Isoelectric Solubilization/precipitation Research Articles

The Emulsion Properties of Chicken Liver Protein Recovered through Isoelectric Solubilization/Precipitation Processes.

This study investigated the feasibility to improve the emulsifying capacity of chicken liver (CL) protein using different isoelectric solubilization/precipitation (ISP) processes. The CL proteins were first solubilized at alkaline pH 10.5, 11.0, 11.5, and 12.0, followed by precipitation at pH 5.0, 5.5, and 6.0, respectively. Fresh CL paste was set as the control (raw). With the increase in solubilization pH, the protein recovery yield increased under the same precipitation pH, and the pH 12.0, 5.5 treatment obtained the highest recovery yield of 82% (p < 0.05), followed by the pH 5.0 precipitation treatments and the pH 12.0, 6.0 treatment. The particle size distribution of D3,2 and D4,3 was smaller for the pH 10.5 (except for the D4,3 of pH 10.5, 5.0) and pH 11.0 solubilization treatments than those of the other treatments (p < 0.05), regardless of precipitation pH. Compared with that of the raw control, the emulsions of the pH 10.5 and pH 11.0 solubilization treatments, and pH 12.0, 6.0 treatment showed good stability. The pH 10.5, 6.0 treatment showed the best emulsification activity, followed by the pH 10.5, 5.5, pH 11.0, 6.0, pH 12.0, 6.0, pH 10.5, 5.0, pH 11.0, 5.5, and pH 11.0, 5.0 treatments, which were uniformly distributed and were stable without the stratification of emulsions. It was concluded that CL protein recovered through suitable ISP showed potential as an emulsifier, and thus expanded the application of CL protein for human consumption.

Effect of high-pressure homogenization on structural changes and emulsifying properties of chicken liver proteins isolated by isoelectric solubilization/precipitation

This study investigated the effect of high-pressure homogenization (HPH) (0, 20, 40 and 60 MPa) on the emulsifying properties and structural changes of chicken liver (CL) proteins isolated by isoelectric solubilization/precipitation (ISP) (with the acid/alkaline solubilization at pH 2.0, pH 3.0, pH 11.0 and pH 12.0 respectively and the precipitation at pH 5.5). Results showed that HPH could significantly decrease the particle size. With the increase of homogenization pressure, the solubility of the same ISP-isolated CL-proteins increased significantly and that of alkali-isolated proteins was the highest (P < 0.05). The preferable emulsifying activity index (EAI) and emulsifying stability index (ESI) were obtained at pH 11.0 after 40 MPa treatment (reaching 34.90 m2/g and 37.77% respectively), which appeared the highest creaming layer. Compared with other treatments, the corresponding same ISP-isolated CL-proteins at 40 MPa HPH had highest surface hydrophobicity index (H0) and free sulfhydryl content. After HPH, Raman spectroscopy revealed that the same ISP-isolated CL-proteins presented a decrease in α-helix accompanied by the increase of the β-sheet to be beneficial to the formation of stable emulsion. This study showed that suitable HPH combined with ISP treatments promoted the emulsifying stability of proteins.

Temperature-dependent in vitro digestion properties of isoelectric solubilization/precipitation (ISP)-isolated PSE-like chicken protein

The effects of various heating strategies (72 °C-20 min, 100 °C-60 min) on the digestibility of isoelectric solubilization/precipitation (ISP)-isolated pale, soft, exudative (PSE)-like chicken protein in an in vitro simulated gastrointestinal model were studied. Untreated PSE-like meat protein was used as the control. The hydrophobic groups were much more exposed in ISP-isolated protein than in the control protein, and the difference diminished after heating. The results of SDS-PAGE analyses and digestion kinetic parameters show the ISP isolates had higher digestibility than the control group when heated at 72 °C for 20 min (P < 0.05), but there was no significant difference between the 100 °C heated groups (P > 0.05). Additionally, all ISP-isolated groups showed higher peptide abundance than the control groups. In summary, heating at 72 °C for 20 min is beneficial to increase the digestion properties of ISP-isolated PSE-like chicken protein, but its gel properties are weaker than those of protein heated at 100 °C for 60 min.

