Effects of −1.5 °C Super-chilling on quality of Atlantic salmon (Salmo salar) pre-rigor Fillets: Cathepsin activity,muscle histology,texture and liquid leakage

The aim of this study was to evaluate the impact of super-chilling on the quality of Atlantic salmon (Salmo salar) pre-rigor fillets. The fillets were kept for 45 min in a super-chilling tunnel at −25 °C with an air speed in the tunnel at 2.5 m/s, to reach a fillet core temperature of −1.5 °C, prior to ice storage in a cold room for 4 weeks. Super-chilling seemed to form intra- and extracellular ice crystals in the upper layer of the fillets and prevent myofibre contraction. Lysosome breakages followed by release of cathepsin B and L during storage and myofibre–myofibre detachments were accelerated in the super-chilled fillets. Super-chilling resulted in higher liquid leakage and increased myofibre breakages in the fillets, while texture values of fillets measured instrumentally were not affected by super-chilling one week after treatment. Optimisation of the super-chilling technique is needed to avoid the formation of ice crystals, which may cause irreversible destruction of the myofibres, in order to obtain high quality products.     

Quality of superchilled vacuum packed Atlantic salmon (Salmo salar) fillets stored at −1.4 and −3.6 °C

The most important factor for increasing shelf life is the product temperature, and since fish is more highly perishable than meat, the temperature is even more important. In the present study, portions of fillets of farmed Atlantic salmon (Salmo salar) were superchilled at two temperature levels, −1.4 and −3.6 °C. Texture, drip loss, liquid loss, cathepsin activities and protein extractability were investigated during storage and compared to ice chilled and frozen references. Drip loss was not a major problem in superchilled salmon. Textural hardness was significantly higher in superchilled salmon fillets stored at −3.6 °C compared to those stored at −1.4 °C, ice chilled and frozen references. Cathepsins B and B + L were not deactivated at the selected storage temperatures. The storage time of vacuum packed salmon fillets can be doubled by superchilled storage at −1.4 °C and −3.6 °C compared to ice chilled storage.     

Muscle structure responses and lysosomal cathepsins B and L in farmed Atlantic salmon (Salmo salar L.) pre- and post-rigor fillets exposed to short and long-term crowding stress

Atlantic salmon (average body weight 2.9 ± 0.1 kg) were subjected to either minimal pre-slaughter crowding stress (NS group), 20 min (short-term stress, SS group) or about 24 h pre-slaughter crowding stress (long-term stress, LS group). Significant negative effects were mostly seen due to long-term stress (LS) at early stages post-mortem, but also short-term stress (SS) had significant negative impacts on muscle quality of pre- and post-rigor fillets. Pre-slaughter long-term stress (LS) significantly lowered muscle pH, softened the fillets and increased muscle cathepsin L gene expression, immediately post-mortem. A tendency of increased cathepsin B gene expression and cathepsin B total activity was also seen. Stress further accelerated the incidence of myofibre–myofibre detachments, increased the percentage of myofibre–myocommata detachments over the storage period and increased the percentage of myofibre breakages and contracted myofibres 96 h post-mortem. Significant correlations were observed between muscle pH and cathepsin B + L activity, muscle texture and muscle degradation parameters. Cathepsin B activity was correlated to muscle degradation and cathepsin L gene expression to muscle degradation and texture. Pre-slaughter stress, especially long-term stress (LS), thus seems to accelerate cathepsin activity, resulting in faster muscle degradation, directly or indirectly connected to the low initial muscle pH. No significant variation was observed between pre-rigor and post-rigor filleting, except that pre-rigor filleting significantly increased the percentage of myofibre breakages.     

A study of the ice crystals in vacuum-packed salmon fillets (Salmon salar) during superchilling process and following storage

The aim of this work was to study the microstructure of vacuum-packed salmon fillets superchilled in an impingement freezer at −30 °C (air temperature) and 227 W/m² K (surface heat transfer coefficient, SHTC) for 2.1 min prior to storage at a superchilling storage temperature of −1.7 ± 0.3 °C for 28 days. The microstructure of vacuum-packed salmon fillets were analysed at the surface, mid-centre and centre layers. Significant differences were observed between the ice crystals formed at the surface, mid-centre and centre layers. The size of ice crystals at the centre of the superchilled fillets was 3 times larger than those at the surface layer. Significant differences were observed between the size of ice crystals formed during the superchilling process and following storage. The results further indicated that, after temperature equalisation (1 day of storage) the growth of the intracellular ice crystal was not significant at (P < 0.05) at any storage time.     

