Functionality of whey proteins covalently modified by allyl isothiocyanate. Part 1 physicochemical and antibacterial properties of native and modified whey proteins at pH 2 to 7

14C-Isotope Use to Quantify Covalent Reactions between Flavor Compounds and β-Lactoglobulin

A 14C-based method was developed to study the rate and extent of covalent bond formation between β-lactoglobulin and three model flavor compounds: a ketone (2-undecanone UDO), an aldehyde (decanal DAL), an isothiocyanate (2-phenylethyl isothiocyanate PEITC), and an unreactive "methods blank" (decane DEC). Aqueous protein solutions with one of the 14C-labeled model flavor compounds were placed in water baths at 25, 45, and 65 °C for 4 weeks measuring the amount of flavor: protein reaction at 1, 3, 7, 14, 21, and 28 days. UDO showed lowest reactivity (max of 0.9% of added compound reacted), DAL (max of 16.4% reacted), and PEITC (max of 71.8% reacted). All compounds showed a rapid initial reaction rate which slowed after ca. 7 days. It appears that only PEITC (at 65 °C) saturated all potential protein-reactive sites over the storage period.

Effect of gum arabic and thermal modification of whey protein isolate on the characteristics of Cornus officinalis flavonoid microcapsules

Whey protein isolates (WPIs) were treated at 50, 60, 70, and 80°C to obtain thermally modified WPI. Gum arabic (GA) and thermal modification of WPI were used as novel wall materials to improve the quality of Cornus officinalis flavonoid (COF) microcapsules using microwave freeze-drying technique in this study. Results showed that all the thermal modification treatment decreased emulsifying activity index of WPI, whereas the solubility and emulsifying stability index (ESI) of WPI gradually increased with the increase of heating temperature. Compared to the untreated protein, the thermal modification treatment at 70°C increased the solubility and ESI of WPI by 14.91% ± 0.71% and 26.70% ± 0.94%, respectively. The microcapsules prepared with the modified protein at 60°C had the highest encapsulation efficiency (95.13% ± 2.36%), the lowest moisture content (1.42% ± 0.34%), and the highest solubility (84.41% ± 0.91). Scanning electron microscopy images showed that COF microcapsules were uniformly spherical, and the sizes of the microcapsules were in the following order: 12.42 ± 0.37 µm (80°C) > 11.7 ± 0.23 µm (untreated group) > 9.44 ± 0.33 µm (60°C) > 9.24 ± 0.14 µm (50°C) > 7.69 ± 0.29 µm (70°C). In the simulated in vitro digestion experiments, the release rate of COF microcapsules in the gastric digestion phase was less than that in the intestinal digestion phase, and it reached 66.46% at intestinal digestion phase. These results suggested that heated WPI and GA could be an effective nanocarrier to enhance the stability of COF.

A review of the structure, function, and application of plant-based protein-phenolic conjugates and complexes

Interactions between plant-based proteins (PP) and phenolic compounds (PC) occur naturally in many food products. Recently, special attention has been paid to the fabrication of PP-PC conjugates or complexes in model systems with a focus on their effects on their structure, functionality, and health benefits. Conjugates are held together by covalent bonds, whereas complexes are held together by noncovalent ones. This review highlights the nature of protein-phenolic interactions involving PP. The interactions of these PC with the PP in model systems are discussed, as well as their impact on the structural, functional, and health-promoting properties of PP. The PP in conjugates and complexes tend to be more unfolded than in their native state, which often improves their functional attributes. PP-PC conjugates and complexes often exhibit improved in vitro digestibility, antioxidant activity, and potential allergy-reducing activities. Consequently, they may be used as antioxidant emulsifiers, edible film additives, nanoparticles, and hydrogels in the food industry. However, studies focusing on the application of PP-PC conjugates and complexes in real foods are still scarce. Further research is therefore required to determine the structure-function relationships of PP-PC conjugates and complexes that may influence their application as functional ingredients in the food industry.

Effects of proteins on emulsion stability: The role of proteins at the oil-water interface

To obtain a stable protein-added emulsion system, researchers have focused on the design of the oil-water interface. This review discussed the updated details of protein adsorption behavior at the oil-water interface. We evaluated methods of monitoring interfacial proteins as well as their strengths and limitations. Based on the effects of structure on protein adsorption, we summarized the contribution of pre-changing methods to adsorption. In addition, the interaction of proteins and other surface-active molecules at the interface had been emphasized. Results showed that protein adsorption is affected by conformation, oil polarity and aqueous environments. The monitoring of interfacial proteins through spectroscopic properties in actual emulsion systems is an emerging trend. Pre-changing could improve the protein adsorption and the purpose of pre-changing of proteins is similar. In the interaction with other surface-active molecules, co-adsorption is desirable. By co-adsorption, the respective advantages can be exploited to obtain a more stable emulsion system.