Functional properties of gonad protein isolates from three species of sea urchin: a comparative study.

Sea urchin Mesocentrotus nudus, Glyptocidaris crenularis, and Strongylocentrotus intermedius gonad protein isolates (mnGPIs, gcGPIs, and siGPIs) were extracted by isoelectric solubilization/precipitation (ISP) from the defatted gonads, and their functional properties were compared. Sodium dodecyl sulfate polyacrylamide gel electrophoresis results showed the similar protein pattern between each protein isolate and defatted gonad, indicating the high efficiency of ISP processing for protein recovery. Amino acid profileconfirmed that the mnGPIs and siGPIs could be potential sources of essential amino acid in nature. As regard to functional properties, mnGPIs showed higher water- and oil- holding capacities followed bysiGPIs and gcGPIs and all protein isolates presented great foaming property. As for emulsifying activity index (EAI), mnGPIs, gcGPIs, and siGPIs showed the minimum solubility and EAI at pH 5, 3, and 4, respectively, and behaved a pH-dependent manner. The gcGPIs revealed the highest EAI from pH 6 to 8 among the samples. In addition, circular dichroism showed increased content of β-sheet at the expense of α-helix and β-turn, suggesting the structure denaturation of the protein isolates. Indeed, no statistical difference was observed between secondary structure of mnGPIs and siGPIs. Moreover, ISP processing increased free sulfhydryl content of sea urchin protein isolates, but no difference was observed among the samples. Furthermore, siGPIs revealed the highest amount of total sulfhydryl and disulfide bonds, whereas both defatted gonads and protein isolates from G. crenularis presented the maximum surface hydrophobicity. These results suggest that gonad protein isolates from three species of sea urchin possess various functionalities and therefore can be potentially applied in food system. PRACTICAL APPLICATION: Sea urchin M. nudus, G. crenularis, and S. intermedius gonads are edible, whereas the functional properties of protein isolates from sea urchin gonad remain unknown. In this case, the extraction and comparison of three species of sea urchin gonad protein isolates will not only confirm functional properties but also screen food ingredients with suitable functions. In this study, functionalities of protein isolates derived from M. nudus, G. crenularis, and S. intermedius gonads would provide potential application in bakery food and meat products or as emulsifier candidates in food system.

Physiochemical Properties and Functional Characteristics of Protein Isolates from the Scallop (Patinopecten yessoensis) Gonad.

Protein isolates were recovered from scallop (Patinopecten yessoensis) gonads to develop a novel functional matrix by investigating their physiochemical and functional properties. Scallop gonad protein isolates (SGPIs) were prepared from degreased scallop gonads (DSGs) by an alkali extraction and isoelectric solubilization/precipitation (ISP) process. The protein compositions of the SGPIs were mainly vitellogenin and beta-actin with molecular weights of 266 and 42kDa, respectively, as determined using Nano-liquid chromatography-mass/mass (Nano-LC-MS/MS). After the ISP process, the protein solubility of the SGPIs was significantly improved, and the surface hydrophobicity of SGPIs intensely increased by 1.1-fold, which were attributed to the exposure of aromatic residues such as phenylalanine, tyrosine, and tryptophan. However, the content of total/reactive sulfhydryl in SGPIs was decreased compared with that of DSGs. Meanwhile, the ISP process caused partial protein unfolding, as indicated by circular dichroism analysis, which exhibited a remarkable rise in the β-sheet content with a parallel decline in the α-helix and random coil contents (P < 0.05). SGPIs exhibited a better oil absorption capacity and foaming property than both DSGs and soybean protein isolates (SPIs). Moreover, the emulsifying capacity of SGPIs was greatly enhanced by the ISP process, which was superior to the effect of commercial SPIs and was ascribed to its favorable solubility as well as surface characteristics. PRACTICAL APPLICATION: During the processing of scallop (Patinopecten yessoensis) adductors, scallop gonad, a high-protein part, is usually discarded as processing by-products despite its edibility. In recent years, scallop gonads are regarded as good sources to develop protein matrices due to their high protein content and numerous nutrients. In this study, scallop gonad protein isolates (SGPIs) were isolated by isoelectric solubilization/precipitation (ISP) process. The preferable solubility, foaming property coupled with high emulsifying property of SGPIs indicated that the SGPIs could be potentially utilized as a good protein emulsifier and additives in production of kamaboko gels, hamburger patties, sausages, and pet foods.

