Effect of combined heat and high-pressure treatments on the texture of chicken breast muscle (pectoralis fundus)

Commercially supplied chicken breast muscle was subjected to simultaneous heat and pressure treatments. Treatment conditions ranged from ambient temperature to 70 degrees C and from 0.1 to 800 MPa, respectively, in various combinations. Texture profile analysis (TPA) of the treated samples was performed to determine changes in muscle hardness. At treatment temperatures up to and including 50 degrees C, heat and pressure acted synergistically to increase muscle hardness. However, at 60 and 70 degrees C, hardness decreased following treatments in excess of 200 MPa. TPA was performed on extracted myofibrillar protein gels that after treatment under similar conditions revealed similar effects of heat and pressure. Differential scanning calorimetry analysis of whole muscle samples revealed that at ambient pressure the unfolding of myosin was completed at 60 degrees C, unlike actin, which completely denatured only above 70 degrees C. With simultaneous pressure treatment at >200 MPa, myosin and actin unfolded at 20 degrees C. Unfolding of myosin and actin could be induced in extracted myofibrillar protein with simultaneous treatment at 200 MPa and 40 degrees C. Electrophoretic analysis indicated high pressure/temperature regimens induced disulfide bonding between myosin chains.     

Physicochemical changes and mechanism of heat-induced gelation of arrowtooth flounder myosin

Physicochemical changes of myosin during heating were investigated to elucidate the mechanism of heat-induced gelation of arrowtooth flounder (ATF) myosin at high ionic strength. Changes in dynamic properties indicated ATF myosin formed a gel in three different stages as shown by the first increase in G' (storage modulus) at 28 degrees C, followed by the decrease at 35 degrees C and the second increase at 42 degrees C. DSC thermogram showed the onset of myosin denaturation at 25 degrees C with two maximum transition temperatures at 30 and 36 degrees C. The decrease in alpha-helical content indicated ATF myosin began to unfold at 15 degrees C and the unfolding continued until it reached 65 degrees C. Turbidity measurement showed myosin began to aggregate at 23 degrees C and the aggregation was complete at 40 degrees C. Surface hydrophobicity increased consistently in the temperature range studied, 20-65 degrees C. Sulfhydryl contents decreased significantly at 20-30 degrees C due to the formation of disulfide linkages but remained constant at temperatures >30 degrees C. ATF myosin was shown to be extremely sensitive to heat, resulting in denaturation at lower temperature than other fish myosin. Denaturation was initiated by unfolding of the alpha-helical region in myosin followed by exposure of hydrophobic and sulfhydryl residues, which are subsequently involved in aggregation and gelation processes.     

Thermally induced gelation of squid (Illex argentinus) actomyosin. Influence of sexual maturation stage.

The biochemical properties and the characteristics of heat-induced gelation of actomyosin from mature and immature squid were investigated. Both Mg(2+)-ATPase activity and reduced viscosity values of actomyosin showed no significant differences between mature and immature squids. A lower content of myosin heavy chain and a higher content of a 160 kDa component were observed in the SDS-PAGE 10% pattern of actomyosin from immature specimens. Gelation of both actomyosins at 10 mg mL(-)(1) protein concentration was optimal at 80 degrees C and pH 6.0. The highest rigidity was reached at 0.25 M KCl with actomyosin from both mature and immature squids. Irrespective of the heating temperature, ionic strength, and pH condition, the rigidity of mature squid actomyosin gel was greater than that of immature squid. Scanning electron micrographs of gels obtained with actomyosin from mature squids showed a better tridimensional structure than those of immature squids.     

