Comparison of air freezing,liquid immersion freezing and pressure shift freezing on freezing time and quality of snakehead (Channa Argus) fillets

The objective of this study was to investigate the freezing time and quality differences in Snakehead fillets frozen by pressure shift freezing (PSF), conventional air freezing (AF) and liquid immersion freezing (LIF) at −20 °C, −40 °C and − 60 °C, respectively. The results showed that liquid immersion freezing at −60 °C maintained the quality best, with a freezing time of 3.62 min and the cross sectional area of 209.11 um². Air freezing at −20 °C had the longest freezing time (184.58 min) and the largest cross sectional area (4470.79 um²), and lowest hardness and springiness of the fillets. Pressure shift freezing did not demonstrate the well established advantages of maintaining better product quality found in similar technique with some other foods. The samples of pressure shift freezing also had higher thawing loss and free water ratio after thawing. Therefore, the liquid immersion freezing at lower temperatures was demonstrated to better maintain the quality of frozen products and held significant potential for commercial application.Industrial relevanceFreezing is a widely used method for extending the shelf life of aquatic products, but some freezing methods, especially the slower ones, often lead to the decrease in the quality and commercial value of frozen products during storage. This paper explored the comparison of industrially used freezing techniques (air freezing and liquid immersion freezing) with the novel pressure shift freezing technique. Liquid immersion freezing at −60 °C was found to be the preferred freezing method for Snakehead fillets, which maintained better frozen product quality, with a simple freezing process and low cost.     

Effect of different freezing processes on the microstructure of Atlantic salmon (Salmo salar) fillets

Salmon fillets were frozen either by pressure shift freezing (PSF, 200 MPa, − 18 °C or 100 MPa, − 10 °C) or by air-blast freezing (ABF, − 30 °C, 1 m/s or 4 m/s) or direct-contact freezing, and then stored at − 20 °C for 6 months. The influence of these treatments on the microstructure of Salmon fillets was studied. The equivalent diameter of the intracellular ice crystals were 14.69 ± 4.11, 5.52 ± 2.11, and 30.65 ± 6.31 μm for the samples subjected respectively to PSF at 100, 200 MPa and ABF (− 30 °C, 4 m/s) after 2 days of storage. Smaller and more regular intracellular ice crystals were observed in fillets frozen by PSF (200 MPa) compared with PSF (100 MPa), ABF and direct-contact frozen ones. Significant differences were observed between the size of the ice crystals obtained after conventional freezing process and PSF. Large and extracellular ice crystals were observed in fillets frozen by ABF (1 m/s) and direct-contact frozen. Minimal changes in the size of ice crystals were observed during a 3 months storage.

Industrial relevance

This paper compares different freezing methods and subsequent frozen storage with respect to their effect on microstructures of salmon fillets. Pressure shift freezing at 200 MPa was superior to conventional freezing regarding small and regular ice crystal formation. Interestingly, during frozen storage for up to 3 months the high quality product obtained via pressure freezing at 200 MPa could be retained. For longer storage periods lower pressures (100 MPa) seem sufficient to achieve stable ice crystals.     

Effects of freezing and thawing processes on the quality of Atlantic salmon (Salmo salar) fillets

ABSTRACT:  High-pressure processing is finding a growing interest in the food industry. Among the advantages of this emerging process is the ability to favorably freeze and thaw food. This study aims at comparing the effect of different freezing and thawing processes on the quality of Atlantic salmon fillets. Atlantic salmon ( Salmo salar ) samples were frozen by Pressure-Shift Freezing (PSF, 200 MPa, −18 °C) and Air-Blast Freezing (ABF, −30 °C, 4 m/s). Samples were stored 1 mo at −20 °C and then subjected to different thawing treatments: Air-Blast Thawing (ABT, 4 °C, 4 m/s), Immersion Thawing (IMT, 20 °C), and Pressure-Assisted Thawing (PAT, 200 MPa, 20 °C). Changes in texture, color, and drip loss were investigated. The toughness of the PSF samples was higher than that of the ABF sample. The modification of color was more important during high-pressure process than during the conventional process. The PSF process reduced thawing drip compared with ABF. The presence of small ice crystals in the pressure-shift frozen sample is probably the major reason leading to the reduced drip volumes. The freezing process was generally much more influent on quality parameters than the thawing process. These results show the interaction between freezing and thawing processes on selected quality parameters.     

