PHYSICOCHEMICAL AND BIOCHEMICAL CHANGES IN WHOLE LIZARDFISH (SAURIDA MICROPECTORALIS) MUSCLES AND FILLETS DURING FROZEN STORAGE

The physicochemical and biochemical changes in whole lizardfish (Saurida micropectoralis) muscles and its fillets kept in air and under vacuum during frozen storage at ?20C for 24 weeks were investigated. The formaldehyde (FA) and dimethylamine contents increased with a concomitant decrease in trimethylamine‐ N‐oxide (TMAO) content as the storage time increased (P < 0.05). The Ca²⁺–adenosine 5′‐triphosphatase activity continuously decreased with a coincidental decrease in salt‐soluble fraction. The disulfide bonds were increasingly formed throughout the storage (P < 0.05). The surface hydrophobicity increased and reached the maximum at week 12 with a subsequent decrease up to the end of storage. In general, the higher changes were observed in samples kept under vacuum than those kept in air. With the same atmosphere used, the whole fish showed slightly higher changes than the fillets. A marked increase in TMAO demethylase (TMAOase) activities was observed up to 12 weeks, followed by the continuous decrease up to 24 weeks of storage. The produced FA might play an important role in inducing protein denaturation and/or aggregation in lizardfish. The TMAOase activity as well as the FA formation could be reduced to some extent with the removal of internal organs and storage in the presence of oxygen. However, a detrimental effect of oxygen, especially on the promotion of lipid oxidation, would be an obstacle.     

Effect of trimethylamine-<Emphasis Type="Italic">N</Emphasis>-oxide demethylase from lizardfish kidney on biochemical changes of haddock natural actomyosin stored at 4 and −10 °C

The addition of partially purified trimethylamine-N-oxide demethylase (TMAOase) from lizardfish kidney to haddock natural actomyosin (NAM) in the presence of cofactors (FeCl₂, ascorbate, and cysteine) accelerated formaldehyde (FA) formation throughout the storage either at 4 or −10 °C (p < 0.05). ¹H NMR spectroscopic study revealed that the formation of dimethylamine was enhanced with a concomitant decrease in trimethylamine oxide (TMAO) content when TMAOase was added, particularly at higher concentration. The loss of protein solubility increased as the result of FA formation, which was associated with the increased denaturation/aggregation of proteins. Lipid oxidation determined as hexanal content occurred during extended storage at different degrees. Generally, simulated systems without TMAOase and TMAO contained the highest hexanal content. Differential scanning calorimetry of NAM after storage at 4 and −10 °C for 15 days and for 8 weeks, respectively, showed the lower T _m and enthalpy of endothermic peaks corresponding to myosin and actin, suggesting the conformational changes induced by FA formed. Therefore, TMAOase exhibited the detrimental impact on haddock NAM, mainly caused by FA formation.     

Proteinase inhibitory activity of sarcoplasmic proteins from threadfin bream (Nemipterus spp.)

BACKGROUND: Thailand is the second largest surimi producer in the world and 50% of surimi is produced from threadfin bream. During surimi processing, sarcoplasmic proteins are removed through water washing and discarded in the waste stream. This study was aimed at investigating the proteinase inhibitory activity of sarcoplasmic proteins. RESULTS: Sarcoplasmic proteins from threadfin bream (TBSP) exhibited inhibitory activity toward trypsin but did not inhibit papain and chymotrypsin. Sodium dodecyl sulfate–polyacrylamide gel electrophoresis under non‐reducing condition stained by trypsin inhibitory activity revealed three protein bands of molecular mass of 95, 41 and 37 kDa. Inhibitory activity of TBSP reached a maximum when subjected to 45 °C and completely disappeared at 60 °C. The breaking force and deformation of lizardfish surimi gel with added TBSP and pre‐incubated at 37° for 20 min increased with additional levels of TBSP (P < 0.05). Trichloroacetic acid–oligopeptide content of lizardfish surimi gel with added TBSP decreased with the addition of 4 g kg^?1 TBSP (P < 0.05). Retention of myosin heavy chain (MHC) increased when TBSP concentration was increased. TBSP effectively protected MHC from proteolysis at 37 °C to a similar extent as egg white powder, but efficacy of TBSP was not observed at 65 °C. CONCLUSION: TBSP could be applied to reduce proteolytic degradation of lizardfish surimi or other surimi associated with trypsin‐like proteinase, rendering an improvement in surimi gelation set at 37–40 °C. Copyright © 2009 Society of Chemical Industry     