Gelation of chicken pectoralis major myosin and heat-denatured beta-lactoglobulin

Thermal, rheological, and microstructural properties of myosin (1 and 2% protein) were compared to mixtures of 1% myosin and 1% heat-denatured beta-lactoglobulin aggregates (myosin/HDLG) and 1% myosin and 1% native beta-lactoglobulin (myosin/beta-LG) in 0.6 M NaCl and 0.05 M sodium phosphate buffer, pH 6.0, 6.5, and 7.0 during heating to 71 degrees C. Thermal denaturation patterns of myosin and myosin/HDLG were similar except for the appearance of an endothermic peak at 54-56 degrees C in the mixed system. At pH 7.0, 2% myosin began to gel at 48 degrees C and had a storage modulus (G') of 500 Pa upon cooling. Myosin/HDLG (2% total protein) had a gel point of 48 degrees C and a G' of 650 Pa, whereas myosin/beta-LG had a gel point of 49 degrees C but the G' was lower (180 Pa). As the pH was decreased, the gel points of myosin and myosin/HDLG decreased and the G' after cooling increased. The HDLG was incorporated within the myosin gel network, whereas beta-LG remained soluble.     

The effect of freezing and aldehydes on the interaction between fish myoglobin and myofibrillar proteins

The interaction between fish myoglobin (Mb) and natural actomyosin (NAM) extracted from fresh and frozen fish was studied. The quantity of soluble Mb in Mb-NAM extracted was less in frozen than in fresh fish (P < 0.05). However, no differences were observed in Mb that remained in solution following preparation of Mb-NAM from frozen whole fish vs frozen fillets (P > 0.05). MetMb formation in Mb-NAM was generally greater than that observed in control Mb (P < 0.05); the greatest MetMb content occurred in Mb-NAM extracted from frozen whole fish (P < 0.05). The effect of different aldehyde oxidation products on the interaction between fish Mb and NAM was also studied in vitro. The loss of soluble Mb from NAM:Mb preparations was greater in the presence of hexenal and hexanal (P < 0.05) relative to controls, and the degree of solubility loss varied with aldehyde type. Hexenal caused greater OxyMb oxidation than hexanal (P < 0.05). Whiteness of washed NAM and NAM-Mb mixtures decreased following aldehyde addition (P < 0.05). In the absence of Mb, the Ca2+ -ATPase activity of NAM was lower with added hexenal than with hexanal (P < 0.05). However, no differences in Ca2+ -ATPase activity between hexanal and hexenal-treated samples were observed when Mb was present (P > 0.05). Reducing and nonreducing sodium dodecyl sulfate-polyacrylamide gel electrophoresis analyses suggested that both disulfide and nondisulfide covalent linkages contributed to aldehyde-induced cross-linking between Mb and myofibrillar proteins.     

Heat-induced gelation of chicken Pectoralis major myosin and beta-lactoglobulin

The denaturation, aggregation, and rheological properties of chicken breast muscle myosin, beta-lactoglobulin (beta-LG), and mixed myosin/beta-LG solutions were studied in 0.6 M NaCl, 0.05 mM sodium phosphate buffer, pH 7.0, during heating. The endotherm of a mixture of myosin and beta-LG was identical to that expected if the endotherm of each protein was overlaid on the same axis. The maximum aggregation rate (AR(max)) increased, and the temperature at the AR(max) (T(max)) and initial aggregation temperature (T(o)) decreased as the concentration of both proteins was increased. The aggregation profile of <0.5% myosin was altered by the presence of 0.25% beta-LG. Addition of 0.5-3.0% beta-LG decreased storage moduli of 1% myosin between 55 and 75 degrees C, but increased storage moduli (G') when heated to 90 degrees C and after cooling. beta-LG had no effect on the gel point of > or =1.0% myosin, but enhanced gel strength when heated to 90 degrees C and after cooling. After cooling, the G' of 1% myosin/2%beta-LG gels was about 1.7 times greater than that of gels prepared from 2% myosin/1% beta-LG.     

