Effect of frozen storage on physical properties of pasta filata and nonpasta filata Mozzarella cheeses

The effects of 1) ripening 2, 7, and 14 d at 7 degrees C before freezing; 2) tempering 7, and 14 d at 7 degrees C after freezing; and 3) frozen storage for 1 and 4 wk at -20 degrees C, on the meltability, stretchability, and microstructure of pasta filata and nonpasta filata Mozzarella cheeses were investigated. Cheeses were cut into 5 x 10 x 7-cm blocks and vacuum-sealed 1 d after manufacture. The results were compared to the corresponding results obtained with unfrozen control samples, aged at 7 degrees C between 2 and 21 d. The changes in physical properties of frozen-stored pasta filata and nonpasta filata Mozzarella cheeses were consistent with critical damage to the cheese microstructure as compared to the unfrozen control samples. Generally, aging before and tempering after freezing resulted in increased meltability of both frozen-stored pasta filata and nonpasta filata Mozzarella cheeses. The stretchability of frozen-stored pasta filata Mozzarella cheese increased during tempering, but that of nonpasta filata Mozzarella cheese decreased during aging and tempering. In most cases, one-week frozen stored pasta filata Mozzarella cheese had higher meltability and stretchability than 4-wk frozen-stored sample. For 1-wk frozen-stored nonpasta filata Mozzarella cheese, the meltability increased but stretchability decreased when it was frozen-stored for 4 wk.     

Effect of freezing and frozen storage on microstructure of Mozzarella and pizza cheeses

Scanning electron microscopy was used to assess the effect of aging before (2, 7, and 14 days at 7 °C) or tempering after (1, 7, and 14 days at 7 °C) freezing, and frozen storage (1 and 4 weeks at −20 °C) on protein matrix of pasta filata Mozzarella and non-pasta filata pizza cheeses using unfrozen samples as controls. Pores and ruptures of reticular structure were observed in frozen-stored pasta filata Mozzarella cheese protein matrix, but cracks and clumps of bacteria were found in frozen-stored non-pasta filata pizza cheese. No obvious differences were discernable between the microstructures of pasta filata Mozzarella cheeses frozen stored 1 and 4 weeks. Formation of the reticular structure in frozen-stored pasta filata Mozzarella cheese progressed during tempering. Microstructure of non-pasta filata pizza cheese frozen stored for 4 weeks contained more extensive cracking and more areas of clumps of bacteria than that was frozen stored for 1 week. Aging of cheese before frozen storage was considered responsible for microstructural cracking; fewer cracks were found in the frozen-stored cheese tempered 1 and 2 weeks, but the clumps of bacteria were still observed.     

Effects of calcium pre-treatments and freezing rates on fluid loss from plantain products

Ripe plantain slices treated with calcium chloride (0, 1360 or 2700 ppm Ca) solutions were packed one layer thick in flexible pouches prior to freezing in still air at −18 to −20°C, liquid immersion at −18 to −20°C, and cryogenically in liquid nitrogen. A new technique in which the extent of fluid loss from thawed plantain slices could be associated with tissue damage was used to assess quality of the thawed plantain slices. Plantain frozen in liquid nitrogen had the least fluid loss followed by liquid immersion and still air feezing. Treating with calcium ions prior to freezing significantly reduced fluid loss in all freezing methods used. In another experiment the treated plantain slices were frozen in still air −18 to −20°C followed by sensory evaluation of the thawed slices after frying in hot peanut oil. Calcium also significantly increased firmness in the treated slices compared to the control and there were no adverse effects on flavour and appearance. The techno-economic implications of the study are discussed.     

