Effects of sodium bicarbonate containing traces of citric acid in combination with sodium chloride on yield and some properties of white shrimp (Penaeus vannamei) frozen by shelf freezing, air-blast and cryogenic freezing

Effects of sodium bicarbonate with traces of citric acid in combination with sodium chloride on yield, freezing time, freezing rate, freezing loss and cutting force of white shrimp frozen by shelf, air-blast and cryogenic freezing with/without precooking were investigated. Shelf freezing was done at −40 °C ± 2 °C while air-blast freezing was carried out at −35 °C ± 2 °C, and cryogenic freezing was done at −35 °C, −40 °C and −60 °C. The freezing loss in the non-treated samples was 8.25, 4.6-5.84 and 1.92-3.48 g/100 g fresh shrimp for peeled samples frozen without precooking and increased to 21.85, 17.54-26.97, 17.92-20.31 g/100 g fresh shrimp in the precooked samples frozen by shelf, air-blast and cryogenic freezing, respectively. The treatment of sodium bicarbonate containing traces of citric acid at 4 g/100 ml with sodium chloride at 3 g/100 ml lead to the increase of yield thus reduced the freezing loss by about 6.83-10.28 and 6.41-12.4 g/100 g fresh shrimp for the frozen-thawed samples frozen as uncooked and cooked products, respectively. The toughening of shrimp was observed while sodium bicarbonate containing traces of citric acid treatment with sodium chloride could reduce the texture change occurred during the freezing.     

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.     

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.     

Experimental study on the freezing characteristics of four kinds of vegetables

Mushroom, green cauliflower, navy bean and pea pod are four kinds of favored vegetables. Their freezing characteristics are studied in this paper. For fresh samples, the moisture contents of mushroom, navy bean, pea pod and green cauliflower were 88.7±4.9, 92.9±0.4, 87.7±1.0 and 89.7±0.9 g/100 g, respectively. After pre-treating, cooling curve method and differential scanning calorimetry (DSC) were employed to measure the end-points of freezing and glass transition temperatures. The initial freezing points varied from −0.1 to −2.7 °C. The end-points of freezing were all below −20.0 °C. The partial glass transition temperatures varied from −50.3 to −76.1 °C. With a cryomicroscope, the sizes of ice crystals in frozen vegetable saps were found to decrease from 26 to 3 μm when the freezing rates increased from 1.0 to 10.0 °C/min.     

Effects of phosphate treatment on quality of red shrimp (Pleoticus muelleri) processed with cryomechanical freezing

This paper presents a study combining the use of cryomechanical freezing and phosphate. Red shrimp (Pleoticus muelleri) were treated with sodium tripolyphosphate at 5 g/100 mL and a phosphate blend at 5 g/100 mL. Treated shrimp were partially frozen in liquid nitrogen (−86 °C) and finish in blast tunnel (−30 °C) before glazing with water. Frozen shrimp were held for 15 days at −25 °C before analysis. Drip loss on thawing and after cooking process was evaluated and sensory attributes were analyzed using acceptance tests. Results indicated that dipping shrimp in phosphates solutions can be used to prevent large cooking-related yield losses. Sensory analysis showed that shrimp treated with phosphate retain sensory attributes, contributing to major preference and acceptance of panellists. Cryomechanical freezing combined with phosphate treatment offers a simple and economical solution to increase freezing capacity, improve water retention and, consequently, improve product quality.     

Detection of frozen-thawed salmon (Salmo salar) by a rapid low-cost method

The aim of this study was to evaluate a rapid low-cost system based on impedance spectroscopy as an alternative method to differentiate between fresh and frozen-thawed salmon. Samples of fresh salmon and others submitted to freezing at −18 °C or to 2 freezing cycles, kept in frozen storage for different times, were analysed. In general, no significant differences in moisture, total volatile basic nitrogen, pH, texture parameters, K₁ value, or microbial counts between the different samples were observed. This revealed that the freezing process, storage time or number of freezing cycles did not affect the physico-chemical parameters of fish samples, except for water holding capacity, which was significantly lower in all frozen samples compared with fresh salmon. The results showed that impedance spectroscopy was unable to differentiate between different storage times under frozen conditions; however, this technique could be a useful tool to detect fish submitted to freezing process.     