Effect of temperature and/or pressure on tomato pectinesterase activity

The activity of tomato pectinesterase (PE) was studied as a function of pressure (0.1-900 MPa) and temperature (20-75 degrees C). Tomato PE was rather heat labile at atmospheric pressure (inactivation in the temperature domain 57-65 degrees C), but it was very pressure resistant. Even at 900 MPa and 60 degrees C the inactivation was slower as compared to the same treatment at atmospheric pressure. At atmospheric pressure, optimal catalytic activity of PE was found at neutral pH and a temperature of 55 degrees C. Increasing pressure up to 300 MPa increased the enzyme activity as compared to atmospheric pressure. A maximal enzyme activity was found at 100-200 MPa combined with a temperature of 60-65 degrees C. The presence of Ca(2+) ions (60 mM) decreased the enzyme activity at atmospheric pressure in the temperature range 45-60 degrees C but increased enzyme activity at elevated pressure (up to 300 MPa). Maximal enzyme activity in the presence of Ca(2+) ions was noted at 200-300 MPa in combination with a temperature of 65-70 degrees C.     

Structural changes in natural actomyosin and surimi from ling cod (Ophiodon elongatus) during frozen storage in the absence or presence of cryoprotectants

Surimi and natural actomyosin (NAM) from ling cod (Ophiodon elongatus) were subjected to frozen storage in the absence or presence of cryoprotectants (sorbitol, sucrose, lactitol, and Litesse, either individually or in combination). Effects of frozen storage were studied for NAM frozen at -10 degrees C for 10 days and for surimi after eight freeze-thaw cycles. A commercial blend cryoprotectant (4% sucrose and 4% sorbitol), individual cryoprotectants at 8%, and optimal blends at 4, 5.5, 6, and 8%, were effective in maintaining the gel strength of surimi and NAM gels. Surimi or NAM frozen in the absence of cryoprotectants or with only 4% individual cryoprotectants, showed increased percent alpha-helical content by Raman analysis. Increased disulfide content was also observed in the treatment without cryoprotectants by the Raman SS stretching band and by chemical determination. Tyrosine residues were in a buried environment before and after freezing for all treatments, and surface hydrophobicity measured by 1-anilinonaphthalene-8-sulfonate decreased after frozen storage in the absence of cryoprotectants.     

Interactive responses of gala apple fruit volatile production to controlled atmosphere storage and chemical inhibition of ethylene action

Gala apples exposed to the ethylene action inhibitor 1-methylcyclopropene (1-MCP) for 12 h at 20 degrees C were stored at 1 degrees C in air or a controlled atmosphere (CA) maintained at 1 kPa O2 and 2 kPa CO2. Volatile compounds were measured after 4, 12, 20, and 28 weeks plus 1 or 7 days at 20 degrees C. Treatment with 1-MCP and then storage in air or CA or storage in CA without 1-MCP treatment reduced volatile production as compared to apples not treated with 1-MCP stored in air. The reduced production of esters, alcohols, aldehydes, acetic acid, and 1-methoxy-4-(2-propenyl)benzene was observed. Ester production by fruit stored in CA decreased throughout the storage period regardless of previous 1-MCP treatment. The production of esters, alcohols, aldehydes, acetic acid, and 1-methoxy-4-(2-propenyl)benzene by 1-MCP-treated fruit stored in air plus 7 days at 20 degrees C increased after 20 or 28 weeks of storage. Continuous exposure to 417 micromol m(-3) ethylene for 7 days at 20 degrees C after 12 or 28 weeks of storage stimulated production of many volatile compounds, primarily esters and alcohols, by fruit stored in CA or 1-MCP-treated apples stored in air. However, exposure to ethylene had no effect on the production of aldehydes or acetic acid.     

Structural changes of hake (Merluccius merluccius L.) fillets: effects of freezing and frozen storage.