Morphological changes in tilapia muscle following freezing by airblast and liquid nitrogen methods

The cross-section spacing between the muscle fibre bundles of fresh tilapia chunks was ≈3.06 μm. After freezing by airblast at −20 and −36°C, and by liquid nitrogen at −87 and −128°C at freezing rates of 0.25, 1.53, 9.74 and 19.4 cm h⁻¹, respectively, the spacing increased to 3.21–7.69 μm, which was 5 to 151% greater than that in the fresh samples. The spacing further increased with storage time. Liquid nitrogen freezing resulted in smaller increases in spacing than airblast freezing. On freezing at constant temperatures of −20 to −128°C followed by storage at −20°C for 1 month, the extracellular spacings were 7.38–13.8 μm, and increased to 22.16–29.38 μm after 2 months. After storage at −20°C or −40°C for 6 months, the muscle fibre bundles showed fragmentation in both the airblast and the liquid nitrogen frozen tilapia chunks. The integrity of muscle structure was maintained better with liquid nitrogen freezing than with airblast freezing. All the differences resulting from freezing methods or freezing rates disappeared upon prolonged frozen storage at −20°C or −40°C. The correlations between the freezing temperature and extracellular spacing, and the activation energy (E_a) was calculated. The time required for freezing-temperature-induced differences in crystal growth, or in the extracellular spacing of muscle fibre bundles to disappear when E_a= 0 can be considered as the high-ultrastructural quality shelf-life, which is predicted to be 2.7 months at −20°C for tilapia frozen with liquid nitrogen.     

Rheological Behavior of Frozen and Thawed Low-Moisture, Part-Skim Mozzarella Cheese

Stress relaxation and dynamic profiles of low-moisture, part-skim (LMPS) Mozzarella cheese cylinders refrigerated 14 days (control), frozen and thawed, and stored frozen and refrigerated up to 90 days were compared. Samples were frozen at ?30°C and stored at ?20°C. Thawing and refrigerated storage were at 5°C. Stress relaxation tests were conducted at 20°C and dynamic spectrometry at 20°C and 60°C. The frozen and thawed Mozzarella cheese tested at 20°C became harder and more elastic with storage time, while refrigerated stored samples became softer and more elasticoviscous with time. Upon melting, both go-day-frozen and go-day-refrigerated cheeses were less elastic and less viscous than 14-day-refrigerated samples.     

Determining effects of freezing on pasta filata and non-pasta filata mozzarella cheeses by nuclear magnetic resonance imaging

The formation of ice during freezing of pasta filata and non-pasta filata Mozzarella cheeses, and the spatial redistribution of water T2 relaxation time and the changes of water self-diffusion coefficient (D) within the unfrozen and frozen-stored cheese samples were observed by nuclear magnetic resonance imaging. Images of water spin number density and water T2 relaxation time were obtained using spin-echo imaging pulse sequence. The water self-diffusion coefficient was measured by pulsed-field gradient spin-echo technique. The ice formation was accompanied by loss of signal intensity in the affected areas of the cheese sample. There was a significant change in T2 and D values of water following freezing-thawing, which can be used to characterize the effect of freezing on cheeses. The D values of the frozen-stored pasta filata Mozzarella cheese samples were higher than those for the unfrozen samples. Such a difference was not observed for the non-pasta filata Mozzarella cheese samples. The T2 distributions of frozen-stored pasta filata Mozzarella cheese samples were narrower, and those for the non-pasta filata Mozzarella cheese samples were broader T2. This may be attributed to the microstructure differences between the two cheeses.     

Application of competitive indirect enzyme-linked immunosorbent assay (Ci-ELISA) for monitoring the degree of frozen denaturation of bovine myosin

The denaturation of myosin on freezing and frozen storage was monitored using competitive indirect enzyme-linked immunosorbent assay (Ci-ELISA) formatted with polyclonal antibodies anti-MWM IgG, anti-S-1 IgG and anti-LMM IgG raised against the antigens (Ags) bovine myosin whole molecules (MWMs), heavy meromyosin S-1 (myosin head part, S-1) and light meromyosin (myosin tail part, LMM) respectively. Beef slices and cuts stored at −20 °C or −50 °C lost immune affinity with all antibodies, in particular anti-LMM IgG. Repeated thawing–refreezing treatment caused more myosin denaturation than simple freezing. Myosin from beef stored at −20 °C was denatured more than that stored at −50 °C. The immune affinities between anti-LMM IgG and thawed samples were similar to those from anti-MWM IgG. We were unable to differentiate reliably between fresh and thawed beef using anti-S-1 IgG. Myosin was denatured by freezing, in particular its tail part (LMM).     

