Lower Surface Hydrophobicity Research Articles

Physical and oxidative stability of oil-in-water (O/W) emulsions in the presence of protein (peptide): Characteristics analysis and bioinformatics prediction

The physical and oxidative stability of soybean protein hydrolysate-stabilized oil-in-water (O/W) emulsions created via limited hydrolysis using Alcalase (15, 30, 45, 60, 90, 120, and 180 min) was investigated. The extracted emulsion protein exhibited significantly lower surface hydrophobicity, higher antioxidant properties, and a greater proportion of β-sheet and α-helix structures than soybean protein isolate. The physical stability of the emulsions was characterized by particle size, zeta-potential, rheological property, and multiple light scattering. The emulsion obtained by enzymatic hydrolysis for 90 min (90 min-E) had the highest physical stability, showing the smallest droplet size, uniform droplet distribution, lowest zeta-potential, lowest Turbiscan stability index, and larger G′ and G″ values. It also exhibited the highest oxidative stability, as evidenced by the thiobarbituric acid-reactive substances test. Due to the good physical and oxidative stability of 90 min-E, LC-MS/MS analysis and bioinformatic tools (Chou−Fasman secondary structure prediction and the BIOPEP database) were conducted on the protein extracted from 90 min-E. These data provided insight into the mechanism of emulsion-stabilizing action by the emulsion protein (peptide) and identified potential bioactive peptides. This new strategy of producing stable O/W emulsions will likely expand its application to nutrient components or effective wall materials.

Extraction and Characterization of Proteins from Pachyrhizus ahipa Roots: an Unexploited Protein-Rich Crop.

Pachyrhizus ahipa is an unexploited crop known to be rich in proteins compared to other edible roots and tubers. These proteins are not prolamins, thus ahipa represents an interesting new source of ingredients for gluten-free foods. In this work, ahipa proteins (AP) were extracted and partially characterized in pursuit of their use as food ingredients. The effect of ultrasound treatment on protein extraction efficiency was evaluated. AP were characterized by their size, amino acid composition, surface hydrophobicity, intrinsic fluorescence, FTIR spectra, solubility, and thermal and emulsifying properties. AP were efficiently removed from the vegetal tissue using PBS or water, regardless of the use of ultrasound, but not easily recovered by precipitation. This protein fraction was composed of small proteins, with sizes ranging from 9 to 30kDa, and highly polar. AP resulted particularly rich in aspartic acid (59% of the total amino acid content), for which they can be classified as Asp-rich proteins. Their elevated content of acidic groups was evidenced in the ATR-FTIR spectrum. The amide I band deconvolution as well as the low surface hydrophobicity and denaturation enthalpy indicated that these proteins are mainly unordered structures. The emulsifying properties of AP were enhanced when the concentration was increased from 0.1 to 1% (w/v) but resulted lower than those of soy protein. The high polarity, small size, and low isoelectric point make AP particularly suitable for acidic food matrices.

Carboxymethylcellulose-induced changes in rheological properties and microstructure of wheat gluten proteins under different pH conditions.

The interaction between gluten and hydrocolloid additive, as well as the pH condition during dough formation is very important in making flour products. In this study, the influence of different pH conditions on the interactions between gluten proteins (including glutenin and gliadin) and carboxymethylcellulose (CMC), and on the rheological and microstructure changes of gluten proteins was investigated. The dynamic frequency sweep indicated CMC-gluten displayed more solid-like behavior under alkaline conditions than that under acidic conditions. The creep-recovery experiment suggested acidic conditions were not conducive to maintain the elasticity of CMC-gluten. Microstructural changes of various glutens with CMC showed that a higher ratio of β-sheets was observed in the CMC-gluten and CMC-glutenin under alkaline conditions. Total free sulfhydryl contents and changes in tryptophan microenvironment showed glutenin played a key role in the G polymerization with the addition of CMC. Lower surface hydrophobicity of CMC-gluten was displayed under acidic conditions. Scanning electron microscopy images showed that neutral and alkaline conditions were conducive to the network structure formation of CMC-gluten and CMC-glutenin. This study investigated the interaction of CMC with gluten, gluten, and gliadin under different pH conditions, providing a basis for expanding dough quality improvement, and extending the in-depth application of CMC in the food industry.

