Differences in textural properties of cooked caponized and broiler chicken breast meat.

This study was aimed at evaluating textural properties of cooked chicken breast meats obtained from 3 production systems (conventional raising, feed modification, and caponization) and determining the relationship between instrumental parameters and sensory attributes associated with the texture of capon meat. Texture of cooked breast meats was determined using 3 instrumental methods: Warner-Bratzler Shear (WBS), texture profile analysis (TPA), and uniaxial compression (UC), and sensory analysis by trained panelists. The results indicated that cooked caponized meat showed the lowest values of WBS force, shear energy, hardness, Young's modulus of UC, and the 2 sensory attributes (firmness and number of chews) (P < 0.05). In contrast, springiness and juiciness were the highest in the caponized meat (P < 0.05), suggesting that capon meat was more tender and juicier than the others. Feed-modified chicken samples showed intermediate textural characteristics between the samples of capon and conventionally raised broiler. Pearson's correlation revealed that WBS force, shear energy, Young's modulus of UC, gumminess, and springiness were strongly correlated with 3 sensory attributes (firmness, number of chews, and juiciness). Partial least squares regression (PLSR) demonstrated that 72% of all sensory attributes for the first 2 PLSR components were explained by 36% of the instrumental parameters and the production systems. Loading and score plot illustrated that conventional raising contributed to a high degree of firmness and number of chews, and positively correlated with shear energy, WBS force, gumminess, hardness, and Young's modulus. Contrarily, caponization was negatively correlated with those sensory attributes. The univariate analysis indicated that firmness and number of chews were positively correlated with all instrumental parameters, except springiness. Juiciness was positively correlated with springiness but negatively correlated with the others. The study suggested that the cooked meat of capons could be differentiated from those of broilers raised conventionally and with feed-modified diets based on textural properties. Based on the optimized simulating equation, texture of caponized breast could be explained by WBS force, shear energy, Young's modulus, and gumminess.

Effects of sodium carbonate and sodium bicarbonate on yield and characteristics of Pacific white shrimp (Litopenaeus vannamei).

Effects of sodium carbonate (Na2CO3) and sodium bicarbonate (NaHCO3) on yield and characteristics of Pacific white shrimp (Litopenaeus vannamei) were studied. Shrimp soaked in 2.5% NaCl containing both compounds at different levels of pH (5.5, 7, 8.5, 10 and 11.5) showed an increase in the weight gain and cooking yield and a reduced cooking loss as pH of solutions increased (p<0.05). Increases in pH and salt content in soaked shrimp muscle were obtained with increasing pH (p<0.05). Higher pH of soaking solution partially solubilized proteins in the muscle as well as carotenoproteins. pH of solutions above 8.5 led to the pronounced leaching of pigments, associated with the lowered redness of cooked shrimp. Shear force of raw and cooked shrimp continuously decreased as pH of solution increased (p<0.05). Solution containing 2.5% NaCl and 2.0% NaHCO3 (pH 8.5) was recommended for treatment of white shrimp as a promising alternative for phosphates to increase the yield and to lower cooking loss without any negative effect on sensory properties.

Amino acid composition and antioxidative peptides from protein hydrolysates of yellow stripe Trevally (Selaroides leptolepis).

Hydrolysates from yellow stripe trevally meat with 15% degree of hydrolysis (DH) obtained using Alcalase (HA) and Flavourzyme (HF) following pH-stat method were characterized. Both hydrolysates, HA and HF, contained glutamic acid and glutamine as the major amino acids, while glycine was the dominant amino acid in fish flesh. Hydrolysates were also rich in aspartic acid, asparagine, alanine, lysine, and leucine. Essential amino acid/nonessential amino acid ratios were 0.55, 0.63, and 0.62 for flesh, HA, and HF, respectively. After separation on a Sephadex G-50 column, antioxidative activity of hydrolysate fractions was determined as Trolox equivalent antioxidant capacity. The fraction of HF with molecular weight (MW) of 1.77 kDa exhibited the strongest antioxidative activity, compared with other fractions. Among all fractions of HA, the one having a MW of 2.44 kDa showed the highest antioxidative activity. Thereafter, the selected Sephadex G-50 fractions from both HA and HF were further chromatographed using a Sephadex C-25 column, followed by HPLC. MW of antioxidative peptides from HA and HF determined by Maldi TOF/TOF was 656 and 617 Da, respectively. However, peptides isolated from both HA and HF possessed a lower antioxidative activity than Trolox at the same concentration (P < 0.05). HA and HF prevented DNA oxidative damage in Fenton reaction system tested by in vitro plasmid DNA relaxation assay. These results indicate that hydrolysates from yellow stripe trevally can be used as an important source of amino acids and serve as alternative natural antioxidants.

