Post-rigor Muscle Research Articles

Pre-rigor salting improves gel strength and water-holding of surimi gel made from snakehead fish (Channa argus): The role of protein oxidation

The purpose of this study was to determine the effect of pre-rigor salting on the quality characteristics of surimi gels prepared from snakehead fish muscle. Pre-rigor and post-rigor muscle were mixed with 0.3% or 3% NaCl (w/w) and made into surimi gels, respectively. Results showed that pre-rigor muscle had a higher content of ATP, longer sarcomere, higher pH and greater protein solubility. Metabolic profile suggested that pre-rigor muscle had higher content (a 28-fold increase) of antioxidants such as butyryl-l-carnitine. Transmission electron microscopy showed more damage of mitochondria in post-rigor muscle. Surimi paste from pre-rigor meat chopped with 3% NaCl generally showed greater radical scavenging ability and had higher content of free sulfhydryl. Surimi gel made from pre-rigor muscle salted with 3% NaCl showed a larger gel strength (3.18 kg*mm vs. 2.22 kg*mm) and better water-holding (86% vs. 80%) than that of post-rigor group. Based on these findings, we hypothesized that: In addition to other factors such as pH, degree of denaturation, etc., less protein oxidation in pre-rigor salted surimi also contributes to the improved gel properties.

Effect of sea tangle extract on the quality characteristics of reduced-salt, low-fat sausages using pre-rigor muscle during refrigerated storage.

The aim of this study was to investigate quality characteristics of reduced-salt, low-fat pork sausage (PS) using pre-rigor muscle and sea tangle extract (STE) to reduce salt level of sausages during refrigerated storage. Pork ham was prepared with pre-rigor and post-rigor muscle from the local market. Sausages using post-rigor muscle were manufactured with the 1.5% of salt content, and samples with pre-rigor muscle were processed by different salt concentrations (0.8%). Accordingly, PSs were prepared in 4 treatments (REF, PS with 1.5% of salt using post-rigor muscle; CTL, PS with 0.8% of salt using pre-rigor muscle; TRT1, PS with 0.8% of salt and 5% of STE using pre-rigor muscle; TRT2, PS with 0.8% of salt and 10% of STE using pre-rigor muscle). For the evaluation of quality characteristics and shelf-life of reduced-salt PS, pH and color values, cooking loss (%), expressible moisture (%), textural properties, lipid oxidation (thiobarbituric reactive substances), protein denaturation (volatile basic nitrogen), and microbiological analysis (total plate counts and Enterobacteriaceae counts) were determined. The pH and temperature of pre-rigor raw pork ham were higher than those of post-rigor pork ham. Hardness of TRT2 was higher than that of REF or CTL. TRT2 had higher gumminess and chewiness than CTL. TRT1 and TRT2 had lower volatile basic nitrogen than CTL. Total plate counts of TRT2 were lower than those of CTL. Expressible moisture values of TRT1 and TRT2 were similar to those of REF. The addition of STE into PS improved functional properties and shelf-life of PS. Reduced-salt PS containing pre-rigor muscle and STE had similar functional properties to those of regular-salt ones, while containing approximately 47% less salt compared to regular-salt level.

Evaluation of salt level and rigor status on the physicochemical and textural properties of low-fat pork sausages added with sea tangle extract using rapidly chilled pre-rigor pork ham.

This study was performed to evaluate the quality characteristics of pork sausage (PS) with sea tangle extract (STE) and rapid chilled pre-rigor muscle (RCPM) for the development of reduced-salt low-fat sausage. Pre- and post-rigor pork ham muscles were prepared to process PSs. Positive control (reference, REF) using post-rigor muscle were manufactured at a regular-salt level of 1.5%. Fresh and rapid-chilled pre-rigor muscle (FPM and RCPM) were used to manufacture reduced-salt sausages with 0.8% salt. Reduced-salt PSs were prepared with four treatments: FT1 (FPM alone), FT2 (FPM with 5% STE), RT1 (RCPM alone), and RT2 (RCPM with 5% STE). The physicochemical and textural properties of the sausages with reduced-salt levels and RCPM combination were measured to determine if the characteristics of RCPM were similar to those with FPM. The pH values of PS with FPM and RCPM were higher than those of REF with post-rigor muscle. Color values (L*, a*, b*) were not affected by different rigor-states and salt addition level. Textural properties of reduced-salt PSs were similar to those of REF due to the improved functionalities of pre-rigor muscle. RT2 had lower expressible moisture (%) than other treatments with post-rigor muscle and RCPM except for RT1. The addition of STE and RCPM to reduced-salt PS increased the waterholding capacity, which was lower than those of PS with STE using RCPM but similar to those of regular-salt sausage.

