Gelling properties of white shrimp (Penaeus vannamei) meat as influenced by setting condition and microbial transglutaminase

The properties of white shrimp (Penaeus vannamei) gel added with different levels of microbial transglutaminase (MTGase) and subjected to setting at 25 °C for 2 h or 40 °C for 30 min, prior to heating at 90 °C for 20 min were studied. Breaking force of gels with and without setting increased with increasing MTGase amount added (P<0.05). However, no changes in deformation in all samples were noticeable (P>0.05). Directly heated gels showed the lower breaking force than those with prior setting at all MTGase levels added (P<0.05). Generally, gels prepared by setting at 25 °C exhibited the greater breaking force than those set at 40 °C, possibly associated with the appropriate protein structure for cross-linking at 25 °C and greater degradation at 40 °C as evidenced by a greater trichloroacetic acid soluble peptide content (P<0.05). Sodium dodecyl sulfate polyacrylamide gel electrophoretic study revealed that myosin heavy chain (MHC) underwent polymerization to a higher extent in the presence of MTGase, but the strengthening effect on gel was dependent on setting temperature. Regardless of setting condition, microstructure of gel added with MTGase was finer with a smaller void, compared with those of gel without MTGase. Therefore, setting temperature played an essential role in gel property of white shrimp meat added with MTGase.     

Impact of microbial transglutaminase on gelling properties of Indian mackerel fish protein isolates

Impacts of microbial transglutaminase (MTGase) (0–0.6 units/g sample) on gel properties of Indian mackerel unwashed mince, surimi and protein isolates with and without prewashing were studied. Generally, lower myoglobin and lipid contents were found in protein isolate with and without prewashing, compared to those of unwashed mince and surimi (P < 0.05). Protein isolate had the decreased Ca²⁺-ATPase and protein solubility, indicating protein denaturation. When MTGase was incorporated, breaking force and deformation of all gels markedly increased, especially as MTGase levels increased (P < 0.05). At the same MTGase level, gel from protein isolate with prewashing exhibited the highest breaking force and deformation (P < 0.05). The addition of MTGase could lower the expressible moisture content of most gels. No change in whiteness of gel was observed with the addition of MTGase (P > 0.05), but gel from protein isolate gels had decreased whiteness as MTGase at high level was added. The microstructure of protein isolate gels without prewashing showed a similar network to unwashed mince gels, whilst a similar network was observed between surimi gel and gel from protein isolate with prewashing. Nevertheless, a larger void was noticeable in gels from protein isolates. All gels incorporated with MTGase (0.6 units/g) showed a slightly denser network than those without MTGase. Thus, gel with improved properties could be obtained from protein isolate from Indian mackerel with added MTGase.     

Effects of combining microbial transglutaminase and high pressure processing treatments on the mechanical properties of heat-induced gels prepared from arrowtooth flounder (Atheresthes stomias)

The objective of this study was to evaluate the effect of setting conditions (25 °C for 2 h or 40 °C for 30 min) and combining of microbial transglutaminase (MTGase) and high pressure processing (HPP) on the mechanical properties of heat induced gels obtained from paste from arrowtooth flounder (Atheresthes stomias). Treatments included fish paste control without added MTGase, fish paste incubated with MTGase but not pressurized (MTGase + cooking), fish paste incubated with MTGase and pressurized at 600 MPa for 5 min (MTGase + HPP + cooking) and fish paste pressurized at 600 MPa for 5 min and incubated with MTGase (HPP + MTGase + cooking). The controls and the treated samples were then subjected to one of two thermal treatments: 90 °C for 15 min or 60 °C for 30 min before cooking at 90 °C for 15 min. Samples of fish paste heated at 60 °C before cooking could not be used to prepare gels for texture profile analysis (TPA). TPA showed that pressurization improved the mechanical properties of gels made from paste treated with MTGase and set at 25 °C. The opposite was observed for samples set at 40 °C. Setting at 40 °C appeared to induce proteolytic degradation of myofibrillar proteins.     

