Isoelectric Point Of pH Research Articles

Characterization of functional properties catfish protein isolates (Clarias sp.)

Production of catfish protein isolates can be an alternative to provide added value to this commodity, which is expected to be a potential source of quality protein and promote human health. This study was aimed to characterize the chemical and functional properties of large-size catfish protein isolates and its functional properties. The stages of this study were to produce catfish protein isolates by using alkaline (pH 11) and isoelectric point (pH 5.5) methods and characterize the chemical and functional properties of catfish protein isolates produced. The result showed that catfish protein isolates contained 9 essential amino acids, protein content of 86.74% (wb) or 90.46% in dry basis(dB) and fat content of 0.54% (wb) or 0.56% (dB). Functionally, the catfish protein isolates produced have the ability in gelling forming a concentration of 5%, 4.08 g/mL oil absorption, 3.38 g/mL water absorption, emulsion capacity and stability of 1.52 mL/mL and stable over 90 minutes, 0.89 mL/mL foam capacity, and 0.64 g/mL density of bulky.

Solubility and emulsifying activity of yam soluble protein.

Yam soluble protein (YSP) has been reported to have many physiological activities, such as scavenging free radicals, immune activation, and anti-hypertensive activities. Protein solubility and emulsifying activity are important protein-associated functional properties for the application of proteins in food systems. During this study, the factors of protein concentration, pH, temperature and salt concentration that influenced the solubility of YSP were investigated. As a result, the solubility was minimal near its isoelectric point (pH 3.5) and washighest at 45°C in a temperature range of 40-60°C. With an increase of protein concentration, the solubility decreased. According to the results of response surface methodology analysis, the interaction between pH and temperature on the solubility of YSP was significant, and the maximum solubility (87.5%) was obtained when the temperature was close to 40°C, the pH was approximately 7 and the NaCl concentration approached 0.5mol/L. As the protein concentration increased, the average particle size of the YSP emulsion decreased, and the particle size distribution gradually became balanced. Additionally, the microphotograph of the YSP emulsion reflected its distribution. The results of this study will provide data and a theoretical basis for the understanding of YSP's physicochemical properties and its application in the food industry.

Influence of pH on interaction of silver nanoparticles - protein: Analyses by spectroscopic and thermodynamic ideology

To investigate the interaction between bovine serum albumin (BSA) and silver nanoparticles (AgNPs) at five different pHs (below (3.0 and 4.0), above (7.4 and 9.2) and at the isoelectric point (4.7) of BSA) by spectroscopic (viz., UV–vis, fluorescence, circular dichroism (CD)), microscopic (viz., atomic force microscopy (AFM), transmission electron microscopy (TEM), field emission scanning electron microscope (FESEM)) and thermodynamic (viz., isothermal titration calorimetry (ITC)) methods. The fluorescence quenching spectra provided binding constants via Stern-Volmer plot, quenching constant (Ksv) and rate constant (Kq) were calculated. From the CD spectra, it is clear that the α-helix decreases by increasing the AgNP’s concentration. However, at isoelectric point (pH = 4.7), BSA shows more helicity in the presence of AgNPs, which indicates that the structures of BSA become more ordered and stable, and aggregation occurs at strong acidic (3.0), and basic medium (9.2) Fluorescence spectra also indicate the aggregation of the protein at strong acidic (pH = 3.0) and basic medium (pH = 9.2). Furthermore, the morphological and topographical evolute ion upon the interaction was examined using TEM, FESEM, and AFM. The studies conclude the effect of the pH in the medium and behavior of AgNPs with BSA by using different spectroscopic and microscopic techniques.

Peanut Oil Body Composition and Stability.

