Plastein reaction enhanced bile-acid binding capacity of soybean protein hydrolysates and whey protein hydrolysates

Soy protein isolate-catechin complexes conjugated by pre-heating treatment for enhancing emulsifying properties: Molecular structures and binding mechanisms

This study aimed to investigate the impact of different pre-heating temperatures (ranging from 40 °C to 80 °C) on the interactions between soy protein isolate (SPI) and catechin to effectively control catechin encapsulation efficiency and optimize the emulsifying properties of soy protein isolate. Results showed that optimal heat treatment at 70 °C improved catechin encapsulation efficiency up to 93.71 ± 0.14 %, along with the highest solubility, enhanced emulsification activity index and improved thermal stability of the protein. Multiple spectroscopic techniques revealed that increasing pretreatment temperature (from 40 °C to 70 °C) altered the secondary structures of SPI, resulting in a more stable unfolded structure for the composite system with a significant increase in α-helical structures and a decrease in random coil and β-sheet structures. Moreover, optimal heat treatment also leads to an augmentation of free sulfhydryl groups within complex as well as exposure of more internal chromophore amino acids on molecular surface. Size-exclusion high-performance liquid chromatography and SDS-PAGE analysis indicated that the band intensity of newly formed high-molecular-weight soluble macromolecules (>180 kDa) increased as the pre-heating temperature rose. Furthermore, fluorescence spectroscopy and molecular docking analysis suggest that hydrophobic and covalent interactions were involved in complex formation, which intensified with increasing temperature.

Development of a Two-Step Hydrolysis Hypoallergenic Cow's Milk Formula and Evaluation of Residue Allergenicity by Peptidomics and Immunoreactivity Analysis

Cow's milk allergy (CMA) is an abnormal immune response that severely affects the nutritional supplementation of allergic infants. Currently, only a limited number of hypoallergenic formulas are available on the market, and these are only categorized according to their degree of hydrolysis, which still poses an allergy risk and cannot be consumed by CMA patients, especially infants. To address this issue, we developed a two-step hydrolysis hypoallergenic formula targeting destruction of allergen epitope from whey protein. Then, a comprehensive evaluation system was constructed, including peptidomics analysis, in vivo and in vitro allergenicity assessments, revealing allergic changes in the product from the epitope structure level to the immunological level. The results showed that 97.14% of hydrolyzed peptides from α-lactalbumin and β-lactoglobulin did not contain allergenic epitopes after treatment with trypsin and flavourzyme. In vitro and in vivo allergenicity assessment results confirmed that the two-step hydrolysis method effectively reduced the allergenicity of whey protein. Compared with the common milk powder, the hypoallergenic formula induced lower levels of basophil degranulation and relieved the body's anaphylactic symptoms caused by cow milk. This study provides a promising solution to the limited hypoallergenic formula problem and may benefit allergic infants who require nutritional supplements.

Impact of the Plastein Reaction of Casein Hydrolysates in the Presence of Exogenous Amino Acids on Their Anti-Inflammatory Effect in the Lipopolysaccharide-Stimulated Macrophages