Chemical reagents as probes: Application to fish protein gels and detection of a cysteine TGase in hake

A new concept was applied to fish products. Chemical reagents targeting specific chemical bonds were incorporated in to gel products for assessing the importance of non-covalent (sodium dodecylsulphate, 1.0%, w/w), disulphide (dithiothreitol, 0.2%, w/w) or transglutaminase-catalyzed (N-ethylmaleimide, 0.2%, w/w) bonding. These reagents acting as chemical probes were applied to the study of sea bass and hake protein gels and the effect of MTGase (0.5%, w/w).These reagents were valuable for reaching conclusions. The action of an endogenous cysteine TGase in hake products was detected. It was found that frozen storage and protein denaturation are fundamental not only for explaining differences between raw materials, but also seem to favour a different action mode of MTGase in each raw material. Moreover, this study may help to improve processed products, for instance, the positive interaction between MTGase and the disruption of disulphide bonds in hake gels may find a useful application through incorporation of cysteine + MTGase.     

Transglutaminase treatment of pea proteins: Effect on physicochemical and rheological properties of heat-induced protein gels

Rheological properties of heat-induced pea protein isolate (PPI) gels with added microbial transglutaminase (MTGase) were studied under various reaction conditions. A positive linear relationship was observed between level of MTGase used (0 to 0.7% w/w) and shear stress and shear strain of heat-set commercial pea protein isolate (PPIc) gels at 92 °C following incubation at 50 °C. Use of MTGase allowed for preparation of PPIc gels of similar strength and elasticity as commercial soy protein isolate gels and commercial meat bologna. MTGase treatment did not alter thermal properties of PPI gels. The shear stress and strain of PPIc gels were also improved following low temperature (4 °C) incubation of PPI with MTGase. Enhancement of shear strain or gel elasticity of heat-induced PPI gels with MTGase has not been reported before and provides opportunities for extending the properties of pea proteins when developing new food products.     

Synergistic action of transglutaminase and high pressure on chicken meat and egg gels in absence of phosphates

The effects of simultaneous application of microbial transglutaminase (MTGase) and high pressure (HP) (500, 700 and 900 MPa/40 °C/30 min), only pressure under the same conditions or heat (75 °C/30 min) were investigated on chicken batters with the addition of egg components and without phosphates. MTGase gels (700 and 900 MPa) showed marked increases in textural parameters compared to gels without enzyme (NE) or those obtained by heat. The addition of enzyme did not show differences between gels obtained at 700–900 MPa; however, gels obtained at 500 MPa were darker and more reddish than those obtained by heat. MTGase gels were more homogeneous and compact. Thermal analysis revealed that pressure levels above 700 MPa caused as much denaturing as did heat. The microstructure and texture of MTGase gels suggest that a higher amount and heterogeneity of crosslinks was produced when meat and egg proteins were treated in the presence of MTGase under specific conditions of pressure.     

Effect of salt and MTGase on the production of high quality gels from farmed sea bass

In order to obtain low salt fish products, the effects of the addition of 0.5% (w/w based on whole product, wp) MTGase and different levels (0.25%, 0.50%, 1.00% and 2.50%, w/w wp) of sodium chloride salt to heat-induced gels from farmed sea bass (Dicentrarchus labrax) trimmings were tested and compared with gels without salt and/or without MTGase.MTGase and salt addition, both, had a favourable effect on texture. However, only salt incorporation augmented water holding capacity (WHC).A synergistic effect was detected between MTGase and salt for several important textural properties, particularly, gel strength, which reached 64.3 ± 8.1 N mm, a value comparable to those of best quality surimi. Moreover, MTGase required addition of salt to the product for its effect to be felt, however only a minimal amount (0.25%, w/w wp) sufficed. In fact, the addition of MTGase enabled reduction in salt content to 1.0% (w/w wp), without significant loss of textural and overall quality.     