Comparison of the Cryoprotective Effects of Trehalose,Alginate, and Its Oligosaccharides on Peeled Shrimp (Litopenaeus Vannamei) During Frozen Storage

The cryoprotective effects of trehalose, alginate, and its oligosaccharides on peeled shrimp (Litopenaeus vannamei) during frozen storage was investigated by monitoring thawing loss, color, texture, myofibrillar protein content, Ca²⁺‐ATPase activity, and performing microscopic structural analysis. Data revealed significant (p < 0.05) inhibitory effects on thawing loss and textural variables (springiness and chewiness) in trehalose‐, alginate oligosaccharides‐, and sodium pyrophosphate‐treated shrimp compared with the control and alginate‐treated batches. L* values revealed that these saccharides had a positive effect on color stability during frozen storage. In addition, the results of chemical analyses showed that trehalose and alginate oligosaccharide treatments effectively maintained an increased myofibrillar protein content and Ca²⁺‐ATPase activity in frozen shrimp. In addition, hematoxylin & eosin staining and SDS‐PAGE confirmed that these cryoprotective saccharides slowed the degradation of muscle proteins and the damage to muscle tissue structures. Overall, the application of trehalose and alginate oligosaccharides to peeled frozen shrimp might maintain better quality and extend the commercialization of these refrigerated products.     

Effect of formaldehyde on protein cross-linking and gel forming ability of surimi from lizardfish induced by microbial transglutaminase

Impact of formaldehyde (FA) at various levels (0–9 μmol/g surimi) on gel properties of surimi from lizardfish added with microbial transglutaminase (MTGase) was studied. During iced storage of 10 days, total and free FA in lizardfish flesh increased continuously (P < 0.05). In the presence of FA, breaking force of gels slightly increased, whilst the deformation decreased (P < 0.05). The addition of MTGase (0.4 units/g surimi) was able to increase gel strength and water holding capacity of resulting gel. Nevertheless, gel strengthening effect of MTGase was lowered when FA at higher level was present. Myosin heavy chain (MHC) dominantly underwent polymerisation to a higher extent when either MTGase or FA was added. The higher reduction in ε-amino group content was observed in natural actomyosin (NAM) when FA at higher levels (0–30 μmol/g protein) was incorporated. Acyl transfer reaction mediated by MTGase was impeded in NAM containing FA, especially at higher levels. Generally, FA had an adverse effect on cross-linking ability towards surimi proteins induced by MTGase. Therefore, cross-linking and gel-forming ability of lizardfish surimi could be maximised by MTGase when surimi contained no FA.     

EFFECT OF CHICKEN PLASMA PROTEIN AND SOME PROTEIN ADDITIVES ON PROTEOLYSIS AND GEL-FORMING ABILITY OF SARDINE (SARDINELLA GIBBOSA) SURIMI

The effect of chicken plasma protein (CPP) and various protein additives on autolysis and gel‐forming ability of sardine (Sardinella gibbosa) surimi was investigated. CPP and other protein additives showed inhibitory activity toward autolysis of sardine surimi incubated at 70C in a concentration‐dependent manner. Porcine plasma protein (PPP) and egg white (EW) were more effective in proteolysis prevention than CPP and other protein additives. Breaking force and deformation of both modori and kamaboko gels increased when CPP and other protein additives were added at levels up to 2% (P < 0.05). Nevertheless, PPP and EW showed a greater gel‐strengthening effect than CPP and other protein additives (P < 0.05). Addition of CPP and other plasma proteins resulted in decreased whiteness, especially with increasing amount (P < 0.05). However, no change in whiteness was observed with gels containing EW and soy protein isolate (SPI) (P > 0.05). Proteolysis of sardine surimi can be retarded by the addition of CPP and protein additives, leading to increased gel‐forming ability.     

