Impact of Transglutaminase-Mediated Crosslinking on the Conformational Changes in a Dual-Protein System and IgE Reactivity of Soy Protein.

Transglutaminase (TGase)-catalyzed crosslinking has gained substantial traction as a novel strategy for reducing allergenic risk in food proteins, particularly within the realm of hypoallergenic food production. This study explored the impact of TGase crosslinking on conformational changes in a binary protein system composed of soy protein isolate (SPI) and sodium caseinate (SC) at varying mass ratios (10:0, 7:3, 5:5, 3:7 (w/w)). Specifically, the immunoglobulin E (IgE) binding capacity of soy proteins within this system was examined. Prolonged TGase crosslinking (ranging from 0 h to 15 h) resulted in a gradual reduction in IgE reactivity across all SPI-SC ratios, with the order of IgE-binding capability as follows: SPI > SPI5-SC5 > SPI7-SC3 > SPI3-SC7. These alterations in protein conformation following TGase crosslinking, as demonstrated by variable intrinsic fluorescence, altered surface hydrophobicity, increased ultraviolet absorption and reduced free sulfhydryl content, were identified as the underlying causes. Additionally, ionic bonds were found to play a significant role in maintaining the structure of the dual-protein system after crosslinking, with hydrophobic forces and hydrogen bonds serving as supplementary forces. Generally, the dual-protein system may exhibit enhanced efficacy in reducing the allergenicity of soy protein.

Effect of transglutaminase crosslinking combined with lactic fermentation on the potential allergenicity and conformational structure of soy protein.

BACKGROUND: Food allergies are a growing concern worldwide, with soy proteins being important allergens that are widely used in various food products. This study investigated the potential of transglutaminase (TGase) and lactic acid bacteria (LAB) treatments to modify the allergenicity and structural properties of soy protein isolate (SPI), aiming to develop safer soy-based food products. RESULTS: Treatment with TGase, LAB or their combination significantly reduced the antibody reactivity of ß-conglycinin and the immunoglobulin E (IgE) binding capacity of soy protein, indicating a decrease in allergenicity. TGase treatment led to the formation of high-molecular-weight aggregates, suggesting protein crosslinking, while LAB treatment resulted in partial protein hydrolysis. These structural changes were confirmed by Fourier transform infrared spectroscopy, which showed a decrease in ß-sheet content and an increase in random coil and ß-turn contents. In addition, changes in intrinsic fluorescence and ultraviolet spectroscopy were also observed. The alterations in protein interaction and the reduction in free sulfhydryl groups highlighted the extensive structural modifications induced by these treatments. CONCLUSION: The synergistic application of TGase and LAB treatments effectively reduced the allergenicity of SPI through significant structural modifications. This approach not only diminished antibody reactivity of ß-conglycinin and IgE binding capacity of soy protein but also altered the protein's primary, secondary and tertiary structures, suggesting a comprehensive alteration of SPI's allergenic potential. These findings provide a promising strategy for mitigating food allergy concerns and lay the foundation for future research on food-processing techniques aimed at allergen reduction. © 2024 Society of Chemical Industry.

Comparison on Protein Bioaccessibility of Soymilk Gels Induced by Glucono-δ-Lactone and Lactic Acid Bacteria.

In this study, the protein bioaccessibility of soymilk gels produced by the addition of glu-cono-δ-lactone (GDL) and fermentation with lactic acid bacteria (LAB) was examined using an in vitro gastrointestinal simulated digestion model. The in vitro protein digestibility, soluble protein content, free amino acids contents, degree of hydrolysis, electrophoretic patterns, and peptide content were measured. The results suggested that acid-induced soymilk gel generated by GDL (SG) showed considerably reduced in vitro protein digestibility of 75.33 ± 1.00% compared to the soymilk gel induced by LAB (SL) of 80.57 ± 1.53% (p < 0.05). During the gastric digestion stage, dramatically higher (p < 0.05) soluble protein contents were observed in the SG (4.79−5.05 mg/mL) than that of SL (4.31−4.35 mg/mL). However, during the later intestinal digestion phase, the results were the opposite. At the end of the gastrointestinal digestion phase, the content of small peptides was not significantly different (p > 0.05) between the SL (2.15 ± 0.03 mg/mL) and SG (2.17 ± 0.01 mg/mL), but SL showed higher content of free amino acids (20.637 g/L) than that of SG (19.851 g/L). In general, soymilk gel induced by LAB had a higher protein bioaccessibility than the soymilk gel coagulated by GDL.

Effect of Transglutaminase Pre-Crosslinking Treatment Incorporated with Glucono-δ-lactone on the Physicochemical and Digestive Properties of Tofu.

