Dodecyl Sulfate-polyacrylamide Gel Electrophoresis Patterns Research Articles

Angiotensin-I-Converting Enzyme (ACE)-Inhibitory Peptides from the Collagens of Monkfish (Lophius litulon) Swim Bladders: Isolation, Characterization, Molecular Docking Analysis and Activity Evaluation.

The objective of this study was to isolate and characterize collagen and angiotensin-I-converting enzyme (ACE)-inhibitory (ACEi) peptides from the swim bladders of monkfish (Lophius litulon). Therefore, acid-soluble collagen (ASC-M) and pepsin-soluble collagen (PSC-M) with yields of 4.27 ± 0.22% and 9.54 ± 0.51%, respectively, were extracted from monkfish swim bladders using acid and enzyme methods. The ASC-M and PSC-M contained Gly (325.2 and 314.9 residues/1000 residues, respectively) as the major amino acid, but they had low imino acid content (192.5 and 188.6 residues/1000 residues, respectively) in comparison with collagen from calf skins (CSC) (216.6 residues/1000 residues). The sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) patterns and ultraviolet (UV) absorption spectrums of ASC-M and PSC-M illustrated that they were mainly composed of type I collagen. Subsequently, three ACEi peptides were isolated from a PSC-M hydrolysate prepared via a double-enzyme system (alcalase + neutrase) and identified as SEGPK (MHP6), FDGPY (MHP7) and SPGPW (MHP9), with molecular weights of 516.5, 597.6 and 542.6 Da, respectively. SEGPK, FDGPY and SPGPW displayed remarkable anti-ACE activity, with IC50 values of 0.63, 0.94 and 0.71 mg/mL, respectively. Additionally, a molecular docking assay demonstrated that the affinities of SEGPK, FDGPY and SPGPW with ACE were -7.3, -10.9 and -9.4 kcal/mol, respectively. The remarkable ACEi activity of SEGPK, FDGPY and SPGPW was due to their connection with the active pockets and/or sites of ACE via hydrogen bonding, hydrophobic interaction and electrostatic force. Moreover, SEGPK, FDGPY and SPGPW could protect HUVECs by controlling levels of nitric oxide (NO) and endothelin-1 (ET-1). Therefore, this work provides an effective means for the preparation of collagens and novel ACEi peptides from monkfish swim bladders, and the prepared ACEi peptides, including SEGPK, FDGPY and SPGPW, could serve as natural functional components in the development of health care products to control hypertension.

Insight into Ionic Strength-Induced Solubilization of Myofibrillar Proteins from Silver Carp (Hypophthalmichthys molitrix): Structural Changes and 4D Label-Free Proteomics Analysis.

In this study, changes in the physical, structural, and assembly characteristics of silver carp myofibrillar proteins (MPs) at different ionic strength (I) values were investigated. Moreover, the differential proteomic profile of soluble MPs was analyzed using 4D proteomics based on timsTOF Pro mass spectrometry. Solubility of MPs significantly increased at high I (>0.3), and the increase in I enhanced the apparent viscosity, fluorescence intensity, surface hydrophobicity, and α-helix content of MPs solution. Particle size and sodium dodecyl sulfate-polyacrylamide gel electrophoresis patterns also supported the solubility profiles. Transmission electron microscopy and atomic force microscopy observations revealed the morphological assembly and disassembly of MPs under different I conditions. Finally, proteomic analysis revealed the evolution law of salt-induced solubilization of MPs and the critical molecular characteristics in different I environments. The number of differentially abundant proteins (DAPs) decreased with the increase of I, and most DAPs related to the muscle filament sliding, contraction and assembly, actinin binding, and actin filament binding. The soluble abundance of myosin and some structural proteins was dependent on I, and structural proteins in the Z-disk and M-band might contribute to the solubilization of myosin. Our findings provide insightful information about the impact of common I on the solubility pattern of MPs from freshwater fish.

