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.     

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.     

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.     

Determination of the nutritional value,protein quality and safety of krill protein concentrate isolated using an isoelectric solubilization/precipitation technique

Despite its abundance, krill is not utilized for human consumption due to the lack of proper technology for protein recovery. The objectives of this study were to isolate krill protein concentrate (KPC) and to determine the nutritional value, health benefits, and safety of KPC for human consumption. Proximate analysis of protein recovered by isoelectric solubilzation/precipitation indicated that KPC was composed of approximately 78% protein and 8% fat (dry weight). In vivo analysis of protein quality indicated that protein digestibility corrected for amino acid score and protein efficiency ratio was equal to casein. KPC safety was indicated by the absence of differences in clinical measures of kidney function compared to casein. Fatty acid analysis of KPC showed that approximately 27% were omega-3 polyunsaturated fatty acids (ω-3 PUFAs). Based on our study, KPC appears to be a promising protein source for human consumption with the advantage of being a rich source of ω-3 PUFAs.     

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.     

Comparison between isoelectric precipitation and ultrafiltration processes to obtain Amaranth mantegazzianus protein concentrates at pilot plant scale

The aim of this study was to compare protein yield, protein concentration and physicochemical characteristics of Amaranth mantegazzianus protein concentrates (APC) obtained at pilot-scale by a conventional process (CP) (alkaline extraction and isoelectric precipitation) and two alternative processes (AP): (1) acid pre-treatment process combined with isoelectric precipitation and (2) acid pre-treatment process combined with ultrafiltration. Although AP resulted in higher protein concentration, protein yield was lower than in CP. SDS–PAGE and size-exclusion chromatography showed high molecular weight fractions only for isoelectric precipitation concentrates (obtained by CP and AP). The amino acids concentration, especially phenylalanine, isoleucine and methionine, increased in all protein concentrates respect to the amaranth flour. Particularly, the product obtained by ultrafiltration was rich in phenylalanine and lysine, and presented no limiting amino acid with respect to the recommendation of the Food and Agriculture Organization of the United Nations (FAO).     

鮰鱼下脚料蛋白质的回收及其凝胶特性研究

通过回收并制备鮰鱼下脚料的蛋白质凝胶,考察溶解pH、离心力、离子强度对鱼下脚料中蛋白质的溶解性及凝胶理化性质的影响。结果表明,溶解pH、离心力、离子强度对鱼下脚料中的蛋白质的溶解性能均有显著影响(P<0.05)。pH=2.5或pH=11.5,离心力为5 500r/min,离子强度为0.6M时,蛋白质溶解性能较好,pH=5.5时蛋白质溶解性最差。溶解pH=11.5时,制备的鱼肉凝胶蛋白质、灰分含量较高,脂类含量较低,并且凝胶的破断强度值、凹陷度以及凝胶强度值较高,但凝胶色泽较差。     

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.     

Dynamic rheology and endothermic transitions of proteins recovered from chicken-meat processing by-products using isoelectric solubilization/precipitation and addition of TiO2

Chicken-meat processing generates large quantities of by-products (backs, necks, etc.). Dark chicken-meat processing by-products present the lowest value and greatest challenge. Therefore, recovery of functional proteins from this source for inclusion in food products resembling those from light chicken-meat presents the greatest value addition and opportunity. Novel isoelectric solubilization/precipitation (ISP) was applied to model, dark chicken-meat processing by-products (skin-on bone-in chicken drumsticks) to recover muscle proteins. Thermal denaturation (endothermic transitions), gelation (elasticity, G′), and fundamental texture properties (shear stress and strain at mechanical fracture) of the ISP-recovered proteins were determined with differential scanning calorimetry (DSC), dynamic rheometer, and torsion test, respectively; and compared to boneless skinless chicken breast. Endothermic transition of myosin was not detected only when TiO₂ was not added, while the ISP-recovered proteins with TiO₂ showed small myosin peak and large actin peak. However, the level of TiO₂ addition did not affect thermal transition/denaturation of the ISP-recovered proteins. The ISP-recovered proteins had a greater transition for actin compared to chicken breast, suggesting that ISP predisposes this protein to thermal denaturation. Similar to endothermic transitions, elasticity (G′) generally increased when TiO₂ was added to the ISP-recovered proteins. Gels made of chicken breast had the highest (P < 0.05) shear stress (i.e., gel strength), but gels made of the ISP-recovered chicken proteins had greater (P < 0.05) shear strain (i.e., gel cohesiveness). Addition of TiO₂ to the ISP-recovered proteins resulted in increased (P < 0.05) gel strength. Based on the present study, addition of TiO₂ is suggested for the development of restructured food products based on proteins recovered from dark chicken-meat processing by-products using ISP. Although the results of this study point towards a novel food product, further studies are recommended.     

