IgE linear allergic epitopes of β-Lg. On the other hand, glycation masking linear allergenic epitopes had a more significant effect on reducing allergenicity in comparison to digestive enzyme hydrolysis. These results indicated that the allergenicity of Ara-β-Lg in the human body might be lower than that of unglycated β-Lg.

Reducing antigenicity of bovine whey proteins by Kluyveromyces marxianus fermentation combined with ultrasound treatment

This work investigated the reduction of bovine whey proteins antigenicity by ultrasonic pretreatment and microbial fermentation. Firstly, bovine whey proteins was pretreated by ultrasonic techniques, and its secondary structure was detected by circular dichroism. The pretreated whey proteins was used as the fermentation substrate by Kluyveromyces marxianus for microbial transformation. The single factor design and Box-Behnken Design (BBD) were carried out with the aim to optimize culture temperature, initial pH, inoculum volume and rotation speed. After optimization process, culture temperature, initial pH, inoculum volume and rotation speed were determined. Under culture temperature 35 °C, pH 7.25, inoculum level 10% and shaking speed 150 rpm, the α-LA and β-LG antigenicity in bovine whey proteins were reduced by 29% and 53%, respectively. The findings showed that combined with microbial fermentation for hydrolysis of whey proteins, ultrasonic pretreatment can be used in order to produce hypoallergenic bovine whey proteins.

Changes in structure and antioxidant activity of β-lactoglobulin by ultrasound and enzymatic treatment

Effects of ultrasound (20-40% amplitudes at 45-55 °C) and enzymatic (pepsin and trypsin) treatment on structure and antioxidant activity of β-lactoglobulin were studied. Changes in structure of β-lactoglobulin were investigated using spectroscopy techniques and changes in antioxidant activity were measured by chemical and cellular-based assays. Ultrasound treatment had considerable impact on the structure of β-lactoglobulin and increased the susceptibility of β-lactoglobulin to both pepsin and trypsin proteolysis. Intrinsic fluorescence intensity of β-lactoglobulin was increased by ultrasound and then decreased after following enzymatic treatment. Compared with control, the β-lactoglobulin after ultrasound and enzymatic treatments showed significantly higher oxygen scavenging activities in Caco-2 cells models, ABTS (2, 2'-Azinobis-3-ethylbenzthiazoline-6-sulphonate) radical scavenging activity and oxygen radical absorbance capacity (p < 0.05). Results indicated that ultrasound treatment increased the proteolysis of β-lactoglobulin by both pepsin and trypsin and improved the antioxidant activity of the protein and its proteolytic products.

The Reduction in the IgE-Binding Ability of β-Lactoglobulin by Dynamic High-Pressure Microfluidization Coupled with Glycation Treatment Revealed by High-Resolution Mass Spectrometry

Our previous study indicated that pretreatment by dynamic high-pressure microfluidization (DHPM) and glycation with galactose was a promising method for decreasing the immunoglobulin E (IgE)-binding ability of β-lactoglobulin (β-LG). In this work, the conformational alteration of β-LG subjected to DHPM and glycation treatment was investigated in relation to IgE-binding ability by orbitrap mass spectrometry. After DHPM pretreatment, lower IgE-binding ability of glycated β-LG was observed with increasing pressures. Prior to DHPM pretreatment, 11 glycated sites were identified, while the number of glycation sites was increased to 12 after pretreatment. However, there was no significant difference of the glycation sites at the pressures of 50, 100, and 200 MPa, respectively. Average degree of substitution per peptide molecule of β-LG (DSP) was investigated to assess the degree of glycation per glycation site. All of the samples pretreated by DHPM exhibited a higher glycation level than those without DHPM pretreatment. The shielding effects of epitopes owing to glycation contributed to the reduction of IgE-binding capacity. Orbitrap mass spectrometry could provide a comprehensive understanding of the nature of protein glycation.

Micro- and nano bio-based delivery systems for food applications: In vitro behavior

Micro- and nanoencapsulation is an emerging technology in the food field that potentially allows the improvement of food quality and human health. Bio-based delivery systems of bioactive compounds have a wide variety of morphologies that influence their stability and functional performance. The incorporation of bioactive compounds in food products using micro- and nano-delivery systems may offer extra health benefits, beyond basic nutrition, once their encapsulation may provide protection against undesired environmental conditions (e.g., heat, light and oxygen) along the food chain (including processing and storage), thus improving their bioavailability, while enabling their controlled release and target delivery. This review provides an overview of the bio-based materials currently used for encapsulation of bioactive compounds intended for food applications, as well as the main production techniques employed in the development of micro- and nanosystems. The behavior of such systems and of bioactive compounds entrapped into, throughout in vitro gastrointestinal systems, is also tracked in a critical manner. Comparisons between various in vitro digestion systems (including the main advantages and disadvantages) currently in use, as well as correlations between the behavior of micro- and nanosystems studied through in vitro and in vivo systems were highlighted and discussed here for the first time. Finally, examples of bioactive micro- and nanosystems added to food simulants or to real food matrices are provided, together with a revision of the main challenges for their safe commercialization, the regulatory issues involved and the main legislation aspects.

T-cell epitope-containing hypoallergenic β-lactoglobulin for oral immunotherapy in milk allergy

BACKGROUND

Optimally hydrolyzed β-Lactoglobulin (βLg) is a promising milk oral immunotherapy (OIT) candidate with respect to showing reduced B-cell reactivity but retaining the T-cell epitope. To demonstrate that an edible hypoallergenic βLg hydrolysate containing the T-cell epitope is suitable for OIT. We tested how chymotrypsin affected the retention of the T-cell epitope of βLg when preparing βLg hydrolysates using food-grade trypsin.

METHODS

We investigated the effect of chymotrypsin activity on the formation of the T-cell epitope-containing peptide of βLg (βLg_102-124 ) and prepared an edible βLg hydrolysate containing βLg_102-124 using screened food-grade trypsins. B-cell reactivity was determined using immunoassays in which ELISA was performed with anti-βLg rabbit IgG and Western blotting was performed with a milk-specific IgE antiserum.

RESULTS

In βLg hydrolysis performed by varying the activity of trypsin and chymotrypsin, chymotrypsin activity inhibited the formation of βLg_102-124 with an increase in hydrolysis time in a dose-dependent manner. βLg_102-124 was generated by two of five food-grade trypsins used at a ratio of 1:50 (w/w, enzyme/substrate) for 20 h at 40°C. The edible βLg hydrolysate retained βLg_102-124 and showed a reduction in molecular weight distribution and antigenicity against IgG and IgE.

CONCLUSIONS

Chymotrypsin activity inhibited the formation of βLg_102-124 in the trypsin hydrolysate of βLg. This βLg trypsin hydrolysate is a novel candidate for peptide-based OIT in cow's milk allergy for safely inducing desensitization.