Decomposition of trimethylamine oxide during iced storage of blue whiting (Micromesistius poutassou)

 Products of the decomposition of trimethylamine N-oxide (TMAO) during iced storage of blue whiting were monitored over 15 days. Increasing amounts of trimethylamine (TMA) and dimethylamine (DMA) were found in the white muscle with increasing storage time. The production of TMA was interpreted as a consequence of bacterial growth, while DMA production was due to enzymatic activity of trimethylamine N-oxide demethylase (TMAOase). TMAOase activity was monitored with time in different organs. The highest activities always corresponded to kidney and spleen. Also, TMAOase was found to remain active during the 15 days of iced storage. A relationship was found between TMAOase in kidney and DMA concentrations in white muscle.     

The Effectiveness of Antibrowning Dip Treatments to Reduce After‐Cooking Darkening in Potatoes

Abstract: After‐cooking darkening (ACD) is an inherent and undesirable trait that develops in cooked potatoes. The objective of this study was to evaluate the effectiveness of sodium acid sulfate (SAS) dip treatments compared to other antigraying treatments and a control to reduce ACD in boiled, Katahdin potatoes. Dip treatments were applied for 3 min prior to boiling and included: 3% SAS, 3% citric acid (CA), 3% sodium acid pyrophosphate (SAPP), along with a distilled water control. SAS‐ and CA‐treated potatoes had slightly, but significantly (P ≤ 0.05) higher b* and chroma values, which indicates a more intense yellow potato color, with less graying, compared to the control. SAS‐ and CA‐treated potatoes also had significantly (P≤ 0.001) lower pH values for inner and outer potato surfaces than the control. No significant (P > 0.05) differences were detected for total phenolic or mineral contents among treatments. CA and SAPP samples had slightly, but significantly (P≤ 0.05) higher moisture contents than the control. Sensory test results showed no significant differences for color, aftertaste, or overall acceptability. However, CA‐treated samples were rated significantly (P≤ 0.05) lower for flavor than all other treatments and panelists commented on sour notes. CA‐ and SAS‐treated potatoes were scored slightly, but significantly lower for texture than other treatments due to a waxy outer layer. However, SAS was the most acidic dip treatment, but did not significantly affect flavor. Overall, results suggest that SAS was similarly accepted by consumers in comparison to CA and SAPP, which is the industry standard to reduce ACD. Practical Application: After‐cooking darkening (ACD) is an undesirable potato trait that occurs after potatoes have been processed. Sodium acid pyrophosphate (SAPP) has been used as the industry standard to reduce ACD. Sodium acid sulfate (SAS) treatments prior to boiling appeared to be comparable to SAPP and citric acid in effectiveness to reduce ACD. SAS did not negatively affect the flavor of boiled potato samples according to sensory results. The SAS treatment may be more beneficial for potatoes intended for potato salad products.     

Effect of reducing agents on physicochemical properties and gel-forming ability of surimi produced from frozen fish

Effects of different reducing agents (cysteine, ascorbic acid and sodium bisulfite) at various levels on physicochemical properties of protein, transglutaminase activity and gel properties of surimi produced from frozen croaker, lizardfish, threadfin bream and bigeye snapper were studied. Addition of cysteine resulted in the highest increase in the breaking force and the deformation of surimi gels, compared with other reducing agents. The optimum levels of cysteine were 0.05, 0.1, 0.05 and 0.1% (w/w) for surimi from frozen croaker, lizardfish, threadfin bream and bigeye snapper, respectively. Surimi from frozen croaker with cysteine added showed a similar breaking force and deformation to that produced from fresh fish. With addition of cysteine, an increase in sulfhydryl content with a concomitant decrease in disulfide bond content was generally observed. Ca²⁺ ATPase activity also increased, indicating the renaturation of the myosin molecule. T_max of peak 1 (myosin peak) of all surimi sols in the presence of cysteine was shifted to higher temperature. The increased transglutaminase activity was observed with addition of cysteine. Therefore, reducing agents, especially cysteine, recovered the denatured muscle proteins and activated the transglutaminase in the muscle, leading to the increased gel-forming ability of surimi produced from frozen fish.     

