Alkaline Solubilization Research Articles

Evaluation of sample preparation methods based on alkaline and acid solubilization for the determination of Na and K in meat samples by atomic spectrometric techniques

Two different sample preparation methods were evaluated for meat samples employing the solubilization in alkaline or acidic media. The aim of this study was to determine Na and K levels after sample solubilization with tetramethylammonium hydroxide (TMAH) at room temperature, and with formic acid and heating in a digester block at 50 oC for ca. 2 h. The alkaline solubilization showed to be a simple and robust method and the better alternative in relation to the mineralization conventional procedures, allowing the complete solubilization of the samples even when small quantities of TMAH were used. The method was validated by using certified reference material as well as by comparing with samples digested with nitric acid. The limits of detection obtained were 0.8 and 2.0 μg g-1 for Na and K, respectively, and showed to be adequate for the analysis purposes.

Effect of pretreatments on chemical compositions of mince from Nile tilapia (Oreochromis niloticus) and fishy odor development in protein hydrolysate

Abstract Fish protein hydrolysates (FPH) have gained increasing attention as nutritious fish products. Lipid oxidation associated with fishy odor in FPH limits its utility. Thus, an appropriate pretreatment of fish mince prior to hydrolysis by lowering pro-oxidants and lipid substrates could tackle such a problem. Different pretreatments of Nile tilapia minces including (1) washing (W), (2) washing and membrane removal (W-MR), and (3) washing/membrane removal followed by acid or alkaline solubilization (W-MR-Ac or W-MR-Al) were conducted prior to hydrolysis. During the hydrolysis process, degree of hydrolysis (DH) and chemical changes were monitored. Color and sensory properties of milk fortified with hydrolysates prepared from mince without and with pretreatment were also determined. Among the pretreated mince samples, W-MR-Al contained the lowest remaining myoglobin and heme iron contents and also showed the lowest total lipid and phospholipid contents (P < 0.05). When mince and W-MR-Al were hydrolyzed using Alcalase for up to 120 min, higher DH were found in W-MR-Al. Furthermore, lower peroxide values, thiobarbituric acid reactive substances, and non-heme iron contents of hydrolysates from W-MR-Al were also observed (P < 0.05). When FPH powder from mince and W-MR-Al (0.3% to 0.5%) were fortified in milk, the former yielded a lower likeness score (P < 0.05) at all levels used. The addition of the latter up to 0.5% had no effect on likeness of all attributes, compared with control (without FPH). An appropriate pretreatment of mince was a promising approach to lower fishy odor problem, caused by lipid oxidation in FPH.

High-yield protein recovery from secondary sludge of paper mill effluent and its characterization

Maximizing recovery and characterization of extractable proteins from secondary paper sludge is essential to explore the potential value from utilization of readily available waste products from pulp and paper mills. A multistep physicochemical recovery process was used, involving optimum alkaline solubilization of protein into an aqueous phase followed by augmented physical disruption of cell membranes. The final precipitation of solubilised protein was carried out using different acidic media. The optimization studies revealed that the best removal of intercellular contents from sludge can be achieved at pH 12; at this level, up to 88% of available protein is solubilised into the aqueous phase. Of all the precipitating agents used, sulphuric acid proved most effective by recovering 90% of disrupted protein. The combined effect of french press and sonication techniques resulted in significant improvement in the overall yield of recovered sludge protein (RSP). The characterization studies showed the presence of common and essential amino acids in RSP in significant quantities; it also showed that the recovery process can significantly reduce or eliminate heavy metals present in the sludge. The molecular weights (MW) of extractable proteins were determined by PAGE, and it was observed that RSP contains both low and high MW fractions.

Protein isolation from blue mussels (Mytilus edulis) using an acid and alkaline solubilisation technique—process characteristics and functionality of the isolates

The pH shift method was developed to isolate proteins from low-value raw materials by solubilisation at high or low pH followed by precipitation. In this paper the application of the pH shift method on isolated mussel (Mytilus edulis) meat and whole mussels is reported. Highest protein solubilisation was achieved at pH values of 2.6 and 12. The optimum precipitation pH values were established as around 5.8 following acid solubilisation and 5.2 following alkaline solubilisation. Protein recoveries were 430 and 580 g kg(-1) with the acid and alkaline processes respectively. Using whole crushed mussels, the corresponding recoveries were 310 and 480 g kg(-1). Process modifications to further improve protein recovery resulted in only a marginal increase. Lipid oxidation was not induced during pH shift processing, but heavy proteolysis occurred during the acid process version. Proteolysis could not be prevented by porcine plasma protein. Alkali-produced proteins performed better in all functionality tests compared with acid-produced proteins. The acid process removed slightly more lipids, recovered relatively more cysteine, methionine and lysine and resulted in whiter isolates. The pH shift method can be successfully used to extract functional proteins from mussels and add value to blue mussels unsuitable for human consumption (with or without shells).

