反复冻结-解冻对黄鳍金枪鱼肉品质的影响

为了研究反复冻结-解冻对金枪鱼品质的影响,对金枪鱼(分别贮藏于-60℃和-18℃)做4次冻结-解冻处理后测定理化指标[解冻汁液流失,红度值a*,质构特性(包括硬度,咀嚼性,黏着性和弹性)],挥发性气味成分(电子鼻),菌落总数。结果表明:随着冻结-解冻次数增加,解冻汁液流失增加,-60℃下汁液流失更多;-18℃贮藏a*值显著降低,-60℃下降趋势不明显;硬度,咀嚼性和弹性都显著降低,然而黏着性变化不大;-60℃相对-18℃贮藏下反复冻结-解冻后挥发性气味差异较显著;菌落总数变化不明显,且在安全范围内。因此,金枪鱼贮藏加工、运输和贮藏过程中保持温度的稳定要避免温度反复波动,且-60℃是作为维持品质的较佳贮藏温度。     

高压冷冻食品的机理及应用

讨论了高压水的相行并以此说明了高压食品冻结和冷冻的机理,重点介绍了压控相转变在食品冻结和解冻中的应用,对食品高压冻结和解冻研究现状进行了综述,分析了目前存在的主要问题,指出了今后研究的主攻方向.     

超高压与低温协同作用对黄花鱼品质影响的研究

食品的高压与低温协同处理是近年来发展的一种新工艺.以黄花鱼为实验原料,进行了高压辅助冻结、高压转移冻结、高压诱导冻结以及高压辅助解冻过程的超高压与低温协同处理的实验研究,考察了经超高压与低温协同处理作用对鱼肉品质和微生物灭活情况的影响.研究结果表明,该工艺相比于常规冷冻与解冻具有明显优势,其中以高压转移冻结的效果最为明显;鱼肉品质得到提高、质地和微观组织得到改善,并且汁液损失减少,同时对微生物的灭活也有显著的作用.     

冻结食品:温度、压力与冷藏保鲜技术

本文介绍了国际上近年来新开发的急速冻结、真空冷冻干燥,高压不冻冷藏、高压解冻、高压速冻等几种新的冷冻保鲜技术。同时简述了温度、压力与食品冷冻保鲜的关系。     

冷却和冷冻食品按贮藏温度分类及其特点——冷藏的新温度带

<正> 食品的低温贮藏可分为冷却贮藏(Cooling storage)和冻结贮藏(freezing storage),两者最大的区别在于食品内是否有冰存在,冻结贮藏处于冻结状态。鱼、肉和果蔬等新鲜食品的冰点大多为0～-1℃,在此温度范围内,食品开始冻结,因此冷却贮藏温度带     

食品在高压静电场中冻结、解冻的实验研究

微能源在食品工业中的应用日益广泛,本文以马铃薯为研究对象,研究了不同场强对食品冻结,解冻过程和解冻后质量的影响,主要考察冻结曲线,解冻曲线、质地特性,液汁流失几方面。研究发现高压直流电场场强对马铃薯冻结过程,及其以后的无电场解冻过程,冻结食品在电场下解冻过程都有很大影响。不同场强对马铃薯解冻后的质地特性、液汁流失影响较小。     

不同冻结速度对食品质量的影响

食品的贮藏方法很多, 然而国内外都是以冷冻为主, 冷冻贮藏在低温条件下, 既能保持高质量的产品品质, 又不会使食品受到污染, 因此得到了广泛应用. 然而食品在冻结过程中存在着不同程度的物理变化、组织变化和化学变化, 致使冻结食品的风味、食味下降.食品冻结速度, 按时间划分通常是指食品中心温度以30分钟之内通过冰结晶最大生成带, 即从-1℃降到-5℃, 称为快速冻结; 反之, 超过30分钟通过冰结晶生成带的为     

冻肉通电加热解冻的研究

解冻是使冻结物料融解恢复到冻结前的新鲜状态。由于冻结物料在自然环境中亦能融解，所以解冻问题往往容易被忽视。从保持解冻物料的新鲜程度不至变化太大的角度出发，尽可能地缩短解冻过程的时间将是非常重要的。这是由于冻解物料，如食品原料在解冻升温过程中细菌随之大量繁殖，引起物品腐败和品质下降。与此同时，食品原料中营养成分随化冻的水流失等。在食品加工行业，如罐头厂、肉联厂等需要大量冻结食品作原料时，尤应注重大块冻结肉的解冻工艺。本文对冻肉通电加热解冻的方法进行了实验研究，给出了通电加热解冻     