Structural changes in hake (Merluccius merluccius L.) fillets as affected by freezing method and frozen storage temperature have been studied through Raman spectroscopy and related to changes in texture and functionality. Changes in protein secondary structure were observed due to storage temperature, accompanied by changes in apparent viscosity and shear resistance. Samples at -10 degrees C showed greater structural alteration than at -30 degrees C in terms of increase of beta-sheets at the expense of alpha-helices. An increase of unordered protein structure was found only in samples stored at -10 degrees C. Exposure of buried tryptophan residues was observed at both storage temperatures. The decrease of the deltaCH(2) band upon storage suggested an increase of hydrophobic interactions of aliphatic residues. Except for liquid air frozen fillets, all samples showed a decrease of the nuO-H/nuC-H band ratio compared to the fresh ones, this decrease being higher the harsher the conditions.     

Reduction of virgin olive oil bitterness by fruit cold storage

Green mature olives (Olea europaea L. cv. 'Manzanilla', 'Picual', and 'Verdial') were stored at 5 degrees C, and the oil extracted from them showed a middle intensity level of sensory-evaluated bitterness. The storage times necessary for this reduction were different for the three varieties tested, requiring 4, 6, and 8 weeks, respectively, for 'Manzanilla', 'Picual', and 'Verdial' olives. The level of commercial quality of the extracted oil did not deteriorate as a consequence of previous fruit storage. Olives matured during refrigeration at 5 degrees C, as the increase of maturation index and the decrease of color index and fruit firmness indicated. Similarly, as the fruit storage period progressed, the total phenolic compound content of the extracted oils decreased. Although the use of green mature olives may require a more prolonged storage time, it allows for a better postharvest handling of the fruits, which are more resistant to physical damage or fungal infections than the riper ones.     

Tyrosinase-aided protein cross-linking: effects on gel formation of chicken breast myofibrils and texture and water-holding of chicken breast meat homogenate gels

The effects of Trichoderma reesei tyrosinase-catalyzed cross-linking of isolated chicken breast myofibril proteins as a simplified model system were studied with special emphasis on the thermal stability and gel formation of myofibrillar proteins. In addition, tyrosinase-catalyzed cross-linking was utilized to modify the firmness, water-holding capacity (WHC), and microstructure of cooked chicken breast meat homogenate gels. According to SDS-PAGE, the myosin heavy chain (MHC) and troponin T were the most sensitive proteins to the action of tyrosinase, whereas actin was not affected to the same extent. Calorimetric enthalpy (DeltaH) of the major thermal transition associated with myosin denaturation was reduced and with actin denaturation increased in the presence of tyrosinase. Low-amplitude viscoelastic measurements at constant temperatures of 25 degrees C and 40 degrees C showed that tyrosinase substantially increased the storage modulus (G') of the 4% myofibrillar protein suspension in the 0.35 M NaCl concentration. The effect was the most pronounced with high-enzyme dosages and at 40 degrees C. Without tyrosinase, the G' increase was low. Tyrosinase increased the firmness of the cooked phosphate-free and low-meat chicken breast meat homogenate gels compared to the corresponding controls. Tyrosinase maintained gel firmness at the control level of the low-salt homogenate gel and weakened it when both salt and phosphate levels were low. Tyrosinase improved the WHC of the low-meat and low-salt homogenate gels and maintained it at the level of the corresponding controls of phosphate-free and low-salt/low-phosphate homogenate gels. Microstructural characterization showed that a collagen network was formed in the presence of tyrosinase. Keywords: Chicken myofibrillar proteins; protein modification; cross-linking; tyrosinase; gelation; thermal stability; texture; water-holding capacity; microstructure.     

Enzyme-aided modification of chicken-breast myofibril proteins: effect of laccase and transglutaminase on gelation and thermal stability