WPI Hydrogels with a Prolonged Drug-Release Profile for Antimicrobial Therapy

Infectious sequelae caused by surgery are a significant problem in modern medicine due to their reduction of therapeutic effectiveness and the patients’ quality of life.Recently, new methods of local antimicrobial prophylaxis of postoperative sequelae have been actively developed. They allow high local concentrations of drugs to be achieved, increasing the antibiotic therapy’s effectiveness while reducing its side effects. We have developed and characterized antimicrobial hydrogels based on an inexpensive and biocompatible natural substance from the dairy industry—whey protein isolate—as matrices for drug delivery. The release of cefazolin from the pores of hydrogel structures directly depends on the amount of the loaded drug and occurs in a prolonged manner for three days. Simultaneously with the antibiotic release, hydrogel swelling and partial degradation occurs. The WPI hydrogels absorb solvent, doubling in size in three days and retaining cefazolin throughout the duration of the experiment. The antimicrobial activity of cefazolin-loaded WPI hydrogels against Staphylococcus aureus growth is prolonged in comparison to that of the free cefazolin. The overall cytotoxic effect of cefazolin-containing WPI hydrogels is lower than that of free antibiotics. Thus, our work shows that antimicrobial WPI hydrogels are suitable candidates for local antibiotic therapy of infectious surgical sequelae.

Milk Whey Hydrolysates as High Value-Added Natural Polymers: Functional Properties and Applications

There are two types of milk whey obtained from cheese manufacture: sweet and acid. It retains around 55% of the nutrients of the milk. Milk whey is considered as a waste, creating a critical pollution problem, because 9 L of whey are produced from every 10 L of milk. Some treatments such as hydrolysis by chemical, fermentation process, enzymatic action, and green technologies (ultrasound and thermal treatment) are successful in obtaining peptides from protein whey. Milk whey peptides possess excellent functional properties such as antihypertensive, antiviral, anticancer, immunity, and antioxidant, with benefits in the cardiovascular, digestive, endocrine, immune, and nervous system. This review presents an update of the applications of milk whey hydrolysates as a high value-added peptide based on their functional properties.

Heparin Enriched-WPI Coating on Ti6Al4V Increases Hydrophilicity and Improves Proliferation and Differentiation of Human Bone Marrow Stromal Cells

Titanium alloy (Ti6Al4V) is one of the most prominent biomaterials for bone contact because of its ability to bear mechanical loading and resist corrosion. The success of Ti6Al4V implants depends on bone formation on the implant surface. Hence, implant coatings which promote adhesion, proliferation and differentiation of bone-forming cells are desirable. One coating strategy is by adsorption of biomacromolecules. In this study, Ti6Al4V substrates produced by additive manufacturing (AM) were coated with whey protein isolate (WPI) fibrils, obtained at pH 2, and heparin or tinzaparin (a low molecular weight heparin LMWH) in order to improve the proliferation and differentiation of bone-forming cells. WPI fibrils proved to be an excellent support for the growth of human bone marrow stromal cells (hBMSC). Indeed, WPI fibrils were resistant to sterilization and were stable during storage. This WPI-heparin-enriched coating, especially the LMWH, enhanced the differentiation of hBMSC by increasing tissue non-specific alkaline phosphatase (TNAP) activity. Finally, the coating increased the hydrophilicity of the material. The results confirmed that WPI fibrils are an excellent biomaterial which can be used for biomedical coatings, as they are easily modifiable and resistant to heat treatments. Indeed, the already known positive effect on osteogenic integration of WPI-only coated substrates has been further enhanced by a simple adsorption procedure.

Characterization of Conjugates between α-Lactalbumin and Benzyl Isothiocyanate-Effects on Molecular Structure and Proteolytic Stability

In complex foods, bioactive secondary plant metabolites (SPM) can bind to food proteins. Especially when being covalently bound, such modifications can alter the structure and, thus, the functional and biological properties of the proteins. Additionally, the bioactivity of the SPM can be affected as well. Consequently, knowledge of the influence of chemical modifications on these properties is particularly important for food processing, food safety, and nutritional physiology. As a model, the molecular structure of conjugates between the bioactive metabolite benzyl isothiocyanate (BITC, a hydrolysis product of the glucosinolate glucotropaeolin) and the whey protein α-lactalbumin (α-LA) was investigated using circular dichroism spectroscopy, anilino-1-naphthalenesulfonic acid fluorescence, and dynamic light scattering. Free amino groups were determined before and after the BITC conjugation. Finally, mass spectrometric analysis of the BITC-α-LA protein hydrolysates was performed. As a result of the chemical modifications, a change in the secondary structure of α-LA and an increase in surface hydrophobicity and hydrodynamic radii were documented. BITC modification at the ε-amino group of certain lysine side chains inhibited tryptic hydrolysis. Furthermore, two BITC-modified amino acids were identified, located at two lysine side chains (K32 and K113) in the amino acid sequence of α-LA.

