Gelation properties of goose liver protein recovered by isoelectric solubilisation/precipitation process

Isoelectric solubilisation/precipitation (ISP) process was applied to goose liver (GL) for protein extraction. The gelation properties of proteins extracted by acid processes (ACP, pH 2.0, 2.5 and 3.0) and alkaline processes (ALP, pH 11.0, 11.5 and 12.0) were estimated, where the unextracted ground GL was set as the control. Nearly 58.39~79.00% of GL proteins were recovered by ISP treatments. High molecular weight (100~250 kDa) proteins were found to be partially hydrolysed by ACP, while few changes in proteins occurred during ALP. As evidenced by rheological and textural measurements, ALP proteins formed gels with high elasticity and superior texture, whereas ACP proteins had inferior gelation properties. Moreover, ALP proteins were able to form a highly interconnected and homogeneous three‐dimensional microstructure. Predominantly, gels produced by 11.0 had optimal texture and the lowest cooking loss (P < 0.05). These results suggested that the ISP process (ALP) is a potential method to improve the economic value of GL.     

Functional properties of proteins recovered from silver carp (Hypophthalmichthys molitrix) by isoelectric solubilization/precipitation

Isoelectric solubilization/precipitation at acidic and basic pH ranges was applied to whole gutted silver carp (Hypophthalmichthys molitrix) in order to recover muscle proteins. Thermal denaturation (T_onset, T_max, and ΔH), viscoelasticity (G′), and texture properties (shear stress) of proteins recovered from carp as affected by functional additives (beef plasma protein, potato starch, exogenous transglutaminase, polyphosphate, and titanium dioxide) were determined and compared to Alaska pollock surimi. Proteins recovered from carp showed typical endothermic transitions only when functional additives were used. Similar to endothermic transitions, viscoelasticity in carp proteins increased only when the additives were used. Typical endothermic peaks and viscoelasticity increase were recorded for Alaska pollock surimi. Carp protein-based gels with functional additives had lower (P < 0.05) shear stress than their surimi counterparts, but greater (P < 0.05) or similar (P > 0.05) when compared to surimi gels without functional additives. In addition, generally higher shear stress was measured for carp protein-based gels developed from basic pH treatments than the acidic counterparts. The present study indicates that proteins can be recovered from whole gutted carp using isoelectric solubilization/precipitation. However, if the recovered proteins are used for subsequent development of restructured food products, functional additives should be used.     

Effect of heat pretreatment before isoelectric solubilisation/precipitation on the characteristics of Pacific oyster (Crassostrea hongkongensis) and Antarctic krill (Euphausia superba) protein isolates

Heat treatment is a convenient way to eliminate the effects of endogenous enzymes on the industrial production of stable products. This study describes the preparation of protein isolates from oysters (OPI and HOPI) and krill (KPI and HKPI) by isoelectric solubilisation/precipitation (ISP) with or without heat pretreatment and comparatively presents their characteristics. The results showed that the solubilities of HOPI (24.08 ± 1.94%) and HKPI (42.29 ± 0.78%) were higher than those of OPI (13.46 ± 0.78%) and KPI (21.71.46 ± 1.51%), and the free and total sulphhydryl (-SH) content and surface hydrophobicity of HOPI and HKPI were higher than those of OPI and KPI, which are related to higher fat content of HOPI (10.37 ± 0.55%) and HKPI (34.89 ± 1.19%). SDS–PAGE and gel chromatography pattern results showed that macromolecular proteins were degraded by endogenous enzymes in OPI and KPI, while they remained unaffected in HOPI and HKPI. The FT-IR spectra showed similar patterns between OPI and HOPI and between KPI and HKPI. While the essential amino acid content was similar for OPI and HOPI (47.06 ± 1.33% and 47.93 ± 1.02%), that of KPI and HKPI (50.89 ± 0.89% and 51.19 ± 1.11%, respectively) was not significantly different.     