Stability of potassium iodide and omega-3 fatty acids in fortified freshwater fish emulsion sausage

Oxidative stability of emulsion sausages prepared from African walking catfish (AF: Clarias gariepinus) and rohu (RH: Labeo rohita) fortified with three levels of the refined tuna oil (2%, 6%, and 10%) with 150 μg KI/100 g sample and without KI was investigated. The control was prepared using 20% soybean oil and without KI. Samples were vacuum-packed and stored at 4 °C. Iodine content decreased approximately 14% after cooking and remained constant throughout storage. Sausages fortified with tuna oil showed higher level of n-3 (eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)), but lower level of n-6 fatty acids (P<0.05) than the control. The ratio of n-6 to n-3 fatty acids of all samples decreased with an increase of tuna oil addition and was stable throughout 4 weeks of storage. Degradation of linoleic (LA) and linolenic acid (LNA) mainly occurred in the samples added 2% tuna oil whereas samples fortified with higher tuna oil (6-10%) exhibited higher loss of EPA and DHA. Hydroperoxide (HPV) and thiobarbituric reactive substances (TBARS) values were increased as addition level of tuna oil increased. Textural properties were not affected during storage at 4 °C for up to 4 weeks (P<0.05). Based on lipid stability results, 2% fortification of the refined tuna oil was recommended for emulsion sausage prepared from both species. Addition of 150 μg KI/100 g had no effect on lipid oxidation of fish sausages (P<0.05).     

Effects of dietary alpha-tocopheryl acetate on lipid oxidation and alpha-tocopherol content of novel omega-3-enhanced farmed rainbow trout (Oncorhynchus mykiss) fillets

A trout diet was supplemented with 0, 8.5, or 15 g/100 g of flaxseed oil (FO). To prevent lipid oxidation of fillets, FO-supplemented diets were also enhanced with 0, 400, and 900 mg/kg of alpha-tocopheryl acetate (α-TA). Total fat, moisture content, lipid oxidation, fatty acid profile, and α-tocopherol content of fillets were determined following fish harvest on days 0, 30, 60, 90, and 120. FO supplementation resulted in increased (P<0.05) concentration of omega-3 fatty acid (ω3 FA) in fillets, mainly due almost two-fold increase (P<0.05) of α-linolenic acid, while docosahexaenoic and eicopentaenoic acids slightly decreased (P<0.05). Regardless of supplementing trout diets with FO or α-TA, no (P>0.05) difference of the total fat in fillets was measured. The highest (P<0.05) α-tocopherol content in fillets was determined when supplementing trout with 900 mg/kg of α-TA at day 120. The effect of retarding lipid oxidation in fillets was recorded after supplementing trout with α-TA for 60 days. Our results indicate that regardless of FO level in trout diet, 900 mg/kg of α-TA can prevent lipid deterioration of fillets. However, to achieve more pronounced antioxidant effect in the ω-3-enhanced trout fillets, a synergetic effect of antioxidants and anaerobic packaging with α-TA supplementation should be investigated.     

Influence of alginate and microbial transglutaminase as binding ingredients on restructured fish muscle processed at low temperature

BACKGROUND: In view of the increasing demand for fresh products in Western countries recently, there is considerable interest in commercialising restructured fish products having the appearance of fresh fish. A number of methods have been studied for the purpose of inducing cold gelification. Two of the most common methods, namely addition of alginates and addition of transglutaminases, have been studied mainly in connection with meat products. The present study deals with the use of alginate and transglutaminase as additives in cold gelification of minced hake (Merluccius capensis) muscle. The experiments were targeted on the effects of concentration and combined effects of additional additives on physicochemical characteristics and mechanical properties. RESULTS: As regards mechanical properties, the effectiveness of sodium alginate was improved by addition of a low concentration (1 g kg^?1) of calcium chloride (CaCl₂), whereas a higher concentration (10 g kg^?1) reduced the binding ability of the alginate. The presence of sodium caseinate (15 g kg^?1) in combination with microbial transglutaminase (MTGase) was important in helping to increase the work of penetration in fish gels induced at low temperature. Examination of the chemical properties of the muscle gels showed that sodium alginate did not establish covalent protein–protein bonds, while MTGase dramatically increased the number of covalent bonds formed between adjacent muscle proteins. CONCLUSION: With both ingredients, thermostable fish gels of good quality were produced at temperatures below 10 °C. Gels induced by sodium alginate were considerably improved by addition of 1 g kg^?1 CaCl₂. However, gels induced by MTGase were better suited for the preparation of restructured products. Copyright © 2008 Society of Chemical Industry     

Dielectric properties of chicken and fish muscle treated with microbial transglutaminase