Mechanical and Microstructural Properties of “Wet” Alginate and Composite Films Containing Various Carbohydrates

Composite “wet” alginate films were manufactured from alginate–carbohydrate solutions containing 5% alginate and 0.25% pectin, carrageenan (kappa or iota), potato starch (modified or unmodified), gellan gum, or cellulose (extracted or commercial). The “wet” alginate films were used as a model to understand co‐extruded alginate sausage casings that are currently being used by several sausage manufacturers. The mechanical, optical, and microstructural properties of the calcium cross‐linked composite films were explored. In addition, the water holding capacity and textural profile analysis properties of the alginate–carbohydrate gels were studied. The results indicate that the mechanical properties of “wet” alginate films/casings can be modified by adding various carbohydrates to them. Alginate films with pectin, carrageenan, and modified potato starch had significantly (P < 0.05) greater elongation values than pure alginate films. The alginate–pectin films also had greater (P < 0.05) tensile strengths than the pure alginate films. Alginate films with extracted cellulose, commercial cellulose, and modified potato starch had lower (P < 0.05) puncture force, distance, and work values than the alginate control films. Transmission electron microscopy images showed a very uniform alginate network in the control films. Several large cellulose fibers were visible in the films with extracted cellulose, while the cellulose fibers in the films with commercial cellulose were difficult to distinguish. Despite these apparent differences in cellulose fiber length, the 2 cellulose films had similar puncture and tensile properties.     

Cryoprotective additives and cryostabilisation effects on muscle fillets of the freshwater teleost fish Rohu carp (Labeo rohita) during prolonged frozen storage

The effects of various cryoprotective additives separately and in combination were studied on the myofibrillar protein integrity, biochemical enzyme activity levels and muscle ultrastructure in the freshwater teleost fish Rohu carp (Labeo rohita). Fish muscle samples were divided into eight groups and immersed in different mixtures of cryoprotective additives (S1–S8), then frozen at ? 20 or ? 30 °C for 24 months. Electrophoretic studies revealed early (within 6 months) alteration of the myofibrillar proteins myosin light chain, α‐actinin and tropomyosin. Reduction of the storage temperature from ? 20 to ? 30 °C slowed down the degradative processes. Sodium dodecyl sulfate polyacrylamide gel electrophoresis indicated that fish muscle treated with cryoprotective mixture S8 (40 g L^?1 sorbitol/3 g L^?1 sodium tripolyphosphate/4 g L^?1 sodium alginate) showed minimal post mortem changes in myofibrillar proteins. Ultrastructural results also revealed post mortem damage to the muscle, seen earliest (within 6 months) in the sample frozen‐stored without additives (S2), as compared with the normal, unfrozen muscle (S1). The influence of cryoprotectants alone and in combination on fish muscle structural proteins, myosin and actin filaments (A and I bands), during prolonged frozen storage was investigated. After 12 months, samples frozen‐stored with various cryoprotective additives (S2‐S7), except S8, showed signs of myofibrillar disintegration. Beyond that time the degradative processes started showing up in all samples, with minimal muscle ultrastructural damage in sample S8. Again, reducing the storage temperature from ? 20 to ? 30 °C slowed down the degradative processes. Ultrastructural results correlated well with levels of biochemical enzymes (Ca²⁺ myofibrillar ATPase and succinic dehydrogenase) during frozen storage. This is the first report of the cryoprotective effects of these additives on this popular edible fish species. Of the various combinations of additives tested, cryoprotective mixture S8 was found to preserve the muscle structure longest under frozen storage conditions. However, even this mixture was only effective for 18 months at ? 30 °C. Beyond that time the myofibrillar degradative processes were apparent with correlative electrophoretic, biochemical and ultrastructural studies. Copyright © 2006 Society of Chemical Industry     

Effects of garlic oil on milk fatty acid profile and lipogenesis‐related gene expression in mammary gland of dairy goats