In this study, papain-generated casein hydrolysates (CH) with a degree of hydrolysis of 13.7% were subjected to a papain-mediated plastein reaction in the absence or presence of one of the exogenous amino acids-Gly, Pro, and Hyp-to prepare four plastein modifiers, or mixed with one of three amino acids to prepare three mixtures. The assay results confirmed that the reaction reduced free NH2 for the modifiers and caused amino acid incorporation and peptide condensation. When RAW264.7 macrophages were exposed to the CH, modifiers, and mixtures, these samples promoted macrophage growth and phagocytosis in a dose-dependent manner. In addition, the CH shared similar activity in the cells as the mixtures, while the modifiers (especially the PCH-Hyp prepared with Hyp addition) exerted higher potential than CH, the mixtures, and PCH (the modifier prepared without amino acid addition). The plastein reaction thus enhanced CH bioactivity in the cells. When RAW264.7 macrophages were stimulated with lipopolysaccharide (LPS), the inflammatory cells produced more lactate dehydrogenase (LDH) release and reactive oxygen species (ROS) formation, and caused more four inflammatory mediators (NO, PGE2, TNF-α, and IL-6) and two anti-inflammatory mediators (TGF-β1 and IL-10). However, the PCH-Hyp, PCH, and CH at dose levels of 100 μg/mL could combat against the LPS-induced inflammation. Overall, the PCH-Hyp was more active than the CH and PCH in reducing LDH release, ROS formation, and the secretion of these inflammatory mediators, or in increasing the secretion of the anti-inflammatory mediators. The qPCR and Western blot analysis results further confirmed that these samples had anti-inflammatory effects on the stimulated cells by suppressing the LPS-induced activation of the NF-κB signaling pathway, via regulating the mRNA/miRNA expression of iNOS, IL-6, TNF-α, IL-1β, COX-2, TLR4, IL-10, TGF-β1, miR-181a, miR-30d, miR-155, and miR-148, as well as the protein expression of MyD88, p-IKKα, p-IκBα, p-NF-κB p65, and iNOS, involved in this signaling pathway. In addition, the immunofluorescence assay results revealed that these samples could block the LPS-mediated nuclear translocation of the p65 protein and displayed the same function as the NF-κB inhibitor BAY 11-7082. It was concluded that CH could be endowed with higher anti-inflammatory activity to the macrophages by performing a plastein reaction, particularly that in the presence of exogenous Hyp.

Plastein from hydrolysates of porcine hemoglobin and meat using Alcalase and papain

Plastein is defined as a protease-induced peptide aggregate and has been explored for over a century. This study investigated the effects of Alcalase and papain on plastein formation in protein hydrolysates of porcine hemoglobin and meat by measuring turbidity, particle size distribution, free amino groups and chemical interactions, as well as identifying the soluble peptides remaining in solution by LC-MS/MS. The results showed that Alcalase induced more peptide aggregation than papain in terms of increases in turbidity and particle size. Porcine hemoglobin was better than meat in inducing plastein formation in a short reaction time. Besides, covalent bonds involving peptide bonds and disulfide bonds were not crucial in the plastein reaction, instead a high proportion of hydrophobic interactions dominated the plastein. Not all peptides of both hydrolysates took part in plastein formation, and the regions of sequence that were prone to aggregation were visualized by Peptigram.

Improvement of chicken plasma protein hydrolysate angiotensin I-converting enzyme inhibitory activity by optimizing plastein reaction

Chicken plasma protein hydrolysate (CPPH) was prepared by trypsin with angiotensin I-converting enzyme (ACE) inhibitory activity of 53.5% ± 0.14% and the degree of hydrolysis (DH) of 16.22% ± 0.21% at 1 mg·ml-1; then, five proteases, including pepsin, trypsin, papain, alcalase, and neutrase, were employed to improve ACE inhibitory ability by catalyzing plastein reaction. The results indicated that trypsin-catalyzed plastein reaction showed the highest ACE inhibitory activity. The exogenous amino acids of leucine, histidine, tyrosine, valine, and cysteine were selected to modify the CPPH. The leucine-modified plastein reaction released the highest ACE inhibitory activity. The effects of four reaction parameters on plastein reaction were studied, and the optimal conditions with the purpose of obtaining the most powerful ACE inhibitory peptides from modified products were obtained by response surface methodology (RSM). The maximum ACE inhibition rate of the modified hydrolysate reached 82.07% ± 0.03% prepared at concentration of hydrolysates of 30%, reaction time of 4.9 hr, pH value of 8.0, temperature of 40°C, and E/S ratio of 5,681.62 U·g-1. The results indicated that trypsin-catalyzed plastein reaction increased ACE inhibitory activity of chicken plasma protein hydrolysates by 28.57%.