This study was aimed to assess the effect of membrane structure on the stability of peanut oil bodies extracted by enzyme-assisted extraction. The influence of pH, NaCl concentration, and temperature on the physicochemical properties of peanut oil bodies was characterized using ζ-potential and particle size. The results indicated that the peanut oil bodies had strong stability (ζ-potential, >20 mV) at pH values away from the isoelectric point (pH 4.8), at a low salt concentration (NaCl concentration, <10 mM), and in a certain temperature range (35 to 55 °C). The stable structure of the oil body was closely related to its structure. Phospholipids, along with membrane proteins, were major components of the oil body membrane. Therefore, the phospholipid composition and content were measured and the types of membrane proteins of the oil bodies were identified. The results showed that phosphatidylcholine and phosphatidylserine were major components of the oil body phospholipids. Two-dimensional electrophoresis showed that the oil bodies contained both intrinsic proteins and extrinsic proteins, which might play an important role in the stability of oil bodies during enzyme-assisted extraction processing.

Encapsulation of Lutein in Nanoemulsions Stabilized by Resveratrol and Maillard Conjugates.

Lutein is incorporated into foods as a natural yellow pigment and nutraceutical. The introduction of lutein into many foods and beverages, however, is problematic because of its strong hydrophobicity and poor chemical stability. In this research, lutein-loaded nanoemulsions were prepared to overcome this problem. Casein-dextran Maillard conjugates or physical complexes were utilized as emulsifiers, while either medium chain triglycerides (MCT) or grape seed oil (GSO) were used as carrier oils. The impact of resveratrol addition on nanoemulsion stability was also examined. The influence of storage temperature, pH, and CaCl2 concentration on the chemical and physical stability of the nanoemulsions was measured. The casein-dextran conjugates were highly effective at improving the physical resistance of the nanoemulsions to environmental stresses, but had a detrimental effect on their color stability. Conversely, nanoemulsions prepared from casein-dextran physical complexes were unstable around the protein's isoelectric point (pH 4.6), as well as upon addition of CaCl2 . Incorporation of resveratrol and GSO into the nanoemulsions decreased lutein degradation and color fading at all temperatures. This study shows that casein-dextran conjugates are highly effective at improving the physical stability of lutein-loaded nanoemulsions, while resveratrol and GSO are effective at improving their chemical stability. PRACTICAL APPLICATION: Lutein can be used by the food industry to create "clean label" and functional food products. The major challenges in incorporating lutein in foods are its poor chemical stability and its high hydrophobicity, which makes it difficult to incorporate. Emulsion-based delivery systems assembled from natural ingredients may address these challenges. In this study, the impact of Maillard conjugates fabricated from caseinate and dextran, as well as resveratrol addition, on the formation and stability of lutein-enriched nanoemulsions was determined. The information obtained from this study will help the formulation of more effective functional foods and beverage products.

Adsorption, aggregation and sedimentation of titanium dioxide nanoparticles and nanotubes in the presence of different sources of humic acids.

Environmental behavior, bioavailability and risks posed by TiO2, nanomaterials (TiO2 NMs) in surface waters are affected by morphologies of the particles and geochemistry, including pH, inorganic and organic matter. Here, the adsorption, aggregation and sedimentation of TiO2 nanoparticles (TiO2 NPs) and nanotubes (TiO2 NTs) were investigated in the presence of Elliott Soil humic acid (HAE) and Suwannee River humic acids (HAS). The adsorption amount of HA on TiO2 NMs was inversely proportional to pH of solution. Maximum adsorption amount of HA on the surface of TiO2 NMs follows the order TiO2 NPs + HAE (236.05 mg/g) > TiO2 NTs + HAE (146.05 mg/g) > TiO2 NTs + HAS (70.66 mg/g) > TiO2 NPs + HAS (37.48 mg/g). Stability of TiO2 NPs and TiO2 NTs largely depended on their isoelectric point, morphology and solution pH in the absence of HA. Dispersion of TiO2 NMs was enhanced with solution pH deviated from the isoelectric point of nanomaterials due to electrostatic repulsion. Moreover, tubular structures of TiO2 NTs with higher length-diameter ratio seem to aggregate more easily than dose sphere-like TiO2 NPs. This might be due to their spherical structure enhancing steric repulsion. Notably, the adsorption of HA led to disagglomeration and significant stability of TiO2 NPs and TiO2 NTs due to steric hindrance under varying solution pH. In addition, adsorption time, concentration and sources of HA also influenced suspension/sedimentation behavior of TiO2 NPs and TiO2 NTs, and aromatic-rich HAE stabilized TiO2 NMs suspension more aggressively than aliphatic-rich HAS.

