Influence of heat and pH on structure and conformation of whey proteins

Separation, enrichment and cytoprotection of antioxidant peptides from Xuanwei ham using aqueous two-phase extraction

An ethanol/(NH4)2SO4 biphasic (aqueous two-phase) system was designed to effectively separate antioxidant peptides from Xuanwei ham, and its potential to prevent ultraviolet A-induced damage to skin cells was explored. Optimization via single factor experiments and response surface methodology revealed that under 20 % ethanol aqueous solution (w/w), 25.5 % (NH4)2SO4 aqueous solution (w/w), and pH 8.80 conditions, the optimal extraction ratio was 59.0 ± 1.73 %. In vitro antioxidant activity and cellular assays showed that the peptide purified in the upper phase exhibited strong antioxidant activity, increasing the viability of HaCat cells damaged by UVA irradiation from 56.14 ± 1.05 % to 66.3 ± 1.76 %. We used an in silico peptide screening strategy and identified 10 with potential antioxidant activity, emphasizing the important role of amino acids Pro, Gly, and Ala in antioxidant activity.

Changes in Secondary Structure and Properties of Bovine Serum Albumin as a Result of Interactions with Gold Surface

Proteins can alter their shape when interacting with a surface. This study explores how bovine serum albumin (BSA) modifies structurally when it adheres to a gold surface, depending on the protein concentration and pH. We verified that the gold surface induces significant structural modifications to the BSA molecule using circular dichroism, infrared spectroscopy, and atomic force microscopy. Specifically, adsorbed molecules displayed increased levels of disordered structures and β-turns, with fewer α-helices than the native structure. MP-SPR spectroscopy demonstrated that the protein molecules preferred a planar orientation during adsorption. Molecular dynamics simulations revealed that the interaction between cysteines exposed to the outside of the molecule and the gold surface was vital, especially at pH=3.5. The macroscopic properties of the protein film observed by AFM and contact angles confirm the flexible nature of the protein itself. Notably, structural transformation is joined with the degree of hydration of protein layers.

Modification and oxidative degradation of β-lactoglobulin by UVB irradiation

Ultraviolet (UV) B irradiation induces protein modification, especially the conformational rearrangement of proteins, and is therefore promising as a non-thermal and non-chemical functionalization technique. Nevertheless, UVB irradiation introduces radicals and oxidizes side chains resulting in the loss of food quality. Thus, assessing the UVB irradiation-based functionalization of β-lactoglobulin (BLG) versus its oxidative degradation is of interest. UVB irradiation of up to 8 h was successfully applied to loosen the rigid folding of BLG and increase its flexibility. Thereby, the cysteine at position 121 and hydrophobic regions became surface-exposed as indicated by the increase in accessible thiol groups and increased surface hydrophobicity. Furthermore, we demonstrated the cleavage of the "outer" disulfide bond C⁶⁶-C¹⁶⁰ by LC-MS/MS after tryptic digestion of BLG. The 2-h-irradiated BLG showed adequate conformational rearrangement for protein functionalization while being minimally oxidized.

Characteristics and qualities of edible bird's nest beverage as affected by thermal pasteurization and sterilization

Edible bird's nest beverage (B-nest-Bev) was produced from edible bird's nest (B-nest) flakes using different thermal processes. Pasteurization of B-nest-Bev at a low temperature for a longer time (LTLT) or at a high temperature for a shorter time (HTST) resulted in lower CIE L * , CIE a * , CIE b * -values, and drained weight (p < 0.05) than sterilization (118 or 121 °C). Sterilized and pasteurized B-nest-Bev had similar soluble solid contents and pH (p < 0.05). Nevertheless, acidified beverages pasteurized via either LTLT or HTST process had a marked decrease in sialic acid content. In addition, drastic protein degradation occurred in pasteurized acidified beverages, regardless of the conditions used, ascertained by the disappearance of major protein bands. However, polymerization of proteins took place in sterilized samples, irrespective of the temperature used. After digestion in a gastrointestinal tract model system (GIMs), all samples had increased (p < 0.05) antioxidant activities including DPPH and ABTS radical scavenging activities, ferric reducing antioxidant power (FRAP) and oxygen radical absorbance capacity (ORAC). B-nest-Bev subjected to HTST pasteurization or sterilization at 121 °C had the best appearance and acceptability among all the treatments used. Therefore, thermal processes directly affected the properties and acceptability of B-nest-Bev.