Compositional Characteristics of Materials Recovered from Headed Gutted Silver Carp (Hypophthalmichthys molitrix) by Isoelectric Solubilization and Precipitation Using Organic Acids

Protein was recovered from headed gutted silver carp by isoelectric solubilization at pH 2.5, 3.0, 11.5, or 12.0 and precipitation (ISP) at pH 5.5 using acetic (AA) or a 30% formic and lactic acid combination (F&L) and 10 N sodium hydroxide. Total protein and fat recovery yields, proximate composition and mineral analyses of fractions were determined. Protein and lipid recovery yields when solubilized under basic conditions were comparable to yields reported from other studies using hydrochloric acid; however, the recovered fractions were less pure. Processing at basic pH using AA was more effective than F&L at removing impurities (P < 0.05) from the recovered protein fraction and impurities were effectively removed from recovered lipids regardless of processing pH or acid type (P > 0.05). For the most part, sodium was greater (P < 0.05) and there was less calcium, phosphorus, magnesium, and iron (P < 0.05) in the recovered protein regardless of acid used when compared to the initial paste. This research shows that organic acids have the potential to recover protein and lipid by ISP processing. Practical Application: This research presents a reliable method for extracting nutritionally valuable fish protein and oils from otherwise hard to process fish and its byproducts. Replacing the traditionally used strong acids with organic acids might further accomplish bacterial load reduction while resulting in similar to or improved protein recovery yields. Therefore, this technology may increase the commercial viability of hard to process fish.     

Effect of isoelectric solubilization/precipitation and titanium dioxide on whitening and texture of proteins recovered from dark chicken-meat processing by-products

Processing of chicken generates by-products containing muscle proteins attached to bones and skin that, if recovered, could be a functional ingredient in restructured food products. However, color of restructured products made of proteins recovered from chicken processing by-products is poor. The by-products contain bones, skin, fat, etc. that affect color of restructured products. Therefore, color properties need to be improved. The objectives of this study were to determine effects of isoelectric solubilization/precipitation (ISP) and TiO₂ on instrumental color and texture properties of heat-set gels made of proteins recovered from dark chicken-meat processing by-products as compared to gels made of chicken breast meat. Skin-on bone-in chicken drumsticks were used as a model dark chicken-meat processing by-products. TiO₂ at 0-1 g/100 g and canola oil at 10 g/100 g were added to the ISP-recovered proteins followed by cooking. Due to higher (P < 0.05) yellowness (b∗) and lower (P < 0.05) lightness (L∗), the whiteness of drumstick gels without TiO₂ was lower (P < 0.05) than breast gels. TiO₂ at 1 g/100 g with canola oil resulted in slightly better (P < 0.05) whiteness of drumstick gels than breast gels. TiO₂ did not deteriorate gel texture, which was generally comparable to breast gels. This research indicates that ISP allows recovery of proteins from skin-on bone-in dark chicken-meat processing by-products without removal of bones, skin, and fat prior to processing. Addition of TiO₂ to proteins recovered from these by-products allows development of heat-set gels with color and texture comparable to chicken breast gels. Although this study shows the potential for a novel, marketable food product, sensory tests are recommended.     

Amino acid, fatty acid, and mineral profiles of materials recovered from rainbow trout (Oncorhynchus mykiss) processing by-products using isoelectric solubilization/precipitation

ABSTRACT:  Protein, lipid, and insolubles (bones, skin, scales, fins, insoluble protein, and more) were recovered from rainbow trout processing by-products by means of isoelectric solubilization/precipitation at basic pH and acidic pH. Isoelectric solubilization/precipitation of the trout processing by-products resulted in the recovery of protein that was higher ( P < 0.05) in essential amino acids (EAAs), non-EAAs, and total EAA/total AA ratio when compared to the processing by-products. Basic pH treatments yielded a higher ( P < 0.05) content of EAAs than the acidic pH treatments. Nutritional quality of the recovered protein was high based on EAAs meeting the FAO/WHO/UNU recommendations for adults. The presence of omega-3 and omega-6 fatty acids (ω-3, ω-6 FAs) and the ω-3/ω-6 ratio in the recovered lipids were similar to the trout processing by-products, indicating that the pH treatments had no effect on these FAs. Ca and P contents of the processing by-products exceeded the recommended dietary allowances (RDA), but Fe and Mg did not. Basic pH treatments yielded protein with the lowest ( P < 0.05) amount of minerals and the highest ( P < 0.05) amount of Ca, P, and Mg in the insolubles when compared to acidic pH. The isoelectric solubilization/precipitation of the processing by-products effectively removed minerals from the recovered protein without removal of the bones, skin, scales, fins, and so on, prior to processing. The results indicated that isoelectric solubilization/precipitation, particularly at basic pH, permitted recovery of high-quality protein and lipids from fish processing by-products for human food uses; also, the recovered insolubles may be used in animal feeds as a source of minerals.     

