Effect of pretreatment and conditions and period of storage on some quality indices of frozen chive (Allium schoenoprasum L.)

Chive leaves for freezing contained 13.9 g dry matter, 133 mg vitamin C, 4.7 mg β carotene, 121 mg chlorophylls (a+b), 40.4 mg nitrates, and 0.19 mg nitrites in 100 g of edible parts. Blanching of the raw material before freezing reduced the level of dry matter by 22%, vitamin C 29%, β carotene 20%, chlorophylls 21%, and nitrates 26%, while that of nitrites increased three times. Freezing and 12-month storage of frozen material caused further losses in the analysed constituents except dry matter. Losses were distinctly higher on freezing non-blanched chive, a further enhancement of losses being observed with a storage temperature at −20°C. After a 12-month storage of frozen chive, the preserved content of vitamin C ranged from 11 to 66%, β carotene 37 to 65%, chlorophylls 65 to 75%, and nitrates 58 to 81%. If the blanching is omitted and the storage temperature is −20°C, a good preservation of vitamin C is not possible even for a period of 3 months. In contrast, the pretreatment of blanching ensures its good preservation at −20°C and at −30°C, and also yields a very good conservation of all the constituents analysed.     

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.     

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     

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.     

Optimisation of freezing process with pressure steaming of potato tissues (cv Monalisa)

Response surface methodology (RSM) was used for determining optimum conditions of the freezing process on pectinesterase (PE) activity, rheological parameters and textural properties in potato tissues. In the process of production of frozen potatoes, the second step of the stepwise blanching prior to freezing was considered as a fixed factor and performed at 97 °C for 2 min as well as the freezing rate in the freezing step itself, which was carried out at −2 °C min⁻¹. The effects of variation in levels of temperature (57.93–72.07 °C) and time (15.86–44.14 min) in the first blanching step on the PE activity were studied using a central composite rotatable design. A Box–Behnken factorial design was used to investigate the effects of simultaneous variation of temperature (60–70 °C) and time (20–40 min) in the first blanching step and steaming temperature (112–122 °C) and time (1–3 min) on rheological parameters and textural properties. Blanching temperature was the independent variable that most influenced either enzymatic activity or rheological parameters. Stationary points showing maximum PE activity had critical temperature and time values of 64.22 °C and 29.37 min before freezing and 64.39 °C and 28.02 min after freezing and steaming of the tissues, and these values were very close to those obtained for some creep compliance parameters. Results show a high correlation between increases in PE activity and tissue firmness below optimum experimental freezing conditions, proving the role of the enzyme as one of the main contributors to the firmness which determines the textural quality of frozen potato tissues. © 1999 Society of Chemical Industry     

Blanching, Freezing and Frozen Storage Influence Texture of White Asparagus

We studied effects of three methods of blanching in conjunction with freezing, on texture of white asparagus as defined by three measures: maximum shear force, cutting energy, and total fiber content. We also assessed shelf life of asparagus kept in frozen storage at -22°C. Methods of blanching were total immersion in hot water, progressive immersion in hot water and steam. An increase in total fiber content was found throughout frozen storage. This increase correlated with lignification of vascular bundles in the basal segment of spears, even during frozen storage. This was reflected in an increase in maximum shear force and cutting energy required. The shelf life of frozen asparagus was 12 mo using total fiber content as a criterion.     

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.     

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.     

Textural and Microstructural Changes in Frozen Stored Sardine Mince Gels

The freezing of sardine mince gels produced slight alterations in texture, microstructure and degree of chemical aggregation of proteins, irrespective of freezing temperature (– 18°C or – 40°C). The most noticeable changes took place during frozen storage 3 mo, particularly in gels frozen at – 18°C which were strongly affected by storage temperature (– 12°C or – 18°C), unlike those frozen at – 40°C. Better gel integrity was found in those frozen at – 40°C, where cavities were more numerous, but smaller and more evenly distributed than in gels frozen at – 18°C.     