Effect of thermal process on connective tissue from jumbo squid (Dosidicus gigas) mantle

The effect of two thermal treatments (fast freezing at −40 °C and vapor cooking at 100 °C) on connective tissue extract (CTE) from jumbo squid (Dosidicus gigas) was investigated. Samples of CTE frozen at −40 °C were taken at 0, 3, 5 and 12 min. Also CTE was cooked at 100 °C and samples were taken at 0, 1, 2.5 and 5 min. Light microscopic observations of CTE after 12 min of freezing showed rupture of fibres. The CTE fibres showed agglutination during cooking time. The CTE insoluble fraction increased with freezing and cooking time. Maximum zeta potential value of untreated CTE was detected at pH 5.0 at +30 mV, meanwhile in the frozen CTE it was detected at pH 7.0 at +30 mV and two peaks (at pH 5.5 and 9.0) were observed at +20 mV in the cooked CTE. One endothermic peak was found at 105.9 °C in the untreated CTE, while in the frozen and cooked CTE the endothermic peaks were found at lower temperatures and enthalpies. Electrophoresis analysis of untreated CTE showed three bands. In the frozen CTE two bands appeared above 200 kDa, and in the cooked CTE, a 45 kDa band disappeared. These results suggest that during freezing and cooking processes there were modifications to molecular bonds that hold the integrity of the structure of the connective tissue of the jumbo squid mantle.     

Characteristics of submicron emulsions prepared by ultra-high pressure homogenisation: Effect of chilled or frozen storage

Model O/W pre-emulsions at an initial temperature of 24 °C and pH 6.3, and containing (w/w) 4.3% whey proteins plus 15, 30 or 45% peanut oil were processed using a ∼15 L/h homogeniser with a high pressure (HP) valve immediately followed by cooling heat exchangers. The effect of ultra-high pressure homogenisation (UHPH) between 100 and 300 MPa (P₁) or of recycling (1–3 homogenisation passes) at 200 MPa was investigated on the droplet size distribution, size indices and viscosity. Fluid temperatures were measured at the inlet (T₁) and outlet (T₂) of the HP-valve, and after immediate cooling downstream of the HP-valve (T₃) as they varied throughout UHPH. Short-life heating phenomena and mechanical energy involved in droplet processing were clearly influenced by emulsion composition. Oil droplet diameters decreased when (P₁) increased from 100 to 300 MPa leading to submicron droplets at ≥200 MPa. Monomodal distributions with droplets well below 0.3 μm were obtained after recycling at 200 MPa for the three oil contents, with a peak at 138 nm (distribution in volume) or 60–70 nm (in number frequency). The emulsion behaviour varied from fluid (and quite Newtonian) to thick (and shear thinning) depending on the droplet size reduction and the oil volume fraction. Emulsions displayed an excellent stability vs. creaming and coalescence after 9 d storage at 5 °C. Freezing followed by 13 d storage at −24 °C then thawing, induced an increase in particle sizes depending both on the oil volume fraction and (P₁). After UHPH at 200–225 MPa (±recycling), the freezing/thawing process maintained most of oil droplet size below 1 μm at 15% (w/w) oil, and induced mainly oil droplet aggregation through SDS-labile interactions at higher oil contents.     

Dehydrofreezing of pineapple

Dehydrofreezing technique involves one step of partial dehydration before freezing, in order to diminish the tissue damage by removing part of water from vegetable tissue prior to freezing. The objective of the present study was to evaluate the effect of osmotic dehydration and hot air-drying, applied previous to the freezing process, on the end quality of pineapple slices. Quality loss was quantified through drip loss, ascorbic acid content and mechanical properties changes of tissue. Freezing was carried out in a conventional air-blast tunnel at −31.5 ± 2 °C. Mechanical properties of fresh and dehydrated fruit, with and without the later process of freezing, were evaluated through compression tests. Ascorbic acid content was quantified by liquid chromatography. Osmotic dehydration and hot air-drying have the beneficial effect of reducing the time necessary for pineapple samples freezing. The freezing–thawing process affects the values of pineapple samples mechanical properties. Ascorbic acid losses were somewhat greater during the osmotic dehydration than with air dehydration.     

