The effect of brine composition and pH on the yield and nature of water-soluble proteins extractable from brined muscle of cod (Gadus morhua)

Fillets of Atlantic cod (Gadus morhua) were held for 36 h in brines of pH 6.5 and 8.5, respectively, containing various combinations of NaCl, KCl, MgCl₂ and CaCl₂. Proximate analyses and chloride content were determined. Soluble muscle protein extracted in distilled water and protein released into the brine following salting was determined by SDS–PAGE. The soluble fraction was not affected by the presence of divalent salts or KCl in the brines, but it was affected by the initial pH. Both actin and myosin heavy chain (MHC) were released in pH 6.5 brines after immersion of the fish. On the other hand, an initial pH of 8.5 did not favour the release of these proteins. There was a smaller variety of remaining soluble proteins in salted muscle with an initial pH of 6.5, than with 8.5. However, this effect of the lower pH was offset to the extent that the ionic strength of the brine was higher.     

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.     

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.     

Use of hydrogen peroxide and carbonate/bicarbonate buffer for soaking of bacalao (salted cod)

Fillets of cod (Gadus morhua), brined and then dry-salted with NaCl, were cut into portions and desalted with different solutions: carbonate/bicarbonate buffer pH 9.5, tap water, or solutions of 0.25 or 1% hydrogen peroxide. The yield was measured after desalting. The moisture content, water-holding capacity, whiteness, firmness, total volatile basic nitrogen content and microbial load were determined during cold storage. When a pH 9.5 carbonate/bicarbonate buffer solution was used during the early hours of desalting, the yield increased and the product presented better protein functional quality but was highly perishable. When 0.25–1% hydrogen peroxide was used during the early hours of desalting, the microbial content of the end product was considerably lower, as was the yield; the firmness and surface whiteness of the product were improved but its water-binding properties were unaffected.     

Cross-Linking of Myosin Heavy Chains from Cod, Herring and Silver Hake During Thermal Setting

Cross-linking of myofibrillar proteins extracted from cod (Gadus morhua), herring (Clupea harengus) and silver hake (Merluccius bilinearis) was studied in 0.6M NaCl, pH 6.5 at 40°C and evaluated turbidimetrically and by SDS polyacrylamide gel electrophoresis coupled with l-ethyl-3-(3-dimethylaminopropyl) carbodiimide as a zero-length crosslinker. Turbidities of heat-treated cod and silver hake myofibril/myosin solutions were significantly higher than those of herring. Electrophoretic results showed that the myosin heavy chain (MHC) was the principal myofibrillar protein cross-linked to form a polymerized complex during the heat treatment. Cross-linking ability of MHC from the three fish species was different; herring MHC formed only small polymers (n≦3) but cod and silver hake MHC formed both small and large polymers (n≦6).     

Development of a Test to Predict Gelation Properties of Raw Turkey Muscle Proteins

A method for extraction and fractionation of muscle proteins into five fractions based on salt (NaCl) solubility was developed. The influence of protein extractability, solubility, muscle pH and total protein on gelation was investigated. Shear stress (gel strength) and shear strain (gel deformability) at failure of cooked (70°C) comminuted turkey breast gels were correlated with the 10 min protein extract and proteins soluble in 0.30–0.35M NaCl. Shear strain was correlated with muscle pH and shear stress was sensitive to total protein. Meat pH and the extraction/fraction method can be used on raw meat to indicate functional properties related to texture of cooked meat.     

Chemical, Microbiological, and Sensory Quality of Cod Products Salted in Different Brines

ABSTRACT: Studies were carried out on the effect of different brines containing high concentrations of calcium chloride (CaCl₂, 0.8%w/w), magnesium chloride (MgCl₂, 0.4%w/w), and potassium chloride (KCl, 50%) on the chemical (chloride and moisture contents), microbial (total viable counts, total coliforms, enterococci, and staphylococci), and sensory quality of salted cod. The brines were prepared from combinations of the Ca, Mg, and K ions and sodium chloride (NaCl) at pH 6.5 and 8.5. Additionally, 3 salts (one composed solely of NaCl, another commercial sea salt from the southern Europe and, finally, a natural salt from northern Europe) were also tested. Principal component analysis structured the chemical and microbiology data in 3 clusters: (1) an extreme cluster, formed by cod brined in the commercial sea salt, which achieved the highest microbiological counts, namely 4.1 log CFU/g on plate count agar (PCA) and 1250 coliforms/g; (2) an intermediate cluster composed of cod salted in brine containing 50% NaCl, 0.4% MgCl₂, and 49.6% KCl (pH 6.5); and (3) a central cluster, including all the other treatments, which presented the lowest microbiological counts, namely 2.4 log CFU/g on PCA and 20 coliforms/g. Although the batches of the intermediate cluster presented slightly higher total viable and staphylococci counts than the central cluster, the presence of Mg and K ions improved the color of the salted product. In the assayed concentrations, CaCl₂, MgCl₂, and KCl can be used in the brining of cod without adversely affecting the microbiological and sensory quality of the salted cod.     