Extraction, gelation and microstructure of Bambara groundnut vicilins

Nowadays there is a growing interest in exploiting new sources of plant proteins as functional ingredients in food products. In recent years, Bambara groundnut (Vigna subterranea (L.) Verdc.) [BGN] has been explored as such a potential plant protein source, as a means of value-addition to this leguminous crop. To elucidate on the macroscopic functionality of BGN protein isolates, the focus of our study was on the extraction and characterisation of the vicilin protein fraction as the known major storage protein present in legume seeds. BGN vicilin had a high protein content (91%) and formed the largest component in relation to the other protein fractions. Together with molecular weight profiles obtained with gel electrophoresis and size-exclusion chromatography coupled with light scattering, the purity of vicilin and its presence as the predominant protein fraction in BGN black-eye seeds were confirmed. The isoelectric point (pH 5.3), solubility profile (highest solubility 86% at NaCl concentrations above 200 mM) and thermal denaturation temperature (92 °C) of BGN vicilin correspond to the range reported for other legume vicilins. Furthermore, the gelation behaviour of BGN vicilin gels was investigated using dynamic oscillatory measurements. These data were further analysed with scaling models, which revealed that fractal scaling was best suited for description of the BGN vicilin gel networks. The gel microstructures were visualised with confocal laser scanning and scanning electron microscopy.

Assessment of the microstructural characteristics and the in vitro bioactive properties of sunflower oil-based emulsions stabilized by fava bean (vicia faba) protein

Much interest is currently focused on plants such as legumes as an alternative source of protein for human nutrition. In this work a Vicia faba (fava bean, FB) protein concentrate was characterised for its ability to stabilise sunflower oil, oil-in-water (o/w) emulsions at three different pHs (3.0, 5.0 and 8.0). Emulsion microstructure was characterised by droplet size distribution (DSD) and optical microscopy, and resulting rheological properties were assessed. Smaller droplet sizes and better rheological properties (G′ and G″) were obtained at pH 3.0 and 8.0, i.e., at pH values away from the isoelectric point (pH 5.0). The in vitro bioactive properties of the emulsions at pH 3.0, 5.0 and 8.0 were tested using the ferric-reducing antioxidant power (FRAP) and the oxygen radical absorbance capacity (ORAC) antioxidant assays. The angiotensin converting enzyme (ACE) and dipeptidyl peptidase IV (DPP-IV) inhibitory activities were also determined. The highest antioxidant activity was observed when the emulsions were generated at pH 8.0 with FRAP and ORAC values of 935.7 ± 151.5 and 368.8 ± 2.3 μmol Trolox Eq. · g−1 of emulsion, respectively. Overall, the emulsions were poor inhibitors of ACE and DPP-IV. However, subjection of the emulsions to in vitro simulated gastro-intestinal digestion (SGID) released peptides which increased ACE and DPP-IV inhibitory activity (67.4 ± 2.7% and 11.2 ± 1.1%, respectively, for emulsions generated at pH 8). The emulsions generated at pH 3.0 displayed the lowest extent of lipid oxidation following 15 d storage. These results show the capability of FB protein concentrate to stabilise o/w emulsions while also demonstrating antioxidant along with ACE and DPP-IV inhibitory properties following gastrointestinal digestion.