Evaluation of the Biochemical and Functional Characteristic of Stinging catfish, Heteropneustes fossilis Muscle Tissue with Emphasize on Myofibrillar Protein and Collagen

Objectives: To evaluate the physico-chemical and functional characteristics of the stinging catfish muscle tissue during the storage time of 18 hours following the death of the fish. Methods: In the present study, stinging catfish were collected from the paddy fields and streams near Tiruvalla Kerala. Fish were slaughtered immediately and analyzed for changes in pH value, cook loss, expressible water content, water holding capacity, sensory demerit score values, and textural profile and were compared with progress of rigor mortis. Study also evaluated the changes in protein fractions present in the muscle tissue and correlated them with autolytic enzyme activities. Findings: In stinging catfish, the rigor mortis occurred within four hours of storage (78.37 %) at ambient temperature. The post rigor stage was attained after the 6th hour and the K value reached above 60% within the 8th hour which indicates the unacceptable range for consumption. The present study also proved that the stinging catfish is an inosine producer. The initial concentration of sarcoplasmic protein in fish muscle (13.71%) decreased to 7.62% at the end of 18 hours of storage. The muscle tissue myofibrillar protein also showed a decrease from an initial concentration of 44.87% to a final concentration of 18.02%. Protein denaturation was evident with an increase from 39.65% to 73.20% at the end of the storage period. Collagen concentration was found to be reduced (31.85% reduction) after the 18th hour of storage. Pepsin soluble collagen was less susceptible to the activity of collagenase enzyme in the pre-rigor stage, confirming its role in post-rigor muscle softening when compared to acid soluble and insoluble collagen. Novelty: The present work authenticated that post-rigor softening of stinging catfish muscle is typically due to the degradation of pepsin soluble collagen and not reported elsewhere. Additionally, myofibrillar proteins have more influence on total hardness and stiffness than collagen, while cohesiveness is a better function of collagen than myofibrillar protein. These findings make it useful to perceive the process thatinduces softening in catfish and to create effective strategies to prevent it. Keywords: Collagen; Myofibrillar Protein; Adenosine Nucleotides; Autolytic Enzymes; Textural Profile

Daily Quantification of Myoglobin Forms on Beef Longissimus Lumborum Steaks Over 7 Days of Display by Near-infrared Diffuse Reflectance Spectroscopy

Near-infrared diffuse reflectance spectroscopy (NIR-DRS) was utilized to develop an algorithm using approximately 18 wavelengths spanning 480 to 650 nm to determine oxymyoglobin (OxyMb), deoxymyoglobin (DeoxyMb), and metmyoglobin (MetMb) contents on beef longissimus lumborum muscles. Daily changes in subsurface myoglobin redox forms were evaluated for 7 d using NIR-DRS and compared with the surface color as assessed by a HunterLab MiniScan spectrophotometer as a reference modality. Both measurements revealed that MetMb increased steadily over the duration of display, showing high correlation (R2 = 0.91) between the 2 methods. Comparatively, whereas NIR-DRS revealed OxyMb to have decreased steadily over the period of display, the HunterLab MiniScan spectrophotometer indicated a much later onset of the apparent decrease of OxyMb, resulting in a moderate correlation (R2 = 0.64) between the 2 methods. No correlation was found between the 2 methods regarding the changes of DeoxyMb over the duration of display. The newly developed NIR-DRS algorithm has potential as an alternative method of color assessment in postrigor skeletal muscle.

Effects of different frozen temperatures of pork sausage batter on quality characteristics of reduced-salt sausages using pre-rigor muscle.

