静电场对冷冻食品冰晶生长影响的相场法模拟

目的:探究外加静电场对食品冷冻过程中冰晶生长的影响规律.方法:基于相场法中经典的Kobayashi模型,将电场自由能密度引入相场模型,采用有限差分法五点差分格式离散偏微分方程,编程实现了冰晶生长的模拟及可视化.结果:模拟结果和其他模拟结果以及试验结果呈现的冰晶组织特征一致,冰晶形态具有典型的六重对称性;随着电场强度的增...     

冰晶生长对冷冻水产品品质影响及新型冷冻方式研究进展

冷冻技术在水产品保鲜方面应用广泛,但水产品在冻结过程中受冰晶形成、晶体生长与冰晶重结晶的影响,易造成细胞结构的破损,导致水产品品质下降。为深入分析冰晶生长与水产品品质变化间的关系,该文总结了冰晶生长对水产品的蛋白质变性、脂肪氧化、持水力、质构及感官特性影响,综述了物理场辅助冻结及添加抗冻剂、重结晶抑制剂等减小冰晶尺寸的新方法,为控制冰晶生长及提高冷冻水产品品质提供了理论参考     

果汁冷冻浓缩过程中冰晶形成规律的研究

本研究测定了橙汁和菠萝汁的冰点曲线,并以此探讨在果汁冷冻浓缩时水分冻结率的变化规律。结果表明,果汁在开始冻结的温度附近结冰率变化最大;以后逐渐减慢。橙汁和菠萝汁的最大冰晶生成区分别是-0.8～-7.9℃和-0.7～-6.7℃。冷却介质温度越低,冰晶的生长速度越快,但最终冰晶尺寸越小。当介质温度为-10℃左右时,可获得较大的冰晶尺寸。本文也研究了搅拌作用及果汁预处理因素对冰晶生长的影响。     

超声辅助冷冻技术的作用机制及其对食品品质影响的研究进展

冷冻是一种重要的食品保藏技术,但冻结也会引起食品品质的变化。作为一项高新加工技术,超声辅助冷 冻技术可以加快冷冻速率,减小冰晶的尺寸,进而改善冷冻食品的品质。本文主要论述了超声辅助冷冻技术的作用 机制及对冰结晶形成的影响,同时综述了超声辅助冷冻技术对食品品质的影响及食品冷冻中常用的工艺参数。最 后,展望了超声辅助冷冻技术的发展方向,为超声辅助冷冻技术在食品中的应用提供理论支持。     

超声波辅助渗透脱水处理及其对西兰花冻结品质的影响

以西兰花为试材,在单因素试验的基础上,以水分流失和西兰花冻结-解冻后硬度为考察指标,通过正交试验优化西兰花冷冻前超声波辅助渗透脱水工艺条件。结果表明,渗透脱水最佳工艺条件为:超声波功率240 W,超声时间30 min,渗透液质量分数50%,在此工艺条件下,西兰花的水分流失为1.26,硬度为39.59 N。在此工艺条件的基础上,对比了普通渗透脱水(OD)和超声波辅助渗透脱水(UOD)对西兰花冻结效率和品质的影响。结果表明:UOD可以在短时间内达到OD较长时间的渗透效果,提高西兰花的冷冻效率,减少西兰花冻藏期的汁液流失,抑制抗坏血酸含量的减少以及色泽的变化。     

水产品冻结贮藏中冰晶的形成及控制研究进展

冻结贮藏是目前水产品保藏的重要方式,最大程度地保留了水产品的新鲜程度。而冻结贮藏的过程中冰晶的生成会对水产品品质产生破坏,影响风味和质构。冻品再解冻又会导致大量汁液流失。本文对冰晶形成的机理进行探讨,分析影响冰晶生成的因素,并介绍目前控制水产品冰晶形成的一些方法。影响冰晶形成的因素有冻结速率、冻结温度、温度波动等,控制冰晶形成的方法有微冻、压力转移冻结等。     

超声波对毛豆浸渍冷冻过程的影响

研究超声波功率、超声波作用时间、超声波脉冲值对提高毛豆仁浸渍冷冻速率的影响.通过响应面分析可知在载冷剂温度为-20℃下超声波辅助浸渍冷冻的最佳工艺参数:超声波功率为58 W,超声波作用模式为50%,超声波作用时间为0.7 min,解冻后毛豆仁质构(硬度)和持水力分别为6.05 kg/cm~2和92%.     