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 29 days. 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, 227 W/m² K, 2.1 min) which is referred to as process F and slow (−20 °C, 153 W/m² K, 4.2 min) 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).     

Correlation between astaxanthin amount and a* value in fresh Atlantic salmon (Salmo salar) muscle during different irradiation doses

The amount of astaxanthin and a* value changes in fresh Atlantic salmon light and dark muscle during cold storage was studied for different e-beam doses (0, 1, 1.5, 2 and 3 kGy). Astaxanthin (mg/kg muscle) and a* value decreased with increasing irradiation dose for both fresh light and dark muscle. The level of irradiation dose gave high correlation between a* value and amount of astaxanthin. The reason for the change in colour or decrease in a* value of Atlantic salmon during irradiation could be due to the destruction of astaxanthin. The amount of astaxanthin and a* value of 1 kGy treated salmon fillets were not significantly different (p > 0.05) from that of the control but significantly different (p < 0.05) from other irradiation treatments. The colour (a* value) of salmon muscle was related to the content of astaxanthin, which decreased as irradiation increased. The amount of astaxanthin in light muscle was three to five times greater than dark muscle. This study demonstrated that irradiating salmon fillets at 1 kGy, can be successfully used and leads to no significant change in colour and amount of astaxanthin.     

The function of endogenous cathepsin in quality deterioration of grass carp (Ctenopharyngodon idella) fillets stored in chilling conditions

Changes of textural properties and cathepsin activity of grass carp fillets during storage in superchilling (?1.5 ± 0.2 °C) and ice (0.2 ± 0.1 °C) was investigated, and the function of cathepsin in quality deterioration of grass carp fillets was discussed. Results showed that shear force of superchilled and ice‐stored fillets decreased by 50% and 55% after 6 days of storage, respectively. The cathepsin activies in different fractions changed significantly during storage at both conditions. Cathepsin B, B+L activities in sarcoplasma, myofibrillar and heavy mitochondrial fraction significantly increased during the early 3 days postmortem, accompanied by remarkable reduction of corresponding activity in lysosome. Cathepsin D activity in sarcoplasma and myofibrillar significantly increased during 6 days of storage with corresponding decrease in lysosome and heavy mitochondria. Correlation analysis showed that changes of shear force of grass carp fillets were significantly correlated with integration of cathepsin B, D and B+L throughout storage time (r² > 0.94). As derived from the first‐order exponential decay model, the enzyme efficiencies (k_a) of cathepsin B and B+L were more than twofold higher than those of cathepsin D, suggesting the major role of cathepsin B and B+L in textural deterioration of grass carp fillets in chilling storage.     

Thermal effects on chicken and salmon muscles: Tenderness, cook loss, area shrinkage, collagen solubility and microstructure

The objective of this study was to gain insight into the mechanisms underlying heating-induced tenderness in muscle food products by comparing tenderness changes in chicken breast (Pectoralis major) and salmon (Oncorhynchus gorbuscha) during high-temperature treatment. Relationships among changes in chicken breast and pink salmon muscle were investigated for tenderness, cook loss, area shrinkage, collagen solubility and microstructure. Small white muscle samples (D 30 mm×H 6 mm) cut from pink salmon fillets and chicken breast were sealed in small aluminum containers (internal dimension: D 35 mm×H 6 mm) and heated in an oil bath at 121.1 °C for different time intervals up to 2 h to simulate various thermal process durations. The changes in salmon tenderness had 4 phases (rapid toughening, rapid tenderizing, slow toughening and slow tenderizing), while that of the chicken breast only had 2 phases (rapid tenderizing and slow tenderizing). Twenty minutes was found to be a critical heating time in which >85% collagen was solubilized and shear force reached a minimum. Cook loss and area shrinkage were significantly (P<0.05) correlated with shear force change for both the salmon and chicken, while collagen solubility was only significant for the chicken.     