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%。     

Angiotensin I-converting enzyme (ACE) inhibitory activities of sardinelle (Sardinella aurita) by-products protein hydrolysates obtained by treatment with microbial and visceral fish serine proteases

The angiotensin I-converting enzyme (ACE) inhibitory activities of protein hydrolysates prepared from heads and viscera of sardinelle (Sardinella aurita) by treatment with various proteases were investigated. Protein hydrolysates were obtained by treatment with Alcalase^®, chymotrypsin, crude enzyme preparations from Bacillus licheniformis NH1 and Aspergillus clavatus ES1, and crude enzyme extract from sardine (Sardina pilchardus) viscera. All hydrolysates exhibited inhibitory activity towards ACE. The alkaline protease extract from the viscera of sardine produced hydrolysate with the highest ACE inhibitory activity (63.2 ± 1.5% at 2 mg/ml). Further, the degrees of hydrolysis and the inhibitory activities of ACE increased with increasing proteolysis time. The protein hydrolysate generated with alkaline proteases from the viscera of sardine was then fractionated by size exclusion chromatography on a Sephadex G-25 into eight major fractions (P₁–P₈). Biological functions of all fractions were assayed, and P₄ was found to display a high ACE inhibitory activity. The IC₅₀ values for ACE inhibitory activities of sardinelle by-products protein hydrolysates and fraction P₄ were 1.2 ± 0.09 and 0.81 ± 0.013 mg/ml, respectively. Further, P₄ showed resistance to in vitro digestion by gastrointestinal proteases. The amino acid analysis by GC/MS showed that P₄ was rich in phenylalanine, arginine, glycine, leucine, methionine, histidine and tyrosine. The added-value of sardinelle by-products may be improved by enzymatic treatment with visceral serine proteases from sardine.     

Properties of protein-based film from round scad (Decapterus maruadsi) muscle as influenced by fish quality

The properties of film prepared from round scad (Decapterus maruadsi) stored in ice for different times were investigated. Degradation of myosin heavy chain (MHC) was more pronounced with the coincidental increase in total volatile base and trimethylamine contents as the storage time increased (P<0.05). Regardless of storage time, no changes in tensile strength (TS) and elongation at break (EAB) of resulting films prepared from unwashed mince were observed (P>0.05). For the films prepared from washed mince, TS decreased, whereas EAB increased when the storage time of fish increased (P<0.05). However, films prepared from washed mince showed the greater mechanical properties with the lower film solubility and protein solubility than did those from mince (P<0.05). Generally, films prepared from fish stored in ice for a longer time became less transparent, darker and more yellowish. The electrophoretic study revealed that similar protein patterns were observed between films, irrespective of storage time of fish and washing. Therefore, the quality of fish did not show the marked impact on the mechanical property of the resulting films, while washing likely affected the film forming ability.     

Protein and water structural changes in fish surimi during gelation as revealed by isotopic H/D exchange and Raman spectroscopy

Structural changes of proteins and water during gelation of fish surimi, have been studied by isotopic H/D exchange of water and Raman spectroscopy assisted by monitoring of rheological characteristics, in order to get insights into the structural and functional properties of surimi gels. The results indicate the following: (i) Protein hydrogen bond rearrangements occur involving mainly α-helix to β-sheet transition, (ii) the relative intensity of the symmetric H₂O stretching band near 3220 cm⁻¹ tends to decrease upon gelation, (iii) H/D exchange reveal a slower deuteration kinetics in the gels as compared to the surimi, (iv) the low temperature scanning electron microscopy shows a smaller pore size of the gel network as compared to the surimi, and suggests that water domains in gel are more inaccessible to D₂O, which is consistent with higher water holding capacity in the gel.     