Benzyl isothiocyanate-modified α-lactalbumin - Two-dimensional high-performance thin-layer chromatography for analyzing modified peptides

In complex food matrices, non-directed reactions between food proteins and secondary plant metabolites (SPM) are conceivable. In this study, the interaction between the bioactive metabolite from garden cress (Lepidium sativum) and selected Brassicaceae - benzyl isothiocyanate (BITC) - and the dairy protein α-lactalbumin (α-LA) was investigated. It was focused on monitoring the proteolytic degradation behaviour of unmodified and BITC-modified α-LA with two-dimensional high-performance thin-layer chromatography (2D-HPTLC). The two-dimensional approach of HPTLC offers high resolution in the separation of complex peptide mixtures and might enable differentiation of protein modifications. Based on the specific peptide patterns of native and modified peptides, conclusions can be drawn about differences in protein/peptide polarity, location of a modification, and digestibility. The aim was to characterize tryptically hydrolyzed unmodified and BITC-modified peptides using the 2D method and to investigate the influence of BITC modification of α-LA on polarity and digestibility. To determine the repeatability of peptide separation by 2D-HPTLC, the unmodified and BITC-modified protein hydrolyzates were separated six times. The absolute standard deviations between the retardation factors of the individual peptide spots varied between 0.52 and 4.79 mm for the x-coordinates and between 0.41 and 6.47 mm for the y-coordinates for all three samples. Here, the mean relative standard deviations ranged from 5.80 to 10.4% for the x-coordinates and from 5.91 to 18.3% for the y-coordinates. The results of the tryptic hydrolysis indicated that, depending on the concentration of BITC used, the modification sterically hinders the cleavage sites for the enzyme, resulting in a reduced digestibility. Covalent binding of the hydrophobic BITC altered the digestibility and polarity of the protein, leading to a difference in peptide patterns between the unmodified and modified α-LA. It was concluded that the reaction was undirected, resulting in a mixture of unmodified and modified peptides, and that elongated modified peptides were formed by BITC blocking of trypsin cleavage sites.

Amine-Rich Coatings to Potentially Promote Cell Adhesion, Proliferation and Differentiation, and Reduce Microbial Colonization: Strategies for Generation and Characterization

Biomaterial surface modification represents an important approach to obtain a better integration of the material in surrounding tissues. Different techniques are focused on improving cell support as well as avoiding efficiently the development of infections, such as by modifying the biomaterial surface with amine groups (–NH2). Previous studies showed that –NH2 groups could promote cell adhesion and proliferation. Moreover, these chemical functionalities may be used to facilitate the attachment of molecules such as proteins or to endow antimicrobial properties. This mini-review gives an overview of different techniques which have been used to obtain amine-rich coatings such as plasma methods and adsorption of biomolecules. In fact, different plasma treatment methods are commonly used with ammonia gas or by polymerization of precursors such as allylamine, as well as coatings of proteins (for example, collagen) or polymers containing –NH2 groups (for example, polyethyleneimine). Moreover, this mini-review will present the methods used to characterize such coatings and, in particular, quantify the –NH2 groups present on the surface by using dyes or chemical derivatization methods.

Immunological Analysis of Isothiocyanate-Modified α-Lactalbumin Using High-Performance Thin Layer Chromatography

Undirected modifications between food proteins and secondary plant metabolites can occur during food processing. The results of covalent interactions can alter the functional and biological properties of the proteins. The present work studied the extent of which covalent conjugation of the bioactive metabolite benzyl isothiocyanate (BITC; a glucosinolate breakdown product) to the whey protein α-lactalbumin affects the protein’s allergenicity. Additional to the immunological analysis of native untreated and BITC-modified α-lactalbumin, the analysis of antigenic properties of proteolytically digested protein derivatives was also performed by high performance thin layer chromatography and immunostaining. As a result of the chemical modifications, structural changes in the protein molecule affected the allergenic properties. In this process, epitopes are destroyed or inactivated, but at the same time, buried epitopes can be exposed or newly formed, so that the net effect was an increase in allergenicity, in this case. Results from the tryptic hydrolysis suggest that BITC conjugation sterically hindered the cleavage sites for the enzyme, resulting in reduced digestibility and allergenicity. Residual antigenicity can be still present as short peptide fragments that provide epitopes. The desire to make food safer for allergy sufferers and to protect sensitized individuals from an allergenic reaction makes it clear that the detection of food antigens is mandatory; especially by considering protein interactions.