EFFECT OF PRESSURE-SHIFT FREEZING VERSUS AIR-BLAST FREEZING OF CARP (CYPRINUS CARPIO) FILLETS: A STORAGE STUDY

Intact carp (Cyprinus carpio) fillets were packaged under vacuum and pressurized at 100, 140, 180 and 200 MPa at 4C for 15 or 20 min. Changes in the lipid fraction and color of the fillets as well as the electrophoretic profiles of the fish proteins were studied to establish the best conditions (time and pressure) for pressure‐shift freezing the carp fillets. Thiobarbituric acid (TBA) values, free fatty acid (FFA) content and color parameters (L*, a*, b*) increased as the pressure level and pressurization time were increased. After 15 min of treatment at any pressure level, the intensity of the protein band with MW < 36 kDa decreased. With these results, the carp fillets were frozen using either pressure‐shift freezing (PSF) (140 MPa, ?14C for 12 min) or air‐blast freezing (ABF) (?20C for 4 m/s) and then stored at ?20C for 75 days. Changes in TBA values, FFA content, texture, total drip losses and size of ice crystal were evaluated. The TBA values and FFA content were relatively lower in the PSF samples than in the ABF samples. The freezing procedure did not seem to have a significant effect (P > 0.05) on the texture of carp fillets. PSF was more effective in reducing total drip losses in cooked samples compared to ABF treatment. Ice crystals found in the PSF fish samples were mainly intracellular, smaller and more regular in shape than those found in the ABF samples.     

Influence of the pressure shift freezing and thawing on the microstructure of largemouth bass

The objective of this study was to use a new self-cooling laboratory system for carrying out the pressure shift freezing (PSF) and evaluate the influence of PSF at 150 MPa on the microstructural properties of largemouth bass relative to liquid immersion freezing (LIF) and conventional air freezing (CAF). CAF, LIF and PSF showed average total freezing times of 176 ± 7.4, 65.3 ± 6.8 and 23.2 ± 3.1 min, and the cross sectional area of ice crystals in the muscle were 1002 ± 778, 501 ± 248 and 143 ± 50.6 μm², respectively, demonstrating a significant reduction in crystal size to be associated with PSF. It was observed that damage caused by the ice crystals during the freezing to the muscle microstructure was irreversible. The thawing and cooking losses of largemouth bass after the freezing were lower for PSF as compared to the other two freezing methods. PSF reduced the damage to myocytes and resulted in lower drip loss due to reduced microstructure disruption due to their small ice crystals, thereby maintaining the muscle tissue to better retain the fluids. Color and texture properties were less affected by PSF.Industrial relevanceFreezing is the most used preservation method for aquatic products. Rapid freezing results in better texture retention while the slow freezing damages the product texture because of the formation of extracellular large ice crystals developed during the freezing process. Thus, the nature of freezing affects the quality of frozen foods. Successful freezing processes aim at employing rapid freezing conditions which result in the formation of small ice crystals. Pressure shift freezing (PSF) is a novel technique with advantages of high degree of super-cooling, short phase transformation time, and results in very small ice crystals. This study makes use of a laboratory self-cooling system to carryout PSF of largemouth bass. This cooling system overcomes the limitation of previous studies on PSF which are expensive, limited to small size and impractical for commercial exploitations. The cooling system employed in this study can be easily adapted to large-scale production of PSF aquatic products. Test results provide a basis for the commercial exploitation of PSF for largemouth bass and such other aquatic foods for driving the quality advantage.     