LOW-TEMPERATURE DESTRUCTION OF Trichinella spiralis USING LIQUID NITROGEN AND LIQUID CARBON DIOXIDE

The destruction of Trichinella spiralis by low temperature treatment has been demonstrated to be an effective tool in combatting this parasite in fresh pork products. Current procedures, however, require a holding period under varying times and temperatures to accomplish this destruction. Freezing with cryogenic materials offers the opportunity to attain ultra low temperatures and, thus, eliminate post–freezing holding periods. Four trials were conducted using trichina-infected fresh pork patties approximately 9 mm thick and 88 mm square. In trials 1, 2 and 3 the patties were frozen with LN, using a modified Heath freezing tunnel to final equilibrated temperatures of –12C, –14°C, –20°C, –23°C, –25°C, –28°C, –29°C, –39°C and −47°C. In trial 4 the patties were frozen in a Certified Multideck tunnel using liquid CO₂ as a refrigerant to −10°C, –17°C, –23°C, –29°C and –39°C. Patties were thawed immediately and checked for viable T. spiralis. No positive samples were found at temperatures of –29°C or below.     

Viscoelastic Behavior of Refrigerated Frozen Low-moisture Mozzarella Cheese

ABSTRACT: The effect of freezing low-moisture Mozzarella before ripening on cheese microstructure and its relationship with caseins degradation and viscoelastic properties were analyzed, and results were compared with refrigerated control samples. Soluble and nonprotein nitrogen contents increased with ripening time although more rapidly in the samples that were frozen before ripening. Scanning electron microscopy (SEM) showed that freezing modified cheese microstructure due to ice formation; ice crystals weakened the casein matrix. Dynamic rheological tests were performed at 50 °C using oscillatory rheometry G'increased with frequency and was higher for refrigerated than for samples frozen before ripening, at the same ripening times; G'diminished as aging time increased, although more rapidly for the samples frozen before ripening.     

Sarcoplasmic Reticulum Ca2+-ATPase and Cytochrome Oxidase as Indicators of Frozen Storage in Cod (Gadus morhua)

ABSTRACT: Activities of 2 membrane-bound enzymes, Ca²⁺-ATPase from the sarcoplasmic reticulum and cytochrome oxidase from the inner mitochondria membrane, were measured during frozen storage of cod. Enzyme activities were higher in cod muscle samples frozen at −30°C than at −20°C. Freezing-induced activation of both enzymes was observed and the activation was amplified by ice storage prior to freezing. Sensory evaluation conducted at 9 mo of frozen storage showed differences between the sensory properties of cod frozen immediately after catch and frozen after 3 d of storage on ice. These results indicated that the enzymes might be useful as indicators of quality changes by frozen storage.     

ICE CRYSTAL FORMATION IN PRESSURE SHIFT FREEZING OF ATLANTIC SALMON (SALMO SALAR) AS COMPARED TO CLASSICAL FREEZING METHODS

Atlantic salmon were frozen either by pressure shift freezing (PSF) at 100 MPa (−8.4C), 150 MPa (−14C) and 200 MPa (−20C) or by conventional air freezing (CAF) at −30C and glycol/water bath freezing (GBF) at −20C. Temperature and phase transformations of fish were monitored during the freezing processes, and microstructures of ice crystals formed were evaluated for size, shape and location. The mean (± standard deviation) cross-section area of the ice crystals were: 11000 ± 7600, 280 ± 340, 260 ± 300, 63 ± 62, and 23 ± 22 μm² for salmon subjected to CAF, GBF and PSF at 100, 150 and 200 MPa, respectively, as compared with that of the muscle fibers (7200 ± 2500 μm²). The roundness of the fish muscle fibers was 0.67 ± 0.07, while the ice-crystal roundness were: 0.38 ± 0.14, 0.55 ± 0.21, 0.57 ± 0.18, 0.63 ± 0.14 and 0.71 ± 0.14 for the salmon, respectively. CAF created larger and irregular ice crystals, and resulted in irreversible damage to muscle tissues. Due to its higher freezing rate, GBF produced smaller ice crystals than CAF, but the cross-section area and roundness values had larger deviations. The PSF process produced large amounts of fine and regular intracellular ice crystals that were homogeneously distributed throughout the salmon. Microscopic images clearly     