Quantitative and qualitative changes in added phosphates in cod (Gadus morhua) during salting,storage and rehydration

Phosphate blend can be used in salted cod processing to improve yields, water holding capacity and appearance of the final product. However, added phosphates are gradually degraded during processing and storage, leading to changes in functional properties of phosphates. The objective of the study was to monitor the quantitative and qualitative changes in added phosphates in cod during salting, storage and rehydration using ion chromatography (IC) and spectrophotometric analysis. The phosphates diffused into the fish muscle during brining but the phosphate content (mg P₂O₅/g sample) decreased again as liquid drained away from the muscle in the following dry salting step. Changes during six months storage of the dry salted products were minor. Further losses were observed during rehydration where the phosphates were washed out to levels lower than in the raw material.The advantage of the IC method was the ability to separate and determine different soluble phosphate species in the fish muscle. The IC results showed that pyrophosphate (P₂O₇) and triphosphate (P₃O₁₀) were partly degraded into orthophosphate (PO₄) during the storage period. Lower values were obtained for the total phosphate content by IC than with the spectrophotometric method, which explained by difference is sample preparation.     

Studies on fish muscle protein. Nutritional consequences of the changes occurring during frozen storage

Samples of cod, whiting, herring, lemon sole and skate muscle were frozen and stored at ? 8°C for up to 20 months. Samples of cod muscle were also stored at ? 30°C. During storage at ?8°C the decrease in the solubility of the muscle proteins in 5% NaCl (denaturation) was most rapid in whiting followed in order by skate, cod, herring and lemon sole. Little change was detected in the NaCl solubility of cod muscle protein stored at ? 30°C. An increase in the pH was found to occur in all the species examined. The relationship between these changes and the toughening that occurs in fish muscle during frozen storage is considered. No nutritionally significant decrease in the lysine availability or the in vitro digestibility of the muscle proteins was found to occur in any of the species examined. In whiting, lemon sole and skate very small, statistically significant, increases in the available lysine content were detected after 7 months of storage at ?8°C and this may indicate that unfolding of the protein chains had occurred.     

ADSORPTION OF POLYGALACTURONASE FROM RECYCLED CUCUMBER PICKLE BRINES BY PURE‐FLO B80 CLAY1

Factors affecting adsorption of polygalacturonase (PG) in recycled cucumber pickle brine by an alumino‐silicate clay (Pure‐Flo B80) were investigated. Adsorption of PG by Pure‐Flo B80 was affected by concentration of clay, NaCl, pH and mixing time. Mixing 5 mg clay/mL of brine for one hour eliminated PG activity in most commercial recycled pickle brines that were tested. Maximum adsorption occurred in brines from pH 3 to 4.5. NaCl greatly enhanced PG and total protein adsorption capacity of the clay. Adsorption of PG did not appear to be affected by source of the commercial brines. Spent clay adsorption was restored by washing the clay in alkaline (pH 12) solution. The results demonstrated that the salt and pH conditions of commercial recycled pickle brines were favorable for adsorption of PG by Pure‐Flo B80 and that the clay could be reused after treatment.     

Fermentation of Cucumbers Brined with Calcium Chloride Instead of Sodium Chloride

ABSTRACT: Waste water containing high levels of NaCl from cucumber fermentation tank yards is a continuing problem for the pickled vegetable industry. A major reduction in waste salt could be achieved if NaCl were eliminated from the cucumber fermentation process. The objectives of this project were to ferment cucumbers in brine containing CaCl₂ as the only salt, to determine the course of fermentation metabolism in the absence of NaCl, and to compare firmness retention of cucumbers fermented in CaCl₂ brine during subsequent storage compared to cucumbers fermented in brines containing both NaCl and CaCl₂ at concentrations typically used in commercial fermentations. The major metabolite changes during fermentation without NaCl were conversion of sugars in the fresh cucumbers primarily to lactic acid which caused pH to decrease to less than 3.5. This is the same pattern that occurs when cucumbers are fermented with NaCl as the major brining salt. Lactic acid concentration and pH were stable during storage and there was no detectable production of propionic acid or butyric acid that would indicate growth of spoilage bacteria. Firmness retention in cucumbers fermented with 100 to 300 mM CaCl₂ during storage at a high temperature (45 °C) was not significantly different from that obtained in fermented cucumbers with 1.03 M NaCl and 40 mM CaCl₂. In closed jars, cucumber fermentations with and without NaCl in the fermentation brine were similar both in the chemical changes caused by the fermentative microorganisms and in the retention of firmness in the fermented cucumbers.     