Modification of whey protein microgel particles with mono- oligo- and polysaccharides through the Maillard reaction: Effects on structural and techno-functional properties

Many food and drink products have a pH value between 4.0 and 6.0, which is near the isoelectric point (pI) of whey proteins. This study evaluated the modification of whey protein microgel (WPM) through Maillard conjugation with several common saccharides including arabinose, glucose, fructose, lactose, inulin, and maltodextrin in a liquid system, which is considered a potential route to boost the utilization of these protein particles in acidic conditions. Glycation degree (22–31 %), pH decrease, presence of final products, FTIR, and SDS-PAGE confirmed the bonding of carbohydrates to WPMs. The conjugates prepared by lactose, glucose, and inulin, i.e. moderately reactive carbohydrates, rendered lower surface hydrophobicity, higher colloidal stability (∼40−50% at pH 4.0), and improved emulsifying properties in comparison with WPM, heated WPM and other glycoproteins. Foaming capacity of Maillard reaction products was lower or without change relative to the WPM; however, foam prepared by maltodextrin-glycated WPM was substantially more stable (up to 24 h). These findings could open avenues for applicability of these pre-denatured densely-packed particles in a range of food products and soft-matter applications.

Physicochemical, functional and bioactive properties of hempseed (Cannabis sativa L.) meal, a co-product of hempseed oil and protein production, as affected by drying process

Hempseed meal after protein isolation (HM-PI) is a co-product obtained from hempseed. The objectives were to characterize and determine the effect of drying on HM-PI. HM-PI was produced using three drying methods: freeze (FD), vacuum oven (VOD), and oven drying (OD). HM-PI contained over 70% protein and had similar or higher level of essential amino acids than recommended values for human adults. Osborne fractionation indicated that glutelin was the most dominant fraction in HM-PI. FD HMPI has a significant lower surface hydrophobicity and higher in vitro protein digestibility than OD and VOD HM-PI. FD HM-PI demonstrated better functional properties than OD and VOD HM-PI. Pepsin-pancreatin digestion of VOD, FD and OD resulted in comparable and considerable antioxidant and anti-inflammatory properties. This is the first report on the characterization of HM-PI, a co-product of hempseed processing. HM-PI could serve as a novel food protein ingredient resulting in increase utilization of hempseed.

Antioxidative Potency of Dolphin Serum Albumin Is Stronger Than That of Human Serum Albumin Irrespective of Substitution of 34Cysteine With Serine.

Serum albumin (SA), the most abundant protein in circulation, functions as a carrier protein, osmoregulator, and antioxidant. Generally, SA exerts its antioxidative effects by scavenging reactive oxygen species. Because marine mammals are superior divers, they are intermittently exposed to oxidative stress induced by rapid reperfusion of oxygen to ischemic tissues after the dive. Although several antioxidants in marine mammals have been described, SA activity remains largely uncharacterized. In this study, we investigated the antioxidative activity of SA in marine mammals by comparing features of the primary and steric structures, biochemical properties, and antioxidative activities of common bottlenose dolphin SA (DSA) and human SA (HSA). Our results revealed that DSA lacked free cysteine at position 34 that is important for the antioxidative activity of HSA; however, the antioxidative capacity and thiol activity of DSA were stronger than those of HSA. Circular dichroism spectra showed different patterns in DSA and HSA. Ultraviolet fluorescence intensities of DSA were higher than those of HSA, suggesting lower surface hydrophobicity of DSA. Additionally, DSA showed higher excess heat capacity than HSA. We then compared a homology model of DSA with a 3D model of HSA. Our results indicate that DSA was more unstable than HSA at least in the body-temperature range, probably due to the mode of molecules involved in the disulfide bonds and/or the lower surface hydrophobicity, and it may be related to the equivalent or stronger antioxidant potency of DSA. These data show that DSA is an effective antioxidant in the circulation of the dolphin.