ObjectiveThe objective of this study was to evaluate quality characteristics of reduced-salt pork sausage (PS) using pre-rigor muscle compared to those of regular-salt PS. In addition, effects of freezing on sausage batter with different temperatures (−30°C vs −70°C) on quality characteristics of both sausage batter and cooked sausages during frozen storage were observed.MethodsPre-rigor and post-rigor pork hams were used to manufacture low-fat sausages. Sausages using post-rigor (Post) muscle were manufactured at a salt level of 1.5%, whereas those with pre-rigor (Pre) muscle were processed at salt level of 1.0%. After these muscles were made at two salt levels (1.5% salt, Post-rigor; 1.0% salt, Pre-rigor), Sausage batters were stored at two frozen temperatures (−30°C vs −70°C). During storage for 12 wks, they were measured for physicochemical and textural properties every 4 wks up to 12 wks.ResultspH values and temperatures of sausage batter of pre-rigor muscle were higher than those of post-rigor muscle regardless of the frozen temperature. The lightness and yellowness values of batter at the initial storage were the highest during storage. For PS, there were no differences in most parameters measured among all treatments. However, expressible moisture values (%) of Pre-30 and Pre-70 were lower than those of Post-30 (p<0.05).ConclusionRegardless of frozen temperature during storage, quality characteristics of pre-rigor PS with salt level of 1.0% salt were similar to those of post-rigor PS with salt level of 1.5%. By using the pre-rigor muscle, salt content could be reduced by one third of the regular-salt level (1.5%) of post-rigor muscle.

PSII-9 Free amino acids in pre- and post-rigor muscles from beef cattle under induced oxidative stress by hydrogen peroxide

Abstract This study examined the effects of oxidative stress induced by hydrogen peroxide on free amino acids in pre-and post-rigor muscles from beef heifers (n = 18). Cattle were supplemented with ground corn and soybean hulls to 310 to 456 kg of BW while grazing cool and warm-season pastures and were evaluated for preliminary oxidative markers; afterward, they were shipped and finished at a commercial feedlot in Iowa. Animals were blocked into three groups based on prior analysis of oxidative stress markers and two treatments of either 20 mg hydrogen peroxide/kg BW (OX, n = 9) or 10 mL of saline (CON, n = 9) were equally and randomly assigned to animals within each block. On the day before slaughter, the OX and CON treatments were administered intravenously through the jugular vein. Pre-rigor muscles were collected at the neck (splenius) during slaughter; whereas post-rigor muscles were collected at the anterior of the beef loins (longissimus lumborum) at 72 h postmortem. Free amino acids were extracted in phosphate buffer, derivatized by propyl chloroformate, and determined by gas chromatography - mass spectrometry. Data were analyzed as a randomized complete block design with treatment, muscle rigor, and their interaction as fixed effects. Twenty-seven amino acids were quantified and ornithine and glutamine were 0.03 and 2.99 mmole/kg greater in OX muscle than in CON muscle (P = 0.031 and 0.024, respectively). Ten amino acids, such as glutamine and glutamic acid, were greater in pre-rigor muscles (P ≤ 0.003); whereas eleven amino acids were greater in post-rigor muscles, such as ß-aminoisobutyric acid and histidine (P ≤ 0.039). No treatment × time interaction was found (P &amp;gt; 0.069). Both ornithine and glutamine have been reported to reduce oxidative stress. Postmortem metabolism also greatly influences free amino acid concentrations.

Physicochemical properties of reduced-salt cured pork loin as affected by different freezing temperature and storage periods.

ObjectiveThe objective of this study was to evaluate functional properties of reduced-salt pork meat products made of pre-rigor pork loin treated by different freezing temperatures (−30°C and −70°C) during storage.MethodsPre-rigor cured pork loin with 1.0% added salt was compared to post-rigor muscle added with 1.5% salt for pH, color (L*, a*, b*), cooking loss (CL), expressible moisture, warner-Bratzler shear value, thiobarbituric acid reactive substances (TBARS), and volatile basic nitrogen (VBN).ResultsPre-rigor cured pork loins had higher pH and temperature than post-rigor ones as raw meat (p<0.05). pH values were higher for pre-rigor pork loins than those of post-rigor pork loins (p<0.05). Color values did not different among treatments (p>0.05). No color differences were observed during storage period after cooking (p>0.05). The CL (%) of pre-rigor cured pork loins was the lowest when frozen at −70°C. The TBARS and VBN increased from 8 weeks of storage (p<0.05), but no further changed thereafter (p>0.05). Pre-rigor cured pork loins added with 1.0% salt showed similar characteristics to post-rigor pork loins added with 1.5% salt.ConclusionCured pork loins could be produced using pre-rigor muscle added with 1/3 of the original salt level (1.5%) and could be stored for up to 4 wks of frozen storage, regardless of a frozen temperature of −30°C or −70°C without detrimental effects.

Changes in physicochemical characteristics and oxidative stability of pre- and post-rigor frozen chicken muscles during cold storage.