Silver carp scale gelatins for the stabilization of fish oil-loaded emulsions

Herein, three types of silver carp scale gelatins were extracted, and their molecular weight distribution, structural properties, functional properties and emulsifying properties were investigated and discussed. Acetic acid-extracted gelatin (AAG), hot water-extracted gelatin (HWG), and pepsin enzyme-extracted gelatin (PEG) showed similar and four clear bands in sodium dodecyl sulfate-polyacrylamide gel electrophoresis pattern, whereas they showed different β chain amounts and β-sheet percentages. The water-holding capacity values (g/g of gelatin) were: AAG (16.8 ± 1.1) > HWG (14.0 ± 0.7) ≈ PEG (13.5 ± 1.6). The fat-binding capacity values (g/g of gelatin) were: AAG (11.8 ± 0.3) > HWG (9.5 ± 1.3) > PEG (5.3 ± 0.4). Emulsion droplet sizes and creaming index values decreased with the increase of gelatin concentrations for all the fish oil-loaded emulsions stabilized by three types of gelatins. Compared with PEG, AAG and HWG show similar and higher emulsion stability at high gelatin concentration (10 mg/mL). The stabilization mechanism of fish oil-loaded silver carp scale gelatin-stabilized emulsions involved an “extraction method-protein molecular weight distribution-protein molecular structure-molecular interaction-emulsibility-droplet structure-emulsion stability” route. This work would be beneficial for the research on the relationship of structure and function of gelatin and to the comprehensive utilization of aquatic products.

Expression of Drosophila melanogaster acetylcholinesterase (DmAChE) gene splice variants in Pichia pastoris and evaluation of its sensitivity to organophosphorus pesticides

Acetylcholinesterase (AChE) is a key enzyme used to detect organophosphorus pesticide residues by the enzyme inhibition method. An accidental discovery of a mutant strain with AChE activity was made in our laboratory during the process of AChE expression by Pichia pastoris. The pPIC9K-Drosophilamelanogaster acetylcholinesterase (DmAChE)-like expression vector was constructed by codon optimization of this mutant strain, which was transformed into P. pastoris GS115, and positive clones were selected on yeast peptone dextrose (YPD) plate with G418 at 4.0 mg/mL. The GS115-pPIC9K-DmAChE-like strain was subjected to 0.5% methanol induction expression for 120 h, with a protein band at 4.3 kDa found by the tricine-sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) pattern of the fermentation supernatant. After preliminary purification by ammonium sulfate precipitation, the enzyme activity was detected to be 76.9 U/(mL⋅min). In addition, the pesticide sensitivity test proved that DmAChE-like is selective and sensitive to organophosphorus pesticides.

Novel Modification of Collagen: Realizing Desired Water Solubility and Thermostability in a Conflict-Free Way.

Because of poor water solubility and low thermostability, the application of collagen is limited seriously in fields such as injectable biomaterials and cosmetics. In order to overcome the two drawbacks simultaneously, a novel bifunctional modifier based on the esterification of polyacrylic acid (PAA) with N-hydroxysuccinimide (NHS) was prepared. The esterification degree of PAA-NHS esters was increased upon increasing the NHS dose, which was confirmed by Fourier-transform infrared (FTIR) and nuclear magnetic resonance spectrascopy. FTIR results indicated that the triple helix of the modified collagens remained integrated, whereas the molecular weight became larger, as reflected by the sodium dodecyl sulfate–polyacrylamide gel electrophoresis pattern. The modified collagens displayed excellent water solubility under neutral condition, owing to lower isoelectric point (3.1–4.3) than that of native collagen (7.1). Meanwhile, denaturation temperatures of the modified collagens were increased by 4.8–5.9 °C after modification. The modified collagen displayed hierarchical microstructures, as reflected by field-emission scanning electron microscopy, while atomic force microscopy further revealed a “fishing net-like” network in the nanoscale, reflecting a unique aggregation behavior of collagen macromolecules after modification. As a whole, the PAA-NHS ester as a bifunctional modifier endowed collagen with desired water solubility and thermostability in a conflict-free manner, which was beneficial to the process and application of the water-soluble collagen.