Bulgarian analytical atomic spectroscopists in the new millennium—integrated in the European research area

The studies from Bulgarian analytical atomic spectroscopists in the fields of atomic absorption spectrometry (AAS), atomic fluorescence spectrometry (AFS), inductively coupled plasma optical emission spectrometry (ICP-OES), inductively coupled plasma mass spectrometry (ICP-MS) and hyphenated atomic spectrometric methods after 2000 are reviewed with an emphasis on direct methods of analysis (slurry and solid sampling), rational sample pretreatment and trace elements enrichment, alternative pretreatments such as alkaline solubilization by tetraalkylammonium hydroxides, in situ treatment in a graphite atomizer by means of chemical modification, speciation and fractionation analysis. There is a clear focus on the development of sample preconcentration methods coupled with atomic spectrometric techniques, particularly in flow and flow injection systems to alleviate interferences and to improve limits of detection (LODs). The most notable publications concerned with methodological developments in the atomic spectroscopic analysis of environmental samples, biological and advanced materials, food and beverages, as well as speciation and fractionation studies are tabulated. Recent reviews, book chapters, bibliographies and monographs with Bulgarian authorship/co-authorship are presented. The integration of Bulgarian atomic spectroscopists in the European research area is illustrated. Some trends in the publication activities are presented.

Physicochemical Properties and Sensory Analysis of Duck Meatballs Containing Duck Meat Surimi‐Like Material during Frozen Storage

The physicochemical properties and sensory analysis of duck meatballs containing duck meat surimi-like material during frozen storage were evaluated. Properties of meatballs containing duck surimi-like material prepared by acid solubilization (ACDS), alkaline solubilization (ALDS), and conventional processing (CDS) as well as duck mince (as the control, CON) were compared. ACDS had significantly higher (P < 0.05) moisture and protein content and lower fat content compared with CON. The thiobarbituric acid-reactive substances (TBARS) value of all samples increased as the storage time increased up to week 8 (P < 0.05), but thereafter it decreased in most of the samples. ACDS and ALDS had significantly higher TBARS values (P < 0.05), and these values remained higher than those of the other samples throughout the frozen storage period. Addition of surimi-like material to the meatballs had significant effects (P < 0.05) on springiness, gumminess, and chewiness values of all samples. Ingredients and frozen storage affected most sensory attributes in samples significantly (P<0.05). No significant increase in growth of organisms occurred during 12-wk frozen storage The results indicate that acid-alkaline solubilization methods improve both physicochemical and sensory properties of duck meatballs containing duck surimi-like material. Thus, these techniques should be applicable to product development of duck surimi-like material. Surimi-like material from duck meat is an alternative source of meat protein to produce ready-to eat or value-added products. Little is known about duck surimi-like material and physicochemical and sensory properties of such products. Therefore, the results of this study are critical for assessing the possibility of duck meat surimi-like material for human food.

Nutritional properties of spent duck surimi-like material prepared by conventional and acid–alkaline solubilization methods

The nutritional properties of surimi-like materials produced from spent duck meat processed conventionally (CDS) and processed with acid and alkaline solubilization (ACDS and ALDS, respectively) were studied. The essential amino acids (EAAs) content was significantly higher (p < 0.05) in the ACDS and ALDS than in control (CON) and CDS, with values of 436.78 ± 13.67, 450.30 ± 9.72, 377.29 ± 7.20 and 400.61 ± 14.7 mg/g protein, respectively. All duck surimi-like materials had a higher chemical score, amino acid score and EAA index than the CON. The saturated fatty acid compositions of the ACDS and ALDS samples were significantly lower (p < 0.05) than that of the CDS sample, whereas the opposite pattern was observed for the polyunsaturated fatty acid content. ACDS samples had significantly higher (p < 0.05) contents of minerals than ALDS samples. The results indicated that acid–alkaline solubilization permitted recovery of high-quality surimi-like material from spent duck meat, which has potential for human food uses.