Production and functional evaluation of a protein concentrate from giant squid (Dosidicus gigas) by acid dissolution and isoelectric precipitation

A protein concentrate from giant squid (Dosidicus gigas) was produced under acidic conditions and its functional–technological capability evaluated in terms of its gel-forming ability, water holding capacity and colour attributes. Technological functionality of the concentrate was compared with that of squid muscle and a neutral concentrate. Protein–protein aggregates insoluble at high ionic strength (I = 0.5 M), were detected in the acidic concentrate as result of processing with no preclusion of its gel-forming ability during the sol-to-gel thermal transition. Even though washing under acidic condition promoted autolysis of the myosin heavy chain, the acidic concentrate displayed an outstanding ability to gel giving samples with a gel strength of 455 and 1160 g cm at 75% and 90% compression respectively, and an AA folding test grade indicative of high gel strength, elasticity, and cohesiveness. The process proved to be a good alternative for obtaining a functional protein concentrate from giant squid muscle.     

Functional properties of fish protein hydrolysates from Pacific whiting(Merluccius productus) muscle produced by a commercial protease

Pacific whiting (Merluccius productus) muscle was used to produce hydrolysates with 10%, 15% and 20% degree of hydrolysis (DH) using the commercial protease Alcalase^® and were characterized at pH 4.0, 7.0 and 10 according their solubility, emulsifying and foaming properties. Protein recovered in soluble fractions increased proportionally with the hydrolytic process, yielded 48.6 ± 1.9, 58.6 ± 4.1 and 67.8 ± 1.4 of total protein after 10%, 15% and 20% DH, respectively. Freeze-dried hydrolysates presented almost 100% solubility (p > 0.05) at the different pHs evaluated. Emulsifying properties (EC, EAI and ESI) were not affected by DH as most samples showed similar (p > 0.05) results. Higher EC (p ? 0.05) than sodium caseinate, used as control, were obtained at pH 4 for most hydrolysates. Hydrolysates showed very low foaming capacity not affected by pH; but foam stability was equal or even better (p > 0.05) than bovine serum albumin (BSA), except at pH 4.0. Results suggest that hydrolysates from Pacific whiting muscle can be produced with similar or better functional properties than the food ingredients used as standards.     

Solubility of a cruciferin‐rich protein product purified from rapeseed pressed cake (Brassica napus L.) by an aqueous processing method

Pressed cake from rapeseed (Brassica napus L.) is a promising plant protein source not yet utilised for human consumption due to the presence of antinutrients such as glucosinolates. Protein solubility is a crucial parameter influencing the functionality and thereby the applicability of proteins as food ingredients. A novel cruciferin‐rich rapeseed protein product was produced by an aqueous processing method in pilot plant scale. Intact glucosinolates were conserved by this procedure and largely removed from the protein products. Protein solubility in this product was examined when dispersed in 50 mm phosphate buffer, pH 8.0 with varying NaCl concentration (0–500 mm ). Unexpectedly, a salting‐out effect was observed of the globulin proteins, as 15.9 ± 0.6% protein was in solution at 500 mm added NaCl, whereas 21.5 ± 1.1% was solubilised without added NaCl; whether the observed effects originates from lipid and fibre constituents in the product remains to be resolved.     

Antioxidant properties of peptide fractions from silver carp (Hypophthalmichthys molitrix) processing by-product protein hydrolysates evaluated by electron spin resonance spectrometry

Silver carp processing by-product protein is usually discarded as an industrial solid waste. In this study the protein was recovered using a pH-shift method, after which seven commercial proteases were separately employed to prepare antioxidative hydrolysates. Among the hydrolysates, pepsin hydrolysates, which had the highest free radical-scavenging activity, were further separated into five peptide fractions, SCPH-I (>10 kDa), SCPH-II (5–10 kDa), SCPH-III (3–5 kDa), SCPH-IV (1–3 kDa), and SCPH-V (<1 kDa), by using ultrafiltration. The antioxidative properties of the peptide fractions were investigated, using a free radical-scavenging assay, by electron spin resonance. The results show that SCPH-V had the highest scavenging effects on DPPH (1,1-diphenyl-2-picrylhydrazyl), hydroxyl and superoxide anion radicals. SCPH-V had potent antioxidant activity in the prevention of the peroxidation of linoleic acid and alleviation of H₂O₂-induced oxidative stress in human intestinal epithelial caco-2 cells. The results indicated that the antioxidant capacity of silver carp by-product hydrolysates could be enhanced by ultrafiltration.