Toxic oligomers of the amyloidogenic HypF-N protein form pores in mitochondrial membranes

Studies on the amyloidogenic N-terminal domain of the E. coli HypF protein (HypF-N) have contributed significantly to a detailed understanding of the pathogenic mechanisms in neurodegenerative diseases characterised by the formation of misfolded oligomers, by proteins such as amyloid-β, α-synuclein and tau. Given that both cell membranes and mitochondria are increasingly recognised as key targets of oligomer toxicity, we investigated the damaging effects of aggregates of HypF-N on mitochondrial membranes. Essentially, we found that HypF-N oligomers characterised by high surface hydrophobicity (type A) were able to trigger a robust permeabilisation of mito-mimetic liposomes possessing cardiolipin-rich membranes and dysfunction of isolated mitochondria, as demonstrated by a combination of mitochondrial shrinking, lowering of mitochondrial membrane potential and cytochrome c release. Furthermore, using single-channel electrophysiology recordings we obtained evidence that the type A aggregates induced currents reflecting formation of ion-conducting pores in mito-mimetic planar phospholipid bilayers, with multi-level conductances ranging in the hundreds of pS at negative membrane voltages. Conversely, HypF-N oligomers with low surface hydrophobicity (type B) could not permeabilise or porate mitochondrial membranes. These results suggest an inherent toxicity of membrane-active aggregates of amyloid-forming proteins to mitochondria, and that targeting of oligomer-mitochondrial membrane interactions might therefore afford protection against such damage.

Determination of the mass transfer rate constant in a laboratory column flotation using the bubble active surface coefficient

This study aimed to introduce a new approach to determine the mass transfer rate constant in a laboratory column flotation through an analogy to a mass transfer process. The RTD of the column at two separate bubble sizes were modeled using both conventional N-mixer and N-mixer with back-mixing flow models. The number of perfect mixers (N) and the corresponding backflow coefficients (λ) were optimized using MINLP solver in MATLAB environment where N = 5 with λ = 0.567 at the bubble size of 1.8 mm and N = 8 with λ = 0.643 at the bubble size of 0.8 mm were obtained. The bubble active surface coefficient was introduced as a new parameter to study the flotation kinetics. Thus, the mass transfer rate constant was determined for various operational conditions based on the bubble active surface coefficient and bubble loading measurements. Results showed that the mass transfer rate depends on the physical and surface properties such as particle size, particle surface hydrophobicity, and the carrying capacity. At the fine particle size, the mass transfer continues such that a long bubble retention time is required. However, for the coarse particles, bubbles reach their maximum loading capacity prior to the pulp-froth interface so that any additional retention time does not contribute to the flotation. Besides, at the coarse particle size, due to the poor stability of the aggregates, especially for particles with low surface hydrophobicity, the mass transfer rate and thereupon the bubble loading decreases remarkably. Moreover, the fine particles show lower flotation kinetics in the presence of the large bubbles.

Subunit composition affects formation and stabilization of o/w emulsions by 11S seed storage protein cruciferin

The 11S globulin cruciferin is the major storage protein in Brassicaceae/Cruciferae seeds and exists as a hexamer in its natural configuration. Arabidopsis thaliana cruciferin is composed of CRUA, CRUB and CRUC subunits. Wild type (WT) cruciferin and cruciferins composed only of identical CRUA, CRUB and CRUC subunits were examined for their ability to form and stabilize oil-in-water (o/w) emulsions. All proteins (0.9% at pH 7.4 and 2.0), except CRUC, formed stable canola oil or triolein emulsions with a dispersed phase volume fraction of 22–23%. A fine emulsion was formed by CRUB at pH 7.4 with droplet sizes of 6.8 and 8.6 μm for canola oil and triolein, respectively. The presence of 0.5 M NaCl reduced the level of adsorbed protein and protein load at the interface at pH 7.4, and resulted in emulsions that were less stable. Emulsions of CRUA and CRUB (pH 7.4, zero ionic strength, canola oil or triolein) had higher stability than emulsions with WT cruciferin up to 15 days after formation. CRUC formed a stable emulsion only at pH 2.0. The low solubility, low surface hydrophobicity and compact structure of the CRUC protein may contribute to its inferior emulsifying properties at neutral pH; however, acidic pH-induced dissociation of the hexameric assembly improved these properties. The abundance and exposure of hydrophobic residues in the hypervariable regions, extended loop regions, and solvent exposed surfaces of cruciferin are critical factors affecting o/w interface stabilization.