不同解冻方式对小黄鱼品质的影响

采用5种不同的解冻方式(静水解冻、流水解冻、微波解冻、低温空气解冻、超声波解冻)对普通冻结和液体浸渍快速冻结处理的小黄鱼进行解冻,对解冻时间、色泽、质构、丙二醛含量、总巯基含量等指标进行测定比较,并测定解冻后鱼肉的硬度、咀嚼性等质构指标。结果表明:5种解冻方式中微波解冻速率最快,低温空气解冻速率最慢。对于快速冻结和普通冻结处理的小黄鱼,超声波解冻能够有效维持解冻后鱼肉的品质。     

高压低温杀菌装置

日本味之素公司研制的高压低温杀菌装置可在6 0℃时 ,使用 6 .0 78× 10 5Ｐａ的压力对食品进行杀菌处理 ,即可把霉菌和芽孢杆菌的数量减少到原先的1/ 10 5,且不破坏食品组织的状态。而一般杀菌方法 ,须把食品加温到 12 0℃ ,并至少持续 30ｍｉｎ ,不仅使食品原有结构受损 ,而且降低了营养价值高压低温杀菌装置     

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.     

PRESSURE-ASSISTED FREEZING AND THAWING: PRINCIPLES AND POTENTIAL APPLICATIONS

The phase diagram of water as a function of temperature and pressure delimits distinct crystalline ice forms with different specific volumes, melting temperatures, and latent heats of fusion. The melting temperature of ice I decreases to -22°C when pressure increases to 207.5 MPa. It is possible to freeze a biological or food sample under pressure (obtaining ice I, III, V, VI, or VII), to enhance ice nucleation by fast pressure release, to keep a sample at subzero temperatures without ice crystal formation, to generate pressure through freezing, to reach the glassy state of water by fast cooling under pressure, or to thaw a frozen sample under pressure below 0°C. Fast pressure release from -10 or -20°C and 100 or 200 MPa (with a prior cooling step under pressure), called “pressure-shift freezing,” induces significant supercooling (as detected by fast data acquisition) and enhances uniform ice nucleation throughout the sample. When freezing is then completed at atmospheric pressure, different microscopy techniques reveal numerous small ice crystals with no specific orientation or marked size gradient. Crystals are smaller in pressure-shift frozen gels than in similarly frozen oil-in-water emulsions. In the latter, increasing solute concentrations in the aqueous phase tends to reduce ice crystal size. Modeling is proposed for pressure-shift freezing, although the supercooling and nucleation steps are not taken into account. Both freezing under various pressure levels and pressure-shift freezing are reported for gels (mainly heat-induced protein gels), emulsions, and plant and animal tissues. In spite of some discrepancies, gel or tissue structure and texture are generally better maintained after thawing, as compared to control samples frozen by air blast or immersion in a cooling medium at 0.1 MPa. Less liquid exudation is also observed. However, some protein denaturation is detected (unfolding of myofibrillar proteins, toughening of meat or seafood), especially when the initial cooling step is carried out at a high pressure level for a long time. Pressure application at subzero temperature is found to inactivate only some enzymes, but causes a significant degree of microbial inactivation for several species of micro-organisms. Freezing gels or vegetables under pressure with the formation of ice III, V, or VI appears to maintain tissue structure and texture, but the mechanisms for these effects are not fully understood. Pressure-assisted thawing markedly enhances the rate of thawing, mainly due to a greater ΔT between the subzero thawing temperature and that of the heating medium. Specific packaging and equipment requirements for pressure-assisted freezing and thawing are discussed. Suggestions are made for further studies on high pressure-subzero temperature treatments, such as the influence of sample size and composition; the effects on cell membranes; the reduced need for blanching before freezing; the viability of pressure-shift frozen cells, embryos, or organs; the mechanisms of protein denaturation; and texture-promoting effects, especially in ice creams.     