This study evaluated the effect of transglutaminase (TGase) pre-crosslinking treatment on the physicochemical and digestive characteristics of tofu coagulated by glucono-δ-lactone (GDL). Results showed that certain TGase pre-crosslinking times (0.5, 1, 2 and 3 h) could promote the colloidal stability of soymilk with increased particle average sizes and absolute values of zeta potential. Particularly, the water holding capacity and gel strength of tofu pre-crosslinked by TGase for 2 h were 6.8% and 47.7% enhancement, respectively, compared to the control, and exhibited the highest score of overall acceptability. However, extensive pre-crosslinking by TGase for 3 h had an adverse impact on the sensory of tofu with poor firmness, rough structure and whey separation. Hence, the tofu gel pre-crosslinked by TGase for 2 h and then coagulated by GDL was recommended which showed a "slow release" mode of soluble proteins during the in vitro digestion phase, and had more chances to release bioactive peptides than soymilk.

Effect of Co-Fermentation with Lactic Acid Bacteria and K. marxianus on Physicochemical and Sensory Properties of Goat Milk.

In this study, a multi-starters fermentation system involved lactic acid bacteria and yeasts was applied to obtain a novel acidified goat milk (AGM). Significant differences were found in the volatile flavor profile among goat milk, goat yogurt, and AGM reflected by principal component analysis of electronic nose (E-nose) data. Gas chromatography-mass spectrometry (GC-MS) results indicated that the relative content of free octanoic acid decreased, and more aromas were formed in AGM, which were considered to mask the goaty smell and give AGM a pleasant flavor. Rheological analysis indicated that AGM had higher apparent viscosity and G' and G'' moduli than goat yogurt and goat milk. Therefore, the goat yogurt fermented by lactic acid bacteria and K. marxianus exhibits a new method to alleviate the goaty flavor in goat milk and provides a novel option for those who were allergic to milk protein and dislike goaty flavor in goat milk.

Gelling behavior of bio-tofu coagulated by microbial transglutaminase combined with lactic acid bacteria.

The aim of this study was to investigate the gelling behavior of proteins in bio-tofu (soymilk-cow milk mixture gel) coagulated by microbial transglutaminase (MTGase) combined with lactic acid bacteria (LAB). It was shown that MTGase (3.0 U/g protein) treatment of soymilk-cow milk mixture (SCMM) could not induce gelation at 43℃ even if the incubation was lasting 4 h. However, the concomitant use of LAB (0.025 UC/L) along with MTGase could induce the formation of denser and finer gel network with smaller pores and higher storage modulus (G') compared to SCMM treated with only LAB. Electrophoresis and mass spectrometry results indicated that LAB improve MTGase-dependent polymerization of proteins. In addition, this study investigates the effect of LAB and MTGase treatment on the rheology behavior of the derived gel products. In general, the use of both bio-coagulants for the manufacture of a mixed protein gel, might open new horizons in the field of novel nutrional and functional foods.

Effect of Fermentation pH on Protein Bioaccessibility of Soymilk Curd with Added Tea Polyphenols As Assessed by in Vitro Gastrointestinal Digestion.

The aim of this study was to compare the effect of fermentation pH on protein bioaccessibility of four soymilk curds enriched with tea polyphenols (TP). The curds were generated by fermentation with Weissella hellenica D1501 and the fermentation terminated at different pH values, namely at pH 5.7, 5.4, 5.1, and 4.8 (SMTP-5.7, SMTP-5.4, SMTP-5.1, SMTP-4.8). Particle-size distribution, soluble protein content, gel electrophoresis, and peptides content were monitored at oral, gastric, and intestinal levels. Results showed that SMTP-4.8 was the matrix most resistant to protein digestion in the gastric phase according to the soluble protein content. Similar particle size distribution and protein degradation patterns were observed for these curds in gastric and intestinal phase. However, there was a significant difference (P < 0.05) in the content of small peptides (<10 kDa) at the end of intestinal digestion among the four curds. Overall, terminating fermentation at pH 5.4-5.7 of soymilk curds enriched with TP is recommended.

In vitro gastrointestinal digestion study of a novel bio-tofu with special emphasis on the impact of microbial transglutaminase.

We have developed a novel bio-tofu, made from mixed soy and cow milk (MSCM), using Lactobacillus helveticus MB2-1 and Lactobacillus plantarum B1-6 incorporated with microbial transglutaminase (MTGase) as coagulant. MTGase was added to improve the textural properties and suit for cooking. However, the effect of MTGase on the digestion of mixed-protein fermented by lactic acid bacteria was unclear. This study aimed at evaluating the effect of MTGase on protein digestion of bio-tofu under simulated gastrointestinal digestion condition. The results showed that addition of MTGase could affect the particle size distribution, degree of hydrolysis, the content of soluble proteins and free amino acids. Based on the electrophoresis data, MTGase addition enhanced protein polymerization. During gastric and intestinal digestion process, proteins from bio-tofu were degraded into low molecular mass peptides. Our results suggested that incorporation of MTGase could lead to enzymatic modification of proteins of bio-tofu which may help in controlling energy intake and decrease the chance of food allergy.