Influence of pH, Temperature and Protease Inhibitors on Kinetics and Mechanism of Thermally Induced Aggregation of Potato Proteins

Understanding aggregation in food protein systems is essential to control processes ranging from the stabilization of colloidal dispersions to the formation of macroscopic gels. Patatin rich potato protein isolates (PPI) have promising techno-functionality as alternatives to established proteins from egg white or milk. In this work, the influence of pH and temperature on the kinetics of PPI denaturation and aggregation was investigated as an option for targeted functionalization. At a slightly acidic pH, rates of denaturation and aggregation of the globular patatin in PPI were fast. These aggregates were shown to possess a low amount of disulfide bonds and a high amount of exposed hydrophobic amino acids (S₀). Gradually increasing the pH slowed down the rate of denaturation and aggregation and alkaline pH levels led to an increased formation of disulfide bonds within these aggregates, whereas S₀ was reduced. Aggregation below denaturation temperature (T_d) favored aggregation driven by disulfide bridge formation. Aggregation above T_d led to fast unfolding, and initial aggregation was less determined by disulfide bridge formation. Inter-molecular disulfide formation occurred during extended heating times. Blocking different protein interactions revealed that the formation of disulfide bond linked aggregation is preceded by the formation of non-covalent bonds. Overall, the results help to control the kinetics, morphology, and interactions of potato protein aggregation for potential applications in food systems.

Development of Whey Protein Concentrate-Pectin-Alginate Based Delivery System to Improve Survival of B. longum BL-05 in Simulated Gastrointestinal Conditions

Bifidobacterium longum BL-05 encapsulated beads were developed by using whey protein concentrate (WPC) and pectin (PE) as encapsulating material through extrusion/ionic gelation technique with the objective to improve survival of probiotics in harsh gastrointestinal conditions. B. longum BL-05 was grown in MRS (de man rogosa and sharpe) broth, centrifuged and mixed with polymeric gel solution. Bead formulations E₄ (2.5% WPC + 1.5% PE) and E₅ (2% PE) showed the highest value for encapsulation efficiency, size, and textural properties (hardness, cohesiveness, springiness) due to increasing PE concentration. The survivability and viability of free and encapsulated B. longum BL-05 was assessed through their resistance to simulated gastric juice (SGJ), tolerance to bile salt, release profile in simulated intestinal fluid (SIF), and storage stability during 28 days at 4 °C. The microencapsulation provided protection to B. longum BL-05 and encapsulated cells were exhibited significant (p < 0.05) resistance to SGJ and SIF as compared to free cells. Bead formulations E₃ (5.0% WPC + 1.0% PE) and E₄ (2.5% WPC + 1.5% PE) exhibited more resistance to SGJ (at pH 2 for 2 h) and at 2% bile salt solution but comparatively slow release as compared to other bead formulations. Free cells lost their viability when stored at 4 °C after 28 days but microencapsulated cells demonstrated promising results during storage and viable cell count was > 10⁷ CFU/g. This study revealed that extrusion using WPC and PE as encapsulating material could be considered as one of the novel technologies for protection and effective delivery of probiotics.

Effect of dynamic ultra-high pressure homogenization on the structure and functional properties of whey protein

The effects of dynamic ultra-high pressure homogenization (UHPH) on the structure and functional properties of whey protein were investigated in this study. Whey protein solution of 10 mg/mL (1% w/w) was prepared and processed by a laboratory scale high pressure homogenizer with different pressures (25, 50, 100, 150, 200, and 250 MPa) at an initial temperature of 25 °C. Then, the solution samples were evaluated in terms of secondary structure, sulfhydryl and disulfide bond contents, surface hydrophobicity, average particle size, solubility, foaming capacity, emulsifying activity, and thermal properties. It was found that the secondary structure of whey protein changed with the dynamic UHPH treatment. The interchange reaction between the disulfide bond and the sulfhydryl group was promoted and the surface hydrophobicity significantly increased. The functional properties of the whey protein accordingly changed. Specifically, after dynamic UHPH treatment, the average particle size of the whey protein and emulsion decreased while the solubility, the foaming capability and the emulsification stability increased significantly. The results also revealed that with the dynamic UHPH at 150 MPa, the best improvement was observed in the whey protein functional properties. The whey protein solubility increased from 63.15 to 71.61% and the emulsification stability improved from 195 to 467 min.