Properties of Canola Protein‐based Plastics and Protein Isolates Modified Using SDS and SDBS

AbstractCanola protein isolates were prepared from canola meal flour using alkaline solubilization and acid precipitation. The isolates were treated with sodium dodecyl sulfate (SDS) and sodium dodecyl benzene sulfonate (SDBS) with concentrations between 1 and 5%. Functional property analysis of modified isolates revealed that water absorption and fat absorption increased by up to 115 and 78%, respectively, with increasing SDBS concentrations. Fat absorption of SDS‐modified isolates showed a similar trend to that of SDBS‐modified isolates (86% increase), but water absorption decreased (by 77%) in the 5% SDS treatment. SDS and SDBS treatments reduced the emulsifying activity of protein isolates by 34 and 30%, respectively. The denaturation effect of SDS and SDBS treatments increased the surface hydrophobicity of proteins and resulted in increased tensile strength (by 14 and 41%), tensile modulus (by 31 and 52%), and toughness (by 44 and 64%) of plastic specimens prepared using modified isolates. Only the 3% treatments of SDS and SDBS increased the elongation of plastics (by 22 and 11%, respectively) while other treatments did not show significant differences from the plastics that used non‐modified isolates. The water absorption of plastics increased by 33% with the 5% SDS treatment; the SDBS treatments showed a 9% decrease in water absorption for the 1% treatment but no significant differences at higher concentrations. Denaturation by SDS and SDBS can be employed to alter functional properties of canola protein isolates as well as the mechanical properties of canola protein‐based plastics.

Determination of fluorine in tea using high-resolution molecular absorption spectrometry with electrothermal vaporization of the calcium mono-fluoride CaF

High-resolution continuum source molecular absorption of the calcium mono-fluoride molecule CaF in a graphite furnace has been used to determine fluorine in tea after acid digestion, alkaline solubilization and preparation of a conventional aqueous infusion. The strongest absorption ‘line’ of the CaF molecule is at 606.440nm, which is part of the rotational fine structure of the X2Σ+−A2Π electronic transition; it has a bond dissociation energy of 529kJmol−1, which is comparable with other molecules used for fluorine determination. One advantage of using Ca as the molecule-forming reagent is that spectral interferences are extremely unlikely in the spectral range of its strongest absorption. Another advantage is that Ca acts both as molecule forming reagent and chemical modifier, so that no other reagent has to be added, making the method very simple. The only disadvantage is that Ca has a somewhat negative influence on the graphite tube lifetime. The limit of detection was found to be 0.16mgL−1 F, corresponding to 1.6ng F absolute, and the calibration curve was linear in the range between 0.5 and 25mgL−1 with a correlation coefficient of R=0.9994. The results obtained for a certified tea reference material were in agreement with the certified value on a 95% confidence level. There was also no difference between the results obtained after an acid digestion and an alkaline solubilization for 10 tea samples, based on a paired t-test. The values found in the 10 samples ranged between 42μgg−1 and 87μgg−1 F; the tea infusions contained between 21μgg−1 and 56μgg−1 F, with an extraction rate between 48% and 74%.

Interactions between Hemoglobin and Cod Muscle Constituents following Treatment at Extreme pH Values

Acid and/or alkaline solubilization is a recent method developed to separate proteins from muscle foods with good functional properties. However, exposure of the muscle and its components to low pH values has been shown to promote lipid oxidation, limiting therefore the applications of this novel method. This research aimed primarily to study the physicochemical changes of the fish membranes brought about during acid or alkali solubilization processes. The effect on lipid oxidation and the possible role of the water soluble fraction of the muscle (press juice) as a potent antioxidant were also investigated. Model systems comprising minced cod muscle or cod microsomal suspensions were used. Results showed that acid or alkaline treatment (pH < 3.5 or pH > 10.5) of cod membranes significantly delayed lipid oxidation. Added triacylglycerols to washed cod system treated at low pH did not enhance hemoglobin-mediated lipid oxidation. Decreased precipitation of hemoglobin was observed with the alkali-treated membranes at all protein concentrations compared to the acid-treated and the untreated membranes. Finally, the addition of press juice to washed cod muscle tissue or to the membrane model system, significantly delayed hemoglobin lipid oxidation. The results of this study can be used to improve pH-shifting technologies to avoid or decrease lipid oxidation problems. Also, the use of press-juice from cod muscle as means of protecting the muscle against lipid oxidation is suggested.