Extraction of crude gelatin from duck skin: effects of heating methods on gelatin yield

The disposal of by-products of duck production, including duck skin, is a serious concern as it results in environmental pollution. The objectives of this study were to investigate the optimal pretreatment conditions for swelling duck skin and their extraction methods as a novel source. Gelatin was extracted using water bath, sonication, superheated steam, and microwave extraction methods. The gelatin extraction yield and gelatin powder yield were the highest with the superheated steam extraction method. The melting point and gel strength of gelatin extracted using the superheated steam method were the lowest. The viscosity of gelatin extracted with the superheated steam and microwave extraction methods was higher than that of gelatin extracted with the other methods. The sodium dodecyl sulfate-polyacrylamide gel electrophoresis patterns of gelatin extracted using the superheated steam and microwave extraction methods showed more intense bands than those of gelatin extracted using the other methods. Our results showed that gelatin extracted from duck skin using the superheated steam extraction method had optimal physical properties and therefore can be used in meat products.

Electroextraction of Insoluble Proteins from the Organic Matrix of the Nacreous Layer of the Japanese Pearl Oyster, Pinctada fucata.

The nacreous layer of shells and pearls is composed of aragonite crystals arranged in an organic matrix. The organic matrix contains chitin and several proteins that regulate the formation of the nacreous layer. Owing to their strong interactions in the organic matrix, the current method for extraction of insoluble proteins from the pre-powdered nacreous layer involves heating to high temperatures in the presence of a detergent (e.g., sodium dodecyl sulfate, SDS) and reductant (e.g., dithiothreitol, DTT), which is likely to induce protein degradation. Therefore, we have developed an electroextraction method to isolate proteins from the organic matrix of a nacreous organic sheet, that was obtained following the decalcification of shells in their original shape. Our electroextraction method employs milder conditions without heating or detergent. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) patterns of the electro-extracted proteins (EEPs) under non-reduced and reduced conditions revealed that this method yielded a greater number of different proteins compared with the conventional extraction method and the isolated EEPs retained their disulfide bonds. Our method is able to easily extract insoluble proteins from the nacreous layer under mild conditions and will undoubtedly aid future analyses into the functions of the nacreous layer proteins.

Ca2+- and Mg2+-Induced Conformational and Rheological Changes of Actomyosin Extracted from Fresh and Freeze-Thaw Tilapia

ABSTRACTThe conformational changes of natural actomyosins prepared from fresh and freeze-thaw tilapia (Oreochromis niloticus) in the presence of Ca2+ or Mg2+ were investigated. The Ca2+-activated adenosine triphosphatase (Ca2+-ATPase) activities of actomyosins extracted from fresh and freeze-thaw fish were comparable (p > 0.05). The denaturation temperatures (Td) of actomyosins extracted from fresh fish were lower than those from freeze-thaw counterparts (p < 0.05). The addition of Ca2+ or Mg2+ reduced the Td of actomyosins. Ca2+ and Mg2+ enhanced protein aggregation at ≥ 40°C (p < 0.05). Based on the sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) pattern, the myosin heavy chain (MHC) and actin bands tended to form large aggregates to a greater extent in the presence of 100mM Ca2+ or Mg2+. Ca2+ and Mg2+enhanced disulfide linkages and hydrophobic interactions among actomyosin molecules. The onset temperature of elastic modulus (G′) of both actomyosins was shifted to lower temperature as 100mM of Ca2+ or Mg2+ was added. Mg2+ at 20mM increased the breaking force of washed tilapia mince at 40°C. Our results revealed that the intrinsic properties of actomyosins extracted from fresh and frozen fish were distinct, and divalent ions Ca2+ or Mg2+ affected their gelation differently.