The effect of laccase and transglutaminase (TG) on cross-linking, gelation, and thermal stability of salt-soluble chicken-breast myofibril proteins was investigated at pH 6. Both enzymes modified the protein pattern detected by SDS-PAGE. Identification of proteins by peptide mass mapping showed that myosin heavy chain (MHC) and troponin T were the most affected proteins. These proteins faded or disappeared as a function of the incubation time with both enzymes on SDS-PAGE. The molecular weight of actin was not, however, affected by either enzyme. The effects that the enzymes had on the gel formation of chicken-breast myofibrils were studied in 0.35 and 0.60 M NaCl solutions at 3% protein content and a constant temperature of 40 degrees C by using a small deformation viscoelastic measurement. TG substantially increased the storage modulus (G') of 3% protein in 0.35 M NaCl. Without the enzymes, gelation was insignificant in 0.35 M NaCl. The increased solubility of the proteins at 0.60 M NaCl intensified gelation with TG. G' increased 32 and 64% at dosages of 10 and 100 nkat of TG, respectively. Also, laccase increased G' of the gel in 0.60 M salt concentration. However, a high laccase dosage decreased the magnitude of G' below the control level. Differential scanning calorimetric (DSC) measurements indicated slightly reduced myosin heat stability after TG pretreatment and increased actin heat stability with both enzymes. Maximum transition temperatures did not alter with either enzyme.     

冷熏对高白鲑理化性质及肌球蛋白构象的影响

以新疆塞里木湖高白鲑为研究对象,研究冷烟熏过程对鱼肉理化性质及肌球蛋白构象的影响。冷熏温度为(20±2)℃,发烟温度140℃,冷熏时间分别为0、6、12、18、24 h,研究冷熏鱼肉理化性质(含水率、水分活度、色泽、质构特性、TVB-N)及肌球蛋白构象(蛋白浓度、总巯基含量、Ca^2+-ATPase、表面疏水性)变化。研究结果表明,冷熏0~24h,鱼肉含水率由75.75%下降至53.03%,水分活度(Aw)由0.988下降至0.952;鱼肉亮度值(L^*)显著降低(P<0.05),红度值(a^*)缓慢增加,黄度值(b^*)显著增加(P<0.05);表征鱼肉质构特性的剪切力与韧性均呈明显上升趋势(P<0.05);鱼肉挥发性盐基氮(TVB-N)由9.81上升至14.23 mg/100g;肌球蛋白浓度、总巯基含量、Ca^2+-ATPase活性均显著降低(P<0.05),表面疏水性增加(P<0.05);综上,控制冷熏时间12~18 h有利于提高冷熏鱼肉品质,降低鱼肉肌球蛋白变性与氧化程度。该研究为特色淡水鱼冷熏制品开发与烟熏过程中蛋白氧化调控提供理论依据与技术参考。     

Degradation kinetics of the antioxidant additive ascorbic acid in packed table olives during storage at different temperatures

The kinetics of ascorbic acid (AA) loss during storage of packed table olives with two different levels of added AA was investigated. Three selected storage temperatures were assayed: 10 degrees C, ambient (20-24 degrees C), and 40 degrees C. The study was carried out in both pasteurized and unpasteurized product. The effect of pasteurization treatment alone on added AA was not significant. In the pasteurized product, in general AA degraded following a first-order kinetics. The activation energy calculated by using the Arrhenius model averaged 9 kcal/mol. For each storage temperature, the increase in initial AA concentration significantly decreased the AA degradation rate. In the unpasteurized product, AA was not detected after 20 days in samples stored at room temperature and AA degradation followed zero-order kinetics at 10 degrees C, whereas at 40 degrees C a second-order reaction showed the best fit. In both pasteurized and unpasteurized product, the low level of initial dehydroascorbic acid disappeared during storage. Furfural appeared to be formed during storage, mainly at 40 degrees C, following zero-order kinetics.     

Raman spectroscopic study of structural changes in Hake (Merluccius merluccius L.) muscle proteins during frozen storage

This paper examines changes in the structure and functionality of fish muscle proteins at frozen storage temperatures known to render very different practical storage lives (-10 and -30 degrees C). Apparent viscosity and dimethylamine (DMA) content showed drastic temperature-related differences during storage. Raman spectroscopy revealed the occurrence of some structural changes involving secondary and tertiary protein structures. The changes in secondary structure were quantified, showing an increase of beta-sheet at the expense of alpha-helix structure. The nuC-H stretching band near 2935 cm(-)(1) increased in intensity, indicating denaturation of the muscle proteins through the exposure of aliphatic hydrophobic groups to the solvent. These structural changes were more pronounced at -10 degrees C but occurred at both storage temperatures, whereas changes in apparent viscosity and DMA only occurred in storage at -10 degrees C. The possible utility of these structural changes for quality assessment is discussed.     