Transglutaminase (MTGase) initiates the formation of covalent bonds between glutamine and lysine residues in proteins. Adding MTGase can improve the thermal stability of meat proteins, imparting desirable properties to reconstructed products during heating. In this study, the dielectric constant and loss factor of MTGase (0.5%)-treated chicken, salmon and trout muscle were determined and compared with untreated muscle at RF (27 and 40 MHz) and MW (433, 915, and 1800 MHz) frequencies from 20 to 130 °C. The MTGase-treated chicken muscle tended to have higher dielectric constant and loss values at RF frequencies at all temperatures tested. At MW frequencies, the dielectric constants were similar between the MTGase-treated chicken muscle and the control, but the dielectric loss was higher for the MTGase-treated tissue. Similar trends were observed for salmon or trout tissue for dielectric constant; however, at RF frequencies, the dielectric loss factor for MTGase-treated fish was not consistently higher than that of the control. Dielectric loss factors were higher for salmon or trout at RF frequencies than for chicken muscle at the same temperature. The addition of MTGase promotes cross-linking and stronger gel formation for RF and MW treatment.     

Effects of Bambara Groundnut Protein Isolates and Microbial Transglutaminase on Textural and Sensorial Properties of Surmi Gel from Sardine (Sardinella albella)

Effects of different bambara groundnut protein isolates (BGPIs) at a level of 6 % (w/w) in combination with microbial transglutaminase (MTGase) at a concentration of 0.6 U g^?1 surimi on gel properties of sardine (Sardinella albella) surimi were investigated. In the absence of MTGase, all BGPIs showed the adverse effect on gel-forming properties of surimi, as evidenced by the decreases in breaking force and deformation (P?<?0.05). When MTGase was incorporated, the increases in breaking force and deformation were found for all BGPIs used. Water-holding capacity of all gels was improved when BGPIs were added in combination with MTGase (P?<?0.05). Whiteness of gels slightly decreased with the addition of BGPIs; however, MTGase had no impact on whiteness (P?>?0.05). Surimi gel added with BGPI prepared from defatted flour with heat treatment in the presence of ethylenediaminetetraacetic acid (DF-BGPI-HE) and MTGase showed well-ordered network and exhibited the lowest peroxide value and thiobarbituric acid-reactive substances than those containing other BGPIs. Gel containing DF-BGPI-HE had negligible beany flavour. Additionally, DF-BGPI-HE had the lower amount of volatile compounds after storage of 30 days at room temperature than other BGPIs. Thus, the addition of DF-BGPI-HE and MTGase was an effective means to render sardine surimi gel with improved gel property and caused no beany flavour in resulting gel.     

Physicochemical characterisation and oxidative stability of fish oil and fish oil–extra virgin olive oil microencapsulated by sugar beet pectin

Spray-dried microcapsules were prepared at 25% and 50% w/w oil load from sugar beet pectin-stabilised emulsions (pH 3) containing fish oil, and a blend of fish oil and with extra virgin olive oil (1:1 w/w). Microencapsulation efficiencies were high (≥90%). However, deterioration in microcapsule wall integrity and an increase in oil droplet size were observed during storage (25 °C, 0–3 months). Lipid oxidation increased with both increased oil load (P < 0.05) and storage duration (P < 0.05), but was independent of oil composition (P > 0.05). These results suggest that sugar beet pectin functions poorly as a wall material and its residual metal ions exacerbate omega-3 oxidation, despite the presence of endogenous antioxidants found in extra virgin olive oil. Interestingly, under accelerated storage conditions (OxiPres® at 80 °C, 0.5 bar oxygen pressure), microcapsules containing the oil blend showed the best oxidative stability (P < 0.05), irrespective of oil load. A possible explanation for the superior oxidative stability of the microencapsulated oil blend at high storage temperature is discussed.     