BACKGROUND: Garlic oil (GO) has blood lipid‐lowering effects. Milk fatty acid (FA) originates partly from plasma, and can be affected by the mammary lipogenesis. This study aimed to investigate GO effects on milk FA profile and mammary lipogenesis‐related gene expression. Early‐lactation goats were randomly allocated to four treatments with six goats each, and offered corn silage ad libitum and fixed amount of 0.79 kg day^?1 dry matter (DM) concentrate mixed with GO (0, 0.57, 1.14, 1.71 g kg^?1 DM) for 30 days consisting of 26‐day adaptation. RESULTS: Intake of corn silage reduced (P≤0.05) as GO level increased in the concentrate. Lipase activity and lactose content linearly increased, while non‐esterified FA concentration quadratically decreased with increasing GO level (P≤0.05). The proportions of short‐ and medium‐chain (C14:0, C15:0 and C16:0) and saturated FA decreased, whereas C18, cis9 trans11 conjugated linoleic acid (c9t11 CLA), t10c12 CLA, monounsaturated and polyunsaturated FA, and some ≥ C20 FA proportions increased in a linear manner with increasing GO level (P≤0.05). The mRNA abundance of genes remained unchanged (P > 0.1) as GO level increased. CONCLUSION: Garlic oil altered milk FA profile and these effects may not be related to the mammary lipogenesis‐related genes expression. © 2012 Society of Chemical Industry     

Decomposition of trimethylamine oxide during iced storage of blue whiting (Micromesistius poutassou)

Products of the decomposition of trimethylamine N-oxide (TMAO) during iced storage of blue whiting were monitored over 15?days. Increasing amounts of trimethylamine (TMA) and dimethylamine (DMA) were found in the white muscle with increasing storage time. The production of TMA was interpreted as a consequence of bacterial growth, while DMA production was due to enzymatic activity of trimethylamine N-oxide demethylase (TMAOase). TMAOase activity was monitored with time in different organs. The highest activities always corresponded to kidney and spleen. Also, TMAOase was found to remain active during the 15 days of iced storage. A relationship was found between TMAOase in kidney and DMA concentrations in white muscle.     

Porcine plasma protein as proteinase inhibitor in bigeye snapper (Priacanthus tayenus) muscle and surimi

Porcine plasma protein (PPP) showed inhibitory activity towards trypsin, papain, digestive enzymes and modori‐inducing proteinases from bigeye snapper. Among the fractions prepared, fraction IV‐1 exhibited the highest inhibitory activity against all proteinases tested and the autolysis of fish muscle. At a level of 0.5% (w/w), both PPP and fraction IV‐1 effectively prevented the degradation of myosin heavy chain in fish muscle. The inhibitory activity of fraction IV‐1 was stable up to 60 °C. Incorporation of fraction IV‐1 significantly increased the breaking force, deformation and water‐holding capacity of surimi gel from bigeye snapper (P < 0.05). However, no increase in breaking force and deformation was found when fraction IV‐1 was added at a level above 0.3% (w/w) (P > 0.05). No significant change in whiteness of surimi gel was observed with the addition of fraction IV‐1 (P > 0.05). © 2001 Society of Chemical Industry     

The rheological properties of exudates from cured porcine muscle: effects of added polysaccharides and whey protein/polysaccharide blends

Meat exudates collected from massaged cured porcine M semimembranosus were used to observe changes in gelation properties of test exudates containing added polysaccharides, both on their own and in combination with selected whey protein concentrates (WPCs). Three polysaccharide powders, namely sodium alginate, low‐methoxy (LM) pectin and modified potato starch, were assessed at a residual powder level of 2% with Na alginate used at a 0.5% level. Polysaccharides were evaluated both individually and as dry blends with selected WPCs. WPCs assessed included high‐gelling A 35%, B 75% and C 55% protein β‐lactoglobulin powders, as well as a regular 76.5% protein, WPC D. All WPCs were incorporated at a 2% residual powder level in the final meat. Treatment and control meat samples and resulting exudates were prepared in duplicate with analysis performed in triplicate. Viscoelastic properties of control and test meat exudate samples (n = 6) were analysed using control stress rheology in oscillatory mode. Exudates were heated from 20 to 80 °C at 1 °C min⁻¹ with subsequent cooling after 30 min to 20 °C at 1 °C min⁻¹. Combinations of high‐gelling WPCs (especially β‐lactoglobulin) together with modified starch or pectin were found to increase storage modulus G′ (Pa) values compared with control values, with significant (P < 0.05) synergies being observed on dry blending these ingredients. Sodium alginate was found to have a negative effect on G′ (Pa) results, giving lower values compared with control treatments. © 1999 Society of Chemical Industry     

