Hydrolysis of whey protein isolate with Bacillus licheniformis protease: fractionation and identification of aggregating peptides

The Effect of Whey Protein Isolate Hydrolysate on Digestive Properties of Phytosterol

Phytosterol (PS) is a steroid, and its bioavailability can be enhanced by interacting with protein in the C-24 hydroxyl group. The interaction between sterols and amino acid residues in proteins can be enhanced by enzymatic hydrolysis. Phytosterol and whey insulation hydrolysates (WPH1-4) fabricated by the Alcalase enzyme at different enzymatic hydrolysis times were selected as delivery systems to simulate sterol C-24 hydroxyl group interaction with protein. Increasing hydrolysis time can promote the production of β-Lg, which raises the ratio of β-turn in the secondary structure and promotes the formation of interaction between WPH and PS. The correlation coefficient between hydrogen bonds and encapsulation efficiency (EE) and bioaccessibility is 0.91 and 0.88 (P < 0.05), respectively, indicating that hydrogen bonds of two components significantly influenced the combination by concealing the hydrophobic amino acids and some residues, which improved PS EE and bioavailability by 3.03 and 2.84 times after PS was combined with the WPI hydrolysate. These findings are expected to enhance the absorption of PS and other macromolecules by protein enzymatic hydrolysis to broaden their applications for food.

Enzymatic hydrolysis of soy and chickpea protein with Alcalase and Flavourzyme and formation of hydrogen bond mediated insoluble aggregates

Food applications involving plant proteins require modification of their functionality to mimic the unique properties of animal proteins. Enzymatic hydrolysis is commonly used to alter the functionality of plant proteins, particularly to improve their solubility near the isoelectric point. Current methodological approaches mostly indicate improved solubility upon hydrolysis. However, published methods include the removal of insoluble material before analysis, and calculations are based on only the solubilized material as a percentage of the filtered protein. This approach artificially increases solubility estimation and gives an incorrect assessment of the efficacy of hydrolysis. By using the total amount of protein, this study aims to determine the effect of two microbial proteases, Flavourzyme and Alcalase, on the solubility and structural and thermal properties of soy and chickpea proteins. Protein isolates were first extracted from soy and chickpea flour and hydrolyzed from 0 to 3 h. Then, their degree of hydrolysis and solubility at a range of pHs were determined using the o-phthaldialdehyde (OPA) and Lowry methods, respectively. Proteins' electrophoretic mobility, protein-protein interactions, thermal properties, and protein secondary structures were also determined. Solubility decreased over time though the solubility of the hydrolysate improved near the isoelectric point. Soy Flavourzyme hydrolysates remained the most soluble and chickpea Flavourzyme hydrolysates showed the least solubility. Thermal data suggested that Alcalase reduced the protein denaturation temperature, leading to a loss of solubility upon thermal enzyme inactivation. The loss of solubility of hydrolysates was strongly associated with hydrogen bonding, which may result from the formation of polar peptide termini. These results challenge commonly accepted beliefs that hydrolysis inevitably improves solubility of plant proteins. Instead, it is shown that hydrolysis causes structural changes that result in aggregation, thus potentially limiting the application of enzymatic hydrolysis without the addition of further processing methods.

Modeling of Proteolysis of β-Lactoglobulin and β-Casein by Trypsin with Consideration of Secondary Masking of Intermediate Polypeptides

The opening of protein substrates during degradation by proteases and the corresponding exposure of their internal peptide bonds for a successful enzymatic attack, the so-called demasking effect, was studied for β-lactoglobulin (β-LG) and β-casein (β-CN) hydrolyzed by trypsin. Demasking was estimated by monitoring the redshift in intrinsic tryptophan fluorescence, characterizing the accessibility of polypeptide chains to aqueous medium. The secondary masking of intermediate polypeptides, giving an inverse effect to demasking, caused a restriction of the substrate opening. This led to the limitations in the red shift of fluorescence and the degree of hydrolysis with a long time of hydrolysis of β-LG and β-CN at a constant substrate concentration and reduced trypsin concentrations. The proposed proteolysis model included demasking of initially masked bonds in the protein globule or micelle, secondary masking of intermediate polypeptides, and their subsequent slow demasking. The hydrolysis of peptide bonds was modeled taking into account different hydrolysis rate constants for different peptide bonds. It was demonstrated that demasking competes with secondary masking, which is less noticeable at high trypsin concentrations. Modeling of proteolysis taking into account two demasking processes and secondary masking made it possible to simulate kinetic curves consistent with the experimental data.

