Effect of ionic strength and temperature on interaction between fish myoglobin and myofibrillar proteins

ABSTRACT:  The effects of ionic strength (0, 0.3, and 0.6 M KCl) and temperature (4 and 25 °C) on the interaction between fish myoglobin and myofibrillar proteins were investigated in a model system. Increases in the relative content of bound myoglobin and metmyoglobin formation in myoglobin-natural actomyosin (NAM) mixtures with concurrent decreases in whiteness and Ca²⁺-ATPase activity were observed with increasing ionic strength ( P < 0.05). The relative content of bound myoglobin and the oxidation of oxymyoglobin were generally greater at 25 °C than at 4 °C ( P < 0.05). Binding of myoglobin to NAM resulted in decreased whiteness ( P < 0.05). Ca²⁺-ATPase was not affected by temperature ( P > 0.05). SDS-PAGE patterns of protein samples suggested that myoglobin-NAM interactions did not involve disulfide bonds. The formation of high-molecular-weight aggregates (>206 kDa) was observed and was more pronounced at higher ionic strength and higher temperature.     

Potential Production of Healthier Protein Isolate from Broiler Meat using Modified Acid-Aided pH Shift Process

Protein isolates from broiler meat were produced using acid-aided process (AP) with some modifications including prewashing prior to pH shift process (PW), homogenisation with 5 mM citric acid plus 8 mM CaCl₂ (CA) and homogenisation with 5 % ethanol (EA). Significant reduction of total cholesterol, nucleic acids and haemoproteins with improved protein yield and whiteness of the isolate was obtained from all modified process (p?<?0.05). CA was the most effective method in elimination of cholesterol (p?<?0.05). However, PW was the best way to remove nucleic acids and haem proteins (p?<?0.05). Among modified processes, CA gel tended to show the highest breaking force, deformation and whiteness but PW gel had the lowest expressible drip (p?<?0.05). EA possessed a negative effect on gel-forming ability. Therefore, CA or PW was a promising means to produce functional protein isolate with reduced nucleic acids, haem pigments and cholesterol.     

Thermogravimetric Analysis of a Cellulosic Fabric Incorporated by Synthetic Ammonium Magnesium Phosphate as a Flame-Retardant

We have investigated the effect of synthetic struvite (MgNH₄PO₄·6H₂o) on the flammability of a cellulosic fabric. It was synthesized by means of the multiple-bath method and deposited onto a cotton fabric. Its uniformity was ensured by means of squeeze rolls, obtaining the optimum effective add-on value of ammonium magnesium phosphate to impart flame retardancy to cotton fabric in the range of around 12 g anhydrous salt per 100 g fabric. A thermogravimetric analysis of pure cotton, treated cotton, and the salt was accomplished, and their thermograms were compared and commented upon. The results obtained fortified the chemical theory expressing the promotion of the formation of solid char rather than the formation of volatile pyrolysis products, during the fulfillment of thermal decomposition of the cellulosic substrate.     

Chemical compositions and characteristics of farm raised giant catfish (Pangasianodon gigas) muscle

Proximate composition, chemical and physical properties of dorsal, ventral and lateral line cuts of farm raised giant catfish were determined. Protein, fat and ash content of the different cuts averaged 16.88, 4.45 and 1.24 g/100 g, respectively. Dorsal contains higher protein concentrations (19 g/100 g) than other two parts (p < 0.05). Ventral showed the highest hydroxyproline content (0.83 mg/g). Differences in lipid composition and fatty acid profiles were found among different cuts with highest phospholipids in the dorsal and highest triglyceride in both ventral and lateral line (p < 0.05). All the meat cuts contained high saturated fatty acid, followed by mono- and polyunsaturated fatty acid. High muscle hardness and toughness was found in the dorsal than that in the ventral (p > 0.05). The highest content of myoglobin and total pigment in lateral line resulted in the highest redness index (a*/b*) of this part. Three major nitrogenous compositions classified based on solubility in giant catfish muscle were myofibrillar, sarcoplasmic and alkaline soluble proteins.     