Dairy-Inspired Coatings for Bone Implants from Whey Protein Isolate-Derived Self-Assembled Fibrils

To improve the integration of a biomaterial with surrounding tissue, its surface properties may be modified by adsorption of biomacromolecules, e.g., fibrils. Whey protein isolate (WPI), a dairy industry by-product, supports osteoblastic cell growth. WPI's main component, β-lactoglobulin, forms fibrils in acidic solutions. In this study, aiming to develop coatings for biomaterials for bone contact, substrates were coated with WPI fibrils obtained at pH 2 or 3.5. Importantly, WPI fibrils coatings withstood autoclave sterilization and appeared to promote spreading and differentiation of human bone marrow stromal cells (hBMSC). In the future, WPI fibrils coatings could facilitate immobilization of biomolecules with growth stimulating or antimicrobial properties.

Protein oxidation during temperature-induced amyloid aggregation of beta-lactoglobulin

Although the connection between protein oxidation, amyloid aggregation and diseases such as Alzheimer's is well known there is no information on such effects during preparation of beta-lactoglobulin fibrils. Different morphologies of amyloid aggregates of beta-lactoglobulin were prepared by incubation at pH 2 or pH 3.5 for up to 72 h. After 5 h, amyloid aggregates at pH 2 formed typical fibrils, which consisted of peptides. At pH 3.5, the amyloid aggregates were worm-like and consisted of intact protein. After 72 h, the building blocks at both pH values changed towards smaller peptides. The apparent tyrosine oxidation reached a maximum after 5 h at both pH values, whereas N-formylkynurenine and carbonyls increased continuously during 72 h. In case amyloid structures are used as edible material, the health related effects caused by protein oxidation needs to be considered.

Spray-drying of grape skin-whey protein concentrate mixture

The aim of this work was to evaluate the effect of process conditions (inlet air temperature, paste flow rate, and whey protein concentration) on the physical and physicochemical characteristics of the powder obtained from spray dried grape skin-whey protein concentrate mixture. The experiments were performed according to the 2³ factorial design, with repetition of the central point. The highest values of anthocyanin retention (> 92%) were obtained with the highest inlet air temperature (190 °C) and the highest whey protein concentration (15% (w/w)). The powder also showed solubility above 78.3%, and low values of moisture content, hygroscopicity and bulk density. Spray drying of grape residues, using whey protein as carrier agent, resulted in a powder with a high level of anthocyanin retention and of good quality, showing a potential application in food products. Therefore, the method indicates a possible alternative to change post-harvesting waste in a natural source of bioactive compounds.

Covalent Whey Protein-Rosmarinic Acid Interactions: A Comparison of Alkaline and Enzymatic Modifications on Physicochemical, Antioxidative, and Antibacterial Properties

The covalent interactions between whey protein isolate (WPI) and rosmarinic acid (RosA) at two different conditions, alkaline (pH 9) and enzymatic (in the presence of tyrosinase, PPO), at room temperature with free atmospheric air were studied. The conjugates formed between WPI and RosA were characterized in terms of their physicochemical and functional properties. The changes in protein structure were analyzed by intrinsic fluorescence and binding of 8-anilino-1-naphthalenesulfonic acid. The findings show that the covalent interactions caused a decrease in free amino and thiol groups and tryptophan content at both conditions. The decrease at enzymatic conditions was lower than at alkaline conditions. In addition, modified WPI at alkaline conditions exhibited higher antioxidative capacity compared to the modification at enzymatic conditions. However, WPI modified at enzymatic condition showed mild antimicrobial activity against Staphylococcus aureus LMG 10147 and MU50 compared to WPI modified at alkaline conditions and unmodified WPI (control). The modified WPI can be used as multifunctional ingredient into various food products with an additional health promoting effect of the bound phenolic compounds.

Glucoraphanin and sulforaphane evolution during juice preparation from broccoli sprouts

Broccoli sprouts are considered functional food as they are naturally enriched in glucoraphanin (GR) that is the biological precursor of the anticancer compound sulforaphane (SFN). Due to its health promoting value, also broccoli sprout juice is becoming very popular. The present study aimed to quantitatively assess the conversion of GR to its hydrolysis products, SFN and SFN-nitrile, during the juice preparation process. We demonstrated that SFN plus SFN-nitrile yield from glucoraphanin is quite low (≈25%) and that some SFN is lost during the juice preparation partially due to the spontaneous conversion to sulforaphane-amine or conjugation to GSH and proteins naturally present in the juice. Our results demonstrate that the detection of the sole SFN free form does not provide reliable information about the real concentration of this functional compound in the juice.