冷冻面条在低温贮藏过程中化学组分的变化

研究不同冻藏时间内面条中的麦谷蛋白、麦醇溶蛋白、SDS可溶性麦谷蛋白、GMP(麦谷蛋白大聚体)、直链淀粉、α-淀粉酶、还原糖和总戊聚糖含量等主要化学组分的变化,初步探讨了冷冻面条食用品质下降的机理。结果表明,随着冻藏时间的延长,麦醇溶蛋白、GMP含量、直链淀粉、戊聚糖含量呈下降趋势,SDS可溶性麦谷蛋白含量呈上升趋势,a-淀粉酶、还原糖含量呈先上升后下降趋势。     

超声波对蔗糖溶液中树枝冰晶生长速度的影响

为了阐明超声波抑制冰晶生长的机理,运用自制的超声波冷却实验台分别研究了超声波对脱气蔗糖稀溶液与未脱气蔗糖稀溶液中树枝冰晶生长的影响。结果显示:超声波对脱气蔗糖稀溶液与未脱气蔗糖稀溶液中树枝冰晶生长速度均有抑制作用,但未脱气蔗糖溶液中树枝冰晶的生长速度要大大低于脱气蔗糖溶液中树枝冰晶的生长速度。这表明超声波在溶液中引起的空化效应是抑制冰晶生长的主要因素。     

Dendritic growth of ice crystals during the freezing of beef

The morphology adopted by ice in frozen tissues is accepted as one of the factors responsible for freezing damage. For this reason ice nucleation and growing mechanisms have been extensively studied. However, under the conditions used in the industry, where important temperature gradients exist, the classical analysis of nucleation and growth, depending on the supercooling, is complicated by the dendritic growth of crystals as well as by the possibility of the location of the ice crystal inside or outside the cells. In the present paper experiments which verify the existence of dendritic ice growth during the freezing of beef are described. The dendritic growth rate of ice in beef is measured as a function of the supercooling and an analysis of the expected mechanism, according to freezing conditions, is also provided.     

Control of ice crystal nucleation and growth during the food freezing process

Freezing can maintain a low-temperature environment inside food, reducing water activity and preventing microorganism growth. However, when ice crystals are large, present in high amounts, and/or irregularly distributed, irreversible damage to food can occur. Therefore, ice growth is a vital parameter that needs to be controlled during frozen food processing and storage. In this review, ice growth theory and control are described. Macroscopic heat and mass transfer processes, the relationship between the growth of ice crystals and macroscopic heat transfer factors, and nucleation theory are reviewed based on the reported theoretical and experimental approaches. The issues addressed include how heat transfer occurs inside samples, variations in thermal properties with temperature, boundary conditions, and the functional relationship between ice crystal growth and freezing parameters. Quick freezing (e.g., cryogenic freezing) and unavoidable temperature fluctuations (e.g., multiple freeze–thaw cycles) are both taken into consideration. The approaches for controlling ice crystal growth based on the ice morphology and content are discussed. The characteristics and initial mechanisms of ice growth inhibitors (e.g., antifreeze proteins (AFPs), polysaccharides, and phenols) and ice nucleation agents (INAs) are complex, especially when considering their molecular structures, the ice-binding interface, and the dose. Although the market share for nonthermal processing technology is low, there will be more work on freezing technologies and their theoretical basis. Superchilling technology (partial freezing) is also mentioned here.     

Effect of cytoskeleton on ice crystal growth in cells during freezing

The factors affecting intracellular ice formation (IIF) and growth is essential to the mechanistic understanding of cellular damage through freezing. In the aid of high speed and high-resolution cryo-imaging technology, the broad bean intracellular ice formation and growth processes were successfully captured during freezing. Cytochalasin B（CB）was used to solubilize the cytoskeleton. Images of IIF were compared between cells with and without cytoskeleton. The behavior of intracellular ice crystal formation in plant tissues with or without CB was evaluated using changes of cell areas, the probability of crystallization, and growing rate of intracellular ice crystal. Moreover, light intensity figures were used to determine cell damage. This study showed that the cytoskeleton was involved in ice crystal nucleation mechanism during freezing responses of the plant cells.     

