ROLE OF INITIAL MUSCLE pH ON THE SOLUBILITY OF FISH MUSCLE PROTEINS IN WATER

The solubility of the myofibrillar and cytoskeletal proteins in water was determined for the muscle tissue often species offish. The flesh of six white-muscled fish had pH's at the time of processing above pH 6.6 and greater than 80% of their myofibrillar/cytoskeletal proteins were soluble in water. The flesh of three pelagic species and a shark had pH values when processed below 6.6 and the water solubility of their myofibrillar and cytoskeletal proteins was less than 40%. When the washed minced muscle of one of the white-fleshed species, cod, was exposed to low pH, the solubility of its myofibrillar and cytoskeletal proteins decreased substantially. The water solubility of the cod myofibrillar and cytoskeletal proteins could be reestablished by washing the acid-treated cod flesh with neutral salt solutions. It is suggested that pH values below 6.6 modify certain proteins which prevent the water-extractability of the rest of the myofibrillar and cytoskeletal proteins from being expressed.     

SURFACE PROTEIN OF BROILER MEAT CHUNKS AS OBTAINED BY WASHING

Surface proteins, both soluble and insoluble, extracted from chicken breast and thigh meat chunks with water or 3% NaCl solution were studied. Soluble proteins were separated by an ammonium sulfate gradient precipitation method, quantified, and characterized using sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The quantities of both soluble and insoluble proteins from chicken breast meat chunk surfaces were higher than those of the thigh meat. The 3% NaCl solution extracted more soluble proteins, particularly those of molecular weight greater than 66,000 daltons, than that extracted by plain water. Most of these higher molecular weight proteins were satisfactorily precipitated by the addition of 20% ammonium sulfate. The amount of extracted water and salt soluble proteins from blended meat chunks were 3.00 and 4.75 times higher than those from washed suspensions, respectively. An increase in mixing time also enhanced the exudation of proteins to the meat surfaces.     

Aggregation of minced hake during frozen storage

 Aggregation in minced hake muscle (Merluccius merluccius) during storage at –20  °C was studied in conditions where there is progressive deterioration of functionality and texture as measured by apparent viscosity and shear resistance. Natural actomyosin was extracted with 0.6 M NaCl over a period of 49 weeks. Insoluble residue was extracted successively with 2% sodium dodecyl sulphate (SDS) and 2% SDS plus 5% β-mercaptoethanol (ME) solutions. SDS–polyacrylamide gel electrophoresis was performed on the extracted fractions. The results showed a 75% decrease in 0.6 M NaCl extractability by the end of the storage period. Initially the remaining precipitate was all extracted in 2% SDS and although the amount extracted in this solution increased as storage time progressed, its proportion decreased, accounting for as little as 40–50% of the protein aggregate by the end of storage. The proteins most involved in formation of the aggregate not extracted in 0.6 M NaCl were myosin and actin. Neither of these proteins was fully recovered in the fractions extracted with 0.6 M NaCl, 2% SDS, or 2% SDS plus 5% ME, and therefore it was inferred that they were forming part of the aggregates, bound by covalent bonds. Received: 17 November 1998     

羧甲基壳聚糖与NaCl组合漂洗制备白鲢鱼糜工艺条件优化

目的：探讨羧甲基壳聚糖（carboxymethyl chitosan,CBC）与NaCl组合漂洗白鲢鱼糜对凝胶品质、鱼糜收率及蛋白损失率等的影响。方法：以鲜白鲢鱼为原料,分别采用去离子水、0.25%、0.5%、0.75%、1.0%的NaCl溶液,0.5%、1.0%、1.5%、2.0%的CBC溶液,1.0% CBC＋1.0% NaCl、1.0% CBC＋0.75% NaCl、1.5% CBC＋1.0% NaCl、1.5% CBC＋0.75% NaCl,对鱼糜进行一次漂洗（鱼肉与漂洗液质量比1∶5）,测定不同漂洗处理对鱼糜凝胶强度、白度、蛋白质组成及流变特性的影响。结果：单独采用NaCl漂洗时,随着其用量的增大,鱼糜凝胶强度、白度呈现增加趋势（P＜0.05）,总蛋白含量呈现先增加后下降的趋势,过高或过低的NaCl质量分数,均不利于提高鱼糜得率。单独采用CBC溶液漂洗时,凝胶强度、白度、水溶性蛋白含量随着CBC质量分数的增大呈上升趋势（P＜0.05）。采用NaCl和CBC组合漂洗时,1.5% CBC＋0.75% NaCl组合得到的鱼糜凝胶强度最高,达232.05 g•cm,显著高于对照的142.22 g•cm（P＜0.01）,此时的盐溶性蛋白含量10.53%和水溶蛋白含量4.91%,显著高于空白对照的9.36%（P＜0.05）及4.06%（P＜0.01）。1.5% CBC＋0.75% NaCl组合漂洗,获得良好的鱼糜凝胶强度、白度及粗蛋白含量。结论：采用1.5% CBC＋0.75% NaCl漂洗可以改善鱼糜的凝胶品质,蛋白损失率比对照组降低10.56%,从而提高鱼糜得率,并降低废水排放。     