Investigation of binding interactions between BSA and [EPMpyr][Sal] through spectroscopy studies, thermophysical and thermodynamic properties

The intensity of research, probing the interactions between proteins and ionic liquid (IL), has been increasing and parallels the fast-growing applications of ILs in biotechnology. The specific aspects which have attracted the involvement of researchers are stabilization, separation, biochemical and enzymatic reactions of proteins. In this work the synthesis of IL, epoxypropyl and N-methyl substituted 2‑oxopyrrolidinium cation with salicylate anion, [EPMpyr][Sal], and its interaction with aqueous BSA{BSA_(aq)-[EPMpyr][Sal]}. Measurements of thermophysical properties (density (ρ), and speed of sound (u)) showed that both moderately strong and weak interactions occur on treatment of BSA with that chosen IL. H-bond formation, dipole-dipole interactions and ionic interactions occurring in this system were investigated via thermophysical and thermodynamic properties as well as spectroscopic data. Thermodynamic data (excess molar volume (V_m^E), isentropic compressibility (k_s), deviation in isentropic compressibility (∆k_s) and intermolecular free length (L_f)) showed that there were stronger interaction between IL and BSA at higher temperature. The data from all the studies were correlated with Redlich Kister polynomial equation. The blue shift observed in the fluorescent spectra was interpreted to indicate that thetryptophan (Trp) residue of BSA moves to a more hydrophobic environment. It was also observed that the addition of more IL to BSA resulted in denaturation of BSA due to high hydrophobic nature of IL. Circular dichroism studies show that there were significant changes in the fine structure of BSA on interaction with IL. From the FTIR spectra the position of H-bond in the secondary structure of BSA was deduced.

Effect of sodium triphosphate on particle size of heat-induced whey protein concentrate aggregates

Thermal treatment has been utilized to improve the functional properties of proteins for many years. In this study, we aimed to investigate the effect of sodium triphosphate (Na5P3O10) on particle size and size distribution of heat-induced whey protein concentrate (WPC) aggregates under different processing conditions. The results showed that high Na5P3O10 level (>0.5%, w/w), long heating time (>15 min), and alkaline condition (pH 8-8.5) facilitated formation of large particles (>10 μm). The WPC aggregates with small-to-medium particle size (1-3 μm) that are suitable to be applied as a fat replacer were obtained by heating the WPC solution (8%, w/v) containing 0.4% (w/w) Na5P3O10 at 85°C for 5 min. We conclude that thermal treatment of whey protein concentrate added with Na5P3O10 can obtain whey protein products with different particle sizes for certain applications.

Evaluation of Models for Temperature-Dependent Viscosity Changes in Dairy Protein Beverage Formulations During Thermal Processing

Rheological modeling as a function of temperature is a useful tool for describing products undergoing thermal processing. The rheological behavior of a range of dairy-based (4%, w/w) protein beverages was investigated for applicability to semi-empirical temperature-dependent viscosity equations. The viscosity at 16.8 rad/s of the beverages was measured during heating, holding, and cooling over a temperature range of 25 to 90 ^o C using a rheometer with starch pasting cell geometry. Five established fitting methods were applied based on the Arrhenius and Williams-Landel-Ferry (WLF) equations using nonlinear regression analysis. A two-parameter WLF (WLF₂ ) model, using viscosity at a reference temperature of 25 ^o C resulted in high R² values (0.974 to 0.988) and a statistically superior fit compared to the Arrhenius, Generalized Arrhenius, and exponential equations (P < 0.001). Deviation from the WLF₂ modeled equation was used to describe and investigate the effect formulation had on the changes in viscosity during thermal heating. This study successfully applied the WLF equation to a liquid protein system, proving that a consistent and close fit can be achieved across a range of formulations. A rapid, quantitative method for viscosity-temperature profile evaluation is presented, which can ease product development and optimization of product processing stability.

PRACTICAL APPLICATION

This study validated the use of the Williams-Landel-Ferry equation to describe the behavior of dairy beverages during thermal processing, providing a better fit to rheological data than the widely used Arrhenius-based equations. In conjunction with the WLF equation, a method was presented which reduced the complex rheological data to a single value, which can aid in the comparison of formulations for product development and optimization in both research and industry.

Application of differential scanning calorimetry to estimate quality and nutritional properties of food products

Over the past years, both food researchers and food industry have shown an increased interest in finding techniques that can estimate modifications in quality, nutritional, and thermophysical properties of food products during processing and/or storage. For instance, differential scanning calorimetry (DSC) has attracted the interest of scientific community because only a small amount of sample is needed for analysis. Moreover, it does not require any specific sample preparation, and is a repeatable and reliable method. In addition, DSC methodology needs a short time for experiments compared with other techniques used for the same purpose. At this stage of investigation, there is a need to evaluate the commonly accepted and new emerging DSC applications to establish the optimum conditions of emerging processing. This paper reviews the current and new insights of DSC technique for the estimation of quality, nutritional, and thermophysical properties of food products during conventional and emerging processing and/or subsequent storage. The estimation of different properties in several food matrices after processing and/or storage is also discussed.