Charging, aggregation, and aggregate strength of humic substances in the presence of cationic surfactants: Effects of humic substances hydrophobicity and surfactant tail length

The binding of natural organic matters (NOM) with organic cations and resulting changes in charging and aggregation of NOMs are important in water science and technology such as the enhanced settling by flocculation and the fate control of contaminants. We measured the electrophoretic mobility and aggregate strength of humic substances (HSs), Suwannee river fulvic acid (SRFA) and Leonardite humic acid (LHA), in the presence of cationic surfactants, cetylpyridinium chloride (CPC) and dodecylpyridinium chloride (DPC), to clarify the effects of carbon content, aromaticity of HSs, and the tail length of cationic surfactants on the charging and aggregation. Both of HSs showed charge reversal in the presence of 0.1 - 0.3 mM CPC and LHA in 1 and 2 mM DPC. The iso-electric point (IEP) pH of LHA-CPC and SRFA-CPC system was higher than that of LHA-DPC system, though more DPC concentration was needed for the charge reversal of LHA in DPC. We also observed pronounced aggregation of both HSs in CPC systems around IEP pH, though LHA in higher DPC concentration showed wider range of aggregation pH including IEP pH than the range at low DPC concentration. The maximum strength of LHA aggregate was higher, around 27.6 nN in LHA-CPC system and 19.1 nN in LHA-DPC system, than that of 5.2 nN in SRFA-CPC system. This higher value of aggregate strength in LHA-CPC system than others indicates more hydrophobic interaction in LHA-CPC system. The maximum strength around IEP pH in all the systems indicates the presence of electrostatic interactions along with hydrophobic and other non-DLVO forces.

Effects of Heating Time and Temperature on Functional Properties of Proteins of Yellow Mealworm Larvae (Tenebrio molitor L.).

Although the yellow mealworm (Tenebrio molitor L.) is a promising alternative protein source, the effects of processing conditions on functional properties are unclear. In this study, a protein extract of yellow mealworm larvae (PEYM) was subjected to different heat temperature (55°C, 75°C, and 95°C) with different time (20, 40, and 60 min) to evaluate the functional properties and protein oxidation. Different heat temperature treatment significantly affected the exposure of surface hydrophobicity of the proteins and protein molecule aggregation, which reached maximum levels at 95°C for 60 min. Protein oxidation was inversely proportional to the temperature. Both the highest carbonyl value (1.49 nmol/mg protein) and lowest thiol value (22.94 nmol/mg protein) were observed at 95°C for 60 min. The heating time-temperature interaction affected several functional properties, including solubility, emulsifying potential, and gel strength (GS). Solubility decreased near the isoelectric point (pH 5 to 6). As the temperature and heating time increased, emulsifying properties decreased and GS increased. The oil absorption capacity and foaming properties decreased and the water absorption capacity increased. These results confirmed that PEYM is a suitable source of proteins for processing and applications in the food industry.

Aggregation of ferrihydrite nanoparticles: Effects of pH, electrolytes,and organics

To better understand the fate and transport of ferrihydrite nanoparticles (FNPs), which carry many contaminants in natural and engineered aquatic environments, the aggregation of FNPs was systematically investigated in this study. The pH isoelectric point (pHIEP), surface zeta potential, and particle size evolutions of FNPs were measured under varied aqueous conditions using dynamic light scattering (DLS). The influence of pH (5.0 ± 0.1 and 7.0 ± 0.1), ionic strength (IS), electrolytes (NaCl, CaCl2 and Na2SO4), and organics (humic acid, fulvic acid and CH3COONa) on the aggregation behaviors of FNPs were explored. Meanwhile, Derjaguin-Landau-Verwey-Overbeek (DLVO) theory was employed to better understand the controlling mechanisms of FNP aggregation. In the presence of sulfate, the surface charge of FNPs was neutralized under varied pH and ionic strength due to ion adsorption and FNPs phase transformation to schwertmannite based on FT-IR results. This phase transformation resulted in rapid aggregation in all water chemistries tested, whereas other salt species affected the aggregation primarily by ion adsorption and charge screening. Presence of increasing concentrations of the organic acids significantly shifted the pHIEP of FNPs (7.0 ± 0.2) to lower pH (< 4.0) due to adsorption of organics on FNPs surfaces making them negatively charged. The adsorption of HA/FA inhibited FNP aggregation significantly while CH3COONa did not, due to different effects on steric and/or electrosteric interactions among FNPs by organics with varied pKa values and molecular weights. After accounting for the important effects of pH, electrolytes, and organics in modifying FNPs’ surface charge, DLVO calculations agreed well with measured critical coagulation concentrations (CCC) values of FNPs at both pH 5.0 ± 0.1 and 7.0 ± 0.1 in the presence of NaCl. This study will hence be useful to better predict and control the fate and transport of FNPs in the presence of electrolytes and organics with different molecular weights, as well as the fate of the associated contaminants in natural and engineered systems.