Changes in water holding capacity and drip loss of Atlantic salmon (Salmo salar) muscle during superchilled storage

Changes in water holding capacity and drip loss of Atlantic salmon (Salmo salar) fillets during superchilled storage were studied. Due to the significant differences in ice crystal sizes observed in our previous study, the liquid loss (LL) was analysed separately, at the surface and centre of the superchilled samples. No significant differences were found in LL between surface and centre parts of the superchilled samples. No significant difference in the LL was observed from surface samples between 1 and 14 days of storage. There was a significant difference in the LL at day 1 of the centre samples, but no significant differences were observed between 3 and 14 days of storage. In contrast, the LL was significantly decreased at day 21 both at the centre and the surface of the superchilled samples. No significant difference (p < 0.05) was found in drip loss between 1 and 14 days of storage for the superchilled samples. A significant increase in drip loss for the superchilled samples was observed at day 21. These findings are significant for the industry because it provides valuable information on the quality of food in relation to ice crystallisation/recrystallisation during superchilled storage.     

VIS/NIR spectroscopy for non-destructive freshness assessment of Atlantic salmon (Salmo salar L.) fillets

Visible/near-infrared spectroscopy has been evaluated for use in freshness prediction and frozen-thawed classification of farmed Atlantic salmon fillets, where fresh samples were stored as whole fish in ice. A handheld interactance probe for performing rapid measurements of single fillets and an imaging spectrometer for online analysis at an industrial speed of one fillet per second, have been used. Freshness as storage days in ice is predicted with an accuracy of 2.4 days for individual fillets, whereas frozen-thawed salmon fillets are completely separated from fresh fillets. The prediction results are comparable to previous results using the Quality Index Method with trained panelists. The region between 605 and 735 nm, which excludes interference by carotenoids and water, is appropriate for both frozen-thawed classification and freshness prediction of salmon fillets. The results indicate that the spectral changes are explained mainly by oxidation of heme proteins during the freeze–thaw cycle and during chilled storage in ice.     

Effects of Chilling and Partial Freezing on Rigor Mortis Changes of Bighead Carp (Aristichthys nobilis) Fillets: Cathepsin Activity,Protein Degradation and Microstructure of Myofibrils

To investigate the effects of chilling and partial freezing on rigor mortis changes in bighead carp (Aristichthys nobilis), pH, cathepsin B, cathepsin B+L activities, SDS‐PAGE of sarcoplasmic and myofibrillar proteins, texture, and changes in microstructure of fillets at 4 °C and –3 °C were determined at 0, 2, 4, 8, 12, 24, 48, and 72 h after slaughter. The results indicated that pH of fillets (6.50 to 6.80) was appropriate for cathepsin function during the rigor mortis. For fillets that were chilled and partially frozen, the cathepsin activity in lysosome increased consistently during the first 12 h, followed by a decrease from the 12 to 24 h, which paralleled an increase in activity in heavy mitochondria, myofibrils and sarcoplasm. There was no significant difference in cathepsin activity in lysosomes between fillets at 4 °C and –3 °C (P > 0.05). Partially frozen fillets had greater cathepsin activity in heavy mitochondria than chilled samples from the 48 to 72 h. In addition, partially frozen fillets showed higher cathepsin activity in sarcoplasm and lower cathepsin activity in myofibrils compared with chilled fillets. Correspondingly, we observed degradation of α‐actinin (105 kDa) by cathepsin L in chilled fillets and degradation of creatine kinase (41 kDa) by cathepsin B in partially frozen fillets during the rigor mortis. The decline of hardness for both fillets might be attributed to the accumulation of cathepsin in myofibrils from the 8 to 24 h. The lower cathepsin activity in myofibrils for fillets that were partially frozen might induce a more intact cytoskeletal structure than fillets that were chilled.     

A histological study of the microstructure sizes of the red and white muscles of Atlantic salmon (Salmo salar) fillets during superchilling process and storage

Atlantic salmon (Salmo salar) fillets were partial frozen in an impingement freezer at −30 °C and 227 W/m2.K for 2.1 min prior to storage at a superchilling storage temperature of −1.7 ± 0.3 °C for 28 days. The aim of this article is to study the microstructure of the red and white muscles during superchilling process and during superchilled storage. The histology and microscopic analysis of the red and white muscles were carried out. It was found that the size of the ice crystals formed in the red muscles was smaller than those formed in the white muscles. The equivalent diameters of the intracellular ice crystals obtained upon superchilling (day 0) were 17 ± 2 and 29 ± 1 μm for the red and white muscles, respectively. Significant differences were initially observed between the size of the ice crystals formed during the superchilling process and after 1 day of storage. However, after temperature equalisation (day 1), there was no significant change in the size of the ice crystals.     