Preparation of glycosylated hydrolysate by liquid fermentation with Cordyceps militaris and characterization of its functional properties

This study aimed to investigate the potential of a novel preparation strategy for glycosylated hydrolysate by liquid fermentation in order to provide a high-quality glycosylated hydrolysate. Protein solubility, surface hydrophobicity and antioxidant activity were evaluated. The results of Fourier transform infrared spectra demonstrated the occurrence of glycosylation reaction. The results of Fluorescence emission spectroscope revealed the decrease of tertiary conformation stability. Circular dichroism spectra revealed significant decrease in α-helix and increase in β-sheet and random coil by glycosylation reaction. In comparison with zein hydrolysate, glycosylated hydrolysate had lower surface hydrophobicity but higher in solubility and in vitro digestibility due to glycosylation. Glycosylated hydrolysate presented higher ABTS (2,2'-Azinobis [3-ethylbenzothiazoline-6-sulfonic acid]-diammonium salt) and superoxide radicals scavenging activities as well as Cu2+ chelating capacity. It is concluded that the glycosylation confer an open structure and modified properties of zein, and glycosylated hydrolysate is a potential ingredient with better hydration and antioxidant activities than zein hydrolysate.

Improving the functional properties of bovine serum albumin-glucose conjugates in natural deep eutectic solvents

Glycation between target proteins and saccharides is time-consuming or requires high temperatures. Here, a promising reaction medium, natural deep eutectic solvents (NADES), for glucose glycation with bovine serum albumin (BSA) was applied to improve the grafting of glucose-glycated BSA by shifting reaction equilibrium. Two types of glucose-glycated BSA products were prepared using NADES and water systems. SDS-PAGE and MALDI-TOF-MS revealed that BSA and glucose were covalently bonded. Compared with in water system, glycated BSA products in NADES system had more –OH groups, more disordered secondary structures, lower intrinsic fluorescence intensity, and higher ultraviolet–visible absorption. Lower surface hydrophobicity (1100 versus 1356), higher emulsifying activity index (66.17 versus 46.49 m2/g), higher emulsion stability index (79.62 versus 63.61%), and lesser free sulfhydryl (8.07 versus 8.98 μmol/g) groups were obtained with NADES system than with water system. The results suggest that NADES is a suitable alternative reaction medium for promoting the glycation of BSA.

Physico-chemical characterization of protein stabilized oil-in-water emulsions

Emulsifying properties of four different proteins (soy, potato, pea and whey) were analyzed and related to their solubility, surface hydrophobicity, surface tension and their ability to modify aqueous phase viscosity. The influence of protein (emulsifier) type and concentration (1, 4 and 7 %), and pH value of the system (protein native pH and pH 9.0) on droplet size distribution parameters, rheological behavior and stability of fish oil-in-water emulsions (5, 15 and 30 % of dispersed phase) was determined. The examined proteins showed similar surface activity. The highest aqueous solution viscosity was exhibited by soy protein, while the viscosity of pea protein aqueous solution was the lowest. Droplet size measurements of emulsions showed that increase in protein concentration from 1 to 4% resulted in the formation of smaller droplets during the homogenization, while further increase in protein concentration up to 7 % did not maintain the trend of droplets size decrease. Increase in emulsions pH from protein native to pH 9.0 for almost all proteins led to decrease in average droplets diameters of emulsions and formation of smaller droplets (except for emulsions stabilized by whey protein where the decrease was not significant). All investigated emulsions showed shear-thinning flow behavior. The consistency indexes (K) of emulsions, which are indicators of the system viscose behavior, increased with the increase in protein concentration, oil content and pH of the system. Despite low solubility and surface hydrophobicity, the soy protein emulsifier was capable of producing the most stable emulsions with the smallest droplets compared to the other three proteins. The soy protein stabilized emulsions were also characterized with the highest emulsion consistency index and continuous phase viscosity in comparison to emulsions containing other proteins indicating the role of protein as thickening agent in stabilizing emulsion.