Biological Pretreatment of Lignocellulosic Substrates for Enhanced Delignification and Enzymatic Digestibility

Sheer enormity of lignocellulosics makes them potential feedstock for biofuel production but, their conversion into fermentable sugars is a major hurdle. They have to be pretreated physically, chemically, or biologically to be used by fermenting organisms for production of ethanol. Each lignocellulosic substrate is a complex mix of cellulose, hemicellulose and lignin, bound in a matrix. While cellulose and hemicellulose yield fermentable sugars, lignin is the most recalcitrant polymer, consisting of phenyl-propanoid units. Many microorganisms in nature are able to attack and degrade lignin, thus making access to cellulose easy. Such organisms are abundantly found in forest leaf litter/composts and especially include the wood rotting fungi, actinomycetes and bacteria. These microorganisms possess enzyme systems to attack, depolymerize and degrade the polymers in lignocellulosic substrates. Current pretreatment research is targeted towards developing processes which are mild, economical and environment friendly facilitating subsequent saccharification of cellulose and its fermentation to ethanol. Besides being the critical step, pretreatment is also cost intensive. Biological treatments with white rot fungi and Streptomyces have been studied for delignification of pulp, increasing digestibility of lignocellulosics for animal feed and for bioremediation of paper mill effluents. Such lignocellulolytic organisms can prove extremely useful in production of bioethanol when used for removal of lignin from lignocellulosic substrate and also for cellulase production. Our studies on treatment of hardwood and softwood residues with Streptomyces griseus isolated from leaf litter showed that it enhanced the mild alkaline solubilisation of lignins and also produced high levels of the cellulase complex when growing on wood substrates. Lignin loss (Klason lignin) observed was 10.5 and 23.5% in case of soft wood and hard wood, respectively. Thus, biological pretreatment process for lignocellulosic substrate using lignolytic organisms such as actinomycetes and white rot fungi can be developed for facilitating efficient enzymatic digestibility of cellulose.

Channel Catfish (Ictalurus punctatus) Muscle Protein Isolate Performance Processed under Different Acid and Alkali pH Values

Channel catfish (Ictalurus punctatus) muscle was subjected to 6 protein extraction and precipitation techniques using acid solubilization (pH 2.0, 2.5, and 3.0) or alkaline solubilization (pH 10.5, 11.0, 11.5) followed by precipitation at pH 5.5. The catfish protein isolate was compared with ground defatted white muscle. Alkali-processed catfish showed increased gel rigidity, gel strength, and gel flexibility compared to acid-processed catfish, which exhibited inconsistent functional performance, increasing and decreasing gel rigidity, gel strength, and gel flexibility. The gel rigidity (G') at pH 3.0 in the absence of salt had the highest G' of the acid treatments and was not significantly different from the alkaline-treated catfish muscle (P>0.05). However in the presence of added salt pH treatment it had the lowest G' and was different from alkaline treatments (P<0.05) during break force testing. These results show that pH-shift processing of channel catfish muscle provides highly functional isolates with a potentially broad range of applications. This range of applications is possible due to the modification of the textural properties of catfish muscle protein produced using different acidic or alkaline pH solubility treatments.

Effects of Protein Separation Conditions on the Functional and Thermal Properties of Canola Protein Isolates

Canola meal protein isolates were prepared from defatted canola meal flour using alkaline solubilization and acid precipitation. A central composite design was used to model 2nd-order response surfaces for the protein yield and the functional properties of protein isolates. The solubilization pH and precipitation pH were used as design factors. The models showed that the protein yield and functional properties of isolates, such as water absorption and fat absorption, were sensitive to both solubilization pH and precipitation pH, whereas the emulsification was sensitive to only solubilization pH. Gel electrophoresis analysis of protein fractions gave evidence to the compositional changes between proteins isolated under different conditions. Differences in glass transition temperatures suggest that proteins tend to be more denatured when solubilized at highly alkaline conditions. These conformational and compositional changes due to different protein separation conditions have contributed to the changes in functional properties of protein isolates. Protein isolation conditions may be determined primarily through optimization of total protein yield. Improvements in protein functional properties may be achieved with a relatively small sacrifice in yield by altering isolation conditions.