Denatured Whey Protein Powder as a New Matrix Excipient: Design and Evaluation of Mucoadhesive Tablets for Sustained Drug Release Applications

PURPOSE

In earlier study, we proposed denatured whey protein (DWP) powder obtained by atomization as a new excipient to promote oral drug delivery. In this work, we evaluate the possibility to formulate tablets based on DWP powders and to characterize their role as a matrix mucoadhesive excipient.

METHODS

Tablets containing increased amount of DWP (10 to 30%) were produced by direct compression after mixing with theophylline, microcrystalline cellulose, Aerosil® and magnesium stearate. Dissolution behaviors of obtained tablets were evaluated in different USP buffers (pH 1.2, 4.5 and 6.8) and in simulated gastric and intestinal fluids and mechanisms analyzed by multiple mathematical models. Swelling, erosion and mucoadhesion were also evaluated. Finally, release and absorption were studied in the artificial digestive system (TIM 1).

RESULTS

Tablets based on DWP and containing 300 mg of theophylline were obtained by direct compression. These tablets exhibited controlled release driven by diffusion starting from 15% DWP content whatever the pH studied. They also showed a great extent of swelling and water uptake while matrix weight loss was limited. Addition of enzymes accelerated drug release which became governed by erosion according to Peppas model.

CONCLUSIONS

The present study shows that DWP powders can be successfully used as a pharmaceutical excipient, and in particular as a matrix mucoadhesive controlled release tablets.

Properties of acid whey as a function of pH and temperature

Compositional differences of acid whey (AW) in comparison with other whey types limit its processability and application of conventional membrane processing. Hence, the present study aimed to identify chemical and physical properties of AW solutions as a function of pH (3 to 10.5) at 4 different temperatures (15, 25, 40, or 90°C) to propose appropriate membrane-processing conditions for efficient use of AW streams. The concentration of minerals, mainly calcium and phosphate, and proteins in centrifuged supernatants was significantly lowered with increase in either pH or temperature. Lactic acid content decreased with pH decline and rose at higher temperatures. Calcium appeared to form complexes with phosphates and lactates mainly, which in turn may have induced molecular attractions with the proteins. An increase in pH led to more soluble protein aggregates with large particle sizes. Surface hydrophobicity of these particles increased significantly with temperature up to 40°C and decreased with further heating to 90°C. Surface charge was clearly pH dependent. High lactic acid concentrations appeared to hinder protein aggregation by hydrophobic interactions and may also indirectly influence protein denaturation. Processing conditions such as pH and temperature need to be optimized to manipulate composition, state, and surface characteristics of components of AW systems to achieve an efficient separation and concentration of lactic acid and lactose.

Enhanced extraction of bovine serum albumin with aqueous biphasic systems of phosphonium- and ammonium-based ionic liquids

Novel aqueous biphasic systems (ABS) composed of phosphonium- or ammonium-based ionic liquids (ILs), combined with a buffered aqueous solution of potassium citrate/citric acid (pH=7.0), were investigated for the extraction of proteins. For that purpose, the phase diagrams, tie-lines and tie-line lengths were determined at 25 °C, and the performance of these ABS for the extraction of bovine serum albumin (BSA) was then evaluated. The obtained results reveal that, with the exception of the more hydrophobic ILs, most of the systems investigated allow the complete extraction of BSA for the IL-rich phase in a single-step. These remarkable extraction efficiencies are far superior to those afforded by more conventional extraction systems previously reported. The composition of the biphasic systems, i.e., the amount of phase-forming components, was also investigated aiming at reducing the overall costs of the process without losing efficiency on the protein extraction. It is shown that the extraction efficiencies of BSA are maintained at 100% up to high protein concentrations (at least up to 10 g L(-1)). The recovery of the BSA from the IL-rich phase by dialysis is also shown in addition to the demonstration of the IL recyclability and reusability, at least for 3 times. In the sequential three-step extractions (BSA recovery/IL reusability), the extraction efficiencies of BSA for the IL-rich phase were maintained at 100%. For the improved ABS, the preservation of the protein native conformation was confirmed by Size Exclusion High-Performance Liquid Chromatography (used also as the quantification method) and by Fourier Transform Infra-Red spectroscopy. According to the results herein reported, ABS composed of phosphonium- or ammonium-based ILs and a biodegradable organic salt represent an alternative and remarkable platform for the extraction of BSA and may be extended to other proteins of interest.