Microbial inactivation by pressure-shift freezing: effects on smoked salmon mince inoculated with Pseudomonas fluorescens, Micrococcus luteus and Listeria innocua

Smoked salmon mince inoculated simultaneously with Listeria innocua, Micrococcus luteus and Pseudomonas fluorescens was subjected to different pressure-temperature conditions. Control freeze-thaw at 0.1 MPa with storage at −15°C or −40°C for 0-5 days did not induce microbial inactivation. Control pressurisation at 207 MPa for 23 min at 20°C (initial sample temperature) with fast (3 s) pressure release had no significant effect on Gram+bacteria while P. fluorescens underwent a 2.8 log cycle reduction. Pressurisation at 207 MPa for 23 min at −3°C (without ice crystal formation) enhanced microbial reduction to 3.8 log cycles for P. fluorescens and to about 0.5 log cycle for Gram+bacteria. “Pressure-shift nucleation” (PSN) from 207 MPa and −21°C (i.e. cooling at 207 MPa for 23 min followed by pressure release in 3 s) caused 1.2, 1.4 and 4.3 log cycle reductions of L. innocua, M. luteus and P. fluorescens, respectively. A reduction of 1.7 log cycle was observed for L. innocua and M. luteus (4.6 log cycle for P. fluorescens) when salmon mince was subjected to pressure-shift freezing (PSF) (i.e. PSN from 207 MPa and −21°C as above followed by further freezing to −25°C at 0.1 MPa). PSF with pressure release in 18 min enhanced reduction to 2 and 2.5 log cycles for L. innocua and M. luteus, respectively.     

Combined effects of freezing rate, storage temperature and time on bread dough and baking properties

This study compares the effects of freezing temperature and rate as well as storage temperature and time on the quality of frozen dough. Yeasted bread dough was frozen using four freezing rates (19-69 °C/h), then stored at −10, −20, −30, or −35 °C for up to 180 days. Dough strength diminished with longer storage time and higher storage temperatures. Cryo-SEM showed that dough stored at −30 and −35 °C had the least damaged gluten network. NMR studies showed that more rapidly frozen dough, and that stored at lower temperatures had lower transverse relaxation (T₂) times (9-10 ms). However, dough stored at −20 °C displayed the highest yeast activity among samples. Bread loaf volume decreased with storage time, and bread made from dough stored at −20 °C showed the highest loaf volume. Breads produced from −30 and −35 °C stored dough displayed less change in the texture profile during storage as well as less change in T₂ values. Response surface analysis showed that optimal properties occurred at freezing rates of around 19-41 °C/h and storage temperatures of −15 to −20 °C.     

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).     

Mass transfer dynamics during high pressure brining of chicken breast

The objectives of this study were to investigate the changes in mass transfer, textural properties and water holding capacity of chicken breast when brine treated under different pressures. Chicken breasts were treated for up to 20 min in 4% sodium chloride solution under five pressures: 50, 100, 150, 200, and 300 MPa at 25 ± 1 °C. The results indicated that the total weight and water uptake of the chicken breast increased with increasing pressure up to 150 MPa, and then decreased with further pressure increase up to 300 MPa. Chicken breast samples brined at 150 MPa, with a sodium chloride effective diffusivity value of 2.96 × 10⁻⁸ m²/s, exhibited minimum hardness and maximum water holding capacity. In general, pressure treatment at 150 MPa was found to be the most suitable level for curing based on its higher yield, effective diffusivity and improved texture and water holding capacity.     

The Effect of Freezing Conditions on the Quality of Freeze-Chilled Reconstituted Mashed Potato

Freeze-chilling involves freezing and frozen storage of food products followed by thawing and chilled retail display. The objective of this trial was to examine the effect of different freezing conditions (−30 °C, −60 °C, −90 °C) on selected quality parameters of freeze-chilled reconstituted potato flakes. Lowering the freezing temperature reduced the time required for freezing, gave a softer product and led to a reduction in drip loss. Freeze-chilling resulted in a firmer product and a higher drip loss compared to chilling alone. There was no difference in vitamin C content or in taste panel acceptability between the chilled and the freeze-chilled products.     