速冻食品的冰晶形态及辅助冻结方法研究进展

文章简述了食品速冻技术以及不同冻结速度下形成的冰晶形态及观测冰晶的方法,综述了压力辅助冻结、电场辅助冻结以及磁场辅助冻结等技术在近几年的研究进展。直接法能直接观察到冻结过程形成的冰晶,而间接法则是通过观察冻结后冰晶在食品内部留下的间隙来分析冰晶特征。压力辅助冻结能提高过冷度,在压力释放时水分瞬间冻结,使形成的冰晶细小且分布均匀;电场辅助冻结能降低成核温度促使形成更小尺寸的冰晶;磁场辅助冻结能增强氢键抑制冰晶的生长,3种辅助冻结方式有利于提高冷冻食品的品质,具有良好的应用前景。     

Effect of static electric field on ice crystal size reduction during freezing of pork meat

The objective of this research was to evaluate the influence of static electric field (SEF) on the freezing of pork meat (pork tenderloin muscle) with respect to the size of ice crystal formulation. The results showed that by increasing the strength of the static electric field, the degree of supercooling was reduced. The measured degree of supercooling varied from 3.93 ± 1.3 °C to 1.92 ± 1.45 °C for the control and the frozen sample under 12 kV SEF, respectively. Meat microstructure was investigated after Carnoy fixation of the frozen tissues. The overall relative surface of the ice crystals was unchanged. The average equivalent circular diameter of the ice crystals was significantly reduced with increasing SEF; values from 32.79 ± 4.04 μm for the control to 14.55 ± 8.20 μm for the sample frozen at the maximum magnitude electric field which was tested were observed respectively. These findings demonstrate clearly the advantage of freezing under SEF which appears as a promising and innovative freezing process for food systems.Industrial relevanceThe reduction of freeze damage exerted to any tissue undergoing freezing remains a challenge. The mechanical and biochemical stress caused by the ice crystals to the cellular membranes results in irreversible tissue damage. Freezing under static electric field (SEF) has been identified as a possible means to reduce the size of ice crystals during freezing of biological tissues. In the present study SEF was applied during freezing of pork meat. Our results indicate that the size of the formed ice crystals was significantly reduced under SEF freezing leading to a lower damage on the microstructure of meat. This paper describes an innovative freezing process that could be used in order for higher quality frozen products to be produced.     

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.     

A novel technique to control ice cream freezing by electrical characteristics analysis

The freezing process is very important in ice cream production affecting quality, taste and yield of the finished product. Batch freezer machines use different control techniques to tightly control the freezing process, based on monitoring of the temperature and/or the viscosity (i.e. consistency) of the product. Temperature control, however, features low sensitivity and need calibration for different product compositions, while product viscosity is essentially inferred from dasher motor load, sensitive to power line fluctuations, volume of product and dasher motor characteristics. In this context, this paper presents a novel technique based on measurements of the product electrical characteristics, tightly linked to temperature and viscosity. The experimental results presented in this work clearly indicate that the proposed technique provides a suitable, nondestructive tool to monitor ice cream quality product that overcomes the drawbacks of the standard methods, thus representing an advance in the state of the art for freezing control.     

冻结方式对凡纳滨对虾贮藏中组织冰晶及品质的影响

新鲜凡纳滨对虾采用液氮、平板及冰柜冻结结合-20 ℃贮藏,研究不同贮藏时间内其组织冰晶形态与品质变化,以评价出最优的冻结方式。结果显示,随着贮藏时间的延长,平板及冰箱冻结的盐溶性蛋白含量、持水性、感官评分显著降低(p<0.05);而液氮冻结形成的冰晶直径比平板速冻小1/3,比冰箱小1/2;冻结后贮藏180 d其挥发性盐基氮(TVB-N值)≤25 mg/100 g,硫代巴比妥酸值(TBA)仅为0.72 mg/100 g,有效抑制了虾肉肌原纤维蛋白变性及脂肪氧化,能较好维持肌肉组织形态和品质,从而使虾肉的货架期延长至180 d以上。