CHARACTERIZATION OF PHYTOCHELATIN-LIKE COMPLEXES FROM FLAX (LINUM USITATISSIMUM) SEED

Proteins were extracted from dehulled and delipidated powder of flaxseed (cv. NorMan), and fractionated by DEAE‐Sephacel onion exchange chromatography. Ultraviolet absorbance scans of ion exchange fractions eluting in buffers at pH 8.6 containing 0.45 M and 0.50M NaCl revealed A₂₅₅ >A₂₈₀. Furthermore, the A₂₅₅ was reduced upon acidification and restored by adjusting to the original pH, confirming spectral characteristics typical of metal‐thiolate complexes. Characteristic circular dichroism spectra and reversible aggregation‐dissociation behavior under low and high salt conditions observed for these fractions are also typical of metal binding phytochelatins reported for other plants, while the presence of aromatic amino acids indicated by fluorescence spectra suggests some similarity to nonmetallothionein proteins. Further work is underway to investigate the prevalence of these and other complexes as well as the distribution of metals in different protein fractions of flaxseed, as a function of cultivar and geographical location.     

Influence of animal and vegetable rennet on the physicochemical characteristics of Los Pedroches cheese during ripening

The effects of rennet type (animal or vegetable) on the physicochemical characteristics (moisture, fat, protein, lactose, lactic acid, NaCl, ash, water activity, pH and nitrogen fractions: SN, NPN, AAN and NH₃-N) of “Los Pedroches” cheese manufactured with pure ewes' milk were investigated. Changes were observed during 100 days of ripening. Analysis of the covariance was carried out, using these chemical composition data, expressed as a function of the dry matter. The rennet type influenced moisture, protein, and water activity values (higher in the cheeses manufactured with animal rennet), fat and SN (higher in cheeses manufactured with vegetable rennet). There was a significant rising trend in the levels of lactic acid, ash, NaCl, and nitrogen fractions during ripening, while a significant decrease was observed in the moisture, lactose, pH and a_w values.     

ELECTROSTATIC EFFECTS ON PHYSICAL PROPERTIES OF PARTICULATE WHEY PROTEIN ISOLATE GELS

Physical properties of particulate whey protein isolate gels formed under varying electrostatic conditions were investigated using large strain rheological and microstructural techniques. The two treatment ranges evaluated were adjusting pH (5.2‐5.8) with no added NaCl and adjusting the NaCl (0.2‐0.6 M) at pH 7. Gels (10% protein w/v) were formed by heating at 80C for 30 min. The large strain properties of fracture strain (γ_f), fracture stress (σ_f), and a measure of strain hardening (R_0.3) were determined using a torsion method. Gel microstructure was evaluated using scanning electron microscopy (SEM) and gel permeability (B_gel). Overlaying σ_f and γ_f curves for pH and NaCl treatments demonstrated an overlap where gels of equal σ_f and γ_f could be formed by adjusting pH or NaCl concentration. The high fracture stress (σ_f～ 23 kPa and γ_f～ 1.86) pair conditions were pH 5.47 and 0.25 M NaCl, pH 7.0. The low fracture stress (σ_f～ 13 kPa and γ_f～ 1.90) pair conditions were pH 5.68 and 0.6 M NaCl, pH 7.0. The 0.25 M NaCl, pH 7 treatment demonstrated higher R_0.3 values than the pH 5.47 treatment. When the sulfhydryl blocker n‐ethylmaleimide was added at 2 mM to the 0.25 M NaCl, pH 7 gel treatment, its rheological behavior was NSD (p>0.05) to the pH 5.47 gel treatment, indicating disulfide bond formation regulated strain hardening. Altering surface charge or counterions, and disulfide bonding, was required to produce gels with similar large strain rheological properties. An increase in gel permeability coincided with an increase in pore size as observed by SEM, independent of rheological properties. This demonstrated that at the length scales investigated, microstructure was not linked to changes in large strain rheological properties.     

Functional characterisation of muscle and skin collagenous material from hake (Merluccius merluccius L.)

The purpose of this paper was to examine the modifications occurring in certain functional hydration properties (protein solubility in 0.5 M acetic acid, apparent viscosity and water-binding capacity) of the collagenous material from skin and muscle of hake (Merluccius merluccius L.) in relation to the pH and the ionic strength (expressed as variation in NaCl concentration) of the medium. At the same time, these modifications were compared with those reported for collagenous material from trout in a previous paper. Generally speaking, skin collagenous material showed higher functionality than muscle collagenous material. It was found that protein solubility, apparent viscosity and water-binding capacity presented maximum values at pH levels between 2 and 4, and at concentrations of less than 0.25 M NaCl. Finally, the functional values were found to be higher in collagenous material from hake than from trout, especially in the skin material. ©     

Chemical and Nutritional Studies on Mesquite Beans (Prosopis juliflora)