Effect of Infrared Blanching on Enzyme Activity and Retention of β‐Carotene and Vitamin C in Dried Mango

The objectives of this work were to evaluate infrared (IR) dry blanching in comparison with conventional water blanching prior to hot air drying of mango to inactivate polyphenol oxidase (PPO) and ascorbic acid oxidase (AAO) enzymes, and to study its effect on color change and retention of vitamin C and β‐carotene. Mango cylinders were blanched under similar temperature–time conditions either by IR heating or by immersion in a water bath during 2 min at 90 °C (high‐temperature‐short‐time—HTST) or for 10 min at 65 °C (low‐temperature‐long‐time—LTLT). After blanching mango was hot air dried at 70 °C. PPO was completely inactivated during the blanching treatments, but AAO had a moderate remaining activity after LTLT treatment (～30%) and a low remaining activity after HTST treatment (9% to 15%). A higher retention of vitamin C was observed in mango subjected to IR dry blanching, 88.3 ± 1.0% (HTST) and 69.2 ± 2.9% (LTLT), compared with water blanching, 61.4 ± 5.3% (HTST) and 50.7 ± 9.6% (LTLT). All‐trans‐β‐carotene retention was significantly higher in water blanched dried mango, 93.2 ± 5.2% (LTLT) and 91.4 ± 5.1% (HTST), compared with IR dry blanched, 73.6 ± 3.6% (LTLT) and 76.9 ± 2.9% (HTST). Increased levels of 13‐cis‐β‐carotene isomer were detected only in IR dry blanched mango, and the corresponding dried mango also had a slightly darker color. IR blanching of mango prior to drying can improve the retention of vitamin C, but not the retention of carotenoids, which showed to be more dependent on the temperature than the blanching process. A reduction of drying time was observed in LTLT IR‐blanching mango.     

Effect of temperature, pressure and calcium soaking pre-treatments and pressure shift freezing on the texture and texture evolution of frozen green bell peppers (Capsicum annuum)

The firmness of green bell pepper (Capsicum annuum) was studied under different processing conditions. Thermal texture degradation kinetics of pepper tissue between 75 and 95 °C could be accurately described by a fractional conversion model. The firmness of pre-processed pepper increased when the samples were submitted to several heat, pressure, and combinations of heat/pressure and calcium soaking pre-treatments. Pre-heating at 55 °C during 60 min and mild heat/high-pressure treatments (200 MPa at 25 °C, 15 min) yielded the best results, which were further improved when combined with calcium soaking. These pre-treatments significantly slowed down thermal texture degradation of pepper at 90 °C, a typical temperature used for pepper blanching prior to freezing. The above-mentioned pre-treated samples showed a significant reduction in firmness when frozen by regular freezing at 0.1 MPa. The same samples showed no changes in firmness when frozen by high-pressure shift freezing at 200 MPa. When freezing was carried out by high-pressure shift and after frozen storage (−18 °C) for 2.5 months, pressure pre-treated pepper showed a better retention of texture than thermal pre-treated pepper.     

Changes in Texture of Green Peas during Freezing and Frozen Storage

The effects of freezing (still-air, air-blast, and Freon immersion freezing) and frozen storage (?5°, ?10° and ?15°C for 0 to 48 wk) on texture of cooked frozen peas were examined. Peas frozen by a Freon-12 immersion method with no appreciable damage to cell structure had firmer and more chewy sensory textural quality compared to those peas frozen by a slower freezing method. Sensory tenderness decreased initially and then increased with storage time to the maximum storage times of 6 wk in ?5°C storage, 16 wk in ?10°C storage, and 48 wk in ?15°C storage. Sensory chewiness increased initially, then remained constant with storage time except in ?15°C storage. Generally, the lower storage temperature resulted in less sensory chewiness. The correlation coefficients (r) between sensory and objective measurements for tenderness and chewiness were 0.76 and 0.88 (P < 0.05), respectively.     