Small Molecular Weight Soybean Protein-Derived Peptides Nutriment Attenuates Rat Burn Injury-Induced Muscle Atrophy by Modulation of Ubiquitin-Proteasome System and Autophagy Signaling Pathway.

This article describes results of the effect of dietary supplementation with small molecular weight soybean protein-derived peptides on major rat burn injury-induced muscle atrophy. As protein nutrients have been previously implicated to play an important role in improving burn injury outcomes, optimized more readily absorbed small molecular weight soybean protein-derived peptides were evaluated. Thus, the quantity, sodium dodecyl sulfate polyacrylamide-gel electrophoresis patterns, molecular weight distribution, and composition of amino acids of the prepared peptides were analyzed, and a major full-thickness 30% total body surface area burn-injury rat model was utilized to assess the impact of supplementation with soybean protein-derived peptides on initial systemic inflammatory responses as measured by interferon-gamma (IFN-γ), chemokine (C-C motif) ligand 2 (CCL2, also known as MCP-1), chemokine (C-C motif) ligand 7 (CCL7, also known as MCP-3), and generation of muscle atrophy as measured by tibialis anterior muscle (TAM) weight relative to total body weight. Induction of burn injury-induced muscle atrophy ubiquitin-proteasome system (UPS) signaling pathways in effected muscle tissues was determined by Western blot protein expression measurements of E3 ubiquitin-protein ligase TRIM-63 (TRIM63, also known as MuRF1) and F-box only protein 32 (FBXO32, also known as atrogin-1 or MAFbx). In addition, induction of burn injury-induced autophagy signaling pathways associated with muscle atrophy in effected muscle tissues was assessed by immunohistochemical analysis as measured by microtubule-associated proteins 1 light chain 3 (MAP1LC3, or commonly abbreviated as LC3) and beclin-1 (BECN1) expression, as well as relative induction of cytoplasmic-liberated form of MAP1LC3 (LC3-I) and phagophore and autophagosome membrane-bound form of MAP1LC3 (LC3-II), and BECN1 protein expression by Western blot analysis. Nutrient supplementation with small molecular weight soybean protein-derived peptides resulted a significant reduction in burn injury-induced inflammatory markers, muscle atrophy, induction of TRIM63 and FBXO32 muscle atrophy signaling pathways, and induction of autophagy signaling pathways LC3 and BECN1 associated with muscle atrophy. These results implicated that small molecular weight soybean-derived peptides dietary supplementation could be used as an adjunct therapy in burn injury management to reduce the development or severity of muscle atrophy for improved burn patient outcomes.

Effect of Setting Condition on the Gel-Forming Ability of Rohu

ABSTRACTTo investigate the setting condition of the gel-forming ability of rohu, optimum setting temperature for strong and weak gels of unwashed and washed rohu gel and optimum setting time for maximum proteolytic activity were investigated. Nine setting temperatures were studied for textural properties and trichloroacetic acid (TCA)-soluble peptide contents. Both unwashed gel (UW-gel) and washed gel (W-gel) showed similar optimum setting conditions for producing a strong gel that was set at 40°C for 30 min, followed by heating at 90°C for 20 min. They displayed different optimum setting conditions for weak gel. Weak gel from the degradation of UW-gel and W-gel formed at 65 and 60°C, respectively. The occurrence of protein degradation of W-gels during setting at 60°C suggested that washing did not remove the endogenous protease, and the degradation of unwashed and washed mince was due to water-soluble protease and myofibril-bound protease, respectively. Eight setting times for maximum proteolytic activity were shown by the TCA-soluble peptide contents, accompanying the sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) pattern. Both gels had similar results for setting for 120 min.