Quality assessment of wild European eel (Anguilla anguilla) stored in ice

The quality assessment of wild European eel (Anguilla anguilla) stored in ice and in boxes without ice (3 ± 1 °C) was investigated by the sensory analysis, levels of nucleotide breakdown products and biogenic amines for up to 19 days. Sensory analysis was assessed using the Tasmanian Food Research Unit Scheme. K and related values (K_i, G, P, H and F_r) were used as freshness indicators. Linear regressions (r²) obtained from K, K_i, G, P, H and F_r were 0.95, 0.96, 0.83, 0.96, 0.99 and 0.96, respectively, for eel stored in ice whereas, for eel kept in boxes without ice, the values were 0.86, 0.86, 0.96, 0.91, 0.98 and 0.86, respectively. When eel stored in ice and in boxes without ice were considered at the limit of acceptability by assessors at ∼12–14 days and ∼5–7 days, respectively, the average K, K_i and P values were ∼70–85%, H values were ∼60% and F_r values were ∼10% for both storage conditions. The level of histamine exceeded the legal limit (5 mg/100 g fish) in eel stored without ice after 6–7 days and, in ice, after 13–14 days of storage, at which time eels were rejected by the sensory panel. The concentrations of biogenic amines were higher in eel stored in boxes without ice than in eel kept in ice. The levels of histamine in the muscle of eel kept in boxes without ice and in ice increased to the maximum levels of 17.9 mg/100 g on day 12 and 12.6 mg/100 g on day 19, respectively.     

Variation in bull beef quality due to ultimate muscle pH is correlated to endopeptidase and small heat shock protein levels

This study set out to determine if ultimate pH (pH_u) affected the performance of intracellular small heat shock protein and endopeptidase dynamics in muscle during beef ageing. Longissimus dorsi muscles from 39 Angus or Limousin × Angus bulls were examined to see if pH_u achieved at 22 h post mortem (rigor) affected tenderness and water holding capacity of beef. Samples were segregated into three pH_u groups termed high (pH > 6.3), intermediate (5.7 < pH < 6.3) and low (pH < 5.7) pH_u beef. More than 30% of bull beef did not achieve acceptable tenderness at 8 days post mortem with this ageing regime. No significant differences in calpain or cathepsin enzyme levels due to meat pH were observed until after 22 h post mortem, but low pH_u beef had elevated caspase 3/7 activity soon after slaughter. At 22 h post mortem, greater levels of μ-calpain enzyme were found in the high and intermediate pH_u beef and cathepsin B levels were superior in the low pH_u beef after 2 days post mortem. Different rates of desmin and troponin T protein degradation were also observed in aged bull beef. Both proteins were degraded within 6 h post mortem for high pH_u beef, but took >3 days post mortem for intermediate pH_u beef. High levels of alpha β-crystallin (aβC) at 22 h post mortem coincided with delayed muscle protein degradation for low pH_u beef. Our results support the hypothesis that aβC shields myofibrils and buffers against endopeptidase degradation of beef structure during ageing.     

Changes in lipoxygenase isozymes and trypsin inhibitor activity in soybean during germination at different temperatures

Influence of germination temperature on lipoxygenase isozymes and trypsin inhibitor activity, the two undesirable components in soybean for human consumption, is not yet reported in soybean sprouts. Two Indian soybean genotypes were incubated for 144 h in a seed germinator at two different temperatures (25 and 35 °C) and the activities of lipoxygenase isozymes and trypsin inhibitor were monitored in the germinating seedlings every 24 h. Lipoxygenase-I as well as lipoxygenase-II + III were degraded continuously over the 144 h and the rate of degradation, of both the classes of lipoxygenase, was faster at the higher germinating temperature (35 °C) in both the genotypes. Trypsin inhibitor was also degraded continuously during germination upto 144 h and the degradation was faster at higher germination temperature. Protein extracts of seedlings of different periods, developed at different temperatures, and analyzed using polyacrylamide gel electrophoresis, indicated that the original Kunitz inhibitor band (R_f = 0.75) declined continuously in intensity during germination at both temperatures in both genotypes, and a new band (R_f = 0.72) possessing trypsin inhibitor activity appeared at 48 h at 35 °C, while it appeared at 72 h at 25 °C. Early appearance of a modified form of Kunitz inhibitor, a degraded product of native form, at 35 °C as compared to 25 °C, confirms that the faster quantitative reduction at higher temperature is due to faster degradation of the original Kunitz inhibitor form at higher temperature.     