Preparation and Evaluation of New Glycopeptides Obtained by Proteolysis from Corn Gluten Meal Followed by Transglutaminase-Induced Glycosylation with Glucosamine.

New glycopeptides were generated by proteolysis from corn gluten meal (CGM) followed by transglutaminase (TGase)-induced glycosylation with glucosamine (GlcN). The glycopeptides exhibited desirable antioxidant and intracellular ROS-scavenging properties. The amount of conjugated GlcN quantified by high-performance liquid chromatography (HPLC) was 23.0 g/kg protein. The formed glycopeptides contained both glycosylated and glycation types, as demonstrated by the electrospray ionization time-of-flight mass spectrometry (ESI-TOF MS/MS). The glycopeptides exhibited scavenging capabilities against free radical diphenylpicrylhydrazyl (DPPH) and hydroxyl radicals by reducing their power. The potential protection of glycopeptides against ethanol-induced injury in LO2 cells was assessed In Vitro based on methyl thiazole tetrazolium (MTT) testing and intracellular reactive oxygen species (ROS) scavenging capacity, respectively. Glycopeptide cytoprotection was expressed in a dose-dependent manner, with the glycopeptides exhibiting good solubility ranging from 74.8% to 83.2% throughout a pH range of 2–10. Correspondingly, the glycopeptides showed good emulsifying activity (36.0 m2/g protein), emulsion stability (74.9%), and low surface hydrophobicity (16.3). These results indicate that glycosylation of CGM significantly improved its biological and functional properties. Glycopeptides from CGM could be used as potential antioxidants as well as comprising a functional food ingredient.

Effect of reverse micelle on physicochemical properties of soybean 7S globulins

In this paper, the structural, thermodynamic, and rheological properties of soybean 7S globulins extracted by bis(2-ethylhexyl) sulfosuccinate sodium salt (AOT)/isooctane reverse micelle method and alkali extraction-acid precipitation method were studied. Amino acid composition results showed that the 7S globulin produced by reverse micelle had more hydrophobic and sulfur-containing amino acids. Fourier transform infrared spectroscopy results demonstrated that the 7S globulin extracted by reverse micelle had more β-sheets but less turn structure, and formed a more compact conformation. However, lower surface hydrophobicity was observed in the 7S globulin extracted by reverse micelle, indicating that the reverse micelle environment could protect the native folded structure of protein. Thermal stability tests showed that the 7S globulin extracted by reverse micelle had poorer thermostability with lower denaturation temperature, which was in accordance with the results of initial gelling temperature. Final storage modulus (G’) and frequency sweep results revealed that the 7S globulin obtained by reverse micelle produced a harder textured gel.

Camel α−lactalbumin at the oil−water interface: Effect of protein concentration and pH change on surface characteristics and emulsifying properties

Camel α−lactalbumin (Ala−C), the main whey protein of camel milk, was purified by membrane filtration. Surface hydrophobicity as well as interfacial tension were examined at different levels of pH (3.0, 6.0, 9.0) and protein concentration (0.1 %, 0.2 %, 0.4 % w/w), and compared to bovine α−lactalbumin (Ala−B). The emulsifying properties (EAI and ESI) of oil-in-water emulsions (20 %/80 %) were investigated for both proteins. The stability of the processed emulsions was characterised by ζ−potential, particle size and viscosity measurements.The main findings indicate that Ala−C exhibited greater surface hydrophobicity and undergone changes in conformational structure when pH decreased from 9.0–3.0. These changes were enhanced by increasing protein concentration from 0.1 % to 0.4 % (w/w). However, high concentrations showed low emulsifying activity, especially at pH 6.0 where interfacial tension was lower. In comparison with Ala−B, maximum EAI was close, despite the lower surface hydrophobicity of Ala−C under similar conditions.Overall, emulsions were more viscous at pH 3.0 due to the greater surface coverage than at 9.0 and 6.0. Under the conditions of this study, a protein concentration of 0.2 % resulted in the finest oil droplets and highest viscosity for both types of α−lactalbumin, and Ala−C conferred the highest long-term stability to the emulsions.