烫漂及冻藏时间对速冻香椿品质的影响

采用不同的处理方法及冻藏时间对速冻香椿进行试验,结果表明:烫漂和速冻可引起香椿Vc、蛋白质、干物质含量的减少;随着冻藏时间的延长水分、Vc的含量会逐渐减少,蛋白质、干物质的含量会呈现先降后升的趋势。     

Protein changes in shrimp (Metapenaeus ensis) frozen stored at different temperatures and the relation to water-holding capacity

To study the effects of freezing temperature on muscle proteins, shrimp (Metapenaeus ensis) were frozen stored at either −18 or −60 °C up to 90 and 210 days. Shrimp frozen at −18 °C had higher thawing and compression loss and poor myofibril water-holding capacity compared with those frozen at −60 °C. In terms of protein characteristics, shrimp frozen at −18 °C had higher levels of carbonyls and reduced sulphhydryls. Moreover, the shrimp frozen at −18 °C had higher surface hydrophobicity and reduced Ca²⁺-ATPase activity, indicating increased protein denaturation. Proteomics revealed that seventy-five proteins were classified as differentially abundant proteins (DAPs) following freezing. There were sixty-four DAPs in the F18-CON comparison group (shrimp frozen at −18 °C vs. control) and thirty-two DAPs in the F60-CON comparison group (shrimp frozen at −60 °C vs. control), suggesting that freezing at −18 °C results in more DAPs than freezing at −60 °C. A comparison between F18 and F60 revealed that ribosomal proteins (L44, L7a) and heat shock protein 21 were downregulated in F18. These results increase our understanding of the variable quality associated with shrimp frozen at different temperatures.     

Effects of Freezing Rate, Frozen Storage Temperature and Storage Time on Tenderness Values of Beef Patties

All-beef and soy-extended patties were frozen to ?18°C in either 24, 48, 72 or 96 hr and stored at ?23°, ?18° or ?7°C for 6, 9, 12, 18 or 24 months. Freezing produced considerable reductions in both sensory and instrumental measures of tenderness with the effects being greater for the slower freezing rates. Thus, just after freezing, and prior to storage, tenderness was found to be higher in patties subjected to faster freezing compared to slower rates of freezing. Storage at ?7°C reduced sensory scores for tenderness and increased stress in relation to strain during shearing. Extending patties with soy reduced the effects of freezing rate, storage temperature and storage time on tenderness.     

Low-temperature transitions in cod and tuna determined by differential scanning calorimetry

Differential scanning calorimetry measurements have revealed different thermal transitions in cod and tuna samples. Transition temperatures detected at −11°C, −15°C and −21°C were highly dependent on the annealing temperature. In tuna muscle an additional transition was observed at −72°C. This transition appeared differently than the thermal events observed at higher temperatures, as it spanned a broad temperature interval of 25°C. The transition was comparable to low-temperature glass transitions reported in protein-rich systems. No transition at this low temperature was detected in cod samples. The transitions observed at higher temperatures (−11°C to −21°C) may possibly stem from a glassy matrix containing muscle proteins. However, the presence of a glass transition at −11°C was in disagreement with the low storage stability at −18°C during practical time scales. It was proposed that freezing of cod could be associated with more than one glass transition, with a glass transition at a temperature lower than −11°C being too small to be detectable with instrument, yet governing important deterioration processes. In order to optimize frozen storage conditions, the relationship between deterioration processes important for preservation of quality and glass transition temperatures still needs to be established.     