Intramuscular fatty acid profile of longissimus dorsi and semitendinosus muscle from Kundi steers fed on pasture with cottonseed cake supplement

The present study was accomplished to evaluate the intramuscular fatty acid (FA) composition of different muscles taken from Kundi steers (n = 15), which were approximately 24 months old, fed on a cottonseed cake supplement, and were made to graze on alfalfa pasture for 95 days prior to slaughter. The samples were taken from longissimus dorsi region (loin and ribeye portion) and distal region of semitendinosus muscle for intramuscular FA analysis. Saturated FA, comprising 49.48–52.09% of total FA composition, in all the muscles were studied. Ribeye portion of longissimus dorsi muscle contain relatively higher (P > 0.05) amount of trans FA (3.37%) as compared with loin portion of longissimus dorsi muscle (3.1%) and distal region of semitendinosus muscle (2.84%). The sum of monounsaturated FA in all the muscles studied was estimated in the range of 32.21–34.64%, while polyunsaturated FA contribute 11.39–12.39% of total FA. The mean conjugated linoleic acid was found to be 0.28, 0.35 and 0.41 in ribeye and loin portion of longissimus dorsi muscle and distal region of semitendinosus muscle, respectively.     

Solution Enhancement and Post-enhancement Storage Effects on the Quality, Sensory, and Retail Display Characteristics of Beef Triceps Brachii Muscles

Beef triceps brachii muscles (6 d postmortem; n= 15; muscle sections n= 45) were sectioned into 3rds and allocated to 1 of 3 treatments. The treatments were untreated (CNT), or injected at a 12% pump rate with either tap water‐only (H₂O) or a solution comprising tetrasodium pyrophosphate and sodium chloride (TSPP/ NaCl) at 0.4% and 1.0% target final product weight concentrations, respectively. Each muscle (comprising all 3 treatments) was then allocated to 2, 14, or 28 d of vacuum‐packaged 1°C storage. Purge losses during storage were greatest (P < 0.05) for H₂O muscles and least (P < 0.05) for TSPP/NaCl muscles. Purge losses also increased (P < 0.05) from 2 d to 14 d of storage. Steaks enhanced with TSPP/NaCl had less (P < 0.05) free water and lower (P < 0.05) cooking losses than either CNT or H₂O steaks. Storage duration did not affect (P > 0.05) Warner‐Bratzler shear force (WBS) or sensory tenderness, but juiciness decreased (P < 0.05) with increased storage duration. While storage duration did not impact (P > 0.05) instrumental color characteristics, aerobic plate counts generally increased during storage. The TSPP/NaCl steaks had lower (P < 0.05) WBS values and improved (P < 0.05) sensory tenderness and juiciness characteristics compared with CNT or H₂O steaks. While CNT steaks had greater (P < 0.05) L* values (lightness) than TSPP/NaCl steaks, TSPP/NaCl steaks had similar (P > 0.05) oxymyoglobin proportions (630/580 nm) and a* values (redness) as CNT steaks. These results suggest enhancement with TSPP/NaCl can improve triceps brachii yield and palatability characteristics. Increased post‐enhancement storage did not impact or worsened palatability while increasing purge losses, suggesting general deleterious effects of increased postmortem storage for this muscle.     