Quality changes during the frozen storage of sea bass (Dicentrarchus labrax) muscle after pressure shift freezing and pressure assisted thawing

Quality of frozen sea bass muscle stored (1, 3 and 5 months) at two levels of temperature (−15 and −25 °C) after a pressure shift freezing process (200 MPa) — PSF — and/or a pressure assisted thawing process (200 MPa) — PAT — was evaluated in comparison with samples frozen and thawed using conventional methods (air-blast AF and AT, respectively). Frozen storage of high-pressure treated samples did not significantly affect initial quality of frozen muscle. Thus, parameters related to protein denaturation and extractability, water holding capacity and color presented similar values than those obtained for not stored samples. In addition, the improvement of the microstructure achieved by PSF application remains unchanged during frozen storage. On the other hand, conventional treated samples experienced significant changes during frozen storage, such as protein denaturation, and water holding capacity and color modifications. Storage temperatures did not have influence in the quality of PSF and PAT samples, but it showed some effects in AF muscle.Industrial relevance: This work demonstrates the potential application and benefits of high pressure (HP) in the freezing and thawing of fish meat in comparison to conventional methods, due to an improvement on the cellular integrity of the tissue. Although some negative effects are produced during processing with HP, no additional modifications occur during the frozen storage. The studied methodologies seemed to be very suitable for fish freezing and thawing, especially for products which will be frozen stored and/or cooked.     

Pressure-shift freezing and its influence on texture,colour, microstructure and rehydration behaviour of potato cubes

Temperature changes during pressure-shift freezing (400 MPa) of potato cubes and its effects on the drip loss (weight and conductivity), texture (shear and compression tests), colour (L, a, b values), drying behaviour, rehydration properties (water uptake, texture after rehydration) and visible cell damage after thawing (micrographs) were investigated and compared with conventional freezing (0.1 MPa, -30 °C), subsequent frozen storage (-18 °C) or pressure treatment (400 MPa) at +15 :C. Pressure-shift freezing resulted in increased crystallization rates compared to conventional freezing at -30 °C. Crystallization and cooling to ?8 =C took 2.5 min during and after pressure release versus 17 min at atmospheric pressure. Drip loss was reduced from 12.0 to 10.8g/100g. Water uptake during 10 min of rehydration (93.9g/100g compared to 77.4g/100g and incomplete rehydration) and texture values were improved. Browning after thawing or after fluidized bed drying was reduced (increased a value, lower L value), suggesting partial enzyme inactivation during pressure treatment. Differences in colour and texture to the untreated controls were smaller after pressure-shift freezing than after conventional freezing. Cooling to ?30 °C after pressure-shift freezing did not significantly affect the results, whereas subsequent frozen storage at ?18 °C resulted in quality deterioration, as observed after frozen storage of conventionally frozen samples. The improved preservation of cell structure was demonstrated using scanning electron microscopy.     

Structure of northern snakehead (Channa argus) meat: Effects of freezing method and frozen storage

This study was conducted to investigate the potential of cryogenic freezing with liquid nitrogen in the shelf-life extension of northern snakehead (Channa argus) and clarify the effects of temperature fluctuations after freezing on the quality attributes and tissue microstructure during frozen storage. The fish fillets were frozen by three methods including freezing using an ultra-low-temperature freezer (?80°C) to the core temperature of ?60°C (T1) or ?18°C (T2), or liquid nitrogen (T3) followed by storage at ?20°C for five months. Cryogenic freezing with liquid nitrogen postponed the decrease in pH and protein extractability. Temperature fluctuations after freezing might promote the accretion of ice crystals and resulted in the loss of tissue integrity and disorganization of myofibrils. The microstructural changes contributed greatly to the increased thawing loss and decreased resilience, as indicated by the enlarged extracellular spacing and the flakiness of myofibrils. Cryogenic freezing with liquid nitrogen showed no superiority in maintaining the microstructure of northern snakehead fillets, which was supposedly attributed to the cracking in tissue during freezing and the accretion of ice crystals during frozen storage.     

Comparison Of Air-blast And Pressure Shift Freezing On Norway Lobster Quality

Pressure shift freezing (PSF, 200 MPa, –18 °C) of whole Norway lobster was compared with air-blast freezing and with pressurized samples (200 MPa, 5 °C) without freezing for its effect on the quality in texture, structure, water, and salt soluble protein extractabilities. For the pressurized Norway lobster meat either with PSF or without freezing, toughness increased while salt soluble protein extractability decreased. Conversely, air-blast freezing did not affect the textural quality of the meat. Scanning electron micrographs showed that PSF yielded smaller ice crystals than air-blast freezing.     