Parameters affecting the isolation of collagen from squid (Illex argentinus) skins

The solubility of collagen from squid (Illex argentinus) skin in salt solutions and the efficiency of removal of skin chromatophores were determined. Homogenization of minced squid skin in 5–15% NaCl solution at 0°C solubilized 35–24% of total amount of crude protein and caused 2–5% loss of collagen but was not effective in removing pigments from the skin. The treatment of whole squid skins in 5–15% NaCl solutions at room temperature led to separation of the chromatophores, but the loss of soluble collagen was 57–16%. Collagen, soluble in dilute acid solutions was isolated from squid skins by 24 h soaking in 10% NaCl solution at room temperature, washing with water and bleaching for 48 h in 1% H₂O₂ in 0.01 M NaOH. The yield of collagen was 53%. It could be increased to 90% by using NaOH solution at pH 11.5 instead of 10% NaCl but the isolate was less soluble in dilute acid and the viscosity of 0.5% dispersion of collagen was four times lower. The rancid off-odour could be prevented by adding 0.5% of a non-ionic detergent to all solution used in the procedure. ©     

Emulsifying properties of an ultrafiltered protein from minced fish wash water

Centrifugation and ultrafiltration were used to concentrate soluble proteins in the water used to wash minced muscle of sardine caught at two different times of year. The proteins thus extracted were largely of less than 67 kDa molecular weight. Part of the resulting concentrate was frozen-stored and part freeze-dried. Irrespective of the season of capture, samples exhibited high emulsifying capacity and emulsion stability, values being higher in freeze-dried samples. Both properties were virtually unaffected by solutions, with NaCl concentrations ranging from 0 to 3%.     

MECHANICAL PROPERTIES OF FISH AND BEEF GELS PREPARED WITH AND WITHOUT WASHING AND SODIUM CHLORIDE

Excellent gels, as measured by fold test, were prepared from three species of fish without first washing the minced tissue. Dependent on species (red hake, cod, or winter flounder), excellent to adequate gels, as determined by the fold test, could be prepared from fish muscle without NaCl provided that the minced tissue was washed prior to gel formation. Postrigor beef formed inadequate gels while excellent to good gels could be produced from prerigor beef although salt was a requirement. The concentration of contractile proteins in fish gels was estimated and they did not appear to be a major factor determining gel quality. Soluble muscle protein did not appear to interfere with gel formation either. Percent expressible moisture, percent recovery, and modulus of deformability did not relate well to fold test scores.     

Solubility of amaranth seed proteins in sodium sulphate and sodium chloride: the main factor in quantitative extraction for analysis

Nitrogen was extracted more efficiently from amaranth seed with 0.04 M Na₂SO₄ (5% w/v) than with either 0.09 M or 0.17 M NaCl (5% or 10% w/v), despite both solutions having the same ionic strength (μ= 1). Solubility of saline soluble proteins (albumin ± globulin) was very poor in either water or 1M NaCl, but increased in 0.4M NaCl at alkaline pH between 7 and 10. Globulins were very soluble in 0.4M NaCl at a pH 9. Albumin was the main storage protein. Saline soluble proteins formed very weak gels.     