The objective of this study was to investigate the effects of rigor state on physicochemical characteristics and the oxidative stability of chicken leg and breast muscles as a function of freezing time. Breast and leg muscles were excised from 24 broiler chickens at 30min or 1.5h postmortem (PM), frozen overnight at - 75°C immediately, and then stored at - 20°C for 90days to measure the meat quality traits. Results showed that longer freezing led to deterioration of meat quality with higher deterioration for post-rigor frozen muscles. Pre-rigor frozen muscles had higher pH, water holding capacity (around 90%), and sarcomere length with a lower thaw and cook loss than post-rigor frozen muscles. The Warner-Bartzler shear force (WBSF) values for chicken leg and breast muscles were insignificant (except pre-rigor leg muscles which had significantly higher WBSF value only at 90thday of storage). The lightness (L*) value increased significantly with increasing storage for all samples. Post-rigor muscles had significantly higher TBARS values (0.62mg MDA/kg) than the pre-rigor muscles. The leg muscles had better physicochemical characteristics compared to breast muscles, except for the cook loss. Therefore, immediate freezing (prior to onset of rigor) could be an effective way to minimize the quality deterioration of frozen chicken muscles.

Effect of high hydrostatic pressure treatment on physical parameters, ultrastructure and shelf life of pre- and post-rigor mortis palm ruff (Seriolella violacea) under chilled storage

To identify processing conditions that better maintain palm ruff quality attributes, high hydrostatic pressure (HHP) was applied to pre- and post-rigor fillets. Physical parameters as whiteness index (WI), water holding capacity (WHC), texture and ultrastructure and shelf life were evaluated after the application of 450 and 550 MPa (3 and 4 min) and during cold storage. Pre-rigor fillets retained less water and were softer than post-rigor, although the onset of rigor increased palm ruff's WHC and firmness. Application of HHP whitened palm ruff's dark flesh; however, this effect reverted at the end of the storage. Pressurized post-rigor samples retained less water than the control and storage caused a WHC increase in samples pressurized at 550 MPa, independent on the rigor condition. Post-rigor fillets softened at pressures of 450–550 MPa appearing to have a lower threshold than beef or cod (above 600 MPa). Ultrastructural changes revealed a subtle contraction (7.4%) of the myofibrils in the unpressurized post-rigor muscle compared to pre-rigor; after 26 days' storage both samples presented extensive muscle degradation and sarcomere length was reduced in 30%. HHP induced pressure-dependent shortening of the sarcomere and modifications to the structure which after 550 MPa was hardly recognizable. After 26 days' storage, there was only slight degradation of the ultrastructure, showing that beyond the structural modifications caused by HHP, post-mortem deterioration is delayed in HHP-treated fillets. Furthermore, HHP extended palm ruff's shelf life to 14–23 days. Thus, HHP may be considered as a technology that maintains the textural quality and shelf life of fresh and stored fish.

Gelation properties of tilapia fish protein isolate and surimi pre- and post-rigor

Abstract The structural changes and rheological properties of tilapia proteins prepared using two refining methods (pH shift processing and surimi processing, respectively) with pre- and post-rigor muscle were investigated. Higher storage modulus (G′) and better gel texture were observed in surimi produced from pre-rigor fish than surimi made from post-rigor fish, but no rigor effect was noted on the gel-forming ability of fish protein isolate (FPI). The effect of salt on the gelation of tilapia muscle with different rigor states or refining method was also determined. The addition of salt appeared to readily unfold protein structures in FPI as measured by surface hydrophobicity, surface reactive sulfhydryl content, dynamic rheology, and Raman spectroscopy. However, the effect of salt on the degree of unfolding in surimi was not as sensitive as in FPI.

Effect of Pre-rigor Salting Levels on Physicochemical and Textural Properties of Chicken Breast Muscles.

This study was conducted to evaluate the effect of pre-rigor salting level (0-4% NaCl concentration) on physicochemical and textural properties of pre-rigor chicken breast muscles. The pre-rigor chicken breast muscles were de-boned 10 min post-mortem and salted within 25 min post-mortem. An increase in pre-rigor salting level led to the formation of high ultimate pH of chicken breast muscles at post-mortem 24 h. The addition of minimum of 2% NaCl significantly improved water holding capacity, cooking loss, protein solubility, and hardness when compared to the non-salting chicken breast muscle (p<0.05). On the other hand, the increase in pre-rigor salting level caused the inhibition of myofibrillar protein degradation and the acceleration of lipid oxidation. However, the difference in NaCl concentration between 3% and 4% had no great differences in the results of physicochemical and textural properties due to pre-rigor salting effects (p>0.05). Therefore, our study certified the pre-rigor salting effect of chicken breast muscle salted with 2% NaCl when compared to post-rigor muscle salted with equal NaCl concentration, and suggests that the 2% NaCl concentration is minimally required to ensure the definite pre-rigor salting effect on chicken breast muscle.