Protein denaturation and oxidation in chilled hairtail (Trichiutus haumela) as affected by electrolyzed oxidizing water and chitosan treatment

ABSTRACTThe effect of chitosan (CH) coating combined with electrolyzed oxidizing water (EOW) on microbiological and physicochemical of hairtail (Trichiutus haumela) was evaluated during 15 days of storage at −3°C. Hairtail samples treated by EOW combined with 1.5% (w/v) CH were compared with samples soaked in single material. For storage of 15 days, the thiobarbituric acid value of hairtails increased steadily to 1.79, 1.52, 1.48 mg/100g (p < 0.05) in the EOW, CH, and EOW+CH group, respectively. All of these were significantly lower than that of the control group (2.01 ± 0.04 mg malonaldehyde/100g; p < 0.05). Microbiological results, total volatile basic nitrogen, pH, and peroxide value also revealed that EOW and CH significantly retarded hairtail spoilage. The sodium dodecyl sulfate–polyacrylamide gel electrophoresis pattern of sarcoplasmic proteins revealed CH+EOW could slow down the protein deterioration of fillet. In this study, CH coating combined with EOW effectively extended the shelf life of hairtail to 6–7 days.

Freeze concentration of proteins in Antarctic krill wash water

Water-washing removes fluoride from Antarctic krill but produces large volumes of wash water containing water- soluble proteins and fluoride. The freeze concentration method was tested to determine if it could be used to recover water-soluble proteins while leaving the fluoride in solution. After freezing and thawing the wash water, protein and fluoride contents of the thawed fractions were determined to explore the melting regularity of components in the wash water. The highest concentration factors of protein and fluoride were obtained after 80 min of thawing, such as 1.48 ± 0.06 and 1.35 ± 0.04 times, respectively. The free amino-nitrogen (FAN) content and sodium dodecyl sulfate-polyacrylamide gel electrophoresis pattern results revealed that the highest concentrations of all ingredients were obtained after 80 min of the process. The degree of hydrolysis of all fractions from the thawing process fluctuated in a narrow range around 12% during the entire process, indicating that the thawing order did not change with various proteins or time during the entire thawing course. These results demonstrate that the freeze concentration method can be used to concentrate protein solutions, even those with fluoride. It was concluded that condensation was achieved and no ingredient could be separated, regardless of fluoride, amino acids, or different proteins in the water.

Influence of spray drying temperatures and storage conditions on physical and functional properties of dried egg white

ABSTRACTThis study investigated the effect of spray drying inlet temperatures (140, 160 and 180°C) and storage conditions (temperature; 25 and 40°C and storage period; 1 and 2 months) on the physical and functional properties of dried egg white. The results showed that the three inlet temperatures did not affect the color of the spray-dried egg white (SDEW) after drying. However, all SDEWs increased in yellow color after storage at 40°C. The solubility (%) of SDEW and gelling properties including gel hardness and water holding capacity of the gel samples were changed when the dried samples were stored, particularly for SDEW drying at 180°C. The changes in gelling properties of the SDEW were related to a decrease in the enthalpy of protein denaturation, an increase in exposed sulfhydryl (SH) contents, a decrease in the total SH contents and the occurrence of protein aggregation as shown by the sodium dodecyl sulfate-polyacrylamide gel electrophoresis pattern.

Effect of Barley β-Glucan on the Gluten Polymerization Process in Dough during Heat Treatment.

Barley (Hordeum vulgare L.) β-glucan (BBG) is of interest as a result of its health benefits, but BBG presents significant disruptions on the gluten network, with a negative impact on food texture. To clarify the interaction between BBG and gluten in dough, the dynamic rheological, thermochemical process of gluten and microstructure of dough with BBG during heating were detected. The results showed that BBG delayed the gluten thermopolymerization reaction during heating and affected polymerization of specific molecular weight protein subunits. These impacts depended upon the heating temperature and time. When heating under 25-65 °C, tan δ of the dough reached the highest level at the BBG concentration of 1%. However, under the temperature of 65-95 °C, tan δ was positively correlated with the BBG content (0-3%). The differential scanning calorimetry curves revealed that the peak temperature (TP) of the two endothermic peaks increased by 3.86 and 3.10 °C. Size-exclusion high-performance liquid chromatography analysis showed that BBG mainly affected the peak area of gliadin and glutenin. Furthermore, after 3% BBG was added, the bands of 59.8 and 64.9 kDa in sodium dodecyl sulfate-polyacrylamide gel electrophoresis patterns delayed, vanishing for 120 s when heating at 95 °C. Therefore, BBG delayed the polymerization reaction of specific molecular weight protein subunits rather than all of the proteins.