Protein denaturation in frozen fish]

To inhibit the rapid deterioration of the production-technological properties of fish meat minced and frozen on board, it is necessary to become acquainted with the causes of protein denaturation under these conditions. It was found that the protein solubility in codfish is impaired by formaldehyde which develops from trimethyl-amine oxide during storage and also by the salt content. After 7 days at -20 degrees C, the solubility of the sarcoplasmic and myofibrillary proteins in minced fish meat added with 80 mg of formaldehyde per 100 g of total protein amounted to almost 70% and 35%, respectively, of the value determined in controls, i.e., samples without formaldehyde. After this period of storage, only 30% of the added formaldehyde were in the free state. After 1 month, the solubility of the myofibrillary proteins in waterleached fish meat was by 30% higher than in unleached controls, 80 mg of formaldehyde per 100 mg of total protein having been added in both cases. After 1 month at -5 degrees C and -20 degrees C, only 90 and 15 p.p.m. of formaldehyde, respectively, were found in minced fish meat, whereas leached samples contained no formaldehyde. The solubility of the myofibrillary proteins in leached fish meat (the initial salt content of which had been restituted) was by 30% lower than in the unleached controls.     

NaCl对猪肉糜加工特性和蛋白质二级结构的影响

NaCl是猪肉糜制品加工过程中必不可少的辅料,为进一步探明NaCl在猪肉糜加工过程中的作用,通过低场核磁共振和拉曼光谱等方法,研究了NaCl对猪肉糜的蒸煮得率、硬度、水分迁移和蛋白质二级结构的影响。结果表明:蒸煮得率和硬度随着Na Cl添加量的增加而显著提高(P0.05),特征峰T_(2b)和T_(22)的自旋-自旋弛豫时间逐渐缩短,T_(21)(不易流动水)的峰面积比例逐渐增加;NaCl添加量从1%增加到2%,对蛋白质二级结构含量影响显著,β-折叠含量提高,从2%增加到3%,二级结构相对含量差异不显著(P0.05);随着Na Cl添加量的增加,—OH基团伸缩振动波峰向高波数方向移动(3226 cm~(-1)和3227 cm~(-1)),水分子内氢键增多。因此,在猪肉糜加工中适量添加Na Cl能够改变猪肉糜蛋白质二级结构,增强蛋白质的水合作用,有助于提高猪肉糜的加工特性。     

Nitrogen extractability of sesame (Sesamum indicum L.) seed and the preparation of two protein isolates

Nitrogen extractability from sesame flour in water is greatest using a flour: solvent ratio of 1:40 and an extraction time of 15 min. At pH 4.0-6.5, <10% nitrogen is extracted, whilst >90% is extracted at pH 11.0. In the presence of NaCl (0.5-1.0M) nitrogen extractability is greatest at pH values > pH 4.0. The two sesame protein isolates produced were bland-tasting, light-coloured and contained approximately 95% protein. The alkali isolate (extracted in water at pH 10.0 and precipitated at pH 4.0) was readily solubilised and showed a good protein recovery (60%). The salt isolate (extracted in 1M NaCl at pH 6.0 and precipitated at pH 4.0) was less soluble and showed a lower protein recovery (50%). The sesame products were extracted sequentially using various solvents. Sesame flour proteins were mainly salt-soluble (67%), alkali isolate proteins mainly water-soluble (41%) and alkali-soluble (41%), and salt isolate proteins mainly alkali-soluble (35%). The amino acid composition of the sesame products is described. Oil-expelled cake showed poor nitrogen extractability (53% at pH 11.0 in water) and was, therefore, a poor source for protein isolate production.     

Antioxidative effect of added tea catechins on susceptibility of cooked red meat,poultry and fish patties to lipid oxidation

The comparative antioxidant activity of added tea catechins on susceptibility of cooked and overwrapped red meat (beef and pork), poultry (chicken, duck and ostrich) and fish (whiting and mackerel) to lipid oxidation was investigated. Fresh meats, poultry and fish, purchased from a local market, were trimmed to remove bones, skin and visible fat and minced through a 4-mm plate. The minced muscle from each species was treated with either 1% NaCl (S), 300 mg tea catechins kg⁻¹ minced muscle (TC) or 1% NaCl plus 300 mg tea catechins kg⁻¹ minced muscle (TCS). Control minced muscle samples (C) contained neither NaCl nor tea catechins. Patties (50 g), prepared from treated and untreated minced muscle, were cooked until the core temperature reached 75°C, cooled down to room temperature and held in a refrigerated (4°C) and illuminated (616 lux) display cabinet for 10 days. Oxidative stability (TBARS) was measured at 3-day intervals. The susceptibility of cooked patties to lipid oxidation was closely related to lipid content, concentration of unsaturated fatty acids and presence of iron in different species. Addition of NaCl to raw minced muscle significantly (P<0.05) promoted lipid oxidation for cooked patties regardless of species sources. Tea catechins added at a level of 300 mg kg⁻¹ minced muscle significantly (P<0.01) inhibited the pro-oxidation caused by NaCl and controlled lipid oxidation for all cooked muscle patties examined. Tea catechins at concentrations greater than 300 mg kg⁻¹ were necessary to reduce oxidation for mackerel patties containing high levels of lipids and unsaturated fatty acids. The high affinity of tea catechins for the lipid bilayers of muscle and the radical scavenging abilities of tea catechins may be possible mechanisms to explain the oxidative stability in cooked muscle foods.     