Physicochemical Response of Gelatin in a Coulombic Soup of Monovalent Salt: A Molecular Simulation and Experimental Study.

The effect of salt on the static properties of aqueous solution of gelatin is studied by molecular dynamics simulation at pH = 1.2, 7, and 10. At the isoelectric point (pH = 7), a monotonic increase in size of the polymer is obtained with the addition of sodium chloride ions. In the positive polyelectrolyte regime (pH = 1.2), collapse of gelatin is observed with increase in salt concentration. In the negative polyelectrolyte regime, we observe an interesting collapse-reexpansion behavior. This is due to the screening of repulsion between the excess charges followed by the screening of attraction of oppositely charged ions as the salt concentration is increased. This mechanism is very different from the charge inversion mechanism which causes the reexpansion in the presence of multivalent ions. The location of salt concentration corresponding to the minimum size of the chain is comparable to the theoretical estimate. The shift in the peak of radial distribution function calculated between monomers and salt ions confirms this spatial reorganization. The predictions from the simulation are verified by dynamic light scattering(DLS) and small-angle X-ray scattering (SAXS) experiments. The size of the hydrodynamic "clusters" obtained from DLS confirms the simulation predictions. Persistence length of the gelatin is calculated from SAXS to get single chain statistics, which also agrees well with the simulation results.

ISOLASI PROTEIN DAN PRODUKSI KONSENTRAT PROTEIN DAUN (KPD) SEBAGAI SUPLEMEN PAKAN TERNAK

The research aim to determine the effect of extraction using various combination of pH alkaline-acid to protein and amino acid content of Lamtoro Protein Concentrate Leaf (LPCL). Completely Randomized Design (CRD) with 3 treatments and 5 replications. The Lamtoro Leaf Meal (LLM) (50 gram) was blended in NaOH (200 ml) for 15 menit and centrifuged to separate the supernatant from extracted LLM. The extracted LLM was re-extracted with buffer acetat pH 4,6 and sentrifuged again to separate supernantant from extracted LLM. Both supernatant from NaOH and buffera acetat pH 4,6 extraction were mixed and precipitated with buffer phospat until isoelectric point. The treatments were tested consisted of extracted with NaOH pH 8, NaOH pH 9 and NaOH pH 10. The parameters measured; isoelectric point at precipited, crude protein, total amino acid (TAA), total essential amino acid (TEAA) and individual amino acid. The results showed that the precipited obtained isoelectric point pH 7 was 2.66; 1.03 and 2.58 gram at the extraction treatments using NaOH at pH 8, 9 and 10, respectively. LPCL extracted using NaOH at pH 9 and 10 contained a high crude protein of 54.82 and 52.60% higher than the extraction using NaOH at pH 8 of 46.98%. The total amount of amino acid and essential amino acid (AAE) of LPCL were highest in treatment using NaOH at pH 10 of 26,58; 13.31 %, respectively. Combination extraction LLM using pH buffer 10 followed by re-extract using acetate buffer pH 4,6 contains crude protein and good essential amino acid, especially leucine. Conclution of the research that the combination extraction using NaOH at pH 10 and followed by re-extract using acetate buffer at pH 4.6 is the best treatment contain crude protein and essential amino acid at LPCL.&#x0D; Keywords : Crude protein, essential amico acid, extraction.