Mesquite beans (Prosopis juliflora) consisted of pericarp, hulls and kernels. With the exception of kernels, composition of beans and their fractions were protein, 10–15%; fat, 2–3%; crude fiber, 20–30%; sucrose, 21%; reducing sugars, 2–6%. Kernels contained 38% protein, 3% fat and 9% crude fiber. Bean trypsin inhibitor content was 1.4 TIU/mg. Bean protein isoelectric point was pH 5. Mesquite protein concentrate and isolate were prepared, however, by increasing solubility at the extraction pH (pH 10) with NaCl and decreasing it at the isoelectric point with (NH₄)₂SO₄. First and second limiting amino acids for bean protein were threonine and isoleucine, respectively; the protein was high in total sulfur amino acids and tryptophan. Corrected PER was 1.4.     

Influence of brine salting prior to pickle salting in the manufacturing of various salted-dried fish species

In Portugal, the production of salted-dried cod and similar species is a relevant fish industry. Pickle salting is the most common salting method in this industry. The objective of this work was to study the influence of brine salting before pickle salting in the characteristics of the final salted-dried product of different fish species. Three salting methods were studied: only pickle salting, brine salting at 16°Baumé followed by pickle salting and brine salting at 25°Baumé followed by pickle salting. Fish species studied were Gadus morhua, Gadus macrocephalus, Theragra chalcogramma. The results showed from 4.7% to 9.2% significant higher yields of salted-dried fish when using the lower salt content brine, but drying time increased from 32 to 45 h (35–65%), depending on size of the fish, and texture became significantly softer, what may imply that salted-dried fish using lower salt content brines may be perceived by consumers as a different product. No significant differences of color were obtained.     

含KCl、氨基酸的低钠盐替代食盐对风干草鱼加工过程中理化特性的影响

本试验以新鲜草鱼为原料,食盐组为对照组,研究不同比例低钠盐替代食盐对风干草鱼加工过程中背侧肌和腹侧肌理化特性以及感官品质的影响。结果显示:干燥结束后,75%和100%低钠盐替代组的水分含量显著高于其他组(p<0.05),且背侧肌的水分含量和水分活度均显著高于腹侧肌(p<0.05)。低钠盐替代组的pH、色泽和质构与食盐组的变化趋势相似。75%低钠盐替代制备的产品咸味纯正,无异味,具有较高的接受度,且背侧肌和腹侧肌钠含量分别降低了31.88%和47.64%。低钠盐部分替代食盐制备的风干草鱼在保证理化和感官特性不受影响的基础上,极大地降低了钠含量,具有较好的应用前景。     

Biochemical and nutritional changes in fish proteins during drying

Biochemical and nutritional changes in the muscle proteins of a lean marine fish Nempiterus japonicus during drying at 50, 60 and 70°C were investigated. Solubility of proteins in water, 0.6 M NaCl, 1.5 M urea, 8 M urea and 10 g litre^?1 sodium dodecyl sulphate (SDS) decreased as drying progressed at all three temperatures; most of the decrease occurring in the initial 4 h of drying SDS-polyacrylamide gel electrophoresis of 1.5 M urea, 8 M urea and SDS extracts showed that higher molecular weight (MW) protein fractions were more sensitive to drying and disappeared much earlier from electropherograms than the lower MW protein fractions. Residual solubility of proteins near the pH range of 4–6 was found to increase during drying, but solubility at acid and alkaline pH was adversely affected. Decrease of solubility by drying was more affected at acid pH, especially at higher temperatures than at alkaline pH. Sulphydryl groups registered a regular and sharp decrease with drying except at 50°C, where initially an increase was observed. Apart from disulphide and hydrophobic bonds, free amino groups also appear to be involved in denaturation reactions during drying. Pepsin digestibility of fish muscle decreased slightly during drying but a clear relationship with drying temperature was not evident. Highly significant differences in proteins between protein efficiency ratio (PER), net protein utilisation (NPU) and biological value were observed between the drying temperatures. The PER and NPU of fish dried at 60°C were significantly higher than those dried at 50 or 70°C.     

The amino acid composition,solubility and emulsifying properties of sweet potato protein

A protein was purified from the high-protein type sweet potato variety 55-2 available in China. The amino acid composition, solubility and emulsifying properties of the sweet potato protein (SPP) were studied. The SPP was rich in aspartic acid (18.5%) and glutamic acid (9.30%) while essential acid amino acids made up approximately 40.7% of the SPP. The SPP was highly soluble in distilled water over a wide range of pH. However, solubility of the SPP in 1.0 M NaCl and 1.0 M CaCl₂ solutions was low especially at pH below the pI of the SPP. The SPP in CaCl₂ demonstrated emulsifying activity index (EAI) and emulsion stability index (ESI) many folds higher than those in distilled water and NaCl solution (P < 0.05).