Pulse protein processing: The effect of processing choices and enzymatic hydrolysis on ingredient functionality

Plant-based protein ingredients are an emerging solution to the environmental and health issues associated with animal-based proteins. Pulses have become a promising source of these plant-based ingredients. In order to produce functional proteins from pulse grains, extensive processing must be conducted to extract their proteins. These processing steps have consequential effects on the composition and structure of the resulting proteins which may modify their functional properties. This study reviews the most prominent options for each unit operation of pulse protein processing such as extraction, isolation, and drying. It also emphasizes the benefits and drawbacks of such methods and their effects on the pulse protein functionality. Furthermore, enzymatic hydrolysis is discussed as an optional processing step that is thought to counteract loss of functionality associated with pulse protein isolation. However, review of enzymatic hydrolysis literature reveals methodological issues in which insoluble and nonfunctional fractions of pulse protein hydrolysates are removed before analysis. This literature may draw into question the validity of the conventional wisdom that enzymatic hydrolysis is always beneficial to protein functionality.

Development of a spray-dried conjugated whey protein hydrolysate powder with entrapped probiotics

Bifidobacterium animalis ssp. lactis ATCC27536 and Lactobacillus acidophilus ATCC4356 were encapsulated in a conjugated whey protein hydrolysate (WPH10) through spray drying. Probiotic cultures were added at the ratio of 1:1 into the conjugated WPH10 solution at a spiking level of about 10 log₁₀ cfu/mL. The mixture was spray dried in a Niro drier with inlet and outlet temperatures of 200°C and 90°C, respectively. The final dried product was determined for cell viability and further stored for 16 wk at 25°, 4°, and -18°C to monitor viability and functionality. Micro images showed the presence of link bridges in non-conjugated WPH10, whereas, in the case of conjugated WPH10, round particles with pores were observed. The mean probiotic counts before and after spray drying were 10.59 log₁₀ cfu/mL and 8.98 log₁₀ cfu/g, respectively, indicating good retention of viability after spray drying. The solubility and wetting time of the WPH10-maltodextrin (MD) encapsulated probiotic powder were 91.03% and 47 min, whereas for WPH10, the solubility and wetting time were 82.03% and 53 min, respectively. At the end of storage period, the counts were 7.18 log₁₀ cfu/g at 4°C and 7.87 log₁₀ cfu/g at -18°C, whereas at 25°C the counts were significantly reduced, to 3.97 log₁₀ cfu/g. The solubility of WPH-MD powder was 82.36%, 83.1%, and 81.19% at -18°C, 4°C, and 25°C, respectively, and wetting times were 61 min, 60 min, and 63 min at -18°C, 4°C, and 25°C, respectively. By contrast, for WPH10 powder, the solubility significantly reduced to 69.41%, 69.97%, and 68.99% at -18°C, 4°C, and 25°C, and wetting times increased to 71 min, 70 min, and 72 min at -18°C, 4°C, and 25°C, respectively. The conjugated WPH10 is thus demonstrated as a promising carrier for probiotics and can be further used as an ingredient for developing functional foods, to harness their enhanced functionality and health benefits derived from both WPH and probiotics.

Occurrence of Peptide-Peptide Interactions during the Purification of Self-Assembling Peptide f1-8 from a β-Lactoglobulin Tryptic Hydrolysate

Self-assembling peptides have gained attention because of their nanotechnological applications. Previous work demonstrated that the self-assembling peptide f1-8 (Pf1-8) that is generated from the tryptic hydrolysis of β-lactoglobulin can form a hydrogel after several purification steps, including membrane filtration and consecutive washes. This study evaluates the impact of each processing step on peptide profile, purity, and gelation capacity of each fraction to understand the purification process of Pf1-8 and the peptide-peptide interactions involved. We showed that peptide-peptide interactions mainly occurred through electrostatic and hydrophobic interactions, influencing the fraction compositions. Indeed, the purity of Pf1-8 did not correlate with the number of wash steps. In addition to Pf1-8, two other hydrophobic peptides were identified, peptide f15-20, and peptide f41-60. The gelation observed could be induced either through peptide-peptide interactions or through self-assembling, both being driven by non-covalent bond and more specifically hydrophobic interactions.