Effects of freezing, thawing and storage on some quality factors for portion-size beef cuts

Portion-size beef cuts packaged in oxygen impermeable plastic bags were used to study the effects of rates of freezing and thawing, and storage time and temperature on drip and cooking losses, shear force, destruction of glutathione and accumulation of protein-breakdown products in meat. Portions weighing 150 g or over and frozen in an air-blast at −30°C gave lower losses of drip and lower amounts of nitrogenous constituents in drip than samples weighing less than 150 g or samples frozen in cardboard boxes in still air at −18°C. Freezing and thawing or frozen storage had no significant effect on shear force of meat frozen after ageing. During frozen storage, the destruction of glutathione and accumulation of protein-breakdown products increased, depending directly on storage temperature and time. The results show that a test based on these two biochemical changes would be suitable for assessing the quality of frozen beef.     

Conventional freezing plus high pressure–low temperature treatment: Physical properties,microbial quality and storage stability of beef meat

Meat high-hydrostatic pressure treatment causes severe decolouration, preventing its commercialisation due to consumer rejection. Novel procedures involving product freezing plus low-temperature pressure processing are here investigated. Room temperature (20 °C) pressurisation (650 MPa/10 min) and air blast freezing (−30 °C) are compared to air blast freezing plus high pressure at subzero temperature (−35 °C) in terms of drip loss, expressible moisture, shear force, colour, microbial quality and storage stability of fresh and salt-added beef samples (Longissimus dorsi muscle). The latter treatment induced solid water transitions among ice phases. Fresh beef high pressure treatment (650 MPa/20 °C/10 min) increased significantly expressible moisture while it decreased in pressurised (650 MPa/−35 °C/10 min) frozen beef. Salt addition reduced high pressure-induced water loss. Treatments studied did not change fresh or salt-added samples shear force. Frozen beef pressurised at low temperature showed L, a and b values after thawing close to fresh samples. However, these samples in frozen state, presented chromatic parameters similar to unfrozen beef pressurised at room temperature. Apparently, freezing protects meat against pressure colour deterioration, fresh colour being recovered after thawing. High pressure processing (20 °C or −35 °C) was very effective reducing aerobic total (2-log₁₀ cycles) and lactic acid bacteria counts (2.4-log₁₀ cycles), in fresh and salt-added samples. Frozen + pressurised beef stored at −18 °C during 45 days recovered its original colour after thawing, similarly to just-treated samples while their counts remain below detection limits during storage.     

Preservation of sweet cherry by isochoric (constant volume) freezing

Due to the perishable nature of fruits and the importance of reducing food waste, an effective preservation technique is required to prolong the shelf life and maintain the physical and nutritional properties of seasonal fruits. In this study, we evaluated isochoric freezing for preserving the quality of sweet cherries. We examined the physical characteristics and nutritional values of thawed cherries frozen to −4 °C or −7 °C in an isochoric system and compared them with those of fresh cherries, thawed cherries that were individually quick frozen and thawed cherries frozen to −4 °C or −7 °C in an isobaric system. We found that isochoric freezing decreased the drip loss and better preserved the color, texture, structure, ascorbic acid, phenolic and antioxidant content of frozen cherries, thereby proving their potential in frozen fruit applications.     

Effects of ultrasound-assisted thawing on the quality of edamames [Glycine max (L.) Merrill] frozen using different freezing methods

The effects of different freezing and thawing methods on the physicochemical indices and nutritive value of edamame [Glycine max (L.) Merrill] were investigated. Air-blast freezing had less of an impact on the drip loss, color, chlorophyll and ascorbic acid contents, and textural hardness of frozen shelled edamames. Ultrasound-assisted thawing significantly (p<0.05) shortened thawing time, compared to water immersion thawing. Ultrasound-assisted thawing at a 900 W power level showed the best retention of ascorbic acid and chlorophyll, and original hardness, and minimized the drip loss of thawed samples. Ultrasonic assisted thawing at a power level of 1,200 W caused the most pronounced loss of ascorbic acid. A combination of fast air-blast freezing and ultrasound-assisted thawing at a power level of 900 W most effectively retained ascorbic acid and chlorophyll, minimized drip loss, and maintained the textural hardness of shelled edamame samples.     