Combined effects of presalted prerigor and postrigor batter mixtures on chicken breast gelation

We examined the combined effects of prerigor and postrigor batter mixtures on protein gelation. The postrigor batter was prepared with 2% salt, whereas the prerigor meat at 5 min postmortem was used to prepare postrigor batters at different salt levels. For 5 treatments, prerigor batters were mixed with postrigor batter that had 2% salt (control) as follows: T1: ground presalted (1%) hot-boned breast with 1% salt for 50% total batch; T2: ground presalted (2%) hot-boned breast for 50% total batch; T3: ground presalted (3%) hot-boned breast for 30% total batch that was mixed with cold-boned batter for 50% total batch; T4: ground presalted (4%) hot-boned breast for 25% total batch that was mixed with cold-boned batter for 50% total batch; and T5: ground presalted (5%) hot-boned breast for 20% total batch that was mixed with cold-boned batter for 50% total batch. Treatments with both presalted prerigor and postrigor muscle showed less cooking loss and lower emulsion stability than the control, except T5. The protein solubility and apparent viscosity of the control was the lowest. Thus, presalted hot-boned muscle combined with cold-boned muscle positively affected physicochemical properties.

A study of the ice crystal sizes of red muscle of pre-rigor Atlantic salmon (Salmo salar) fillets during superchilled storage

Pre-rigor salmon fillets were superchilled in an impingement freezer and stored at −1.7±0.3°C for 29days. The objective of this work was to study the ice crystal sizes in red muscle of pre-rigor salmon fillets that were partially frozen at fast (−30°C, 227W/m2K, 2.1min) which is referred to as process F and slow (−20°C, 153W/m2K, 4.2min) which is referred to as process S during superchilled storage. It was observed that the size of intracellular ice crystals in pre-rigor muscles at faster superchilling rate was significantly (p<0.05) smaller than that at slower superchilling rate. The size of ice crystals formed in pre-rigor muscle was significant (p<0.05) smaller than that formed in post-rigor muscle. It was also observed that the size of intracellular ice crystals formed in pre-rigor red muscles was significant smaller than that in white muscle. In addition, a large number of small ice crystals are formed within the muscle during partial freezing of pre-rigor muscle compared to post-rigor muscle. Future research should focus on tests of the quality parameters separately in red and white muscles (pre- and post-rigor) during superchilled storage of food products in order to understand more about their characteristics (quality and shelf life).

Effects of rigor state, thawing temperature, and processing on the physicochemical properties of frozen duck breast muscle

The objectives of this study were to evaluate effects of rigor state, thawing temperature, and processing on the physicochemical properties of intact frozen duck breast muscle and homogenates prepared with the frozen-thawed muscles. Prerigor breast muscle was frozen at -25°C and thawed at 4 and 15°C, and the physicochemical properties of duck breast frozen prerigor compared with those in frozen postrigor and 4°C chilled postrigor muscles. The homogenates prepared with duck breast frozen prerigor showed similar physicochemical properties as the frozen-thawed postrigor muscle homogenate. The thawing temperature did not affect the physicochemical properties of homogenates prepared with duck breast muscle frozen prerigor. Also, no significant differences (P > 0.05) in the ultimate pH value and color parameters were observed among the frozen-thawed treatments despite the differences in rigor state and thawing temperature. However, a higher thawing temperature of the intact frozen prerigor muscle resulted in an increase in thawing loss and shear force due to excessive muscle shortening. In this study, the intact duck breast that has undergone thaw-rigor showed main problems associated with thaw-rigor, such as higher thawing loss and shear force, regardless of thawing temperature. However, the processing (grinding and salting) decreased the difference in physicochemical properties due to rigor state before freezing and thawing temperature. Therefore, the frozen-thawed duck breast muscle used to manufacture ground-type meat product may be frozen before rigor onset.

