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.     

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.     

Superchilling of rested Atlantic salmon: Different chilling strategies and effects on fish and fillet quality

Rested Atlantic salmon was superchilled in seawater slurry (−1.93 ± 0.27 °C). The chilling efficiencies of slurry and crushed ice were compared. The feasibility of using slurry to produce subzero core temperatures before packing was also evaluated. Simulated transport to market, with or without ice after initial superchilling (1 day), was also studied. Fish quality (Quality Index, fillet colour, pH, water content, water-holding capacity, hardness and bacterial loads) was evaluated at arrival to ‘market’ and after keeping the fish ‘in the market’ for 1 week. The results were compared with continuous ice (control) or slurry storage. In terms of quality, pre-chilling in slurry and continuous storage in slurry were evidently not advantageous over traditional ice storage, as evaluated after 4 days. After 11 days, both advantages and disadvantages of continuous superchilling were observed. Notably, subsequent ice storage of superchilled fish resulted in increased bacterial load and inferior fillet hardness.     

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.     

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).     

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.     

Salmon by-product storage and oil extraction

Oils extracted from wild salmon by-products are excellent sources of long chain omega-3 polyunsaturated fatty acids including eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). However, quality loss is expected if time delays are encountered before oil extraction. The free fatty acid levels (FFA), fatty acid profile and total fat soluble antioxidant activity in extracted oil from aging pink salmon heads and viscera stored at two temperatures (6 and 15 °C) for four days were determined. The FFA values in raw salmon heads and viscera increased with storage time and temperature. A significant difference (p < 0.05) from the starting material was noted at day 1 at both temperatures for FFA. Fatty acid composition data indicated no changes in the levels of long-chain omega-3 fatty acids with the respective temperature. The concentration of long-chain omega-3 fatty acids EPA ranged from 9.3 to 11.3 g/100 g of crude oil and DHA ranged from 12.3 to 13.1 g/100 g of crude oil. The antioxidant activity of the pink salmon oils at day 0 was 0.89 ± 0.15 μmole Trolox equivalent/g of crude oil. Significant decreases (p < 0.05) from the starting material were noted on day 2 for 15 °C samples and day 3 for 6 °C samples. After four days of storage antioxidant levels (Trolox equivalent/g of crude oil) were approximately 25% of initial values. Oil extracted from raw salmon heads and viscera remained a good source of long chain omega-3 fatty acids even after 4 days of raw material storage at 15 °C; however, fat soluble antioxidant activity was reduced and free fatty acid levels increased with increased raw material storage temperature and time.     

Salt uptake and water loss in hams with different water contents at the lean surface and at different salting temperatures

The salt uptake homogeneity is crucial in assuring quality in dry-cured hams. The aim of this study was to evaluate the effect of the water contents at the lean surface before salting and of the temperature during salting on the salt uptake. Pieces of loin stored at 3 °C for 3 days before salting absorbed less salt through a surface that has been dried during storage. A group of raw hams were subjected to different pre-salting storage times (0, 3 and 6 days) and another group subjected to different set room temperatures during salting (− 1.0, 0.5 and 4.0 °C). The duration of storage before salting and the temperature during salting had a negative and a positive effect on the average salt absorption, respectively. The most important effects appeared after 6 days of storage and at 4 °C. No significant differences in salt uptake homogeneity were found between storage times and between salting temperatures.     

Quality changes during superchilled storage of cod (Gadus morhua) fillets

Superchilling is a method with potential for extending the shelf life of food products by partial freezing. For centuries, Atlantic cod (Gadus morhua) has been the most important commercial species in the North Atlantic fisheries and is now regarded as a very promising species in cold water fish farming. In the present work, superchilled storage at −2.2 °C of fillet portions of farmed cod was investigated. Superchilled cod showed increased shelf life with respect to reduced growth of sulphide producing bacteria compared to ice chilled. Drip loss was lower in superchilled cod. However, liquid loss by low-speed centrifugation was higher in superchilled cod fillets compared to ice chilled. This can be explained by freeze denaturation of muscle proteins, which is supported by the lower extractability of salt soluble proteins. There is a need for process optimization to minimize protein denaturation.     

Influence of Salmon Provenance and Smoking Process on Muscle Functional Characteristics

ABSTRACT: Ocean-ranched and farm-reared Atlantic salmon were compared on the basis of compositional and functional/mechanical properties of the raw and the corresponding smoked muscle. Several procedures based on different salting methods (brine and dry salting) and smoking temperature (20 °C and 30 °C) were tested, as well as an electrostatic smoking method. Also, raw material samples were studied without and with frozen storage (-20 °C) for 30 d prior to salting/smoking, and the effect of frozen storage on the smoked muscle was evaluated. The electrostatic method induced considerably lower shear force values than the other smoking treatments. Ocean-ranched salmon were more susceptible to protein aggregation and loss of binding properties (water and fat) than farmed fish as a consequence of frozen storage of the raw material or smoking treatment.     