Using whey protein gel as a model food to study dielectric heating properties of salmon (Oncorhynchus gorbuscha) fillets

It is desirable to develop rapid commercial microwave and radio frequency sterilization processes to produce high quality shelf stable muscle foods, particularly aquatic foods. Whey protein gels containing d-ribose and salt were studied as a model food to determine heating patterns in salmon fillets during high temperature microwave sterilization processes. Dielectric constant (?′) and loss factor (?″) of whey protein gels with d-ribose (0.5 g/100 g, 1 g/100 g, and 1.5 g/100 g) at different salt contents (0, 0.1 g/100 g, 0.2 g/100 g, 0.3 g/100 g, 0.4 g/100 g, and 0.5 g/100 g) and frozen and thawed pink salmon (Oncorhynchus gorbuscha) fillets were determined over the frequency range of 27-1800 MHz at temperatures ranging from 20 to 120 °C. The dielectric properties of whey protein gels containing 1 g/100 g d-ribose and 0.2 g/100 g or 0.3 g/100 g salt closely matched the dielectric behavior of salmon fillets in both radio frequency (RF, 27 MHz) and microwave (MW, 915-1800 MHz) ranges. Altering the salt content had a greater impact on dielectric constant and loss factors at lower frequencies. These results suggest that whey protein gel may be a good model food for microwave sterilization process development, particularly for determining the locations of cold and hot spots in complex muscle foods.     

Ice fraction assessment by near-infrared spectroscopy enhancing automated superchilling process lines

The objective of the current study was to analyze and develop some important automation steps in a superchilling process line. In order to control the product quality there is a need for online measurements of ice fraction and distribution in inhomogeneous products. Moreover, automatic handling of such superchilled products is currently commercially unavailable. The current study presents a new method for monitoring and handling superchilled product of varying form and consistency. Observation of the shift in the water absorption peak, measured by near-infrared spectroscopy (NIR) transflection mode, was used to determine the ice level in superchilled salmon, scanning approximately 1.5 cm into the fillets. The salmon fillets were stored on ice at 0 °C for 5–7 days before superchilling at −24 °C to target ice contents of 10%, 15% and 30%. Online NIR measurements of ice fraction showed promising results, with a low prediction error of 2.5%. The storage study confirmed former quality results with a microbiological shelf life of 15–17 days with only minor differences in values for drip loss and water-holding capacity between superchilled and chilled samples.     

Solubility, absorption and desorption of carbon dioxide in chicken breast fillets

The solubility for carbon dioxide (CO₂) in skinless chicken breast fillets was investigated. Henry's constant for chicken breast fillets was calculated to be 42.8 ± 3.7 Pa (mg kg^-1)^-1 at 275 K.In addition, the effects of soluble gas stabilization (SGS) time and waiting time before MA packaging on amount of solubilized CO₂ were investigated. Increasing SGS treatment time, significantly (P < 0.001) increased the amount of dissolved CO₂, while increasing waiting time significantly (P < 0.001) reduced the dissolved CO₂. Desorption of CO₂ showed to be a time consuming process, giving the industry enough time to repackage SGS treated products without loosing vast amounts of dissolved CO₂.     

Effects of pan-frying in margarine and olive oil on the fatty acid composition of cod and salmon

Effects on the fatty acid composition of cod (Gadus morhua) and salmon fillets (Salmo salar) after pan-frying in margarine and olive oil were determined. The fatty acids of the margarine used were 55.5% saturated (SFA), 33.0% mono-unsaturated (MUFA) and 11.5% polyunsaturated (PUFA). The olive oil used contained 15.4% SFA, 76.1% MUFA and 8.5% PUFA. Using margarine or olive oil increased the SFA and MUFA percentages, respectively, in both species. For cod fillets (lean), pan-frying increased the fat content (0.55–4.15 g/100 g and 0.55–2.30 g/100 g before and after pan-frying, with margarine and olive oil, respectively), whereas, for salmon fillets (fat), it decreased (13.91 to 10.57 g/100 g and 15.35 to 12.95 g/100 g before and after pan-frying with margarine and olive oil, respectively). In conclusion, the culinary fat selection affects the total fatty acid content and composition of the prepared fish fillet.