PRESSURE-ASSISTED FREEZING AND THAWING: PRINCIPLES AND POTENTIAL APPLICATIONS

The phase diagram of water as a function of temperature and pressure delimits distinct crystalline ice forms with different specific volumes, melting temperatures, and latent heats of fusion. The melting temperature of ice I decreases to ?22°C when pressure increases to 207.5 MPa. It is possible to freeze a biological or food sample under pressure (obtaining ice I, III, V, VI, or VII), to enhance ice nucleation by fast pressure release, to keep a sample at subzero temperatures without ice crystal formation, to generate pressure through freezing, to reach the glassy state of water by fast cooling under pressure, or to thaw a frozen sample under pressure below 0°C. Fast pressure release from ?10 or ?20°C and 100 or 200 MPa (with a prior cooling step under pressure), called “pressure-shift freezing,” induces significant supercooling (as detected by fast data acquisition) and enhances uniform ice nucleation throughout the sample. When freezing is then completed at atmospheric pressure, different microscopy techniques reveal numerous small ice crystals with no specific orientation or marked size gradient. Crystals are smaller in pressure-shift frozen gels than in similarly frozen oil-in-water emulsions. In the latter, increasing solute concentrations in the aqueous phase tends to reduce ice crystal size. Modeling is proposed for pressure-shift freezing, although the supercooling and nucleation steps are not taken into account. Both freezing under various pressure levels and pressure-shift freezing are reported for gels (mainly heat-induced protein gels), emulsions, and plant and animal tissues. In spite of some discrepancies, gel or tissue structure and texture are generally better maintained after thawing, as compared to control samples frozen by air blast or immersion in a cooling medium at 0.1 MPa. Less liquid exudation is also observed. However, some protein denaturation is detected (unfolding of myofibrillar proteins, toughening of meat or seafood), especially when the initial cooling step is carried out at a high pressure level for a long time. Pressure application at subzero temperature is found to inactivate only some enzymes, but causes a significant degree of microbial inactivation for several species of micro-organisms. Freezing gels or vegetables under pressure with the formation of ice III, V, or VI appears to maintain tissue structure and texture, but the mechanisms for these effects are not fully understood. Pressure-assisted thawing markedly enhances the rate of thawing, mainly due to a greater ΔT between the subzero thawing temperature and that of the heating medium. Specific packaging and equipment requirements for pressure-assisted freezing and thawing are discussed. Suggestions are made for further studies on high pressure–subzero temperature treatments, such as the influence of sample size and composition; the effects on cell membranes; the reduced need for blanching before freezing; the viability of pressure-shift frozen cells, embryos, or organs; the mechanisms of protein denaturation; and texture-promoting effects, especially in ice creams.     

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.     

Minimizing texture loss of frozen strawberries: effect of infusion with pectinmethylesterase and calcium combined with different freezing conditions and effect of subsequent storage/thawing conditions

Vacuum infusion (VI), freezing, frozen storage and thawing conditions were optimized in order to minimize the texture loss of frozen strawberries. Slow freezing caused severe loss in textural quality of the strawberries. This quality loss could not be prevented by the application of VI prior to slow freezing, or by the application of rapid, cryogenic or high-pressure shift freezing conditions on non-infused fruits. A remarkable texture improvement was noticed when infusion of pectinmethylesterase (PME) and calcium was combined with rapid or cryogenic freezing. The highly beneficial effect of PME/Ca-infusion followed by HPSF on the hardness retention of frozen strawberries was ascribed to the combined effect of the infused PME (53% reduction in degree of esterification (DE) of the strawberry pectin) and the high degree of supercooling during HPSF. During frozen storage, textural quality of PME/Ca-infused high-pressure frozen strawberries was maintained at temperatures below −8 °C, whereas the texture of PME/Ca-infused strawberries frozen under cryogenic freezing conditions was only preserved at temperatures below −18 °C. Thawing at room temperature seemed to be an appropriate method to thaw strawberries. Fast thawing by high-pressure induced thawing (HPIT) did not prevent textural quality loss of frozenstrawberries.     

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.     

Recent developments in novel freezing and thawing technologies applied to foods

This article reviews the recent developments in novel freezing and thawing technologies applied to foods. These novel technologies improve the quality of frozen and thawed foods and are energy efficient. The novel technologies applied to freezing include pulsed electric field pre-treatment, ultra-low temperature, ultra-rapid freezing, ultra-high pressure and ultrasound. The novel technologies applied to thawing include ultra-high pressure, ultrasound, high voltage electrostatic field (HVEF), and radio frequency. Ultra-low temperature and ultra-rapid freezing promote the formation and uniform distribution of small ice crystals throughout frozen foods. Ultra-high pressure and ultrasound assisted freezing are non-thermal methods and shorten the freezing time and improve product quality. Ultra-high pressure and HVEF thawing generate high heat transfer rates and accelerate the thawing process. Ultrasound and radio frequency thawing can facilitate thawing process by volumetrically generating heat within frozen foods. It is anticipated that these novel technologies will be increasingly used in food industries in the future.     

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.     

冻结和解冻过程对水产品品质的影响

冻结是水产品保鲜的一种有效的方法,冻结后的水产品一般会进行冻藏。影响冻品质量的因素很多,主要有冻结速率、冻藏温度、解冻速率、冻藏中温度波动、冻结-解冻循环次数等。本文在简要介绍食品的冻结解冻方法的基础上,综述了冻结解冻过程对水产品物理、化学特性的影响。