How stable are the collagen and ferritin proteins for application in bioelectronics?

One major obstacle in development of biomolecular electronics is the loss of function of biomolecules upon their surface-integration and storage. Although a number of reports on solid-state electron transport capacity of proteins have been made, no study on whether their functional integrity is preserved upon surface-confinement and storage over a long period of time (few months) has been reported. We have investigated two specific cases—collagen and ferritin proteins, since these proteins exhibit considerable potential as bioelectronic materials as we reported earlier. Since one of the major factors for protein degradation is the proteolytic action of protease, such studies were made under the action of protease, which was either added deliberately or perceived to have entered in the reaction vial from ambient environment. Since no significant change in the structural characteristics of these proteins took place, as observed in the circular dichroism and UV-visible spectrophotometry experiments, and the electron transport capacity was largely retained even upon direct protease exposure as revealed from the current sensing atomic force spectroscopy experiments, we propose that stable films can be formed using the collagen and ferritin proteins. The observed protease-resistance and robust nature of these two proteins support their potential application in bioelectronics.

Structural characterization of calcium-binding sunflower seed and peanut peptides and enhanced calcium transport by calcium complexes in Caco-2 cells

BACKGROUND

Peptide-Ca complexes can promote Ca absorption. The present study aimed to determine the transport mechanism and structural characteristics of sunflower seed and peanut peptides with high Ca binding capacity with respect to developing third-generation Ca supplements and functional food ingredients.

RESULTS

High Ca-binding fractions of 1-3 kDa sunflower seed peptide (SSP₄ ) and ≥ 10 kDa peanut peptide (PP₁ ) had higher amount of Ca transported than CaCl₂ and two hydrolyzed proteins in Caco-2 cells. SSP₄ and PP₁ were separated by Ca ion metal chelate affinity chromatography, and high Ca-binding fractions were observed for SSP₄ -P₂ and PP₁ -P₂ . The amino acid sequences of SSP₄ -P₂ and PP₁ -P₂ were characterized by high-performance liquid chromatography-electrospray ionization-time of flight mass spectrometry. Seven and eight peptides were identified from SSP₄ -P₂ and PP₁ -P₂ , respectively. These peptides had molecular weights ranging from 1500 Da to 2500 Da and a large number of characteristic amino acid sequences, such as EEEQQQ, EQ-QQQ-QQ, QQ-QQQQQ, E-EEE, EE-EEQ, RR, Q-QQ-QQQ, EE-EQ-EE-Q, QQ-QQQQ, and Q-QQQQ, where 'E' is glutamic acid and 'Q' is glutamine.

CONCLUSION

SSP₄ and PP₁ can promote Ca transport in Caco-2 cells without affecting cell permeability. The amino acid sequences of SSP₄ -P₂ and PP₁ -P₂ with high Ca-binding abilities contain characteristic sequences, such as continuous glutamic acid and glutamine, and have low molecular weights. © 2020 Society of Chemical Industry.

Biological and conventional food processing modifications on food proteins: Structure, functionality, and bioactivity

Food proteins are important nutrients for human health and thus make significant contributions to the unique functions of different foods. The modification of proteins through physical and biological processing could improve the functional and nutritional properties of food products; these changes can be attributed to modifications in particle size, solubility, emulsion stability, secondary structure, as well as the bioactivities of the proteins. Physical processing treatments might promote physical phenomena, such as combined friction, collision, shear forces, turbulence, and cavitation of particles, and lead to changes in the particle sizes of proteins. The objective of this review is to illustrate the effect of physical and biological processing on the structure, and physical and chemical properties of food-derived proteins and provide insights into the mechanism underlying structural changes. Many studies have suggested that physical and biological processes, such as ultrasound treatment, high pressure homogenization, ball mill treatment, and enzymatic hydrolysis could affect the structure, physical properties, and chemical properties of food-derived proteins. Some important applications of food-derived proteins are also discussed based on the relationships between their physical, chemical, and functional properties. Perspectives from fundamental or practical research are also brought in to provide a complete picture of the currently available relevant data.