Color and gelling properties of dried egg white: Effect of drying methods and storage conditions

ABSTRACTDried egg white is extensively used as a food ingredient due to its unique functional properties and extensive shelf life. This study investigated the effect of drying methods and storage conditions on the color and gelling properties of dried egg white. Egg white was dried with two drying methods; freeze drying and hot-air drying, then stored at 25 and 40°C for 4 months. The result showed that the color of hot-air-dried egg white, especially after storage at 40°C, was darker yellow than for freeze-dried egg whites. The gelling properties of both samples were altered during storage, however, substantial changes in the gelling properties were found in the gel made from stored hot-air-dried egg white. A decrease in the enthalpy of protein denaturation that indicated a partially unfolded protein conformation, an increase in exposed sulfhydryl and a decrease in the total sulfhydryl contents were found, especially in stored samples of hot-air-dried egg whites. The sodium dodecyl sulfate-polyacrylamide gel electrophoresis pattern of proteins in the stored samples showed protein aggregation, and this was related to the increased glass transition temperature. This study revealed that drying egg white using hot-air drying and storage especially at high temperature induced changes in their color and protein conformation. These have contributed to protein aggregation which affected dried egg white’s gel properties.

Protective Effects of Maillard Reaction Products of Whey Protein Concentrate against Oxidative Stress through an Nrf2-Dependent Pathway in HepG2 Cells.

Whey protein concentrate (WPC), which contains α-lactalbumin and β-lactoglobulin, is utilized widely in the food industry. The Maillard reaction is a complex reaction that produces Maillard reaction products (MRPs), which are associated with the formation of antioxidant compounds. In this study, the hepatoprotection activity of MRPs of WPC against oxidative stress through the nuclear factor-E2-related factor 2 (Nrf2)-dependent antioxidant pathway in HepG2 cells was examined. Glucose-whey protein concentrate conjugate (Glc-WPC) was obtained from Maillard reaction between WPC and glucose. The fluorescence intensity of Glc-WPC increased after 7 d compared to native WPC, and resulted in loss of 48% of the free amino groups of WPC. The sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) patterns of Glc-WPC showed the presence of a high-molecular-weight portion. Treatment of HepG2 cells with Glc-WPC increased cell viability in the presence of oxidative stress, inhibited the generation of intracellular reactive oxygen species by tert-butyl hydroperoxide (t-BHP), and increased the glutathione level. Nrf2 translocation and Nrf2, reduced nicotinamide adenine dinucleotide phosphate (NAD(P)H)-quinone oxidoreductase 1 (NOQ1), heme oxygenase-1 (HO-1), glutamate-L-cysteine ligase (GCL)M and GCLC mRNA levels were increased by Glc-WPC. Also, Glc-WPC increased the phosphorylation of extracellular signal-regulated kinase (ERK) 1/2 and c-Jun N-terminal kinase (JNK). The results of this study demonstrate that Glc-WPC activates the Nrf2-dependent pathway through the phosphorylation of ERK1/2 and JNK in HepG2 cells, and induces production of antioxidant enzymes and phase II enzymes.

Effect of γ-irradiation on the physicochemical properties and structure of fish myofibrillar proteins

Abstract The influence of γ-irradiation on physicochemical properties and structures of myofibrillar protein from grass crap exposed to dose up to 10 kGy was investigated. Irradiated samples exhibited decreased emulsifying property and increased surface hydrophobicity. Increasing dose resulted in decreasing free and total sulphydryl groups, decreasing myosin heavy chains in the sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) patterns. This study demonstrated that γ-irradiation decreased the myofibrillar protein ordered structure and generated the crosslinking and provided a possible reference for the identification of irradiated fish products.

