Gel Formation of Peptides Produced by Extensive Enzymatic Hydrolysis of β-Lactoglobulin

Self-assembly and hydrogelation of a potential bioactive peptide derived from quinoa proteins

In this work the identification of peptides derived from quinoa proteins which could potentially self-assemble, and form hydrogels was carried out with TANGO, a statistical mechanical based algorithm that predicts β-aggregate propensity of peptides. Peptides with the highest aggregate propensity were subjected to gelling screening experiments from which the most promising bioactive peptide with sequence KIVLDSDDPLFGGF was selected. The self-assembling and hydrogelation properties of the C-terminal amidated peptide (KIVLDSDDPLFGGF-NH2) were studied. The effect of concentration, pH, and temperature on the secondary structure of the peptide were probed by circular dichroism (CD), while its nanostructure was studied by transmission electron microscopy (TEM) and small-angle neutron scattering (SANS). Results revealed the existence of random coil, α-helix, twisted β-sheet, and well-defined β-sheet secondary structures, with a range of nanostructures including elongated fibrils and bundles, whose proportion was dependant on the peptide concentration, pH, or temperature. The self-assembly of the peptide is demonstrated to follow established models of amyloid formation, which describe the unfolded peptide transiting from an α-helix-containing intermediate into β-sheet-rich protofibrils. The self-assembly is promoted at high concentrations, elevated temperatures, and pH values close to the peptide isoelectric point, and presumably mediated by hydrogen bond, hydrophobic and electrostatic interactions, and π-π interactions (from the F residue). At 15 mg/mL and pH 3.5, the peptide self-assembled and formed a self-supporting hydrogel exhibiting viscoelastic behaviour with G' (1 Hz) ~2300 Pa as determined by oscillatory rheology measurements. The study describes a straightforward method to monitor the self-assembly of plant protein derived peptides; further studies are needed to demonstrate the potential application of the formed hydrogels in food and biomedicine.

Enzyme-Based Strategies for Structuring Foods for Improved Functionality

Enzyme technologies can be used to create food dispersions with novel functional attributes using structural design principles. Enzymes that utilize food-grade proteins and/or polysaccharides as substrates have gained recent interest among food scientists. The utilization of enzymes for structuring foods is an ecologically and economically viable alternative to the utilization of chemical cross-linking and depolymerization agents. This review highlights recent progress in the use of enzymes to modify food structures, particularly the interfacial and/or bulk properties of food dispersions with special emphasis on commercially available enzymes. Cross-linking enzymes such as transglutaminase and laccase promote the formation of intra- and intermolecular bonds between biopolymers to improve stability and functionality, whereas various degrading enzymes such as proteases alter the native conformation of proteins, leading to self-assembly of hierarchically ordered colloids. Results of this bio-inspired approach show that rational use of structure-affecting enzymes may enable food manufacturers to produce food dispersions with improved physical, functional, textural, and optical properties.

Improved Functional Characteristics of Whey Protein Hydrolysates in Food Industry

This review focuses on the enhanced functional characteristics of enzymatic hydrolysates of whey proteins (WPHs) in food applications compared to intact whey proteins (WPs). WPs are applied in foods as whey protein concentrates (WPCs), whey protein isolates (WPIs), and WPHs. WPs are byproducts of cheese production, used in a wide range of food applications due to their nutritional validity, functional activities, and cost effectiveness. Enzymatic hydrolysis yields improved functional and nutritional benefits in contrast to heat denaturation or native applications. WPHs improve solubility over a wide range of pH, create viscosity through water binding, and promote cohesion, adhesion, and elasticity. WPHs form stronger but more flexible edible films than WPC or WPI. WPHs enhance emulsification, bind fat, and facilitate whipping, compared to intact WPs. Extensive hydrolyzed WPHs with proper heat applications are the best emulsifiers and addition of polysaccharides improves the emulsification ability of WPHs. Also, WPHs improve the sensorial properties like color, flavor, and texture but impart a bitter taste in case where extensive hydrolysis (degree of hydrolysis greater than 8%). It is important to consider the type of enzyme, hydrolysis conditions, and WPHs production method based on the nature of food application.

Effect of disulfide interactions and hydrolysis on the thermal aggregation of β-lactoglobulin

The roles of sulfhydryl/disulfide interactions and acid/pepsin hydrolysis on β-lactoglobulin (β-lg) thermal aggregation at acidic pH 3.35 and 2 were studied using rheology, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), transmission electron microscopy (TEM), and Western blotting. Pepsin promoted additional hydrolysis compared to the acid-hydrolyzed control sample based on a 12% increase in free amino groups. Hydrolysis with pepsin also resulted in an increase in the apparent viscosity by 2 logs upon heating 8% β-lg solutions at pH 3.35. Seemingly, hydrolysis promoted thermal aggregation of β-lg, correlating well with viscosity increases. Large microgels were observed in heated pepsin hydrolysates using TEM, supporting the increased viscosities of these dispersions. During thermal aggregation (85 °C, 3 h) of β-lg at pH 3.35, beyond the existence of limited disulfide interactions, acid hydrolysis and noncovalent interactions more likely play a crucial role in defining the functionality of acidified powdered modified whey ingredients.

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.

Exploiting enzymatic (reversed) hydrolysis in directed self-assembly of peptide nanostructures

Enzyme-catalyzed reactions can be exploited to control molecular self-assembly under physiological conditions by converting nonassembling precursors into self-assembly building blocks. Two complementary approaches based on aromatic short-peptide derivatives that form molecular hydrogels are demonstrated. Firstly, it is shown that esterase-directed self assembly via hydrolysis of hydrophobic N-(fluorenyl-9-methoxycarbonyl) (Fmoc)-peptide methyl esters give rise to formation of transparent hydrogels composed of defined peptide nanotubes. The internal and external diameters of these tubes are highly tunable, depending on the amino acid composition and chain length of the building blocks. Secondly, protease-directed self-assembly of Fmoc-peptide esters is achieved via amide-bond formation (reversed hydrolysis) for combinations of Fmoc-threonine and leucine/phenylalanine methyl esters, producing fibrous hydrogels. Upon treatment with an esterase, these systems revert back to solution, thus providing a two-stage solution-gel-solution transition.