Freezing tilapia by airblast and liquid nitrogen – freezing point and freezing rate

Processing data was obtained for the freezing of tilapia meat. The initial freezing point of tilapia meat was measured by differential scanning calorimetry (DSC), and also by measuring the centre temperatures of meat chunks during cooling. the freezing point was −1.03°C by DSC, and between −0.81 and −0.90°C by the cooling method, determined at the point where the standard deviation of the mean temperature was close to zero, i.e. a minimum.
Tilapia chunks, 0.95 to 1.45 cm thick, were frozen in an airblast freezer at −7, −20 and −36°C, and in a liquid nitrogen freezer at −87 and −128°C.
Freezing rate, defined as the half thickness of a meat chunk divided by the time for the centre temperature to decrease from 0 to −5°C, was 0.09 cmh⁻¹ at −7°C. At freezing temperatures of −20, −36, −87 and −128°C, the rates were respectively 4, 19, 158 and 331 times faster than that at −7°C, and correlated with freezing temperature ( r = 0.99) regardless of the freezing method.     

Optimization of the Freezing Conditions on Mackerel and Amberfish for Manufacturing Minced Fish

Optimal freezing, frozen storage and thawing conditions in preserving mackerel and amberfish for producing minced fish products were investigated. Based on assessments of extractability of 0.6M KCl-soluble proteins and actomyosin, Ca-ATPase activity of actomyosin, and gel-forming ability of kamaboko (kind of minced fish meat product), semi-dressed, dressed, and filleted samples showed stable and good quality of gel-forming ability during 3 months storage at −20°C. Optimal ultimate freezing temperatures of mackerel and amberfish were −20°C and between −30°C and −40°C, respectively. The optimal storage temperatures for mackerel and amberfish were −20°C and −40°C, respectively. Appropriate thawing methods for frozen mackerel were microwave and 20°C running water defrosting, while those for frozen amberfish were microwave, 20°C running water, and room temperature defrosting.     

Influence of Cooling Rate on Glass Transition Temperature of Sucrose Solutions and Rice Starch Gel

ABSTRACT: The study's objectives were to determine the influence of cooling rate through the primary zone of freezing on T_g in sucrose solutions and rice starch gels. The influence of cooling rate, water content, and annealing on T_g were evaluated. Results indicated that the observed T_g values for sucrose solutions were lower after rapid cooling (70% solids: rapid cooling −66.7°C; slow cooling −64.6 °C; 30% solids: rapid cooling −34.6 °C; slow cooling −33.3 °C). The T_g values of annealed samples are higher than the T_g of both rapidly and slowly cooled samples (70%: −44.2 °C; 30%: −32.7 °C). The T_g of the rice starch gel was −9.0 °C after rapid cooling and −7.5 °C after slow cooling.     

Comparative Rates of IMP Degradation in Unfrozen and Frozen-and-Thawed (Slacked) Fish

SUMMARY— The comparative rates of IMP degradation between fresh and frozen-and-thawed (slacked) fish were compared on six different species of fish. Several factors that could contribute to a rate change of IMP degradation were evaluated. These included freezing temperatures, time in frozen storage, pre- and post-rigor freezing, and method of killing the fish.
English sole and rainbow trout showed slight increases in the rate of IMP degradation when they were frozen and then thawed within 48 hr. Silver salmon and halibut that were frozen and then thawed within 48 hr showed no change in the rate of IMP degradation. Halibut, however, that was frozen and stored at −20°F for 3 months showed a slight decrease in the rate of IMP degradation after it was thawed; but king salmon handled under the same conditions did not.
The method of kill or freezing the fish either pre- or post-rigor did not alter the rate of IMP degradation after the fish was thawed.
No loss of IMP occurred in fish (halibut) stored at −20°F. Over one-third of the original IMP content was lost in halibut stored at +15°F after 3 months of storage.
These results show that there is no significant difference in the rate of IMP degradation between fresh and slacked fish. The flavor-contributing effect of IMP in slacked fish therefore should be the same as in fresh fish, provided the fish was frozen and stored at or near a temperature of −20°F.     

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.     