Effects of Soybean Sauce and Pre-rigor Muscle on Physicochemical Properties of Frozen Hanwoo Patties

In this study, we evaluated the physicochemical and sensorial properties of frozen Hanwoo beef patties prepared from prerigor and post-rigor muscle with soybean sauce or sodium chloride. The pH of the soybean sauce treatments was lower than the sodium chloride treatments (p<0.05); however, the Hanwoo patty prepared from pre-rigor muscle with soybean sauce had a lower cooking loss and smaller diameter than the Hanwoo patty prepared under the same conditions from post-rigor muscle (p<0.05). The addition of the soybean sauce inhibited lipid oxidation due to the antioxidative materials in soybean sauce such as melanoidin. The hardness of patties prepared from pre-rigor treatment was lower relative to those prepared from post-rigor muscle (p<0.05); however, there was no significant difference between springiness, cohesiveness, and chewiness (p>0.05). In the sensory evaluation, patties prepared from pre-rigor muscle with soybean sauce had a significantly high score in all traits (p<0.05); thus, pre-rigor muscle with soybean had the highest overall acceptability. Furthermore, the addition of soybean sauce to pre-rigor muscle produced similar effects as those observed for the addition of sodium chloride in regards to psychochemical properties. Moreover, meat products produced from pre-rigor muscle will have better antioxidative and sensorial properties.

Near-infrared tissue oximetry of beef longissimus muscle for the improvement of meat color and meat color stability (2009)

Introductioncolor as perceived by consumers serves as a valuable guide for assessing overall quality and wholesomeness of meat. The bright cherry-red color of beef is influenced by tissue oxygen consumption, obstacles to oxygen diffusion, and thickness of the oxymyoglobin layer. The dynamics of meat color depend on several physical properties of muscle including myoglobin redox status and concentration. Physical, chemical, and anatomical differences in muscles cause large variations in color from cut to cut, within a cut, and in cuts made parallel or perpendicular to muscle fibers. Clearly, muscle fiber orientation affects measurements of tenderness and cooking yields; however, variations in myoglobin redox dynamics, oxygen penetration, and color stability due to muscle fiber orientation (parallel or perpendicular) are not well documented. Among the various meat color measurement techniques available, near-infrared (NIR) methods have the advantages of being nondestructive, rapid, inexpensive, and adaptable for online measurements. The NIR tissue oximeter is a relatively new biomedical device that has been used in exercise physiology and in medicine to measure hemoglobin and myoglobin oxygen saturation in brain tissue and cardiac and skeletal muscle. This instrument seems to have promise for use in measuring inherent properties of meat that are related to meat color stability. NIR tissue oximetry may provide continuous real-time measurements of changes in myoglobin oxygen status, thus providing information on tissue oxygenation and hemodynamics. The unique feature of the tissue oximeter is that it uses the theory of photon migration through tissue, allowing for absolute measurement of absorption in, for example, human or animal tissue. If the NIR absorption properties of any chromophore are known, quantitative analysis of color compounds is possible without constant calibration and validation. We are not aware of any research in which NIR tissue oximetry has been used to evaluate color of post-rigor meat. This study was designed to evaluate whether NIR tissue oximetry has promise for measuring meat properties related to meat color. Specific objectives were to determine: (1) effects of parallel vs. perpendicular muscle fiber orientation of meat cuts on NIR measurements, (2) amounts of deoxymyoglobin (DMb), oxymyoglobin (OMb), and total myoglobin (TMb) in the superficial and subsurface layers of beef muscle (longissimus) stored in several packaging formats, and (3) tissue oximeter responses to post-rigor muscle fiber orientation and surface measures of color.

Gel Color and Texture of Surimi-like Pork from Muscles at Different Rigor States Post-mortem

Gels were made from surimi-like pork (SLP) made from muscles obtained at 1, 24 and 72 h post-mortem. The SLP from pre-rigor muscle had higher pH and moisture percentage compared to in- or post-rigor muscles. Also, SLP from pre-rigor muscle showed higher concentration of water-soluble protein that was washed out during the process. Gel from post-rigor muscle exhibited higher a* and b* value, and also resulted in higher Chroma and lower hue values. The dark color of gel from post-rigor muscle was related to higher concentration of sarcoplasmic protein in SLP and denser structure in the gel matrix. SDS-PAGE showed higher intensity of the phosphorylase in the sarcoplasmic protein fraction from pre-rigor muscle. Gel from post-rigor muscle showed higher hardness and sensory firmness, and the greater firmness was related to higher concentration of protein in SLP, and a compact network with smaller pockets in the gel matrix.