The effects of an iron-catalyzed oxidation system on lipids and proteins of dark muscle fish

The effects of a hydroxyl radical-generating system induced by iron catalyzed oxidation (Fe²⁺/H₂O₂) on lipids and proteins of sardine, Atlantic bonito, anchovy and bluefish were investigated. Thiobarbituric acid-reactive substances (TBARs, mg malonaldehyde/kg fish muscle) formation was used to evaluate oxidative damage of the lipid in dark muscle fish due to iron catalyzed oxidation. The amount of TBARs was observed to increase significantly in sardine and anchovy as the incubation time increased, while Atlantic bonito and bluefish reached their maximum values of TBARs within the first 3 h of incubation, and after that did not change (p < 0.05). Carbonyl contents (nmol carbonyl/mg protein) of all fish samples measured as an index of protein oxidation were affected differently by the iron-catalyzed oxidation system during incubation. However, significant increases in the carbonyl groups were detected in sardine, Atlantic bonito and bluefish, but not in anchovy as a result of the long incubation time (5 h) (p < 0.05). When comparing to increases Atlantic bonito showed the maximum increase protein carbonyl. The electrophoretic patterns in the presence and absence of β-mercaptoethanol showed that a loss of proteins generally occurred in all fish at the end of incubation, and the greatest alteration in protein bands was observed in anchovy during Fe²⁺-catalyzed oxidation. The bands above 50 kDa disappeared within the first 1 h of incubation. The loss of protein (both high and low molecular weight) may involve disulfide and non-disulfide covalent linking during the iron catalyzed incubation. These data suggest that an increase in TBARs and fragmentation, and a loss of proteins exposed to iron-catalyzed oxidation may explain the oxidative damage of lipids and proteins which causes quality loss and limits the storage life of dark muscle fish.     

Quality differences between heat-induced gels from farmed gilthead sea bream (Sparus aurata) and sea bass (Dicentrarchus labrax)

The effect of farmed fish species (sea bream, Sparus aurata, versus sea bass, Dicentrarchus labrax) on the quality of heat-induced gel products was evaluated. Additionally, the effect of microbial transglutaminase (MTGase) incorporation (0.5%, w/w) into the gels on their quality was also assessed.Both sea bream and sea bass yielded gel products of high quality. The fat content of the gel products attained from sea bass was higher than that of those prepared from sea bream (7.6% vs. 6.1%). Therefore, fat gels prepared with unwashed mince from farmed fish species may present a great potential for the aquaculture sector because, besides adequate gelling ability, these gels have a higher nutritional value than commercial gels, especially given their high eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) levels. Moreover, MTGase improved textural quality and reduced protein solubility. The gel strength, cohesiveness, and rupture properties of sea bream gels were higher than those of sea bass gels (mainly for gels containing MTGase), thus indicating a higher textural quality. Sea bass proteins were less soluble than sea bream proteins. Different hypothesis were put forward concerning the protein phenomena underlying such differences between the two farmed fish species.     

Quality characteristics of Dutch-style fermented sausages manufactured with partial replacement of pork back-fat with pure, pre-emulsified or encapsulated fish oil

Dutch-style fermented sausages were manufactured with 15% and 30% pork back-fat substitution by pure or commercial encapsulated fish oil, either added as such or as pre-emulsified mixture with soy protein isolate. Adding commercial encapsulated fish oil was the most important factor influencing the chemical composition. The fat content was not significantly different between products (p > 0.05). The n−6/n−3 ratio decreased from 8.49 in controls to 0.90-2.47 in modified products. Lipid oxidation parameters (propanal and hexanal) showed much higher values for sausages with pure fish oil than for products with encapsulated oil. For the latter, lipid oxidation was similar to controls. Products with encapsulated or pre-emulsified oil were significantly firmer than products from other treatments in physical and sensory analysis (p < 0.05). Overall, it is technologically feasible to enrich dry fermented sausages with n−3 fatty acids from fish oil and the application of commercial encapsulated fish oil seems to be the best in retaining overall quality.     

Lipid oxidation and fishy odour development in protein hydrolysate from Nile tilapia (Oreochromis niloticus) muscle as affected by freshness and antioxidants

Lipid oxidation and fishy odour development in protein hydrolysate from fresh and ice-stored Nile tilapia (Oreochromis niloticus) were investigated. During iced storage of 18 days, heme iron content decreased with a concomitant increase in non-heme iron content (P < 0.05). Peroxide value (PV) and thiobarbituric acid reactive substances (TBARS) values increased. Phospholipid content decreased with a corresponding increase in free fatty acid content. The results suggested that lipid hydrolysis and oxidation took place during storage. When protein hydrolysates were produced from fresh and 18 days ice-stored Nile tilapia muscle, higher lipid oxidation and fishy odour/flavour along with higher amount volatile compounds were obtained in hydrolysate for unfresh sample (P < 0.05). However, the addition of mixed antioxidants during hydrolysis process markedly lowered lipid oxidation, b^∗, ΔC^∗, ΔE^∗ values, fishy odour/flavour as well as the formation of volatile compounds in the resulting hydrolysates prepared from both fresh and unfresh samples. Therefore, hydrolysate from Nile tilapia muscle with reduced fishy odour and lighter colour could be prepared by using fresh fish and incorporation of mixed antioxidants during hydrolysis.     