Functional and nutritional characteristics of proteins and lipids recovered by isoelectric processing of fish by-products and low-value fish: A review

Several fisheries are over-exploited and may collapse; yet the amounts of fish processing by-products containing muscle proteins and ω-3-rich oil are staggering. The by-products are land-filled, ground and discarded or otherwise diverted from human consumption. Due to the lack of technology to recover proteins and lipids from by-products or low-value species, this tremendous resource is unavailable for human consumption. Isoelectric solubilisation/precipitation (ISP) allows efficient recovery of fish proteins and oil which retain functionality and nutritional value of food products. Isoelectric point (pI) is a pH where protein maintains zero electrostatic charge. At pI, protein–protein hydrophobic attraction overcomes protein–water electrostatic attraction resulting in isoelectric precipitation. Conversely, isoelectric solubilisation occurs at a pH different from pI, whereby protein–water attraction and protein–protein electrostatic repulsion are favoured. Therefore, protein solubility/insolubility is induced by ISP, respectively. Consequently, ISP allows selective protein recovery. Lipids are also recovered during ISP processing. This article reviews recent ISP developments to recover proteins and lipids from by-products and low-value marine species.     

Color improvement by titanium dioxide and its effect on gelation and texture of proteins recovered from whole fish using isoelectric solubilization/precipitation

Whiteness is a critical attribute for restructured fish products such as surimi seafood. However, the whiteness of gels made from proteins recovered from fish processing by-products or whole fish using isoelectric solubilization/precipitation is poor. The by-products and whole fish contain bones, scales, skin, etc. that affect gel color. Therefore, whiteness needs to be improved if marketable products are to be developed from recovered proteins. The objectives of this study were to determine effects of titanium dioxide (TiO₂) on: (1) color; (2) texture; and (3) viscoelasticity (G′) of gels made from isolated carp proteins and Alaska pollock surimi. Carp proteins were recovered with isoelectric solubilization/precipitation. TiO₂ was added to carp proteins at 0-0.5 g/100 g. TiO₂ was not added to surimi. Due to much higher (P < 0.05) yellowness (b^∗) and lower (P < 0.05) lightness (L^∗), the whiteness of carp gels without TiO₂ was lower (P < 0.05) than surimi gels. TiO₂ at ≥ 0.2 g/100 g resulted in better (P < 0.05) whiteness of carp gels than surimi gels without chalky and artificially white appearance. TiO₂ did not affect texture or viscoelasticity. This research demonstrates that whiteness of restructured fish products based on proteins recovered from whole fish via isoelectric solubilization/precipitation can be similar to the whiteness of surimi seafood.     

Effect of microbial transglutaminase and setting condition on gel properties of blend fish protein isolate recovered by alkaline solubilisation/isoelectric precipitation

The effect of microbial transglutaminase (M-TGase) (0–0.6 units g⁻¹ sample) and setting condition (25 °C/180 min, 30 °C/120 min, 35 °C/60 min and 40 °C/30 min) on gel properties of blend protein isolate of gutted kilka and silver carp was studied. The protein isolate provided a good substrate for M-TGase activity so that a low amount of M-TGase (0.2 unit g⁻¹ sample) substantially improved textural properties and water holding capacity (WHC) of the gels. Breaking force of the gels was positively affected by M-TGase up to 0.6 unit g⁻¹ sample, but it negatively affected their WHC. Prior setting at 25–35 °C increased the breaking force of proteins compared to directly heated gel, resulting in maximum breaking force at 35 °C/60 min. However, the setting at 40 °C/30 min caused proteolysis, which was reflected in higher amounts of TCA-soluble peptides and gel weakening. Denser microstructure and higher myosin heavy chain polymerisation observed in the gels which experienced the setting was well correlated with improvement in textural properties.     