Effects of High Hydrostatic Pressure on the Solubilities and Structures of Alaska Pollock Protein

Alaska pollock is an important protein source which is extensively used in the food industry. Pollock protein isolates (PPI) with significantly enriched protein contents could be prepared using isoelectric solubilization/precipitation (ISP) processing; however, the functional properties of this process is limited by the large amount of water-insoluble proteins. In this study, we investigated the influence of high hydrostatic pressure (HHP) treatment on the solubility and structural changes of PPI. PPI obtained using ISP is treated with hydrostatic pressures of 200, 300, 400, and 500 MPa for up to 15 min, and the HHP-treated samples were observed to exhibit significantly improved solubilities. Further biochemical assays reveal that the continuous HHP treatments reduce the contents of free sulfhydryl groups and promote the formation of macromolecules with better water solubilities, which may induce the solubility improvements of the HHP-treated PPI. Our results indicate that HHP can be utilized to effectively prepare highly water- soluble Alaska pollock protein in food processing.

Oxidative stability of isoelectric solubilization/precipitation-isolated PSE-like chicken protein

The effects of a hydroxyl radical generating system (Fe3+/H2O2) at different H2O2 concentrations (0, 1 and 10 mM) on the chemical and structural properties of isoelectric solubilization/precipitation (ISP)-isolated PSE (pale, soft, exudative)-like chicken protein were investigated. Both acid and alkaline treatments effectively reduced the pro-oxidant contents in PSE-like meat systems, such as lipids, pigments and myoglobins. The ISP samples generated less carbonyl derivatives and Schiff base but yielded higher sulfhydryl and free amine loss in response to oxidation. Correspondingly, sulfur-contained amino acids in ISP samples were more easily converted, even at the 1-mM H2O2 concentration, than in the PSE-like meat paste. Moreover, the ISP-isolated proteins have possibly maintained their gelling properties after oxidation compared to the PSE-like meat paste. In regards to chemical and structural modification, the ISP treated protein showed a different susceptibility to oxidation in vitro.

Effect of κ-carrageenan on gelation and gel characteristics of Antarctic krill (Euphausia superba) protein isolated with isoelectric solubilization/precipitation.

Isoelectric solubilization/precipitation (ISP) was used to extract krill protein isolate (KPI). Due to krill endogenous proteases ISP-KPI barely forms gel which is a major hurdle in wide application of this tremendous protein source for direct human consumption. The objective was to improve gelation and elucidate interaction mechanism between κ-carrageenan and KPI. κ-Carrageenan was added to KPI at 0.00, 0.75, 1.50, 2.25, and 3.00 g/150 g and heated at 90 °C for 15 min. Added κ-carrageenan improved texture of KPI gels. However, the level of addition had minimal effect. SDS-PAGE revealed severe proteolysis of KPI even during heating. Total and free sulfhydryl were not different, while surface hydrophobicity and water-holding-capacity slightly decreased and increased, respectively with added κ-carrageenan. Fourier-transform-infrared-spectroscopy showed none-to-minimal shift of β-sheet and α-helical protein structure; while CC and CO stretching as well as CH bending of κ-carrageenan showed the greatest shift, indicating that κ-carrageenan was mainly responsible for gel formation.