Measurement of malondialdehyde in fish: A comparison study between HPLC methods and the traditional spectrophotometric test

Alternative methods to the traditional spectrophotometric determination of the malondialdehyde-thiobarbituric acid (MDA-TBA) complex (method A) and to the overestimation of MDA levels in the TBA reaction have been develop for the evaluation of lipid oxidation in fish. In this study, two HPLC separation methods of the MDA-TBA (method B) and MDA-dinitrophenylhydrazine (MDA-DNPH) adduct (method C) were investigated and compared to the traditional spectrophotometric TBA test (method A) in samples of chilled fish (hake, sea bream and sardine). Detection limits were 0.16, 0.10 and 0.20 μM MDA and quantification limits were 0.23, 0.17 and 0.26 μM MDA, for methods A, B and C, respectively. Recovery of method B ranged between 100% and 108% and of method C between 90% and 112%. Method A presented low recovery levels (under 71%). Overall method performance followed the order HPLC method MDA-DNPH > HPLC method MDA-TBA > traditional spectrophotometric TBA test. Though showing a better accuracy and specificity, method C had, however, some disadvantages, a relatively high limit of detection (0.20 μM MDA) and a lower reproducibility at lower MDA contents in standards and samples. Nevertheless, these are not critical drawbacks for an application in routine fish analysis, given the high MDA concentrations in oxidised fish. The application of the modified HPLC methods in fish samples with different levels of MDA, showed that these methods are useful for the samples with low amounts of oxidation products, such as chilled hake as well as in samples with high levels of oxidation, like 15 days chilled stored sardine.     

Changes in heme proteins and lipids associated with off-odour of seabass (Lates calcarifer) and red tilapia (Oreochromis mossambicus × O. niloticus) during iced storage

Changes in heme proteins and lipids associated with off-odour development in seabass (Lates calcarifer) and red tilapia (Oreochromis mossambicus × O. niloticus) muscles during 15 days of iced storage were studied. Fresh seabass contained the higher contents of myoglobin and heme iron, compared with red tilapia (P < 0.05). An increase in metmyoglobin proportion was observed during storage. After 3 days of storage, a decreased heme iron content and a concomitant increase in non-heme iron content were noticeable in both fish (p < 0.05). Oxidation of myoglobin and released non-heme iron were associated with lipid oxidation. The increases in oxidation products and free fatty acids were observed as the storage time progressed. Fishy and rancid odours were detected at day 6 of storage for both fish and a higher intensity was found in seabass muscle. Thus, the off-odour in fish muscle was mostly governed by lipid oxidation and species specific.     

Total volatile basic nitrogen and trimethylamine nitrogen levels during ice storage of European hake (Merluccius merluccius): A seasonal and size differentiation

Whole ungutted European hake (Merluccius merluccius) caught by trawling off the Central Tyrrhenian coast of Italy in winter and in summer were stored in ice. The dynamics of changes of total volatile basic nitrogen (TVB-N) and trimethylamine-nitrogen (TMA-N) levels during ice storage of small- (20 ± 3 cm length) and large-sized (37 ± 6 cm length) hake caught in either season were studied. The TVB-N and TMA-N levels of hake caught in winter remained low (below 20 mg and 3 mg/100 g, respectively) throughout the experiment regardless of the body size. In summer TVB-N and TMA-N levels increased sharply (P < 0.05) during ice storage and at a higher rate in small than in large fish, a fact ascribable to fish exposure to high temperatures first in the water, during trawling, and then in the fishing vessel before ice-boxing. On the basis of the results obtained in this work, it may be concluded that ungutted European hake show a clear seasonal and size differentiation of the evolution of TVB-N and TMA-N during ice storage.