Effect of Homogenization at a Lower Pressure on Structural and Functional Properties of Soy Protein Isolate.

In this paper, the effects of homogenization at low pressure (1~40 MPa) on structural and functional properties of soy protein isolates (SPI) are investigated. Homogenization at low pressure increase solubility, surface hydrophobicity, emulsification activity and foaming capacity of SPIs, these all functional properties increases and then decreases with the homogenization pressure. Whereas, emulsion stability and foaming stability of SPIs treated by homogenization initially decrease and then increase with homogenization pressure. There is a dramatic decrease in hardness, springiness and cohesiveness of homogenized SPI gels. Generally, homogenization at low pressure do not change the subunit composition of SPIs. It is observed that, when the homogenization pressure is lower than 10 MPa than there is no significant impact on structural change. The content of β-sheet decreased, while unordered structure significantly increased, when the homogenization pressure increased from 10 MPa to 20 MPa. Furthermore, the content of β-sheet increases, when the content of the other structures decreases with the increasing homogenization pressure. The maximum emission wavelength (λmax) for SPIs increases with homogenization pressure increases from 10 Mpa to 20 Mpa, which is attributed to the gradual structural unfolding exposing more hydrophobic residues in protein surface. While, the decreased λmax of SPIs treated with 20 Mpa to 40 Mpa homogenization corresponds to the protein aggregation. It can be deduced that appropriate selection of homogenization pressure is important for improving the functional properties of SPIs.

Assembling of the interfacial layer affects the physical and oxidative stability of faba bean protein-stabilized oil-in-water emulsions with chitosan

This study investigated how different ways of assembling of faba bean protein isolate (FBPI) and chitosan (CH) affected the oil-in-water emulsion stability. Emulsions were prepared either by a soluble FBPI-CH complex to make EMC, or by FBPI first and then added non-interactive CH to make EMN, or by FBPI first and then added a secondary layer of CH via electrostatic attraction to make EML. A control emulsion EMFB was prepared by only FBPI. All emulsions contained 5% (w/v) oil and 0.5% (w/v) FBPI. EMC/EML/EMN contained 0.05% (w/v) CH. The emulsion stability was monitored at 37 °C for 7 days. EML not only showed better physical stability as indicated by the changes in droplet size, Turbiscan stability index, and microstructure (by confocal microscopy), but also exhibited superior oxidative stability as indicated by lipid oxidation products (less conjugated dienes and secondary oxidation products) and protein oxidation biomarkers (less tryptophan loss and carbonyls formation). This might be attributed to that CH enhanced formation of a layer-by-layer (LBL) interfacial structure, which increased the interfacial layer thickness/compactness and maintained the interfacial protein adsorption. In contrast, EMC demonstrated worse stability, albeit with thicker interfacial layer due to CH. This could be explained by the lower surface hydrophobicity and surface charge of soluble FBPI-CH complex. The free aqueous CH also impaired physical stability and promoted oxidation, as shown in EMN. In conclusion, CH improves the oxidative and physical stability of FBPI-containing emulsion when added as a LBL model.