Effect of freezing on the physicochemical, textural and sensorial characteristics of salmon (Salmo salar) smoked with a liquid smoke flavouring

This study reports the effect of different refrigeration/freezing treatments on the physicochemical, textural and sensorial properties of farmed Atlantic salmon (Salmo salar) treated with a commercial liquid smoke flavouring. Observations were made on three groups of fillets - group RFS: salted, smoked and stored at 4 °C; group BFS: frozen at −25 °C for 24 h, thawed, salted, smoked and stored at 4 °C; and group AFS: salted, smoked and frozen at −25 °C for 24 h and stored at −18 °C - over a period of 45 days. Scores (on a scale of 1-9) were provided for different sensorial attributes by a panel of 10 trained tasters. Sixty percent of the panellists consistently preferred the AFS fillets. The maximum shelf life associated with each treatment was defined as the last sampling day on which a mean score of ≤5 was awarded for the fillet sensorial attributes by ≥50% of the panellists. Freezing the salmon for 24 h before smoking (BFS) did not increase its shelf life (30 days) over that of refrigerated smoked salmon (RFS). In addition, the former treatment had a negative effect on the adhesiveness, cohesiveness, smoke odour intensity and colour intensity of the flesh. However, maintaining the fish frozen at −18 °C (AFS) increased its shelf life (>45 days) and invested the flesh with greater firmness, cohesiveness and colour intensity.     

Effect of freezing conditions and storage on ice crystal and drip volume in turbot (Scophthalmus maximus): Evaluation of pressure shift freezing vs. air-blast freezing

Turbot fillets were frozen either by pressure shift freezing (PSF, 140 MPa, −14°C) or by air-blast freezing (ABF), and then stored at −20°C for 75 days. Smaller and more regular intracellular ice crystals were observed in fillets frozen by PSF compared with air-blast frozen ones. Ice crystals area in PSF samples was approximately 10 times smaller than that of ABF samples, on average. The PSF process reduced thawing drip compared with air-blast freezing. Conversely to this classical freezing process, the storage time did not adversely influence the thawing drip of PSF samples. In addition, PSF appeared to reduce cooking drip after 45 days of storage at −20°C. Differential scanning calorimetry analysis showed a significant reduction of the total enthalpy of denaturation for the pressure shift frozen samples compared to fresh and conventional frozen samples. Besides, a new melting transition appeared on the thermogram of PSF samples at approximately +40°C.     

Kinetics of quality changes of pumpkin (Curcurbita maxima L.) stored under isothermal and non-isothermal frozen conditions

The effects of freezing process and frozen storage at isothermal (−7, −15 and −25 °C) and non-isothermal (accelerated life testing with step-stress methodology; temperature range from −30 to −5 °C) conditions on pumpkin quality were investigated. Storage temperature conditions were selected to embrace the limits practiced in the cold chain. Quality changes, such as texture, colour CIE Lab and vitamin C (ascorbic acid) content, were evaluated for both frozen storage regimes. The freezing process (that included a pre-blanching step) and subsequent frozen storage had significant impacts on all quality parameters analysed.A fractional conversion kinetic model was adequate in colour, texture and vitamin C data fits. The storage temperature effect was successfully described by the Arrhenius law.This study shows that non-isothermal frozen storage has a marked effect on pumpkin quality.     

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.     

The Effect of Fluctuating vs. Constant Frozen Storage Temperature Regimes on Some Quality Parameters of Selected Food Products

Samples of frozen raw salmon, smoked mackerel, stewed pork pieces, ice cream, pizza (with a mozzarella cheese topping), hollandaise sauce, strawberries, and blanched broccoli were mildly temperature abused by subjecting them to temperature fluctuations below the freezing point. This involved three temperature fluctuation cycles of −30 °C to −10 °C to −30 °C on consecutive weeks followed by storage at a constant −30 °C for 8 mo. The samples were compared with duplicate sets held for 8 mo at a constant −60 °C (superfreezing) or −30 °C (control) and testing (objective and sensory) was conducted after 0, 1, 2, 4 and 8 mo. The temperature regimes had a larger effect on peroxide (PV) and free fatty acid (FFA) values than on any of the other parameters tested over the product range. The pattern in the data was the same for each fat-containing product in that superfreezing (−60 °C) gave the lowest PVs and FFAs, the control (−30 °C) was intermediate, while the fluctuating regime gave the highest values. PVs and FFAs also increased with length of time in frozen storage. While smoked mackerel had relatively high PVs and FFAs, rancidity was not a major problem in any of the fat-containing products as indicated by sensory tests. The temperature regimes had a minimal effect on texture, colour, water-holding capacity and drip loss on thawing for most of the products. However, superfreezing resulted in a better retention of vitamin C in strawberries.     

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.