Conformational and Functional Properties of Soybean Proteins Produced by Extrusion-Hydrolysis Approach

The conformational and functional changes of soybean protein after a hybrid extrusion-hydrolysis method were evaluated. Three extrusion temperatures (60, 80, and 100°C) were used prior to enzymatic hydrolysis. The hydrolysis degrees, molecular weight profiles, solubilities, surface hydrophobicities, sulphydryl contents, disulfide bound, water holding capacity, emulsion, and foam properties of the protein isolated from the enzyme-hydrolyzed extruded soybeans were analyzed. It shows that extrusion caused significant changes in the hydrophobicity, molecular weight distribution, solubility, surface hydrophobicity, emulsification activity, and stability of the protein. The increase of molecular weights could be attributed to the formation of protein aggregates during extrusion. Extrusion and enzymatic hydrolysis led to a sharp increase in the number of disulfide bonds with a decrease of the sulphydryl group. The water holding capacity and the solubility of protein increased with the increase of extrusion temperature and hydrolysis time. Extrusion improved the emulsifying activity but reduced the emulsifying stability of the recovered proteins. Extrusion improved the foam capacity but reduced the foam stability of the proteins. The data demonstrated that the extrusion-hydrolysis treatment significantly altered the conformational and functional properties of soybean protein, which may be further optimized for the development of new soy protein ingredient with desired functional properties.

Mechanism of the discrepancy in the enzymatic hydrolysis efficiency between defatted peanut flour and peanut protein isolate by Flavorzyme

Both defatted peanut flour (DPF) and peanut protein isolate (PPI) are widely used to prepare peanut protein hydrolysates. To compare their enzymatic hydrolysis efficiencies, DPF and PPI were hydrolysed by Alcalase, Neutrase, Papain, Protamex and Flavorzyme. Alcalase and Flavorzyme were found to be the most efficient proteases to hydrolyse both DPF and PPI. The efficiency was comparable to each other when using Alcalase, while PPI was hydrolysed less efficiently than DPF when using Flavorzyme. Analysis of changes in the protein solubility, subunit and conformation, and amino acid composition of DPF, PPI and their Flavorzyme hydrolysis residues indicated that the PPI preparation process had minimal effect on it, but peptide aggregation via non-covalent bonding (including hydrophobic interactions and hydrogen bonds) during hydrolysis and/or thermal treatment after hydrolysis were likely responsible for the reduced hydrolysis efficiency of PPI by Flavorzyme.

Identification of bitter peptides in whey protein hydrolysate

Bitterness of whey protein hydrolysates (WPH) can negatively affect product quality and limit utilization in food and pharmaceutical applications. Four main bitter peptides were identified in a commercial WPH by means of sensory-guided fractionation techniques that included ultrafiltration and offline two-dimensional reverse phase chromatography. LC-TOF-MS/MS analysis revealed the amino acid sequences of the bitter peptides were YGLF, IPAVF, LLF, and YPFPGPIPN that originated from α-lactalbumin, β-lactoglobulin, serum albumin, and β-casein, respectively. Quantitative LC-MS/MS analysis reported the concentrations of YGLF, IPAVF, LLF, and YPFPGPIPN to be 0.66, 0.58, 1.33, and 2.64 g/kg powder, respectively. Taste recombination analysis of an aqueous model consisting of all four peptides was reported to explain 88% of the bitterness intensity of the 10% WPH solution.