The effect of preliminary processing and period of storage on the quality of frozen Boletus edulis (Bull: Fr.) mushrooms

This paper investigates the effect on the quality of frozen Boletus edulis (Bull: Fr.) mushrooms of blanching or soaking and blanching in aqueous solutions containing combinations of added substances safe for human consumption, or period of frozen storage. During 12 months of storage, sensory evaluations, instrumental colour measurements and chemical analyses of the frozen products were carried out every four months. Based on the results of the sensory evaluation, a maximum storage period of four months was set for the frozen product obtained from unblanched mushrooms. Frozen products having undergone preliminary processing retained good sensory quality for up to 12 months. Soaking, blanching and freezing resulted in the appearance of colours, such as yellow, honey and pink–violet. As a result of freezing, decreases in the contents of thiamine, riboflavin and vitamin C were noted. Blanching in water, as a method of pre-processing, was sufficient for maintaining acceptable sensory quality.     

Influence of pressurised cryogenic nitrogen technology on Arthrospira platensis (spirulina) preservation during storage

In this study, preservation of spirulina using the new pressurised cryogenic nitrogen technology (PCN) was compared to classical methods used in laboratories and industry. Spirulina morphology was better preserved by PCN compared to unpressurised cryogeny and classical freezing at −20 °C that led to cells fragmentation. A 25% loss of Phycocyanin-C content against 60% were measured after 98 days storage for 6-Bar PCN process and frozen samples, respectively. The Total AntiOxidant Power (PAOT Liquid Technology^®) was used for determination of total antioxidant and oxidant power of spirulina extracts. PAOT value of PCN samples was 50% higher than the frozen sample. From ABTS measurements on PCN spirulina fractions sonicated or not, it was suggested that pressurisation at 6 bars allowed a better preservation of free antioxidants (outside the cells) due to replacement of oxygen by nitrogen in the frozen beads. After dehydration, phycocyanin-C content variation during storage at 20 °C and 33% RH showed higher loss for freeze-dried spirulina treated at 0 compared to 6 Bars.     

Effect of freezing and storage on quality factors in Hamburg and leafy parsley

Two types of parsley — the Hamburg cv Berli ska and leafy type cv Paramount — were frozen and stored at temperatures of −20 and −30 °C for 9 months. One half of the material was blanched before freezing and the other half was non-blanched. In 100 g fresh leaves of Hamburg parsley there were 20.0 g of dry matter, 310mg of vitamin C, 7.5mg of β-carotene, 203mg of chlorophyll, 30.8 mg N---NO₃ and 0.078 mg N---NO₂. For the leafy type the corresponding values were 17.3 g, 257 mg, 9.4mg, 68.5mg, and 0.077mg. The material blanched before freezing showed significant losses in the contents of vitamin C (47–51%), nitrates (22–33%), and nitrites (43–55%) and distinctly smaller ones but also significant in the case of dry matter. During freezing and storage of frozen products there were losses in vitamin C, β-carotene, and chlorophyll while the levels of nitrates and nitrites were variable. Particularly great losses of vitamin C and β-carotene were observed in the non-blanched frozen leaves stored at −20 °C. After 9 months' storage, frozen products preserved 10–44% of vitamin C, 37–91% of β-carotene, 78–95% of chlorophyll, and 78–153% of nitrates. Of the types of parsley analyzed the Hamburg type was a better raw material for freezing because of a significantly higher content of vitamin C and chlorophyll and significantly less nitrates in frozen products. When the storage temperature was −30 °C, the blanching of leaves was not necessary, although it helped their pressing into cubes.     

Chemical, Physical, and Sensory Properties of a Sweet Potato French-Fry Type Product During Frozen Storage

Chemical, physical, and sensory properties of a sweet potato Frenchfry type product were determined after 0, 3, 6, 9, and 12 months frozen storage. Analyses included measurements of dry matter, sugars, alcohol insoluble solids, carotene, vitamin C, color, texture and sensory panel scores for color, flavor and texture. Few changes were observed except for an appreciable loss (58%) in vitamin C and an apparent increase in carotene (27%). A partial drying treatment before freezing increased the rate of ascorbic acid loss. For the fried product, no appreciable storage-induced changes were noted in the sensory scores for color, flavor and texture thus indicating that the product had good stability in frozen storage.