卵黄高磷蛋白提取的工艺研究

研究了以鸡蛋黄为原料,通过分离其它水溶性蛋白,脱除脂类,然后用1.75mol/LNaCl溶液提取卵黄高磷蛋白的工艺条件。探讨了用水量、有机溶剂种类及用量、NaCl溶液浓度对卵黄高磷蛋白收率的影响。经过正交试验,确定了最佳工艺条件,为批量生产提供了依据。     

TEXTURE PROFILE ANALYSIS AND COMPOSITION OF A MINCED CATFISH PRODUCT1

Texture Profile Analysis of minced catfish products indicated that minced proteins from the belly flap meat have excellent functional properties to form gels or restructured products. Belly flap meat is considered a low‐value trimming, with about 16.9% protein and 11.2% total lipid. Washing of minced catfish trimmings increased the moisture content from 71.5% to 77.9% while reducing mechanical hardness (19.1 N to 11.9 N), chewiness index (14.2 N to 8.83 N) and shear energy (0.82 J to 0.51 J). No significant changes were found in cohesiveness, resilience, and springiness of the minced fish after washing or the addition of 3.3% (v/w) of 4% starch solution. Washing of minced fish reduced the total lipid content from 9.82% to 4.39%. Overall, washed minced channel catfish belly flap meat had functional characteristics that enabled its proteins to be formed and restructured. Products made from minced catfish had acceptable textural characteristics.     

Timed Emulsification Studies with Chicken Breast Muscle: Whole Muscle, Low-Salt Washed Muscle and Low-Salt Soluble Proteins

Emulsion formation with chicken breast muscle was investigated using timed emulsification. Emulsions were made at a fixed oil/water ratio of 2:1 by Omni-mixing for various lengths of time between 0 and 5 min; then the emulsions were centrifuged and the aqueous layer analyzed for protein. Emulsions formed using whole muscle or muscle washed with low molarity salt solution and suspended in buffered (10 mM sodium phosphate, pH 7.0) 0.6M NaCl were superior in stability upon centrifugation to those made with muscle in distilled water, buffered 0.025M NaCl or buffered 0.05M NaCl. Size of insoluble protein pellets from the centrifuged emulsions decreased as emulsification time increased. Little emulsifying effect of the low-salt soluble (sarcoplasmic) protein, defined as those proteins extracted with buffered 0.05M NaCl, was observed in the presence or absence of high-salt solubilized protein.     

Effect of soaking with hydrogen peroxide and carbonate/bicarbonate buffer solutions on chemical composition and protein extractability of desalted cod

Cod salted with various combinations of NaCl, KCl, MgCl₂ and CaCl₂ were soaked for the first 24 h with a 0.2 M carbonate buffer solution (pH 9.5) or for the first 5 h with 1% hydrogen peroxide (pH 7.16). Chloride, ions and ash content in muscle were measured during the soaking process. After soaking, the composition of soluble muscle protein extracted in NaCl 0.86 M was determined by SDS-PAGE. The divalent, cation content was not affected by the salting and soaking processes. The protein extractability was low, especially when H₂O₂ was used. The use of alkaline buffer solution produced better protein functional quality. When the alkaline solution was used for soaking, the soluble fraction was constituted of a larger variety of proteins. Actin was soluble only when MgCl₂ and KCl were used for salting and the alkaline solution for soaking. The use of carbonate/bicarbonate buffer solution for soaking could therefore be useful to improve the functional quality of muscle protein of desalted cod.     