Efficient recovery of whole cell proteins in Oenococcus oeni—a comparison of different extraction protocols for high-throughput malolactic starter applications

In this study, we compared different total protein extraction protocols to achieve highly efficient isolation and purification of total proteins for the specific protein profiling of Oenococcus oeni. The sodium dodecyl sulfate-polyacrylamide gel electrophoresis patterns obtained for the different extraction protocols revealed not only a qualitative similar protein pattern but also quantitative variations with different intensity bands depending on the extraction method used. The selected extraction method added with sonication proved to work extremely well and efficiently and was able to obtain a high-resolution 2-D electrophoresis (2-DE) map. Prominent spots were successfully identified by matrix-assisted laser desorption-ionization time-of-flight mass spectrometry and corresponded to 76 different proteins involved in the main metabolic pathways. The approach allowed to achieve a protein profiling specific for O. oeni from Aglianico wine with numerous characterized protein products corresponding to many different O. oeni genes and associated with main cellular pathways. Further investigations of the 2-DE protein expression profile will provide useful and interesting information on the molecular mechanisms at the protein level responsible for growth and survival of O. oeni in wine.

Effect of Temperature on Protein Compositional Changes of Big Head Carp (Aristichthys nobilis) Muscle and Exudates

Effect of cooking temperature (40–100°C) on changes in protein composition of big head carp muscle and exudate was investigated. The results showed that the proportion of salt-soluble and water-soluble proteins in cooked muscle decreased with temperature up to 50°C and 60°C, respectively. Alkali-soluble proteins content in muscle increased with increasing temperature in the range of 40–98°C, while both non-protein nitrogen (NPN) and alkali- insoluble proteins content showed no significant change. Content of soluble collagen in muscle and collagen in exudates increased with increasing temperature. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS- PAGE) patterns revealed disappearance of most muscle protein bands when the temperature reached 60°C for water-soluble proteins, and 50°C for salt-soluble proteins, but proteins with molecular weight (MW) about 37 kDa was observed when heated to 98°C. Visible β and a band of collagen in exudates were clear.

A COMPARATIVE STUDY ON THE PHYSICOCHEMICAL, FUNCTIONAL AND PROTEIN ELECTROPHORETIC PATTERN OF OSTRICH MEAT AND BEEF DURING FROZEN STORAGE

The interest for new and emerging meats is rapidly growing. Ostrich meat has many nutritional and functional properties that make it superior to other types of meats. The purpose of this research was to evaluate changes in physicochemical and functional properties of ostrich meats (m. iliofibularis) and beef (longissimus dorsi) during storage at −18C. Results showed that Warner–Bratzler shear force values, colorimetric parameters (L*, a*, b*), pH and water-holding capacity significantly decreased by increasing storage time. Nitrogen solubility index increased after 3 months and decreased thereafter. Buffering capacity, emulsifying capacity, emulsifying stability, foaming stability and cooking loss increased during 6-month storage. Slight changes in sodium dodecyl sulfate-polyacrylamide gel electrophoresis pattern of myofibrillar proteins indicate protein denaturation followed by aggregation during prolonged frozen storage. Taken together, within the parameters of the present study, it is concluded that ostrich meat has superior functional attributes compared with beef initially and during the frozen storage. PRACTICAL APPLICATIONS Because of the superior quality and functional attributes of ostrich meat as compared with beef, the food industry should be aware of possible application of this excellent source of proteins to be included in human nutrition. To achieve this goal, ostrich meat should be evaluated in terms of possible alterations in different quality attributes during various processes, including prolonged frozen storage. In this work, changes in several functional properties of ostrich meat, especially those related to proteins are evaluated.