Preservation of spinach by isochoric (constant volume) freezing

Efforts are currently directed towards improving the quality of vegetables after freezing and thawing. One of the methods under investigation is isochoric freezing. In this study, we evaluated isochoric freezing for preserving the quality of baby-leaf spinach. We compared the properties of thawed spinach frozen to −4°C in an isochoric system with those of fresh spinach, thawed spinach frozen to −4°C in an isobaric system and thawed spinach that were commercially frozen. Spinach leaves frozen under isobaric conditions lost mass and thickness, making them softer and translucent. They also lost much of their nutrient content. In comparison, isochoric freezing maintained cell integrity and turgidity. Thawed leaves remained crunchy with characteristics similar to fresh leaves. Isochoric freezing also preserved nutritional content better than isobaric freezing, although significant nutrient losses still occurred.     

Synergistic mechanism of steam blanching and freezing conditions on the texture of frozen yellow peaches based on macroscopic and microscopic properties

Freezing and blanching are essential processing steps in the production of frozen yellow peaches, inevitably leading to texture softening of the fruit. In this study, the synergistic mechanism of stem blanching, freezing conditions (−20°C, −40°C, −80°C, and liquid nitrogen [−173°C]), and sample sizes (cubes, slices, and half peaches) on macroscopic properties of texture, cellular structure, and ice crystal size distribution of frozen yellow peaches were measured. Blanching enhanced the heat and mass transfer rates in the subsequent freezing process. For nonblanched samples, cell membrane integrity was lost at any freezing rate, causing a significant reduction in textural quality. Slow freezing further exacerbated the texture softening, while the ultra-rapid freezing caused structural rupture. For blanched samples, the half peaches softened the most. The water holding capacity and fracture stress were not significantly affected by changes in freezing rate, although the ice crystal size distribution was more susceptible to the freezing rate. Peach cubes that had undergone blanching and rapid freezing (−80°C) experienced 4% less drip loss than nonblanched samples. However, blanching softened yellow peaches more than any freezing conditions. The implementation of uniform and shorter duration blanching, along with rapid freezing, has been proven to be more effective in preserving the texture of frozen yellow peaches. Optimization of the blanching process may be more important than increasing the freezing rate to improve the textural quality of frozen yellow peaches.     

Studies on freezing of partially dehydrated spinach

Spinach (Spinacea oleracea) was dehydrated at 70 °C, partially dehydrated frozen (dried to its critical moisture ratio and frozen at ?20 °C) and frozen at ?20 °C. Results indicated that the time required for spinach dehydration was 7 h. Thus, the moisture ratio was 10.1 and 0.054 for the fresh and dried spinach, respectively. The critical moisture ratio during dehydration process was 2.20 after 2.65 h of drying time. Reducing sugars, free amino nitrogen, ash, iron and magnesium were slightly decreased in the partially dehydrated frozen spinach relative to the fresh samples. Dehydration markedly degraded the total chlorophyll, chlorophyll a, chlorophyll b, carotenoides and ascorbic acid whereas the freezing of partially-dehydrated spinach and freezing process were less effective. On the other hand, freezing of partially dehydrated spinach increased phaeophytin. There were no changes in pH-values of studied preserved samples. Freezing of partially dehydrated spinach improved the reconstitution of product at 100 °C and at room temperature (25 °C) comparing to dehydration. The drip loss of frozen spinach was 16.4% after 105 min of thawing time. Cooked fresh and frozen spinach were better in colour, flavour, texture, appearance and shape and over-all acceptability than that of dehydrated cooked one. Moreover, freezing of partially dehydrated spinach improved the aforementioned properties.     