Characteristics of film based on protein isolate from red tilapia muscle with negligible yellow discoloration

The properties of film from fish protein isolate (FPI) prepared by prior washing followed by alkaline solubilization process (ASP) from red tilapia muscle were monitored during the storage of 20 days at 50% RH and 25 °C, in comparison with those of films from washed mince. Lipid, heme iron and non-heme iron contents in FPI were decreased by 98.8, 36.8 and 91.9%, respectively in comparison with those of washed mince ( p < 0.05). Films from FPI had higher tensile strength (TS) and elongation at break (EAB) than those from washed mince for both pH (3 and 11) used for film preparation ( p < 0.05). Film from FPI at pH 3 showed the highest TS, while that from washed mince at pH 11 had the lowest TS ( p < 0.05). Nevertheless, films from FPI had higher WVP than those from washed mince for both pH used ( p < 0.05). At the same pH used for film preparation (3 or 11), films from FPI showed the lower TBARS values than those from washed mince ( p < 0.05). Nevertheless, films from both FPI and washed mince had the higher TBARS values when pH 3 was used for film preparation, compared with pH 11 ( p < 0.05). Among all films, those from FPI prepared at pH 3 had the highest transparency and no yellow discoloration was observed during the storage of 20 days, in comparison with other films ( p < 0.05). Conversely, film from washed mince prepared at pH 3 had the higher increase in b*-value and Δ E*-value than other films. Therefore, FPI could serve as a potential material for film preparation with lower contents of lipid and prooxidants, thereby preventing the yellow discoloration of the fish myofibrillar protein-based film during extended storage.

Gelation Properties of Spent Duck Meat Surimi‐Like Material Produced Using Acid–Alkaline Solubilization Methods

The gelation properties of spent duck meat surimi-like material produced using acid solubilization (ACS) or alkaline solubilization (ALS) were studied and compared with conventionally processed (CON) surimi-like material. The ACS process yielded the highest protein recovery (P < 0.05). The ALS process generated the highest lipid reduction, and the CON process yielded the lowest reduction (P < 0.05). Surimi-like material produced by the CON process had the highest gel strength, salt extractable protein (SEP), and water holding capacity (WHC), followed by materials produced via the ALS and ACS processes and untreated duck meat (P < 0.05). The material produced by the CON process also had the highest cohesiveness, hardness, and gumminess values and the lowest springiness value. Material produced by the ACS and ALS processes had higher whiteness values than untreated duck meat gels and gels produced by the CON method (P < 0.05). Surimi-like material produced using the ACS and CON processes had significantly higher myoglobin removal (P < 0.05) than that produced by the ALS method and untreated duck meat. Among all surimi-like materials, the highest Ca(2+)-ATPase activity was found in conventionally produced gels (P < 0.05). This suggests that protein oxidation was induced by acid-alkaline solubilization. The gels produced by ALS had a significantly lower (P < 0.05) total SH content than the other samples. This result showed that the acid-alkaline solubilization clearly improved gelation and color properties of spent duck and possibly applied for other high fat raw material.

Development of New Excess Sludge Reduction System with Combination of Alkaline Solubilization and High Speed Mixing

To develop a compact and low cost excess sludge reduction system, alkaline treatments were carried out using sludge from a petroleum refinery. Alkaline treatment with a concentration of 0.025-0.05 mol/L solubilized about 30% of the sludge after 1 h. Alkaline wastes from petroleum refinery such as sodium sulfide, sodium hydrosulfide, and diisopropanol amine could be used to solubilize about 10-30% of the sludge. Combination of alkaline solubilization (0.05 mol/L NaOH) and high speed mixing achieved about 50% solubilization rate after 1 h at 25°C. Application of this system in a petroleum refinery (600 m3 aeration vessel and 450 m3 sedimentation vessel, 3 m3 solubilization vessel) resulted in average solubilization rate of 44% and reduction rate of sludge of 47% during 64 days operation. Return of alkaline solubilized broth into the aeration vessel did not affect the treatment. In 40 L bench scale experiments, solubilization rate of 59% and sludge reduction rate of 94% were obtained when the amount of sludge solubilization was increased up to 2-3 times of excess sludge produced under the standard activated sludge treatment without the solubilization process.