Gel properties of silver carp (Hypophthalmichthys molitrix) and chicken mixture gels as affected by setting temperatures

This study aimed to evaluate the effect of setting temperatures (30°C, 35°C, 40°C, 45°C, and 50°C) on gel properties and protein profiles of paste gels derived from silver carp (Hypophthalmichthys molitrix) and chicken meat. The mixture composed of 50% (w/w) chicken meat and 50% (w/w) silver carp meat, and the three paste gels, were assessed based on color, gel strength, TPA, water distribution, chemical interactions, and SDS-PAGE. Chicken gels had better gel properties and a higher content of immobilized water than the mixture or fish gels, regardless of setting conditions. On the other hand, an appropriate setting temperature for the three paste gels promoted aggregation of the myosin heavy chain (MHC) and the formation of hydrophobic interactions and disulfide bonds, which resulted in superior gel properties. Pre-incubation at 40°C enhanced gel properties of fish meat, but pre-incubation at 45°C and 50°C were appropriate for achieving better gels for the mixture and chicken, respectively. These results indicated that there is the potential to obtain mixed products and new meat products by utilizing chicken and fish meat that have improved gel properties.     

酸溶条件及高强度超声波对鲢鱼肉分离蛋白的提取及凝胶特性的影响

研究了不同酸溶条件（鱼肉匀浆液的pH值）和高强度超声波（High Intensity Ultrasonic treatment, HIU）对酸溶等电点沉淀法鲢鱼肉分离蛋白（protein isolate, PI）的提取、蛋白组成以及凝胶特性的影响。数据显示：降低pH能显著提高蛋白回收率（由pH 4.0到3.0,提高了21.11%）,但pH<3.0时,进一步降低pH对蛋白回收率不再有提高作用;HIU显著提高了蛋白回收率（pH 3.0时,提高了3.77%）;PI中以肌原纤维蛋白为主,pH降低能够显著减少等电点处可溶性中等分子蛋白种类及浓度,而HIU对此影响不大。pH降低和HIU均会增加PI凝胶亮度（89.24→94.25）和白度（83.24→88.45）。HIU显著提高了PI凝胶硬度（1531.74→1756.24 g）,降低pH能够提高PI凝胶硬度（1162.55→1683.41 g）,但当3.0后,作用不显著。pH低于4.0时,pH变化和HIU对PI凝胶弹性无显著影响（0.792~0.823）。降低pH和HIU引起PI凝胶蒸煮损失率的显著增加（2.05%→4.43%）。结论：极酸pH（pH<3.0）并不会提高蛋白回收率,且对PI凝胶特性无益。采用pH 3.0的酸溶条件并辅以HIU,能够得到最高的蛋白回收率及最优的PI凝胶特性。     

Comparison of functional properties and secondary structures of defatted wheat germ proteins separated by reverse micelles and alkaline extraction and isoelectric precipitation

The functional properties and secondary structures of defatted wheat germ protein separated by reverse micelles (DWGRMPI) were investigated and compared with those of defatted wheat germ protein separated by alkaline extraction and isoelectric precipitation (DWGPI). The results showed that DWGRMPI had a higher nitrogen solubility index, fat absorption capacity, foaming capacity, foaming stability and emulsifying stability compared to DWGPI, whilst water holding capacity, surface hydrophobicity and emulsifying activity of DWGRMPI were relatively lower than those of DWGPI. DWGRMPI contained high levels of threonine, histidine, alanine, arginine, glycine, serine, cysteine, proline and especially lysine compared to DWGPI. The denaturation temperature and denaturation enthalpy of DWGPI were both lower than those of DWGRMPI, and DWGPI contained more random coil and less α-helix than DWGRMPI, which suggested that DWGPI has lost its ordered secondary structure. This may possibly due to the conditions the used in protein extraction.     