Effects of flavourzyme on yield and some biological activities of Mungoong, an extract paste from the cephalothorax of white shrimp.

The use of Flavourzyme as a processing aid for the production of Mungoong, an extract paste from the cephalothorax of white shrimp, and its effect on biological activities were investigated. Flavourzyme increased the yield of Mungoong. Mungoong prepared from raw cephalothorax with the addition of 0.15% or 0.30% (w/w) Flavourzyme showed higher yields than those prepared from the cooked counterpart with a higher formal content and nitrogen solubility index when the same levels of Flavourzyme were used (P < 0.05). Higher ammonia and amino nitrogen contents were also observed in Mungoong prepared with the aid of Flavourzyme, particularly for the raw cephalothorax (P < 0.05). All Mungoong contained protein as the major constituent. For antioxidative activity, Mungoong prepared from raw cephalothorax with 0.15% Flavourzyme (Mungoong RF 15) exhibited the highest antioxidative activity as evidenced by the highest 2,2-diphenyl-1-picryl hydrazyl and 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) radical scavenging activities as well as ferric reducing antioxidant power, compared with other samples. Additionally, angiotensin I converting enzyme inhibitory activity was greater in Mungoong produced with the aid of Flavourzyme, regardless of processes used (P < 0.05).

Interaction of fish myoglobin and myofibrillar proteins.

Interactions between fish myoglobin (Mb) and myofibrillar proteins were investigated in a Mb-natural actomyosin (NAM) model at 4 degrees C. Increases in metmyoglobin (MetMb) formation and the relative content of bound Mb were observed, as were decreases in whiteness and Ca(2+)-ATPase activity (P < 0.05). During the first 6 h of incubation, Mb bound preferably to myosin at domains other than the head portion, as evidenced by measurable ATPase activity. The potential binding of Mb to myosin heads occurred after 24-h incubation as evidenced by the marked decrease in Ca(2+)-ATPase activity of the NAM-Mb mixture when compared to that of NAM alone (P < 0.05). The interaction between fish Mb and myofibrillar proteins was more pronounced with increased storage time; formation of high-molecular-weight aggregates (> 206 kDa) also increased with time. Electrophoretic study revealed that disulfide bonds were not involved in Mb-NAM interactions.

Tuna pepsin: characteristics and its use for collagen extraction from the skin of threadfin bream (Nemipterus spp.).

Pepsin from the stomach of albacore tuna, skipjack tuna, and tongol tuna was characterized. Pepsin from all tuna species showed maximal activity at pH 2.0 and 50 degrees C when hemoglobin was used as a substrate. Among the stomach extract of all species tested, that of albacore tuna showed the highest activity (40.55 units/g tissue) (P < 0.05). Substrate-Native-PAGE revealed that pepsin from albacore tuna and tongol tuna consisted of 2 isoforms, whereas pepsin from skipjack tuna had only 1 form. The activity was completely inhibited by pepstatin A, while EDTA (ethylenediaminetetraacetic acid), SBTI (soybean trypsin inhibitor), and E-64 (1-(L-trans-epoxysuccinyl-leucylamino)-4-guanidinobutane) exhibited negligible effect. The activity was strongly inhibited by SDS (sodium dodecyl sulfate) (0.05% to 0.1%, w/v). Cysteine (5 to 50 mM) also showed an inhibitory effect in a concentration dependent manner. ATP, molybdate, NaCl, MgCl(2), and CaCl(2) had no impact on the activity. When tuna pepsin (10 units/g defatted skin) was used for collagen extraction from the skin of threadfin bream for 12 h, the yield of collagen increased by 1.84- to 2.32-fold and albacore pepsin showed the comparable extraction efficacy to porcine pepsin. The yield generally increased with increasing extraction time (P < 0.05). All collagen obtained with the aid of tuna pepsin showed similar protein patterns compared with those found in acid-solubilized collagen. Nevertheless, pepsin from skipjack tuna caused the degradation of alpha and beta components. All collagens were classified as type I with large portion of beta-chain. However, proteins with molecular weight (MW) greater than 200 kDa were abundant in acid-solubilized collagen.