Potential of recovered proteins from invasive green crabs (Carcinus maenas) as a functional food ingredient

Invasive green crabs contain high-quality proteins that have potential as functional ingredients in formulated foods. This study evaluated the functional properties and compositional characteristics of green crab proteins recovered by isoelectric solubilization/precipitation (ISP). Mechanically separated green crab mince (control) was solubilized at pH 2 (PP2) and pH 10 (PP10), then proteins were precipitated at pH 5.5 and subsequently dried. Yield of recovered protein powder was approximately 1.5 times higher for PP2 than for PP10. Compared with the control (230 g kg-1 ), ash content was reduced in PP2 (54 g kg-1 ) and PP10 (23 g kg-1 ) samples. PP2 contained predominantly large-molecular-weight proteins, while small-molecular-weight proteins were distributed in PP10. With regard to functional properties, at pH 7 and 8, solubility of PP10 was significantly higher than that of PP2. At pH 7.5, PP10 exhibited significantly higher emulsifying activity (1482 m2 g-1 ) than PP2 (858 m2 g-1 ) and the control (958 m2 g-1 ). PP2 showed statistically higher gelation activity and had higher L* value than PP10 and the control. The results indicate that recovered green crab proteins have functional properties potentially useful for formulated foods, and that these functional properties can be modified by the solubilization pH during the recovery process. © 2018 Society of Chemical Industry.

Turning Invasive Green Crab (Carcinus maenas) into Opportunity: Recovery of Chitin and Protein Isolate Through Isoelectric Solubilization/Precipitation

PURPOSE: The potential of the isoelectric solubilization/precipitation (ISP) process as a sustainable method for recovering value-added bio-products from invasive European green crab was investigated. METHODS: Protein isolate and chitin were extracted from green crab through ISP procedure. Both bio-products were characterized in terms of physicochemical composition. Protein profile and surface morphology were also determined for the extracted protein isolate and chitin, respectively. RESULTS: Green crab proteins were mostly soluble at neutral and alkaline pH values (> 88%). The minimum green crab protein solubility (40.40%), corresponding to the isoelectric pH, occurred at pH 4.0. The application of the ISP process to green crab resulted in the generation of two fractions: crab protein isolate and chitin-rich crab shell, with high recovery yields (83.35 and 88.92%, respectively, on a dry weight basis). The recovered protein isolate contained high protein and fat contents and low ash level (68.60, 11.95 and 0.71%, respectively, on a dry basis). The recovered crab shell contained 11.25% chitin, which was nearly twice the amount of chitin in the whole green crab. Chitin extracted from the shell after the application of the ISP process did not differ from that extracted directly from the whole green crab. Both chitins had similar (P > 0.05) degree of deacetylation (31.0 and 32.4%, respectively) as well as similar surface morphology as revealed by scanning electron microscopy (SEM). CONCLUSIONS: The present study demonstrated that protein isolate and chitin rich shell can efficiently be recovered from green crab using isoelectric solubilization/precipitation and subsequently be used as value-added bio-products.

Rheological and physical properties of O/W protein emulsions stabilized by isoelectric solubilization/precipitation isolated protein: The underlying effects of varying protein concentrations

To better understand the potential of using isoelectric solubilization/precipitation (ISP)-isolated protein on emulsion-type meat products, the influences of protein concentration on the physical and rheological properties of protein emulsions were investigated. An oil-in-water (O/W) emulsion containing 20% soybean oil was stabilized by pale, soft and exudative (PSE)-like muscle protein (CON) and ISP-isolated PSE-like muscle protein (ISP) at the concentrations of 50, 100 and 150 mg/ml. Morphologically, the ISP-isolated protein demonstrated better emulsion capacity compared to the CON group, which formed uniform, long-lasting emulsions and dispersed smaller emulsified oil droplets. The apparent viscosity of all emulsion samples was fitted well by the Ostwald-de-Waele model (R2 > 0.9). All emulsions exhibited non-Newtonian, pseudoplastic behaviors with the fitting parameters being highly dependent on both protein type and concentration. In the frequency sweep, all emulsion systems were classified as a “strong gel” because G’’ >> G’, especially when concentrations were 100 or 150 mg/ml. Based on a temperature sweep oscillatory curve, the heat-induced gelation behaviors of PSE-like protein emulsions were modified by ISP processing. In addition, the elasticity of the final emulsion gel was higher in the ISP group when compared to the CON group. The thermal gelling properties of ISP-isolated protein emulsions appeared to be impaired when the concentrations reached 150 mg/ml. It was concluded that ISP processing could effectively improve the emulsion properties of PSE-like meat protein.