Alkali-aided protein extraction of chicken dark meat: Composition and stability to lipid oxidation of the recovered proteins

Chicken dark meat has been considered as a major underused commodity due to the increasing demand for further-processed breast meat products. One option to increase the utilization of chicken dark meat is to extract myofibrillar proteins and separate them from fat and pigments to enhance their application for the preparation of further-processed meat products. The objective of the current study was to determine the effect of pH, in the range of 10.5 to 12.0, on the alkaline solubilization process of chicken dark meat. Aspects studied were the effect of the alkali-aided process on protein content, lipid composition, lipid oxidation, and color characteristics of the extracted meat. Each experiment and each assay were done at least in triplicate. Lipid content of the extracted meat showed a 50% reduction compared with the chicken dark meat. Neutral lipids were reduced by 61.51%, whereas polar lipids were not affected by the alkali treatments. There was a higher amount of TBA reactive substances observed in the extracted meat compared with chicken dark meat, indicating that extracted meat was more susceptible to oxidation. Long-chain polyunsaturated fatty acids (22:4n-6, 20:3n-3, 20:5n-3, 22:5n-3, and 22:6n-3), which were detected only in the polar lipids, were responsible for increasing lipid oxidation susceptibility of extracted meat compared with chicken dark meat. Alkali-aided extraction of chicken dark meat lightened the color of the meat. The redness, yellowness, and total heme pigments in extracted meat significantly decreased by 83, 11, and 53%, respectively, compared with chicken dark meat. Even though this process did not remove polar lipids, based on our early findings, the extracted meat had considerable physicochemical and textural properties for product preparation compared with those of raw dark meat. Hence, alkali recovery of protein can be considered a potentially useful method to increase the utilization of dark chicken meat.

A study of the distribution of aluminium in human placental tissues based on alkaline solubilization with determination by electrothermal atomic absorption spectrometry.

Aluminium (Al) is a nonessential element known to induce neurotoxic effects, such as dialysis dementia, in patients on hemodialysis, with compromised kidney function. The role of Al in the progression of some neurodegenerative diseases, such as Alzheimer's disease (AD), is controversial, and remains unclear. The effects of Al on other vulnerable populations, such as fetuses and infants, have been infrequently studied. In the present study, Al has been measured in human placenta samples, comprising ∼160 each of placenta bodies, placenta membranes, and umbilical cords, using electrothermal atomic absorption spectrometry (ETAAS) after atmospheric pressure digestion with tetramethylammonium hydroxide (TMAH) and ethylenediaminetetraacidic acid (EDTA). The sensitivity, or characteristic mass (m(0)), for Al at the 309.3-nm line was found to be 30 ± 4 pg. The instrumental detection limit (IDL) (3s) for Al in solution was calculated as 0.72 μg L(-1) while the method detection limit (MDL) (3s) was 0.25 μg g(-1). Accuracy was assessed through analysis of quality control (QC) materials, including certified reference materials (CRMs), in-house reference materials (RMs), and spike recovery experiments, of varying matrices. Placental tissue analyses revealed geometric mean concentrations of approximately 0.5 μg g(-1) Al in placenta bodies (n = 165) and membranes (n = 155), while Al concentrations in umbilical cords (n = 154) were about 0.3 μg g(-1). Al was detected in 95% of placenta bodies, and 81% of placenta membranes, but only in 46% of umbilical cords.

Gel-Forming Ability of Mackerel (Rastrelliger Branchysoma) Protein Isolate as Affected by Microbial Transglutaminase

The properties of gel from short-bodied mackerel ( Rastrelliger branchysoma ) alkaline-solubilized protein isolate with different levels (0, 0.25, 0.5, 1.0 and 1.5 unit/g sample) of microbial transglutaminase added (MTGase) and subjected to setting at 40 °C for 30 min, prior to heating at 90 °C for 20 min were investigated. The breaking force of the protein isolate gels with MTGase added at all levels was higher than that of the control gel (without the addition of MTGase) ( p 0.05). From the result, no changes in deformation in all gels treated with and without MTGase were noticeable ( p > 0.05). The lowest expressible moisture was found in the gel with 0.25 unit/g of MTGase ( p < 0.05). Generally, the whiteness of all gels incorporating MTGase were lower than that without MTGase ( p < 0.05). Therefore, the addition of MTGase at 0.25 unit/g sample in combination with an appropriate heating regime was a promising means to improve the gel properties, especially strength and water holding capacity, of short-bodied mackerel protein isolate prepared by alkaline solubilization.

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 Ca 2+-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.