Effects of Rosemary Extract and Sodium Lactate on Quality of Vacuum-packaged Ground Ostrich Meat

ABSTRACT Vacuum‐packaged ground ostrich meat patties containing 2% sodium lactate (SL), 0.2% rosemary extract as oleoresin (RE), or their mixture (MIX) were evaluated and compared with control for their storage stability at 3 ± 1 °C in the dark by measuring pH, 2‐thiobarbituric acid‐reactive substance (TBARS) values, sample color (CIE L*, a*, b*, Hue and Chroma), and microbiological content. The pH values of ostrich patties, ranging from 6.03 to 6.13, were not affected by treatment (P < 0.05). At 9 d of storage, TBARS concentration for control samples containing no additives was 1.64 mg malonaldehyde/kg meat. Addition of RE to the ground ostrich meat inhibited lipid oxidation during storage at 3 ± 1 °C (P < 0.05). TBARS values of SL‐added samples were lower than control samples (P < 0.05); addition of SL also delayed the oxidation. It was found that RE had a protective effect on color, whereas addition of SL decreased CIE a* values (P < 0.05). SL, either alone or with RE, was effective in inhibiting total aerobic bacteria (TAB), coliforms, lactic acid bacteria (LAB), and Brochothrix thermosphacta in ostrich patties (P < 0.05) and provided a 2‐log reduction in microbial population during storage. In addition, RE did not have a significant effect on microbial growth at the concentration used in this study.     

海藻糖类抗冻保水剂对冻藏南美白对虾(Litopenaeus vannamei)品质的影响

以冻藏南美白对虾(Litopenaeus vannamei)虾仁为研究对象,0.5%和1.0%(w/v)海藻糖、海藻酸钠、海藻酸钠寡糖溶液作为抗冻保水剂,蒸馏水、0.5%和1.0%(w/v)焦磷酸钠分别为阴性对照组和阳性对照组,于-18 ℃下贮藏6周,通过对冻藏南美白对虾仁的解冻损失、颜色、肌原纤维蛋白含量、Ca2+-ATPase活性以及微观结构等指标进行分析,评价海藻糖类等对冻藏虾仁品质的影响。结果表明,与对照组相比,海藻糖、海藻酸钠寡糖、焦磷酸钠处理组虾仁的解冻损失显著降低(p<0.05)。海藻糖类提高了南美白对虾冻藏期间颜色的稳定性。海藻糖和海藻酸钠寡糖处理有效地保持了冻藏虾仁中肌原纤维蛋白含量和Ca2+-ATP酶活性,其中肌原纤维含量分别为104.2、103.2 mg/g,Ca2+-ATP酶活性分别为0.141、0.142 μmol Pi/mg·min。染色实验和电泳实验结果表明,海藻糖类对冻藏后肌肉蛋白质的降解和肌肉组织结构的损伤具有减缓作用,虾仁肌肉肌纤维结构完整,肌肉间无较大空隙形成,较好地保持了冻藏虾仁组织完整性,副肌球蛋白和肌动蛋白条带的强度都没有明显的降低。研究表明:在南美白对虾的冻藏过程中,海藻糖和海藻酸钠寡糖抗冻剂起到了良好的抗冻效果,能够更好地保证冻藏虾仁的质量和品质,得到一种冻藏水产品复合磷酸盐保水剂的较好替代品。     

Improvement of Gelling Properties of Lizardfish Mince as Influenced by Microbial Transglutaminase and Fish Freshness

ABSTRACT:  The effects of microbial transglutaminase (MTGase) at different levels (0 to 0.8 units/g sample) on the properties of gels from lizardfish ( Saurida undosquamis ) mince set 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 and deformation of gels increased with increasing MTGase amount added ( P < 0.05). At the same MTGase level used, gels with the prior setting at 40 °C for 30 min showed a higher breaking force compared with those subjected to prior setting at 25 °C for 2 h ( 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. Regardless of setting condition, microstructure of gel added with MTGase was finer with a smaller void compared with that of gel without MTGase. Therefore, setting temperature affected the property of gels added with MTGase. Gel properties of mince obtained from lizardfish stored in ice for different times (0 to 10 d) with and without MTGase at a level 0.6 units/g were determined. Irrespective of MTGase addition, breaking force and deformation of all gels decreased as the storage time of lizardfish increased ( P < 0.05). The addition of MTGase was able to increase both breaking force and deformation of the resulting gel produced from lizardfish kept in ice for all storage times used. Therefore, both freshness and MTGase addition had the direct impact on gel properties of lizardfish mince.