Use of an isoelectric solubilization/precipitation process to modify the functional properties of PSE (pale, soft, exudative)-like chicken meat protein: A mechanistic approach

The functionality of pale, soft, exudative (PSE)-like chicken protein was improved by isoelectric solubilization/precipitation (ISP) treatment. PSE-like chicken proteins were solubilized at an acidic pH 3.5 or an alkaline pH 11.0, followed by precipitating at pH 5.5 and 6.2. PSE-like meat paste was treated as control (CON). Precipitated at pH 6.2 led to a more elastic gel than at pH 5.5. Water distribution of ISP-isolated protein was affected by precipitation pH. More tryptophan residues exposed and –SH was partially oxidized to disulfide bond after ISP treatment, which led to large aggregates formation and higher viscosity of ISP isolated proteins than of CON. Absolute zeta potential of alkali-treated protein was higher than other counterparts, indicating stronger electric repulsion. ISP treatments could convert α-helix structure to relatively irregular structures. Overall, solubilizing at pH 11.0, combined with a precipitation pH 6.2 ISP treatment offers a potential for enhanced functionality of PSE-like chicken protein.

Micro-emulsification/encapsulation of krill oil by complex coacervation with krill protein isolated using isoelectric solubilization/precipitation

This study determined feasibility of krill protein isolated with isoelectric solubilization/precipitation (ISP) as wall material to microencapsulate krill oil by freeze-drying. Effects of krill oil/krill protein ratio on properties of microcapsules were investigated. With increased ratio, crude protein of microcapsules decreased, while total lipid increased. Although microcapsule oil loading capacity increased, loading and encapsulation efficiencies decreased. Thin layer chromatography (TLC) confirmed abundance of phospholipids, which are amphiphilic; and thus, resulted in stable emulsion (emulsion stability index). Microcapsules contained ω-3 polyunsaturated fatty acids (PUFAs) at 43–60, including eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) at 28–41 and 9–11 g/100g of total FAs, respectively. SDS-PAGE electrophoresis revealed proteolysis of ISP krill protein, probably causing reduced loading and encapsulation efficiencies. SEM showed that krill oil/krill protein ratio affected surface microstructure. ISP krill protein showed potential as a wall material to microencapsulate krill oil; and thus, expand application of krill oil/protein for human consumption.

Optimised protein recovery from mackerel whole fish by using sequential acid/alkaline isoelectric solubilization precipitation (ISP) extraction assisted by ultrasound

The growing fishery industry needs to find new green-processes in order to provide a solution to the huge amount of wastes and by-products that such industrial activity produces. Currently, around a 40% of the total weight of the mackerel is considered a by-product, because just the fillets are used in the food market. ISP method has been revealed as a useful tool for protein recovering, however the yield of this process is traditionally lower than enzymatic methods. In present work, the use of sequential acid/alkaline extraction and alkaline extraction assisted by ultrasound, have been implemented in order to increase the yield of the process. It has been demonstrated that (i) sequential extraction is able to recover practically 100% of total protein, and (ii) applying ultrasound to alkaline extraction is possible to recover more than 95% of total protein from mackerel by-products. Extracted proteins were characterized according to their size, and the amino acid profile of final product was determined.

Amino acid and fatty acid profiles of materials recovered from Prussian carp, Carassius gibelio (Bloch, 1782), using acidic and basic solubilization/ precipitation technique

Isoelectric solubilization /precipitation (ISP) process was used to isolate protein from muscles of Prussian carp, Carassius gibelio (Bloch, 1782). Fish protein and lipid were recovered from whole gutted Prussian carp using acidic and basic isoelectric solubilization/precipitation followed by assaying amino acid and fatty acid profile. Essential amino acids content in acidic and basic pH treatment of ISP of Prussian carp were 216.6 and 218.7 mg.g-1, respectively. Results showed that identified amino acids in Prussian carp protein isolated by ISP method, could meet all needs of adults, but a supplementary protein must be used for children. Limiting amino acids in both acidic and basic treatments were methionine and cysteine. Nineteen fatty acids of saturated (SFA), monounsaturated (MUFA) and polyunsaturated (PUFA) groups were identified in lipid recovered in isoelectric solubilization/precipitation process. Total PUFA in basic treatment was noticeably higher than in acidic one. N-3/n-6 ratio in basic pH treatment was also higher than in acidic one.

