食品的低温高压处理技术及其研究进展

文中介绍了低温高压处理技术的基本原理、应用范围和研究进展。在 0～ 6 32 4MPa范围内 ,高压下水的冻结点均较常压下的低 ,并在低于 0℃的温度下形成一个水的不冻结区域。高压还使水的体积收缩、温度升高。低温高压处理技术可应用于食品杀菌和抑酶、高压冻结和高压解冻、低温高压不冻结贮藏。低温高压具有比常温高压更好的杀菌效果 ;高压冻结和高压解冻可缩短食品冻结和解冻的时间、改善冻藏食品的品质 ;低温高压下的不冻结贮藏能更好地保持食品原有的风味和质地     

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。     

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     

高压技术在肉制品加工中的作用

近年来 ,高压技术在食品的贮藏和加工中的应用引起了人们广泛的关注。文中主要介绍高压技术应用于肉类加工时 ,对微生物、肌肉蛋白质、肉的冻结和解冻、肉与肉制品货架期的影响     

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。     

冻结食品的解冻技术

就冻结食品的解冻技术进行了综述。对各种解冻方法的解冻原理及其在食品中的应用做了论述和分析,着重介绍了微波解冻、超声波解冻和高静水压解冻技术。     

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。     

高频解冻的原理及其设备的特点

随着食品工业的发展,冻制品的产量和种类不断增多,工艺上对解冻的要求也越来越高。目前我国冻制品多在空气或水中解冻,解冻的时间长,易导致脂肪氧化等多种品质劣化现象。本文介绍一种能提高冻制品的解冻品质,改善操作环境,且能迅速大量地对冻肉或其他冻制品解冻的高频感应加热解冻设备。1 冻结和解冻对同一食品的冻结和解冻,虽使食品中大部分水分冻结到某一低温所消耗的能量应和其解冻所用的加热能量相等,但解冻的时间是冻结时间的2     

食品原料真空快速解冻的研究

食品原料真空解冻是一种快速解冻方法,可以获得比一般自然解冻(空气或水中解冻)质量高的原料。本文介绍真空解冻的原理和国外真空解冻设备的结构。通过对鱼、肉类块状冻结原料的真空解冻实验,了解其解冻过程的特点、效率、失重和质量。并以传热学的理论分析食品原料在真空解冻过程中热传导的特点。初步确定了应用真空解冻法对我国鱼、肉类块状冻结原料进行解冻的条件和工况,并为设计这种快速解冻设备取得理论依据。     

高压技术在肉品加工中的应用

高压技术是一种新兴的食品处理技术,对高压技术在肉品加工中的应用现状作了阐述,包括高压对肉类品质与功能特性、肉的冷冻和解冻以及贮藏性等方面的影响,并对高压技术在肉类工业中的应用前景作了展望。     

Determination of thermophysical properties of foods under high hydrostatic pressure in combined experimental and theoretical approach

In the present contribution high pressure phase change of food in a 3.4 ml high pressure chamber is investigated by means of numerical simulation and experimental techniques. The researches of freezing and thawing in samples of potato, pork and cod at atmospheric pressure and two high pressure levels up to 200 MPa are carried out. In order to enable numerical simulations at high pressures the comparison with experimental results and determination of thermophysical properties of food were necessary. The numerical model is based on the enthalpy method. Additionally, a dimensional analysis of phase transition is carried out. The results indicate a strong influence of high pressure on the kinetics of phase transition. Thermophysical properties of food at high pressure are determined and discussed.Industrial relevanceKnowledge about thermophysical properties and kinetics of freezing and thawing of food is of major importance for proper planning of industrial food processing and developing new technological processes. The proposed dimensional analysis enable the scale-up and transfer of explored in laboratories processes into the industrial scale.     

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.     

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.     

物理场技术在水产品冷冻冷链中的应用

在冷链流通过程中, 对新鲜水产品进行冷冻处理能够大大提高其保质期。然而, 传统的冷冻和解冻方法有传热效率低、耗时较长的缺陷, 且难以控制冰晶对食品原料的损伤。所以冷冻水产品经常会面临一系列的质量问题, 如质构劣化、蛋白质变性、持水能力下降等。因此有必要采用高效的冷冻/解冻技术以防止品质劣变。相比于传统方法, 基于物理场(如高压、超声、电场等)的新型冷冻和解冻技术具有高冷冻/解冻速率、低能耗、对产品品质维持更好等优点。本文综述了近年来物理场技术在水产品中的应用, 分析了它们各自的原理、特点、缺陷及未来的发展趋势, 为这些新技术在水产品冷冻冷链中的应用提供相关参考。     

超高压处理对鸡肉品质影响的研究进展

超高压是超过100MPa的压力,作为一种新型的食品加工技术,超高压具有抑菌、改善肉质、节能等优点。本文综述超高压处理对鸡肉的色泽、嫩度、脂肪氧化、微生物及冻结和解冻等方面的影响。     

食品超高压处理过程中传热模型和相转变的研究进展

食品超高压处理技术是食品领域的一项新技术,在食品工业中的应用越来越广泛.但目前超高压处理过程中食品的温度分布和传热模型仍未研究清楚,采用数学方法对食品超高压处理过程中的传热现象进行模拟可以有效地均匀化和优化超高压处理条件,这对于实际生产具有指导意义.本文综述了食品在超高压处理过程中的传热模型和相转变的研究进展,对超高压低温条件下的冻结和解冻过程也进行了讨论.     

Quality and safety characteristics of bread made from frozen dough

During the last few years, consumers and buyers are becoming increasingly aware of the importance of safe and high quality food products. Interest becomes greater since new products are introduced to the market and modern technologies are being used even in the production of traditional or conventional food products (use of freezing in bakery products). The objective of this work is to examine the factors, which influence the safety and quality characteristics of bread made from frozen dough. A common bread formula consists of wheat flour, water, active dry yeast, salt, sugar, margarine and ascorbic acid while the breadmaking procedure usually involves dough preparation, freezing, thawing and baking. For each ingredient, the main safety and quality parameters, the storage conditions and the requirements for specific use are presented and the potential microbiological, chemical or physical hazards throughout the breadmaking procedure are determined according to HACCP procedure. Finally, consideration is given on how raw material/dough characteristics (water content, pH, initial spore count etc.), and processing parameters, such as freezing time, temperature and duration, baking time and temperature affect bread quality and how they can ensure the safety of the final product.