Pomegranate seed oil stabilized with ovalbumin glycated by inulin: Physicochemical stability and oxidative stability

Pomegranate seed oil is rich of conjugated fatty acids which are highly appealing for a variety of applications in food industry. In this research, ovalbumin (OVA) and ovalbumin-inulin glycoconjugates with different Maillard reaction times were used to stabilize pomegranate seed oil emulsions and their impact on physicochemical stability and oxidative stability of the products was investigated. The OVA-inulin glycoconjugate produced on 10th day of Maillard reaction has exhibited significantly higher conjugation efficiency, lower surface hydrophobicity and lower surface tension than other glycoconjugates. The secondary conformation of OVA and conjugates determined by far-UV circular dichroism spectroscopy has remarkably changed. The reduction in intensity of Trp-fluorescence observed in glycated proteins with inulin indicated that the glycation affected partially the side chains of protein in tertiary structure through the Maillard reaction without great disruption of native structure. The emulsion stabilized by OVA-inulin glycoconjugate obtained by 10 days Maillard reaction has shown the best physicochemical stability. Compared with the OVA emulsion, the oxidative stability of the glycated OVA emulsion system was significantly improved (p < 0.05). Fatty acid profile results also confirmed that OVA-inulin glycoconjugates were able to prevent the pomegranate seed oil from oxidation. It is suggested that the inulin attached to OVA by glycation played a vital role in physicochemical stability and oxidative stability of pomegranate seed oil emulsions.

Effects of the enzymatic hydrolysis treatment on functional and antioxidant properties of quinoa protein acid-induced gels

Partial enzymatic hydrolysis is frequently used as strategy to improve the functional and nutritional properties of vegetable proteins. The aim of this work was to evaluate the hydrolysis of quinoa proteins, as well as the functional and antioxidant properties of their acid-induced gels. In order to fulfil this purpose, quinoa protein hydrolysates were obtained using a fungal serin protease. The hydrolysis degree, surface hydrophobicity, sulphydryl group content and the electrophoretic profile of hydrolysates were assayed. Hydrolyzed quinoa protein acid-induced gels were carried out and gels obtained were tested for their textural characteristics, water holding capacity, appearance (color and microstructural properties) as well as for their in vitro antioxidant activity. The changes occurring during the enzymatic hydrolysis affected the gel-forming ability of quinoa proteins and therefore the characteristics of gels. After 3 h of proteolysis, protein hydrolysates with 17 ± 2% hydrolysis degree and low surface hydrophobicity were obtained. Gels obtained of these hydrolysates presented less interconnected protein network and thus, lower textural parameters and lower water holding capacity than control gels. In conclusion, even though the hydrolysis treatment negatively affects the gelling properties of the quinoa proteins, limited hydrolysis enables us to obtain gels with antioxidant capacities which present differential characteristics.

Probing effects of molecular-level heterogeneity of surface hydrophobicity on hydrophobic interactions in air/water/solid systems

HypothesisHydrophobic interaction is crucial in various colloidal phenomena and engineering processes involving air/water/solid systems where polar and nonpolar substances usually mingle with each other. The molecular-level heterogeneity of surface hydrophobicity could potentially disorder the interfacial water molecules and thus influence the hydrophobic interaction strength, but the underlying mechanism is not completely clear. ExperimentsThe hydrophobic interactions between air bubbles and self-assembled monolayer surfaces bearing methyl and different polar moieties were precisely quantified via bubble probe atomic force microscope coupled with theoretical modeling analysis. FindingsIncreasing coverage of surface polar moieties on binary-component surfaces can apparently lower surface hydrophobicity θc, but hardly affect hydrophobic interaction’s decay length D0. Changing pH has no detectable effect on hydrophobic interactions involving CH3 and CH3/OH-ended surfaces. In contrast, θc and D0 decrease monotonically with pH rising for CH3/COOH-ended surface, because high pH tends to dissociate –COOH, enhancing the surface hydrophilicity and weakening the hydrophobic interaction. For CH3/NH2-ended surface, θc and D0 decrease sequentially with pH declining, because protonation of –NH2 can lower the surface hydrophobicity and weaken the hydrophobic interaction. This work improves the fundamental understanding of hydrophobic interactions in air/water/solid systems and provides useful insights into the interfacial assembly processes in relevant engineering applications.