EFFECT OF IN SITU FORMALDEHYDE PRODUCTION ON SOLUBILITY AND CROSS-LINKING OF PROTEINS OF MINCED RED HAKE MUSCLE DURING FROZEN STORAGE

Three forms of minced red hake muscle representing whole-mince, mince with the low molecular weight fraction removed (reconstituted-minced) and mince with low and high molecular weight soluble fractions removed (washed-minced) were stored frozen with added Fe⁺² and ascorbate (trimethylamine oxide (TMAO) was added when necessary). The production of DMA and free formaldehyde was measured as were the decreases in water-soluble and salt-soluble proteins and TMAO as a function of increasing concentrations of ascorbate. Dimethylamine (DMA) production and loss of overall protein extractability were greatest in minced muscle, followed by reconstituted-minced muscle, and least in washed-minced muscle. The minced muscle lost water-soluble proteins, however, less rapidly than the reconstituted-minced muscle. The percentage of formaldehyde that was bound was highest in the minced, next in the reconstituted-minced and least in the washed-minced muscle. This supports earlier data and indicates that formaldehyde reacts with both the small molecular weight fraction and the water-soluble proteins as well as the contractile proteins. Loss of protein extractability in all samples appeared to be heavily dependent on hydrophobic interactions. Disulfide interactions appeared to occur to some extent in the reconstituted-minced and washed-minced muscle but were a minor factor with the minced muscle samples. Surface hydrophobicity of the proteins was inversely related to their extractability. In the sample of minced muscle with the highest concentration of added ascorbate where approximately 79% of the proteins became inextractable, some 2% of the muscle proteins were covalently linked in polymers with molecular weights greater than that of the myosin heavy chains. The data indicate that cross-linking of protein components occurs as well as hydrolysis of a considerable amount of the protein.     

Capillary electrophoresis for bovine and ostrich meat characterisation

The objective of this study was to characterise, compare and quantify the water soluble protein (WSP) and salt soluble protein (SSP) fractions from bovine and ostrich muscle by using sodium dodecyl sulphate polymer-filled capillary gel electrophoresis (CE-SDS). Samples were raw ostrich leg and eye round beef collected 24 and 48 h, respectively, after sacrifice from local slaughter houses. WSP were extracted with cold double distilled deionized water and SSP with 0.6 M NaCl/0.01 M phosphate buffer pH 6 with 0.5% polyphosphates. Separation of WSP and SSP extracts was achieved by CE-SDS. Quantitative data for individual proteins was generated by constructing a calibration curve using bovine serum albumin (BSA) as a standard. The WSP profiles showed differences for bovine and ostrich meat, both qualitatively and quantitatively and could be employed for species differentiation. Quantitative data derived for WSP and SSP from bovine and ostrich muscle showed significant differences among individual proteins. A comparison of protein profiles form ostrich and bovine meat should be useful for meat species differentiation and muscle characterisation for establishing relations to meat quality.     

Influence of Temperature, Time and Solvent on the Solubility of Corium Collagen and Meat Proteins

Collagen replacement (0, 10, 20, 30, or 100%) of minced muscle reduced the quantity of salt (NaCl) soluble nitrogen in unheated samples. This dilution of salt soluble meat protein with salt insoluble collagen was evident at each time period (0, 15, 30, 45, 60, 75, or 90 min) of heating. When sufficient heat was applied (i.e. high temperature for prolonged period), the solubilization of the collagen component of the meat block negated the difference in soluble nitrogen associated with collagen replacement. The presence of sodium tripolyphosphate (STPP) appeared to suppress the solubilization of collagen as a result of the initial high pH but enhanced the solubilization of minced muscle.     

The effects of salt concentration on conformational changes in cod (Gadus morhua) proteins during brine salting

The effects of different salt concentrations (6%, 15%, 18% and 24% NaCl (w/w)) on the conformational changes of cod muscle proteins during brine salting were examined in this study. Proteins were extracted from the brine salted samples with solutions of 1 M (5.9%) and 4 M (23.4%) NaCl and the quantity of salt soluble proteins (SSP), disulfide bond (S–S), total sulfhydryl (SH) and available SH content in the soluble fraction were determined. Increased salt concentration in cod muscle promoted protein denaturation and aggregation. The SSP and total SH content decreased, whereas the S–S bond and available SH content increased with increased salt concentration in cod muscle. Disulfide bond formation correlated (r = −0.6) with a decrease in total SH groups. Higher SSP and available SH groups of the samples at lower brine concentrations was explained by smaller concentration gradients and salt diffusion rates, resulting in stronger salting-in at early stages of the brining process. There was a significant difference in conformational changes in proteins extracted with a salt solution of 1 and 4 M, mainly due to a different degree of protein aggregation.