A new strategy for recovery of two peptides without Glu employing glutamate-specific endopeptidase from Bacillus licheniformis

The difficulty in the purification of bioactive peptide limited its application in food, drug and cosmetic industry. Here we report a new strategy for the recovery of two peptides employing glutamate-specific endopeptidase from Bacillus licheniformis (GSE-BL), which shows strong specificity for Glu residue. Human glucagon and human beta-defensin-2 (HBD-2) were peptides without Glu residue, and Glu residue was introduced between affinity tag and target peptide as recognition site of GSE-BL. Tagless human glucagon with the same HPLC retention time as native human glucagon and mature HBD-2 with antibacterial activity and cytotoxicity were obtained after GSE-BL treatment. This strategy has great potential in the recovery of bioactive peptide without Glu residue, thus facilitating large scale preparation of peptide and widening the application of bioactive peptide.

Isolation and characterization of an aggregating peptide from a tryptic hydrolysate of whey proteins

Spontaneous precipitation of a peptide mixture has been observed during the concentration by reverse osmosis of a tryptic hydrolysate of whey protein. The precipitated material collected by centrifugation could not be solubilized by urea, mercaptoethanol, or sodium dodecyl sulfate. However, a complete solubilization of the aggregates was observed when the pH of the solution was lowered to 2.0. Analysis of the insoluble fraction has allowed the identification of beta-lactoglobulin (beta-lg) fragment 1-8 as the major peptide involved in the formation of aggregates. Peptide beta-lg f1-8 accounted for >94% of the peptide content in the precipitate washed twice with distilled water. The investigation of the secondary structure using circular dichroism evidenced that the peptide beta-lg f1-8 isolated from the flocculated peptide mixture is under random coil conformation at acidic and neutral pH and tends to adopt a beta-sheet conformation at basic pH. The findings of this study provide evidence that peptide beta-lg f1-8 forms aggregates via an efficient self-assembly process.

Effects of thermal treatment on the coagulation of soy proteins induced by subtilisin Carlsberg

The effects of thermal treatment on the subtilisin Carlsberg-induced coagulations of soy protein isolate (SPI) and soy proteins in 7S and 11S fractions, most of which are beta-conglycinin and glycinin, respectively, were examined by measuring the turbidity (OD(660)) of the reaction solutions. With the treatment at 37-60 degrees C, the turbidity did not increase at all by the proteolysis, while with the treatment at 70-96 degrees C, it drastically increased. The degree of the coagulation is the highest for the treatment at 80 degrees C and the most remarkable for 11S soy protein. Changes in the sodium dodecyl sulfate-polyacrylamide gel electrophoresis pattern of the digests during the proteolysis were in good agreement with those in the turbidities for SPI and 7S and 11S soy proteins. Circular dichroism analysis revealed that the amounts of nonstructured protein in SPI and 7S and 11S soy proteins were initially 40-50%, increased to 55-60% by the treatment at 80 degrees C, and further increased to 65-75% by the proteolysis. The maximum fluorescence intensity of SPI and 7S and 11S soy proteins increased with an increase in the incubation temperature up to 80 degrees C. These findings suggest that the thermal treatment at 80 degrees C most effectively changes the secondary structure of soy proteins and renders them coagulate when hydrolyzed by subtilisin Carlsberg.

Hydrolysis of whey protein isolate with Bacillus licheniformis protease: aggregating capacities of peptide fractions

In a previous study, peptides aggregating at pH 7.0 derived from a whey protein hydrolysate made with Bacillus licheniformis protease were fractionated and identified. The objective of the present work was to investigate the solubility of the fractionated aggregating peptides, as a function of concentration, and their aggregating capacities toward added intact proteins. The amount of aggregated material and the composition of the aggregates obtained were measured by nitrogen concentration and size exclusion chromatography, respectively. The results showed that of the four fractions obtained from the aggregating peptides, two were insoluble, while the other two consisted of 1:1 mixture of low and high solubility peptides. Therefore, insoluble peptides coaggregated, assumedly via hydrophobic interactions, other relatively more soluble peptides. It was also shown that aggregating peptides could aggregate intact protein nonspecifically since the same peptides were involved in the aggregation of whey proteins, beta-casein, and bovine serum albumin. Both insoluble and partly insoluble peptides were required for the aggregation of intact protein. These results are of interest for the applications of protein hydrolysates, as mixtures of intact protein and peptides are often present in these applications.