Effects of pressure-shift freezing and conventional freezing on model food gels

Summary Gels of agar, starch, ovalbumin, gelatin and an industrial β-lactoglobulin protein isolate, were frozen conventionally in a −30 °C freezer and by pressure-shift freezing at 200 MPa at −15 °C. Thawing was carried out conventionally at 20 °C and by the application of a pressure of 200 MPa. The microscopic structure and mechanical properties of the thawed gels were compared with those of the initial gels. Microscopic examination showed that pressure-shift freezing produces smaller and more uniform ice crystal damage than conventional freezing at −30 °C. The results also suggest that the freeze-thaw behaviour of food gels can be categorized into two general types: (1) gels which have a reduced gel strength as a result of mechanical damage to the gel microstructure caused by ice crystal formation, and (2) gels which have an enhanced gel strength, as a result of molecular structural changes that take place in the frozen state. Agar and gelatin were found to be typical of type (1) gels, whereas starch, β-lactoglobulin protein isolate and ovalbumin were found to be typical of type (2) gels. In the case of starch, retrogradation during thawing was found to be the most important factor.     

State Diagram of Freeze-dried Garlic Powder by Differential Scanning Calorimetry and Cooling Curve Methods

ABSTRACT: The state diagram of freeze-dried garlic powder was developed using freezing curve, glass transition line, and maximal-freeze-concentration condition. Freezing points of garlic powder were measured by differential scanning calorimetry (DSC) and the cooling curve method, whereas glass transitions were measured by DSC. The freezing curve and glass transition line were modeled using the Clausius-Clapeyron equation, adjusted with unfreezable water, and the Gordon-Taylor model, respectively. Maximal-freeze-concentrated condition was found as X '_s (characteristic water content) = 0.82 [ X '_g (characteristic solids content) = 0.18] with the characteristic temperature of glass formation being T '_m (characteristic glass transition) =−38.6°C and T '_m (characteristic end point of freezing) =−26.0°C. Other characteristic glass transitions T "_g and T ‴_g equal to −29.3°C and −48.6°C, respectively.     

Development of a Model System to Mimic Beef Bone Discoloration

ABSTRACT: Some current practices used in the meat industry (blast chilling, enhancement, modified atmosphere packaging [MAP]) appear to result in darkening of the bone in fresh meat. The objective of this study was to develop a model system that could be used to evaluate intervention strategies to prevent this discoloration. Beef rib bones were removed from carcasses, split along the transverse plane from the proximal to the distal end of the rib, and then frozen (−20 °C) or held at 4 °C for 24 h. Half were exposed to a phosphate/salt enhancement solution while half served as the control. Samples were packaged in air or modified atmosphere packaged (MAP: 80% O₂/20% CO₂) and displayed in a retail case (4 °C, 24 h). Visual discoloration occurred during the 1st 10 h of display. More darkening (brown, green/black) was observed in previously frozen samples, whereas samples held at refrigeration temperature were redder. CIE L *, a *, and b * values determined after 24 h indicated that samples held in refrigeration before packaging were lighter and redder. After 24 h at 4 °C, previously frozen samples contained more methemoglobin/g protein in the bone marrow than did bone samples that had never been frozen.     

Effects of freezing and frozen storage on the microstructure and texture of ewe's milk cheese

Semi-hard ewe's milk cheeses, frozen immediately after manufacture either slowly at –35 °C or rapidly at –80 °C and stored at –20 °C for 4 months were studied for microstructural and textural characteristics during subsequent ripening. Two control groups were used to establish the effect of freezing: the fresh unfrozen cheese and cheese thawed immediately after freezing. Freezing proper did not result in any marked changes in the textural parameters of the cheeses, but considerable changes were found in slowly frozen cheeses after 4 months of frozen storage. Shear strength values were lower in all frozen and stored cheeses, particularly in cheese samples frozen slowly compared to those in the unfrozen control batch. This parameter and firmness values were significantly lower in both slowly and rapidly frozen cheeses at the completion of ripening. Ripening tended to offset differences in elasticity, noticeable in the cheeses during the first 30 days of ripening. Light microscopy and electron microscopy revealed small cracks and ruptures in the cheeses which could not be observed by the naked eye. More extensive damage to the cheese microstructure was found in slowly frozen cheese samples stored frozen for 4 months.