Comparative characterization of protein and lipid fractions from camel and cow milk, their functionality, antioxidant and antihypertensive properties upon simulated gastro-intestinal digestion

In-depth characterization of protein and lipid fractions from cow and camel milk (four breeds; CM-1 to 4), their functional and thermal properties and bioactivity upon simulated gastro-intestinal digestion was reported. Results revealed that proteins from cow and camel milk showed a noticeable separation on sodium dodecyl sulphate-polyacrylamide gel electrophoresis and high-performance liquid chromatography. Functional properties of whole milk proteins from cow and camel milk at different pH revealed that emulsifying activity index (EAI), foaming capacity (FC) and protein solubility was higher towards acidic and alkaline pH and lowest at isoelectric point (pH = 4). Moreover, the water absorption capacity (WAC) and solubility in water were higher in milk from cow (CW) compared to those from camel breeds (CM 1–4). Camel milk, which contains lower saturated and higher unsaturated fatty acids and demonstrated higher antioxidative and angiotensin-1 converting enzyme (ACE) inhibitory potential compared to cow milk upon simulated gastro-intestinal digestion, can be considered as a healthier option.

Removal of strontium from simulated low-level radioactive wastewater by nanofiltration.

The performance of different nanofiltration (NF) membranes for the treatment of strontium-containing radioactive wastewater was investigated. The effects of the initial strontium concentration, solution pH and complexation phenomena on strontium removal were described. For all the three membranes, the strontium rejection increased with decreasing initial strontium concentration. Meanwhile, the strontium rejection was minimum at the membrane isoelectric point (pH 5) primarily due to decreased co-ion electrostatic repulsion. In the presence of a complexing agent (polyacrylic acid or ethylenediamine tetraacetic acid disodium salt), the strontium rejection was generally higher than those obtained without a complexing agent for NF 270 and XN 45. Membrane cleaning experiments were also conducted to recover the performance of the membranes, which exhibited degradation during long-time filtration. The performance of the membranes after cleaning was close to that of the virgin membranes, especially for XN 45, whose recovery percentage was nearly 100%.

Modulation of physical properties of microfluidized whey protein fibrils with chitosan

There is an increasing market for food and beverage products enriched in proteins and dietary fibers due to their potential health benefits. In this study, the effect of heating (85 °C, 20 min), microfluidization (20,000 psi), and pH (2 to 6.5) on the physicochemical properties of aqueous solutions containing mixtures of whey protein fibrils (7.5%; WPF) and chitosan (0.5%; CN) were examined. Heating of the mixed systems increased their turbidity and apparent viscosity, which was attributed to the formation of protein-rich particles. Interestingly, heating the mixed systems and then applying microfluidization led to phase separation and a lower apparent viscosity, which was attributed to high-pressure disruption of the whey protein fibrils. The pH of the systems significantly influenced their appearance, turbidity, particle size, and apparent viscosity, with high turbidity and viscosity, and large particle size occurring from pH 3.5 to 5.5. These effects were attributed to protein aggregation close to its isoelectric point (pH 5) coupled with electrostatic attraction between anionic groups on the whey protein and cationic groups on the chitosan. The addition of chitosan increased the net isoelectric point from pH 5 for pure whey protein to pH 6 for the mixed system. Overall, this study showed that the appearance and rheological properties of protein-dietary fiber mixtures could be manipulated by heating, microfluidization, and pH adjustment. This information may be useful for designing protein and fiber enriched food and beverage products with desirable physical and sensory properties.

New Polyampholyte Polymers Based on Polypropylene Glycol Fumarate with Acrylic Acid and Dimethylaminoethyl Methacrylate

The possibility of preparing new polyampholyte polymers based on polypropylene glycol fumarate–acrylic acid–dimethylaminoethyl methacrylate terpolymers was demonstrated. The main relationships of radical terpolymerization in dioxane, including binary systems participating in the terpolymerization, were studied. The block lengths, transition probabilities, and Harwood block structure parameter were calculated for the terpolymers from the copolymerization constants for the binary systems. These parameters reflect the arrangement of the macroradicals in the chain. The morphology of the polymer surface was studied by scanning electron microscopy, and the surface pore size was estimated. The influence of organic solvents and pH on the sample swelling was studied, and the isoelectric point (pH 6.00) of the terpolymer was determined.