Effect of gamma radiation and cold storage on chemical and organoleptic properties and microbiological status of liquid egg white and yolk

This investigation aims to establish a feasible radiation dose for treating liquid egg white (LEW) and yolk (LEY) at room temperature to improve their microbial safety. Samples of LEW and LEY were subjected to gamma irradiation doses of 0,1,2,3 and 4 kGy at room temperature followed by storage at 4 ± 1 °C. Then the effects of irradiation and cold storage on proximate composition, pH, soluble protein and free sulfhydryl content (SH) were determined for LEW and LEY in addition to the contents of total carotenoids in LEY. Moreover, free fatty acids (FFA) and peroxide value (PV) were determined for lipids of LEY.The microbial safety of LEW and LEY was established during storage throughout the enumeration of the total plate count, enterobacteriaceae, Staphylococcus aureus as well as the detection of Salmonella. The effects of irradiation at 3 kGy dose, which was enough for improving the microbial safety of samples, on amino acid composition of LEW and LEY and fatty acid profiles of LEY lipids were studied. In addition, sensory evaluation was carried out for liquid and scrambled egg white and egg yolk samples. The results showed that gamma irradiation and refrigerated storage had no significant effects on proximate composition and pH of liquid egg samples, while significantly decreased the contents of total carotenoids in LEY samples. Furthermore, gamma irradiation had no significant effects on protein solubility and the contents of free SH in LEW, while induced significant slight decreases in protein solubility and the contents of free SH in LEY. Cold storage, however, showed no significant effects on protein solubility and free SH in all liquid egg samples. FFA contents and PV of LEY lipids significantly increased post irradiation treatments and during storage, but the observed values were relatively low and acceptable. In addition, gamma irradiation at 3 kGy dose had no significant effects neither on the amino acid composition of LEW and LEY nor on fatty acid profiles of LEY lipids. The sensory preference did not alter neither for the liquid egg samples nor for scrambled egg samples that prepared from irradiated liquid egg products. Finally, gamma irradiation at 3 kGy dose appeared to be the optimum for treating LEW and LEY at room temperature followed by cold storage at 4 ± 1 °C.     

Amino acid profile of raw and as-eaten products of spinach (Spinacia oleracea L.)

The aim of the work was to evaluate the amino acid composition of fresh spinach and spinach products prepared for consumption. The investigation included fresh and cooked spinach and two kinds of frozen product: one obtained using the traditional method (blanching-freezing-refrigerated storage) and then cooked; and the other, of the ready-to-eat type, obtained using the modified method (cooking-freezing-refrigerated storage) and then prepared for consumption in a microwave oven. In 100 g of edible parts of the as-eaten products, the content of amino acids exceeded that in the raw material from which they were obtained, except for sulphur amino acids and tyrosine. In the as-eaten products, the content of amino acids in protein calculated in 16 g N was similar to that in the raw material, except for lower tyrosine and higher arginine content in the traditional frozen product prepared for consumption. Cystine with methionine was the amino acid limiting the quality of protein in the investigated samples, except for the traditional frozen product prepared for consumption, where the Chemical Score (CS) index was 100.     

Effect of alkaline pH-shift processing on in vitro gastrointestinal digestion of herring (Clupea harengus) fillets

The effect of alkaline pH-shift processing on herring (Clupea harengus) protein oxidation, salt solubility and digestibility, has been evaluated. For the latter, herring mince and pH-shift produced herring protein isolate, both raw and heat-treated, were digested using a static gastrointestinal in vitro model. The pH-shift process resulted in drastically lowered protein salt solubility and increased lipid oxidation while protein carbonyl formation was unaffected. Yet, no significant differences in the degree of hydrolysis (DH) were observed between mince and isolates after completed gastrointestinal digestion, something which was confirmed by a similar release of proteinaceous material <3 kDa and similar free amino acid profiles. The polypeptide profiles of digested samples however revealed that two peptides (33 and 36 kDa) were present in larger amounts in the digested protein isolate compared to the digested herring mince. The results indicate that alkaline pH-shift processing had limited quantitative influence on the gastrointestinal digestibility of herring proteins despite its negative effects on protein salt solubility and lipid oxidation.     

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.     

Chemical changes during farmed coho salmon (Oncorhynchus kisutch) canning: Effect of a preliminary chilled storage

A relevant farmed fish species (coho salmon; Oncorhynchus kisutch) was studied as a raw material for the canning process. The effects of preliminary chilling storage and thermal treatment (cooking and sterilisation) on the chemical constituents (lipids and non-protein nitrogen compounds) of the canned fish were analysed. An increasing previous chilling time led to an important autolysis (K value) development, and to an increasing formation of free fatty acids, and interaction compounds (fluorescence and browning assessments) (p < 0.05) in the canned product. The thermal treatment led to the formation of volatile amines (total and trimethylamine), free fatty acids, secondary lipid oxidation compounds (anisidine and thiobarbituric acid values) and interaction compounds in canned fish. Interaction compound assessment was found the most useful tool to study the lipid oxidation and non-enzymatic browning developments, while the K value showed to be an interesting index for assessing the freshness stage of the raw material employed.     