Electrophoretic pattern, thermal denaturation, and in vitro digestibility of oxidized myosin

Physicochemical changes and in vitro digestibility of chicken breast myosin oxidized with a nonenzymic free-radical-generating system (FeCl(3)/H(2)O(2)/ascorbate) were studied by SDS-PAGE, differential scanning calorimetry, and o-phthaldialdehyde assay. Oxidation caused fragmentation and polymerization of myosin. Myosin polymers were cross-linked mainly through disulfide bonds. Hydroxyl radicals destabilized myosin, lowering its denaturation temperature by up to 4 degrees C. Oxidized myosin also produced a new thermal transition in the 60-80 degrees C temperature range, which could be attributed to the formation of disulfide-stabilized polymers. The proteolytic susceptibility of myosin to pepsin, trypsin, and chymotrypsin was increased by oxidation. Under nonreducing conditions, however, oxidized myosin showed decreased digestibility. The results may help explain variations in the functionality and nutritional quality of muscle foods in meat processing in which oxidation is involved.     

Effect of storage temperature and water activity on the content and profile of isoflavones, antioxidant activity, and in vitro protein digestibility of soy protein isolates and defatted soy flours

The aim of this work was to study the effect of 1 year of storage at different temperatures and 1 month of storage at different water activities on the content and profile of isoflavones, antioxidant activity, and in vitro protein digestibility of defatted soy flours (DSF) and soy protein isolates (SPI). The storage for up to 1 year, at temperatures from -18 to 42 degrees C, had no effect on the total content of isoflavones, but the profile changed drastically at 42 degrees C, with a significant decrease of the percentage of malonylglucosides with a proportional increase of beta-glucosides. A similar effect was observed for SPI stored at a(w) = 0.87 for 1 month. For DSF, however, there was observed a great increase in aglycons (from 10 to 79%), probably due to the action of endogenous beta-glucosidases. The antioxidant activity decreased after storage at 42 degrees C, but the in vitro protein digestibility did not change.     

Protein and lipid oxidation during frozen storage of rainbow trout (Oncorhynchus mykiss)

This study aimed at investigating protein and lipid oxidation during frozen storage of rainbow trout. Rainbow trout fillets were stored for 13 months at -20, -30, or -80 degrees C, and samples were analyzed at regular intervals for lipid and protein oxidation markers. Lipid oxidation was followed by measuring lipid hydroperoxides (PV), as well as secondary oxidation products (volatiles) using dynamic headspace GC-MS. Free fatty acids (FFA) were measured as an estimation of lipolysis. Protein oxidation was followed using the spectrophotometric determination of protein carbonyls and immunoblotting. Significant oxidation was observed in samples stored at -20 degrees C, and at this temperature lipid and protein oxidation seemed to develop simultaneously. FFA, PV, and carbonyls increased significantly for the fish stored at -20 degrees C, whereas the fish stored at -30 and -80 degrees C did not show any increase in oxidation during the entire storage period when these methods were used. In contrast, the more sensitive GC-MS method used for measurement of the volatiles showed that the fish stored at -30 degrees C oxidized more quickly than those stored at -80 degrees C. Detection of protein oxidation using immunoblotting revealed that high molecular weight proteins were oxidized already at t = 0 and that no new protein oxidized during storage irrespective of the storage time and temperature. The results emphasize the need for the development of more sensitive and reliable methods to study protein oxidation in order to gain more explicit knowledge about the significance of protein oxidation for food quality and, especially, to correlate protein oxidation with physical and functional properties of foods.