Effect of pyrophosphate and 4-hexylresorcinol pretreatment on quality of refrigerated white shrimp (Litopenaeus vannamei) kept under modified atmosphere packaging.

The effect of pretreatment with pyrophosphate and 4-hexylresorcinol in combination with modified atmosphere packaging (MAP) (80% CO(2), 10% O(2), 10% N(2), or 80% CO(2), 20% N(2)) on the quality of white shrimp during storage at 4 degrees C was investigated. Shrimp pretreated with 2% pyrophosphate and 0.25% 4-hexylresorcinol and stored under MAP showed the lower microbiological and chemical deteriorations as evidenced by delayed microbial growth as well as lower trimethylamine (TMA) and total volatile base nitrogen (TVB) production (P < 0.05). Additionally, the growth of coliforms was inhibited effectively. White shrimp pretreated with 4-hexylresorcinol had the lower melanosis throughout the storage compared with those without treatment (P < 0.05). This was associated with the lowered polyphenol oxidase (PPO) activity in shrimp treated with 4-hexylresorcinol. Therefore, the effective retardation of microbiological and chemical deterioration of white shrimp stored under MAP with the decrease in melanosis could be achieved by pretreatment of the shrimp with pyrophosphate and 4-hexylresorcinol. Furthermore, decapitation could be another means to lower the microbial load and melanosis in white shrimp, particularly those stored under MAP.

Autolysis of Pacific white shrimp (Litopenaeus vannamei) meat: characterization and the effects of protein additives.

Autolytic activity of Pacific white shrimp (Litopenaeus vannamei) mince in the absence and in the presence of 2.5%NaCl was investigated. Pacific white shrimp mince exhibited the maximum autolytic activity at 35 and 40 degrees C in the absence and in the presence of 2.5%NaCl, respectively, as evidenced by the highest TCA-soluble peptide content and the greatest disappearance of myosin heavy chain (MHC). The autolysis was more pronounced in the acidic pH values, followed by alkaline pH ranges. Pepstatin A showed the highest inhibition toward autolysis in the acidic condition, revealing that aspartic proteinase was dominant in shrimp muscle. Nevertheless, soybean trypsin inhibitor effectively inhibited the autolysis at neutral and alkaline pH values, suggesting that serine proteinase was present in shrimp mince but contributed to autolysis at a lower extent in shrimp meat. Autolysis in shrimp meat could be inhibited partially by all protein additives, including bovine plasma protein (BPP), egg white (EW), and whey protein concentrate (WPC). The inhibition of autolysis increased when the level of protein additives increased with the concomitant increase in band intensity of MHC retained. WPC and BPP in the range of 2% to 3% exhibited the highest inhibition toward autolysis of shrimp mince.

Properties, translucence, and microstructure of Pacific white shrimp treated with mixed phosphates as affected by freshness and deveining.

Effects of freshness and deveining on some properties, translucence, and microstructure of Pacific white shrimp (Litopenaeus vannamei) soaked in 2.5% NaCl containing different phosphates were studied. Shrimp soaked in all solutions had increases in weight gain and cooking yield with lowered cooking loss, compared with the control (P < 0.05). However, efficacy of mixed phosphates in quality improvement of ice-stored shrimp was lower than fresh shrimp. Deveining resulted in increased weight gain and yield (P < 0.05). Nevertheless, samples treated with phosphates became more translucent. Shrimp stored in ice for 7 d and treated with mixed phosphates were generally more translucent than fresh counterparts (P < 0.05). Shrimp soaked in 2.5% NaCl containing 0.875% sodium acid pyrophosphate (SAPP) and 2.625% tetrasodium pyrophosphate (TSPP) were generally less translucent and had high weight gain and cooking yield along with low cooking loss. The microstructure study revealed that the muscle fibers were less attached with the loss of Z-disks after being treated with mixed phosphates. Cooked meats of fresh shrimp and ice-stored shrimp had more compact fiber arrangement with the shrinkage of sarcomere compared with raw samples. Disintegration was observed at the M-line in ice-stored shrimp treated with mixed phosphates after cooking, while such a phenomenon was not found in the cooked fresh sample treated with phosphates. T(max) and enthalpy of both myosin and actin peaks shifted to lower values when shrimp were treated with mixed phosphates (P < 0.05). Those changes were generally more pronounced in ice-stored shrimp. Therefore, freshness and deveining process had an impact on the quality of Pacific white shrimp treated with phosphates.