Muscle and flesh quality traits in wild and farmed Atlantic salmon

Muscle characteristics that are important for flesh quality traits were assessed in populations of wild and farmed Atlantic salmon ( Salmo salar L.). The wild fish were obtained from a commercial fishery on the North Esk, Scotland in 2001 and 2003. The farmed fish comprised 7 families from the Stofnfiskur breeding programme (Stofnfiskur A/S, Iceland) grown in 5 m × 5 m × 5 m net pen sea cages in a dedicated trial unit on South Uist, Scotland. Total carotenoid pigment (mg kg − 1 wet mass flesh) concentrations were higher in farmed (7.68 and 8.43 for grilse and salmon, respectively) than wild fish (5.53 and 6.44 for grilse and salmon, respectively). In contrast, the average flesh colour, measured with a SalmonFan™, was similar for all groups (27.4 to 28.0), indicating a superior colour visualisation per unit pigment concentration in wild fish. The flesh lipid content was 46%-higher (grilse) and 84%-higher (salmon) in farmed than wild fish. Vitamin E concentrations per unit wet mass lipid were similar in wild and farmed salmon and in the range (208–259 mg kg − 1 ). Fillet firmness was measured using a shear test and instrumental texture analyser. The work done (WD) to shear standardised post-rigor muscle samples was higher in grilse than salmon and was significantly greater for the wild (710 and 811 mJ, respectively) than farmed (415 and 602 mJ, respectively) fish, indicating a firmer texture in the wild fish. The grilse and salmon sampled had stopped recruiting fast muscle fibres and both wild and farmed fish had around 650,000 fibres per trunk cross-section. Thus differences in fillet texture and colour between these populations could not be explained by the muscle cellularity which was similar between groups. Hydroxyproline (HYP) was used to estimate collagen concentration. Alkaline-insoluble HYP was 72.5% higher in wild than farmed salmon (14.0 vs. 8.1 μmol g − 1 dry mass, respectively) whereas alkaline-soluble HYP was 5.2-fold higher in farmed than wild salmon (31.0 vs. 6.0 μmol g − 1 dry mass, respectively). The alkaline-insoluble collagen fraction is thought to be enriched with reducible and non-reducible cross-linked collagen. There was a significant positive correlation between pyridinoline (PYD) crosslink concentration and WD, explaining 25% of the within population variation in firmness. However, PYD concentration (pmol g − 1 dry mass) was similar between wild (476) and farmed (445) salmon and cannot explain the differences in flesh firmness observed between populations. It was hypothesised that the higher average values of firmness in the wild than farmed salmon flesh can in part be attributed to higher concentrations of reducible immature collagen crosslinks.

Hydroxylysyl Pyridinoline Cross-Link Concentration Affects the Textural Properties of Fresh and Smoked Atlantic Salmon (Salmo salar L.) Flesh

A simple HPLC method is presented to quantify the low concentration of hydroxylysyl pyridinoline (PYD) cross-links in Atlantic salmon (Salmo salar L.) muscle. The method involved the extraction of tissue with NaOH prior to hydrolysis, which greatly reduced the amount of protein to be hydrolyzed and made downstream operations easier and more reproducible. The concentration of PYD was 426 pmol g(-)(1) dry mass muscle in post-rigor muscle stored at 0 degrees C and sampled 3 d after death. Hydroxproline (HYP) concentration was determined following NaOH extraction as a measure of collagen content. In post-rigor samples, the alkaline-insoluble HYP fraction comprised 18.3% of the total HYP. Scanning electron microscopy revealed shrinkage of muscle fibers and a retraction of the connective tissue matrix in smoked salmon. PYD concentration was relatively resistant to processing to the smoked product, decreasing by around 11.7%, as compared to a 22.2% decrease in HYP. There was a positive correlation between PYD concentration and the firmness of post-rigor muscle samples as measured by an instrumental texture analyzer, explaining 25% of the total variation. A weaker but still significant correlation was found between PYD concentration and firmness in the smoked product. There was no relationship between fillet firmness and total collagen concentration, although the correlation with HYP in the alkaline-insoluble fraction was significant at the 6% level (P = 0.057). Our results indicate that only 1-3% of collagen molecules are linked by nonreducible mature cross-links in harvest size farmed Atlantic salmon and that PYD concentration is an important raw material characteristic for flesh quality.