Lessening of high-pressure-induced changes in Atlantic salmon muscle by the combined use of a fish gelatin–lignin film

Salmon muscle is considerably affected by cooking with the resulting loss of its appealing red colour. The combined use of high pressure with fish gelatin–lignin film is proposed as an alternative to the more aggressive thermal processing procedures, with the aim of improving the appearance and overall quality of salmon fillets in ready-to-eat or semi-prepared dishes. The effects of high pressure processing (300 MPa, 10 min, 5 °C or 40 °C) and conventional heating (90 °C, 10 min) were evaluated in terms of colour changes, protein denaturation, as well as protein and lipid oxidation, by comparison with raw muscle. The stability of the processed products was assessed by monitoring changes in microbial growth and total volatile basic nitrogen and thiobarbituric acid reactive substances during 23 days of chilled storage. Fourier transform infrared spectroscopy (FTIR), apparent viscosity and dynamic oscillatory studies revealed notable differences in the overall degree and nature of protein aggregation between high pressure and heating treatments, especially when performed at 5 °C instead of 40 °C. SDS–PAGE of the protein fraction solubilised in 0.8 M NaCl showed MHC and α-actinin to be the main myofibrillar proteins denatured by high pressure processing at 40 °C, while actin was more denatured when pressurised at 5 °C. The film attenuated colour changes associated with high pressure treatment, especially at 5 °C, where redness was more preserved without jeopardising the appearance of a ready-to-eat product. High pressure processing at 5 °C in combination with gelatin–lignin film was found to improve protein quality of salmon fillets. The film reduced the levels of carbonyl groups formed immediately after processing, and prevented lipid oxidation from taking place at advanced stages of chilled storage. However, the effect on microbial growth was negligible, since total counts were similar for muscle with or without the film.     

Changes in free amino acids and biogenic amines of Egyptian salted-fermented fish (Feseekh) during ripening and storage

The aim of this study was to investigate changes in the formation of amino acids and biogenic amines in Egyptian salted-fermented fish (Feseekh) during ripening (20 days) and storage (40–60 days). The total concentration of free amino acids increased from 8 (dry weight; DW) to 72 g/kg (DW) after 60 days of storage. The predominant free amino acids were leucine, glutamic acid, lysine, alanine, valine, aspartic acid, isoleucine and citrulline. Their concentrations accounted for 68% of the total concentration of amino acids after 60 days. The total contents of biogenic amines ranged from 84 to 1633 mg/kg (DW) during the investigated period. Cadaverine was the major amine detected in Feseekh at all sampling stages and its concentration varied between 21 and 997 mg/kg (DW). The histamine content (211 mg/kg DW) only exceeded the maximum tolerance level (200 mg/kg) after 60 days. It could be concluded that Feseekh can be consumed without any health risks between 20 and 40 days but it can be hazardous after 60 days due to the biogenic amine content.     

Relevance of season and nucleotide catabolism on changes in fillet quality during chilled storage of raw Atlantic salmon (Salmo salar L.)

Farmed 5–6 kg Atlantic salmon were pre-rigor filleted, vacuum packed and subsequently analysed after 1, 9 and 13 days of storage at 4 °C. The study was repeated in February, April, August and October. The conversion of hypoxanthine (Hx) showed the highest seasonal variation among the nucleotide metabolites, with an inverse relationship with sea temperature at harvesting (R² = 0.95–0.96). The Hx content was inversely related to fresh odour and flavour (R² = 0.81–0.83), but positively to tenderness (R² = 0.87). Hence, these results suggest that salmon reared in seawater of 11–15 °C (August–October) maintain a superior sensory quality for a longer period post-mortem than salmon reared at 6–8 °C (February–April). The colour intensity increased from days 1 to 9 post-mortem, probably due to rigor contraction. The highest increase in drip loss was observed in October and the lowest in April. It is proposed that seawater temperature significantly influences the storage life of raw salmon, and that Hx is a valuable biomarker for sensory quality.     

Changes in the flesh of cooked farmed salmon (Oncorhynchus kisutch) with previous storage in slurry ice (−1.5 °C)

Whole, farmed Coho salmon (Oncorhynchus kisutch) were sacrificed in slurry ice (−1.5 °C) then stored in this medium for further processing after 0, 5 and 9 days. They were cooked whole and the flesh was evaluated by sensory, physical and chemical techniques to establish if significant changes had occurred as a result of the storage period. Initial samples from harvest were also evaluated for comparison. There was evidence of increases in trimethylamine, lipid hydrolysis, lipid oxidation (anisidine and thiobarbituric acid values) and interaction compound formation (fluorescence and browning measurements). The fish structure became more breakable with longer storage but there were no changes in sensory assessments for rancid and putrid odours, so that scores were less than 0.5 on a 11-point scale. From the present results, primary and secondary lipid oxidation development and further interaction compound formation appear to be the main measurable indicators of quality changes in cooked Coho salmon. However, and according to sensory appreciation, slurry ice has shown to be a suitable medium for previous storage of Coho salmon for periods of up to 9 days.