Physicochemical and gelling properties of short-bodied mackerel (Rastrelliger brachysoma) protein isolate prepared using alkaline-aided process

This study demonstrated the characteristics and gel properties of short-bodied mackerel (Rastrelliger brachysoma) surimi prepared by the conventional washing process and protein isolate prepared by alkaline solubilization process without and with prewashing. A decrease in Ca²⁺-ATPase activity (P < 0.05), with changes in the tryptophan fluorescence intensity of natural actomyosin, was observed in protein isolate from alkaline solubilization process. However, higher reactive sulfhydryl (SH) content was found in protein isolate, compared with that in conventional surimi (P < 0.05). Generally, the higher amounts of lipid and myoglobin in fish mince were removed by using the alkaline-aided process, compared with the conventional process (P < 0.05). Protein isolate from the alkaline solubilization process formed gels with higher breaking forces than conventional suirmi, especially with 2-step heating (40 °C, 30 min/90 °C, 20 min) (P < 0.05). The lowest expressible moisture was found in the gel of protein isolate prepared by alkaline solubilization process (P < 0.05). However, the highest whiteness was found in the conventional surimi gel prepared by 2-step heating (P < 0.05). Protein isolate prepared by the alkaline solubilization process yielded superior gels compared with the conventional surimi. Therefore, it can be concluded that the gelling properties of surimi or protein isolate are governed by the physicochemical properties of proteins and are affected by processing conditions.     

Functional properties of pH-shifted protein isolates from bigeye snapper (Priacanthus tayenus) head by-product

The functional properties of pH-shifted protein isolates from bigeye snapper head were evaluated. Alkaline isolate showed a superior salt-solubility and gel forming ability to acid counterpart as indicated by a regular gel structure (i.e., imaged by scanning electron microscope) with higher gel strength and lower expressible drip (p < 0.05). Acid isolate exhibited higher surface hydrophobicity (p < 0.05) and thereby improved interfacial properties. Emulsifying activity index of acid isolate was lower than commercial whey protein and egg-white (p < 0.05) but its emulsion stability was better (p < 0.05). Both protein isolates had lower foamability than commercial proteins but their foam stability was not different (p > 0.05).     

Physicochemical properties and gel-forming ability of surimi from three species of mackerel caught in Southern Thailand

Physicochemical and gelation properties of surimi prepared from three species of mackerel were investigated. The highest whiteness with the lowest redness index corresponding to the lowest myoglobin content especially its oxidised form, metmyoglobin, was found in short-bodied mackerel (Rastrelliger brachysoma) surimi (p < 0.05). Frigate mackerel (Auxis thazard) surimi contained the highest lipid content (p < 0.05). The pH of all surimi was in the range of 6.58–6.80. The highest sulfhydryl group and Ca²⁺-ATPase activity was found in natural actomyosin extracted from short-bodied mackerel surimi (p < 0.05). The highest TCA-soluble peptide content was found in frigate mackerel surimi gels (p < 0.05). Kamaboko gel of short-bodied mackerel surimi exhibited the highest breaking force with the lowest expressible drip (p < 0.05). Heating regime had no effect on deformability of gels from Indian mackerel (Rastrelliger kanagurta) and short-bodied mackerel but not for frigate mackerel. The highest metmyoglobin content with the lowest whiteness was found in frigate mackerel surimi gel (p < 0.05). Therefore, short-bodied mackerel was the best suited for the production of surimi with superior functional attributes including whiteness and gel-forming ability.     

A Preliminary Study on Classification of Mango Maturity by Compression Test

A preliminary study toward the design of a firmness tester suitable for mango maturity classification was conducted through an experiment consisting of two parts: (1) probe selection, followed by (2) evaluation of the selected probe in mango maturity classification using a texture analyzer. This resulted in a technique based on the firmness of the fruit measured by a compression test with a maximum force of 3N using a 5mm diameter spherical stainless steel probe. This technique demonstrated the possibility of classifying the maturity of mangoes into two different stages, i.e., 60% and 80% of full ripeness. However, it could not detect the difference between 60% and 70% of full ripeness or between 70% and 80% of full ripeness.     

Biodiesel Synthesis from Palm Fatty Acid Distillate Using Tungstophosphoric Acid Supported on Cesium-Containing Niobia

Tungstophosphoric acid supported on cesium-containing niobia (TPA/Cs _x /Nb₂O₅, x = 1.0–2.5) catalysts were prepared by a two-step impregnation method, and their physico-chemical properties were investigated. The initial studies on the esterification of oleic acid with methanol revealed that TPA/Cs ratio affected the acidity as well as the activity of the catalysts. Among the catalysts tested, TPA/Cs_1.0/Nb₂O₅ exhibited the best performance. In addition, the efficiency of TPA/Cs_1.0/Nb₂O₅ for biodiesel synthesis from palm fatty acid distillate (PFAD), a by-product from palm oil industry, was demonstrated, and the reaction parameters were also evaluated. Over 90% yield of FAME was achieved, and the properties of the biodiesel obtained from PFAD met the standard requirements for biodiesel fuel. However, deactivation of the catalysts was observed, possibly due to structural transformation or organic residues blocking the active sites.