Precipitation and ultimate pH effect on chemical and gelation properties of protein prepared by isoelectric solubilization/precipitation process from pale, soft, exudative (PSE)-like chicken breast meat

Pale, soft, exudative (PSE)-like chicken breast is considered deteriorated raw material in the poultry meat industry that has inferior processing ability. The chemical and gelation properties of PSE-like chicken breast meat paste were studied. These pastes were prepared by the pH adjustment method and protein isolation using the isoelectric solubilization/precipitation (ISP) process from PSE-like chicken meat. The ISP-isolated samples were solubilized at pH 11.0 and recovered at pH 5.5 and 6.2. The ultimate pH of the ISP-isolated protein and meat paste was adjusted to 6.2 and 7.0. The ultimate pH in this article referred to the final pH of the extracted protein and meat paste. Higher reactive sulfhydryl content and surface hydrophobicity were found in the precipitation at pH 6.2 than at pH 5.5. However, various ultimate pH values showed no significant influence on the surface hydrophobicity. The hardness of gel, as measured by textural profile analysis, was improved using 6.2 as the precipitation pH compared with pH 5.5. The viscoelastic modulus (G′) of gel pastes prior to the thermal gelation was higher with ISP treatment. However, lower G′ was seen after thermal gelation compared with the control. Dynamic rheological measurement demonstrated a different gel-forming mechanism for protein precipitated at pH values of 5.5 and 6.2 compared with the meat paste. The cooking loss showed that the recovered protein failed to form a gel with good water-retention capacity unless the ultimate pH was adjusted to 7.0. Gels made from protein extracted by the ISP method had higher yellowness and lower redness values, probably due to protein denaturation. Precipitation at pH 6.2 formed a harder gel with lower water-retention ability than that at pH 5.5, and this result was possibly due to higher surface hydrophobicity and S-S bridge formation. Overall, network characteristics of ISP-treated protein gels were strongly dependent on precipitation pH and ultimate pH.

Mass balance for isoelectric solubilization/precipitation of carp, chicken, menhaden, and krill

Mass balance analysis was conducted for isoelectric solubilization/precipitation (ISP) processing of carp, chicken, menhaden, and krill based on proximate composition of input materials and recovered fractions (i.e., protein, lipid, insoluble, and process water). Protein recovery yield and lipid reduction were also determined. Thin layer chromatography (TLC) and SDS-PAGE electrophoresis allowed determination of lipid classes and protein electrophoretic patterns. ISP concentrated crude protein (72–90 g/100 g, dry basis) and reduced total lipid (3–16 g/100 g, dry basis) in the protein fraction recovered with ISP when compared to the input materials (48–68 g of crude protein and 15–45 g of total lipid per 100 g, dry basis). Protein recovery yield and lipid reduction were 45–66 and 79–98 g/100 g, respectively. However, lipid fraction did not form when menhaden and krill were processed with ISP. Krill and menhaden lipids were distributed in the process water in addition to the protein and insoluble fractions. TLC showed that krill and menhaden lipids had high phospholipid (PL), but low triglyceride (TAG) content, contributing to emulsification and preventing formation of lipid fraction. SDS-PAGE confirmed presence of myosin and actin in protein fraction recovered from carp and chicken as well as proteolysis in menhaden and severe protein degradation in krill.