Effect of freezing/thawing conditions and long‐term frozen storage on the quality of mashed potatoes

The effects of freezing temperature (−80, −40 or −24 °C) and thawing mode (microwave or overnight at 4 °C) on quality parameters of mashed potatoes made from tubers (cv Kennebec) and from potato flakes were examined, as was the effect of long‐term frozen storage on the quality of mashed potatoes. Mashed potatoes were tested for texture profile analysis (TPA) and cone penetration, oscillatory and steady rheometry, colour, dry matter, Brix and sensory analyses. In natural mashed potatoes, TPA hardness and oscillatory parameters showed that processing resulted in a softer product than the fresh control. The parameters were lower in the samples thawed at 4 °C than in those thawed by microwave at all the freezing temperatures used, which may be ascribed to gelatinisation of the starch released from damaged cells. Differences from the freshly prepared product decreased when the samples were frozen at −80 °C and thawed by microwave. No difference was found in sensory acceptability between samples frozen at −80 and −40 °C, which probably reflects the panellists' mixed preferences for air‐thawed versus microwave‐thawed samples. Increasing the time in frozen storage led to a natural mash with a firmer texture, higher L*/b* value and Brix; nonetheless, panellists found the samples at 0, 3 and 12 months of frozen storage equally acceptable. In commercial mash, penetration and oscillatory parameters showed that processing made for a firmer product than the fresh control, probably owing to retrogradation of gelatinised starch. Thawing mode had a significant effect on parameters, which were lower in the samples thawed at 4 °C. The structure and quality of commercial mash was more detrimentally affected by freezing and, therefore, we would not recommend either freezing or frozen storage of this mashed potato in the used conditions. Natural mash made from Kennebec potatoes should be frozen quickly and thawed by microwave in the conditions described to obtain a product more similar to that freshly made. If the samples are frozen by air blasting at −40 °C, the product can withstand frozen storage for one year. Copyright © 2005 Society of Chemical Industry     

Changes in texture,microstructure and nutritional quality of carrot slices during blanching and freezing

Thermal processing of vegetables has pronounced effects on the cell structure, often lowering the final textural properties of the product. In order to investigate the effect of thermal processing on carrot, slices were subjected to different blanching and freezing treatments before frozen storage. Microwave-, steam- or water-blanched material was frozen and then stored at −24 °C. Steam-blanched carrots were subjected to blast freezing or cryogenic freezing at different temperatures before frozen storage. The influence of these process conditions on the texture (maximum load and slope), microstructure, dry matter, sugars, carotene and drip loss was investigated. Microwave blanching differed from the other blanching methods by resulting in a heterogenic cell structure. The content of dry matter, carotene and sucrose was higher following microwave blanching. Blast freezing resulted in low maximum load which seemed to be caused by major tissue damage. Concerning cryogenic freezing, lowering the temperature from −30 °C to −70 °C resulted in better preservation of the native microstructure together with an increase in maximum load, which was most pronounced after one month of storage. No significant effect was observed when lowering the temperature from −30 °C to −70 °C for any of the other measured parameters. © 1999 Society of Chemical Industry     

Ultrastructure of Pork Liver after Freeze-Thaw Cycling and Refrigerated Storage

Pork liver was subjected to repeated freezing (-20°C) and thawing (+ 5°C) to simulate conditions of temperature abuse of frozen liver during commercial transport. Ultrastructure was compared to that of refrigerated pork liver. Liver cells deteriorated more with freezing and thawing (F-T) than with refrigerated storage (R-S). After one cycle F-T, hepatocyte organelles were damaged and cytoplasmic components appeared in the sinusoids. After four cycles F-T, membranes were extensively damaged and sinusoids contained organelles. The tissue organization was stable during six days of refrigerated storage, although cell structure deteriorated. Evidence from ultrastructure indicated that drip from F-T liver and R-S liver arose from different kinds of tissue damage.     

Assessment of cell damage in high-pressure-shift frozen broccoli: comparison with market samples

Pressure-shift freezing (PSF) is one of the most promising methods for obtaining high-quality frozen products. The aim of this work was to analyse the differences between broccoli that was frozen using two different PSF processes. In one of the processes, all the freezing was done inside the high-pressure vessel tempered at −20.5 °C. In the other process, the sample was taken out of the vessel after expansion, and freezing was completed using liquid N₂. Colour, texture, electrical conductivity, microstructure and drip losses after centrifugation were analysed and a sensory test was performed. The results were compared with those for conventionally frozen broccoli purchased at the market. PSF broccoli presented less cell damage, lower drip losses and better texture than the market samples. The two different PSF processes assayed produced no significant differences in the final quality of the samples.