Improvement of gelling properties of lizardfish mince as influenced by microbial transglutaminase and fish freshness.

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 degrees C for 2 h or 40 degrees C for 30 min prior to heating at 90 degrees 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 degrees C for 30 min showed a higher breaking force compared with those subjected to prior setting at 25 degrees 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.

Effect of ionic strength and temperature on interaction between fish myoglobin and myofibrillar proteins.

The effects of ionic strength (0, 0.3, and 0.6 M KCl) and temperature (4 and 25 degrees C) on the interaction between fish myoglobin and myofibrillar proteins were investigated in a model system. Increases in the relative content of bound myoglobin and metmyoglobin formation in myoglobin-natural actomyosin (NAM) mixtures with concurrent decreases in whiteness and Ca(2+)-ATPase activity were observed with increasing ionic strength (P < 0.05). The relative content of bound myoglobin and the oxidation of oxymyoglobin were generally greater at 25 degrees C than at 4 degrees C (P < 0.05). Binding of myoglobin to NAM resulted in decreased whiteness (P < 0.05). Ca(2+)-ATPase was not affected by temperature (P > 0.05). SDS-PAGE patterns of protein samples suggested that myoglobin-NAM interactions did not involve disulfide bonds. The formation of high-molecular-weight aggregates (>206 kDa) was observed and was more pronounced at higher ionic strength and higher temperature.

Cathepsin L: a predominant heat-activated proteinase in arrowtooth flounder muscle.

Characterization of the autolytic profile of arrowtooth flounder (ATF) muscle indicated the involvement of heat-activated proteinases active at both acidic and alkaline pH values. Further assay of fish extract exhibited the maximum activity at 60 degrees C against casein used as a substrate at both pH 5.5 and 8.0. The maximum activity shifted to lower temperatures by the addition of urea with two distinctive patterns: activity reduction at pH 5.5 and activity enhancement at pH 8.0. The highest inhibition by E-64 indicated the proteinase belongs to the cysteine proteinase class. At pH 5.5, the proteinase hydrolyzed Z-Phe-Arg-NMec and all types of protein substrates tested at higher rate than that at pH 8.0. Activity bands, observed on the activity-stained substrate gels, indicated similar proteinases are responsible for the proteolytic activity observed at both pH values. When proteins of fish extract were separated by HPLC-SEC, only one proteolytic peak was observed at the retention time of 26 min with an estimated molecular weight of 39800 Da. The results implied cathepsin L is a predominant proteinase responsible for autolysis of ATF muscle at elevated temperatures.

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.

Effects of proteolysis and mechanism of gel weakening in heat-induced gelation of fish myosin.

Addition of papain decreased the onset temperature and the rate at which G' developed during heat-induced gelation of arrowtooth flounder myosin. Frequency sweep results revealed that G' markedly decreased in proportion to the amount of papain added. However, use of E-64, a cysteine proteinase inhibitor, reversed the effects of papain and protected myosin heavy chain from degradation. DSC thermograms indicated papain significantly decreased the enthalpy required to induce myosin denaturation without significant changes in onset and maximum transition temperatures. Thermal denaturation kinetics indicated decreases in both the activation energy and the rate of myosin denaturation. CD studies revealed a rapid decrease in alpha-helical content, indicating the initial degradation of myosin molecules mostly occurred in the tail region. These results suggested that proteolysis affected thermal properties and reactivity of myosin during heating. Although myosin gel could be formed, structural disruption resulted in lower gelling ability and rigidity of the formed gel.