Changes of Molecular Forces During Thermo-Gelling of Protein Isolated from PSE-Like Chicken Breast by Various Isoelectric Solubilization/Precipitation Extraction Strategies

Changes in protein intermolecular interactions during thermo-gelling were measured to compare the gelation properties of isoelectric solubilization/precipitation (ISP)-isolated protein extracted (solubilized at 3.5 and 11.0, precipitated at 5.5 and 6.2) from pale, soft, and exudative (PSE)-like chicken breast meat with raw meat paste. The solubility of both in water and salt (0.6 M NaCl) decreased significantly after ISP treatments. Protein profile analysis revealed that precipitation pH showed little influence on protein profile. Under pH 3.5 and pH 11.0 solubility conditions, the recovered protein at pH 6.2 showed significantly higher gel hardness than that at pH 5.5, which can be induced by hydrophobic change. Surface hydrophobicity (SH0) and hydrophobic interactions at 25 °C presented similar results, indicating that the soluble protein at pH 11.0 exhibited a higher value after precipitation at pH 6.2 than that at pH 5.5, and the hydrophobicity of pH 3.5 isolates was higher than that of the pH 11.0 groups. However, the maximum hydrophobicity upon heating was inconsistent with initial tendencies. Given that the hydrophobic residues were exposed sufficiently during the ISP process, the ISP-treated proteins, particularly the samples extracted at pH 3.5, might be less susceptible to heat-induced exposure. The gelation behavior of the ISP-treated proteins had been modified on the basis of the intermolecular bonds during heating. In conclusion, the precipitation condition demonstrated excellent relevance for product development based on functionality.

Preparation and characterization of protein isolate from Yellowfin tuna Thunnus albacares roe by isoelectric solubilization/precipitation process

Isoelectric solubilization/precipitation (ISP) processing allows selective, pH-induced water solubility of proteins with concurrent separation of lipids and removal of materials not intended for human consumption such as bone, scales, skin, etc. Recovered proteins retain functional properties and nutritional value. Four roe protein isolates (RPIs) from yellowfin tuna roe were prepared under different solubilization and precipitation condition (pH 11/4.5, pH 11/5.5, pH 12/4.5 and pH 12/5.5). RPIs contained 2.3–5.0 % moisture, 79.1–87.8 % protein, 5.6–7.4 % lipid and 3.0–3.8 % ash. Protein content of RPI-1 and RPI-2 precipitated at pH 4.5 and 5.5 after alkaline solubilization at pH 11, was higher than those of RPI-3 and RPI-4 after alkaline solubilization at pH 12 (P < 0.05). Lipid content (5.6–7.4 %) of RPIs was lower than that of freeze-dried concentrate (10.6 %). And leucine and lysine of RPIs were the most abundant amino acids (8.8–9.4 and 8.5–8.9 g/100 g protein, respectively). S, Na, P, K as minerals were the major elements in RPIs. SDS-PAGE of RPIs showed bands at 100, 45, 25 and 15 K. Moisture and protein contents of process water as a 2’nd byproduct were 98.9–99.0 and 1.3–1.8 %, respectively. Therefore, yellowfin tuna roe isolate could be a promising source of valuable nutrients for human food and animal feeds.

Extracting Protein from Antarctic Krill (Euphausia superba)

ABSTRACTThe isoelectric solubilization/precipitation (ISP) process was applied to Antarctic krill protein extraction. The solubility of Antarctic krill proteins and their fluoride content were studied between pH 1.00–13.75. The previous krill protein extraction conditions using ISP were improved. Excess fluoride in Antarctic krill was removed using a water-washing method according to its solubility. To save water, a multistage countercurrent system was used to optimize the ISP method. The results showed that the solubility of Antarctic krill proteins reached a minimum at pH 4.5 and a maximum at pH 13.5, while the concentration of dissolved fluoride was relatively unchanged (16.78–20.50 mg/L), with pH 2.00–13.50. Water-washing 4 times could reduce fluoride 98.14 ± 0.01% from krill with about a 5.14 ± 0.21% protein loss. The reduction allows krill protein to meet the Chinese National Standard (GB 2762-2005) for fluoride. Meanwhile, the four-stage countercurrent system achieved almost the same high fluoride removal rate (98.58 ± 0.01%) using only 25% of the water.