Properties and Stability of Perilla Seed Protein-Stabilized Oil-in-Water Emulsions: Influence of Protein Concentration, pH, NaCl Concentration and Thermal Treatment.

Perilla seed protein (PSP) was extracted from defatted perilla seed meal and applied in oil-in-water (O/W) emulsions as an emulsifier. We investigated the influences of protein concentration (0.25–1.5 wt %), pH (3.0–9.0), NaCl concentration (0–350 mmol/L) and thermal treatment (70–90 °C, 30 min) on the physical characteristics of O/W emulsions, including volume-average diameter, ζ-potential, interfacial protein concentration, microstructure and so on. Results showed that increasing PSP concentration would decrease the d4,3 and a 1.0 wt % PSP concentration was sufficient to ensure the stability of emulsion. Under pH 3.0–9.0, emulsions were stable except at pH 3.0–5.0 which was proximal to the isoelectric point (pH 4.5) of PSP. At high NaCl concentrations (250–350 mmol/L), the emulsions exhibited relatively lower absolute ζ-potential values and a large number of aggregated droplets. A moderate thermal treatment temperature (e.g., 70 °C) was favorable for the emulsion against aggregation and creaming. However, when 90 °C thermal treatment was performed, a clear layer separation was observed after 2 weeks storage and the emulsion showed a poor stability. The findings of this work are of great importance for the utilization and development of PSP as an emulsifier for food emulsions.

Interactions and emulsifying properties of ovalbumin with tannic acid

Ovalbumin (OVA) is a good emulsifier; however, its emulsifying properties are easily affected by food components. In this study, tannic acid (TA) was used as a model polyphenol to interact with OVA. The OVA-TA complexes were characterized with circular dichroism, dynamic light scattering and interfacial tension measurements. The emulsions stabilized by OVA and OVA-TA were analysed by droplet size measurements. The results indicated that TA could bind well with OVA. Generally, the surface activity of OVA decreased after binding with TA due to the sheltering of the hydrophobic groups of OVA, decreasing the emulsion capacity of OVA. However, the particle size and interfacial tension of the OVA-TA complexes at pH 5.0 were significantly smaller than those of free OVA due to reduced aggregation from increased electrostatic repulsions. Therefore, the stabilities of the emulsions containing TA were improved at pH values near the isoelectric point (pH 4.75) of OVA. Heat treatment decreased the particle sizes of OVA-TA. On the other hand, heating could increase the interfacial tension, decreasing the emulsifying properties of OVA. Our work provides new insights into the influence of polyphenols on the emulsion efficiency of OVA.

Storage stability of minced beef supplemented with chickpea legumin at 4 °C as a potential substitute for nisin

Chickpea legumin has a high molecular weight (300 KDa), consists of 5 subunits (25–45 KDa) and has a relatively high isoelectric point (pH 6.5). It could inhibit the growth of four bacteria strains (Staph. aureus, P. aeruginosa, E. coli and B. subtilis), grown in agar (MIC = 100–150 g/ml) and bring the liquid bacterial growth to their minimum levels after 24 h of incubation using 1 MIC. Transmission electron microscopy micrographs of Staph. aureus (Gram positive) and P. aeruginosa (Gram negative) treated by 150 μg/ml chickpea legumin (1 MIC) showed cellular swelling and cell membrane disintegration explaining the mode of action of this protein. Minced beef samples supplemented with 200 μg/g chickpea legumin extended the storage time to 14–15 days instead of 7–8 days in case of un-supplemented control and 10–11 days in case of nisin, reducing the total viable count by 2.6–2.9 log compared to control against a reduction of 1.6 log in case of nisin.