谷氨酰胺转氨酶对碱溶酸沉法提取南极磷虾(Euphausia superba)蛋白质得率的影响

通过碱溶酸沉法提取了南极磷虾蛋白质,研究了谷氨酰胺转氨酶的应用对蛋白质得率的影响。结果表明:碱溶酸沉法能够较好地回收南极磷虾蛋白质;在酸沉过程中,合理添加谷氨酰胺转氨酶能够提高蛋白质得率约5%。     

Gel properties of surimi from silver carp (Hypophthalmichthys molitrix) as affected by heat treatment and soy protein isolate

The effects of setting conditions and soy protein isolate (SPI) on textural properties of surimi produced from silver carp were investigated. Effects of setting temperature, setting time and protein concentration on the gel strength were evaluated and compared utilizing response surface methodology. Models for breaking force and breaking distance of silver carp surimi were established. The total protein content was 13.4% in all experimental samples. Setting temperature and protein concentration were the major factors affecting the gel strength. In the range of the additive SPI protein (10–40%), breaking force and distance of silver carp surimi gels decreased when the protein ratio of SPI was increased in the total protein at 30 and 40 °C for 60 min setting and heating at 85 °C for 30 min, but the breaking force obtained for 90% surimi protein plus 10% SPI protein was higher than surimi alone at 50 °C for 60 min incubation and heating at 85 °C for 30 min.     

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

BACKGROUND: 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. RESULTS: 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. CONCLUSION: 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). Copyright © 2012 Society of Chemical Industry     

Amino Acid and Mineral Composition of Protein and Other Components and Their Recovery Yields from Whole Antarctic Krill (Euphausia superba) Using Isoelectric Solubilization/Precipitation

ABSTRACT:  Proteins and insolubles were recovered from whole Antarctic krill via novel isoelectric solubilization/precipitation using different pH treatments. The protein recovery yield was 45% to 50% (dry basis). The recovered proteins had higher ( P < 0.05) content of essential amino acids (EAAs) and non-EAAs as well as higher ( P < 0.05) ratio of total EAA/total AA than whole krill. The EAAs constituted almost 50% of total AAs. The least extreme pH treatments (pHs 3 and 12) yielded highest ( P < 0.05) content of EAAs. The quality of recovered proteins was high based on EAAs meeting FAO/WHO/UNU recommendations for adults and infants. The basic pH yielded proteins with the lowest ( P < 0.05) amount of minerals and the highest ( P < 0.05) amount of Ca, P, and Mg in the insolubles when compared to the acidic treatments. However, both basic and acidic treatments effectively removed minerals from recovered proteins without the removal of the exoskeleton before processing. Therefore, besides high-quality proteins, the insolubles may provide a mineral supplement in the animal diet.     

Effect of acid- and alkaline-aided extractions on functional and rheological properties of proteins recovered from mechanically separated turkey meat (MSTM)

Functional and rheological characteristics of acid- and alkali-extracted proteins from mechanically separated turkey meat (MSTM) have been investigated. Extractions were carried out at 4 pH values (2.5, 3.5, 10.5, and 11.5). The study demonstrated that alkali and acid extractions resulted in significant (P < 0.0001) decreases of cooking and water loss compared to raw MSTM; however, the cooking loss was found to be similar (P = 0.5699) among the different protein isolates. Proteins extracted at pH 10.5 showed the lowest (P = 0.0249) water loss. Emulsion and foaming properties were found to be slightly higher in alkali-extracted proteins compared to those for acid extractions. The myofibrillar protein fraction showed better ability to form and stabilize emulsions compared to sarcoplasmic proteins. Myofibrillar proteins also showed better foam expansion; however, foam volume stability was similar for both myofibrillar and sarcoplasmic protein fractions. Textural characteristics (hardness, chewiness, springiness, and cohesiveness) of recovered proteins were found to be unaffected (P > 0.05) by different extraction pH. The protein extracted at pH 3.5 formed a highly viscoelastic gel network as evidenced by storage modulus (G') values, whereas the gel formed from proteins extracted at pH 10.5 was found to be the weakest. The work also revealed that acid treatments were more effective for removal of total heme pigments from MSTM. Color characteristics of protein isolates were markedly improved compared to the initial material and tended to be better when subjected to acid extractions. PRACTICAL APPLICATION: Mechanically separated meat is one of the cheapest sources of protein obtained by grinding meat and bones together and forcing the mixture through a perforated drum. The use of mechanically separated turkey meat (MSTM) for the production of further processed poultry products is limited due to its undesirable color and textural properties. Recovery of proteins from MSTM using pH shifting process will help the poultry processors to get better returns and also create opportunity to produce functional food ingredients.