超声波辅助冷冻技术及其在食品中的应用

冷冻是实现食品长期贮藏保鲜的主要手段,冷冻过程中水分的成核与结晶决定着食品冷冻效率和冷冻食品的质量。超声波辅助冷冻作为一种新型的冷冻技术,能在食品冷冻过程中有效地诱导成核并控制结晶过程,提高冷冻食品质量,引起研究者的广泛关注。该文介绍超声波辅助冷冻机制、冷冻效果的影响因素,总结超声波辅助冷冻技术在水产品、果蔬、肉类等食品冷冻加工中的应用研究进展,为超声波辅助冷冻技术在食品领域的深入研究和推广应用提供参考和借鉴。     

食品乳状液冻融稳定性的研究进展

文中详细分析了食品乳状液冻融过程中的失稳机理,特别是油水两相在冷冻过程中的结晶化特点,并总结了影响乳液冻融稳定性的因素及改善方法,如控制油相和水相组成、控制冷冻速率和合理设计乳液组成等。     

冷冻对肉质量的影响

冷冻在商业上的应用对于肉的食用质量和货架期都产生了极大的影响 ,尤其是猪肉。冷冻是保存易腐烂食品的一种普遍而且最有效的方法 ,如果对食品正确的冷冻 ,冷藏过程本身不会引起食品质量的变化 ,而且比较安全卫生。消费者对冷冻食品的质量有许多误解 ,消费者需要认识到冷冻食品的质量、外观、味道和营养 ,确实可与新鲜食品媲美。1　冷冻速度的影响冷冻速度对肉品质量最明显的影响是与冷冻期间形成的冰晶体大小有关。当温度降到冰点以下时 ,在“结晶核”周围形成大量的冰晶 ,慢速冷冻使先形成的冰晶增大 ;温度下降得越快 ,形成的结晶核越多 …     

超声波辅助冷冻技术作用机理及在冷冻食品中的应用

结晶过程中冰晶的形状、大小及粒径分布和解冻过程中的解冻时间是影响冷冻食品品质的主要因素。超声波辅助冷冻技术作为一项新兴的冷冻技术得到广泛的研究,且研究表明超声波对结晶过程和解冻过程都有积极的影响。本文主要阐述超声波辅助冷冻技术中超声波影响冰晶形成过程的作用机制,主要涉及超声波对晶核形成、冰晶大小和粒径分布的影响;从冷冻食品的冷冻、解冻、无损检测3个方面介绍了超声波在冷冻食品中的应用。     

食品冷冻理论和技术的进展

冷冻贮藏对食品保藏和运输具有重要意义,冷冻食品加工行业发展势头良好,与食品冷冻相关的理论与技术也有长足的进展。本文介绍了与食品冷冻过程相关的传递、玻璃化转变和冰结晶理论的现状和进展,指出由食品物料及其在冷冻过程变化的特殊性所引起的建立系统的食品冷冻理论的复杂性;综述了超声强化冷冻、高压冷冻、冷冻蛋白技术、CAS冻结系统和冰温技术的简要原理,及其在食品行业的应用进展。     

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。     

甜蜜的陷阱 警惕糖尿病

控制冷冻食品冰结晶的生成和长大迄今为止是一项较难完成的课题。为解决这项难题，不冻蛋白质已被食品工业界寄以很大的期望。不冻蛋白质不仅使冰点降低，而且对冷冻贮藏和解冻过程中的再结晶有阻止作用，从而防止了冰晶的增大；这无疑是对冷冻食品延长贮藏期和提高产品质量，特别是提高冰淇淋口感质量有划时代意义的突破性研究成果，具有科学研究和生产实践两方面的积极意义。开创了冷冻食品业界提高产品质量的全新局面。     

肉类冷冻理论与冷冻新技术

介绍了肉类冷冻的主要理论,包括传递理论、玻璃化转变理论和冰结晶理论;对目前出现的冷冻新技术如高压冷冻技术、超声冷冻技术、冰核细菌冷冻蛋白技术、CAS冻结系统和减压冷冻技术进行了综述。     

水-冰-水动态变化引起冷冻肉类食品品质变化机理及控制技术研究进展

低温冷冻是最古老、应用最广泛和最经济有效的肉类食品保鲜方法,但肉类食品经过冻结、冻藏和解冻后,其中80%的水分经历水-冰-水两次相变,冰晶的形成以及后续冰晶的融化会破坏肌细胞结构,使肌肉主要成分如蛋白质和脂肪发生氧化,导致冷冻肉类食品保水性降低、颜色变暗、组织软塌和营养价值减少或丧失。因此,本文拟从水-冰-水动态变化角度概述冰晶的形成和生长过程（冰晶的成核、生长和重结晶）;分析不同温度和过饱和度下冰晶的形态、冻融引起肌肉中发生水-冰-水动态变化的过程;重点综述水-冰-水动态变化迫使冷冻肉微观结构、保水性、氧化稳定性（脂肪氧化、蛋白质氧化和构象改变）以及感官品质（质构、色泽和风味）发生劣变的机理;简述目前一些提升冷冻肉类食品品质的新兴冷冻技术（超声波技术、高压技术、电磁场技术以及添加抗冻剂）,为提高冷冻肉类食品品质及工业化生产提供科学理论依据。     

新型食品添加剂——不冻蛋白质的研究开发及应用的新进展

控制冷冻食品的冰结晶的生成和长大迄今为止是一项较难完成的课题。为解决这项难题，不冻蛋白质已被食品工业界寄以很大的厚望。这种不冻蛋白质不仅是冰点降低，而且对冷冻贮藏和解冻过程中的再结晶有竭力阻止作用，从而防止了冰晶的增大。这无疑是对冷冻食品延长贮藏期和提高产品质量，特别是提高冰淇淋口感质量有划时代意义的突破性研究成果，具有科学研究和生产实践两方面的积极意义，开创了冷冻食品业界提高产品质量的全新局面。     

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.     

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.     

Freeze-drying of cooked beef—some effects of freezing rate and freezing method

Summary. Results are given from comparative freeze-drying experiments studying the effects of freezing rate and of so-called thermal treatment on drying rate, water uptake and general quality of freeze-dried cooked beef. Unlike raw meat, cooked beef appeared to be little affected by freezing rate in connection with freeze-drying, except for markedly poorer appearance in the dried condition for the very slowly frozen product. Thermal treatment seemed to have no positive effect on drying rate or quality.     

白灵菇液氮速冻工艺研究

采用喷雾式流态化液氮速冻及缓冻,探讨了选用不同的筛板、风速和食品层高时,白灵菇的流化状态,冻结速率与解冻后冻品汁液流失率之间的关系等.结果表明:选用开孔率为50%,孔径为5mm的筛板,用3.0m/s的循环风速对床层高度为7cm的新鲜白灵菇进行流态化速冻效果最佳;建议采用-60℃以下温度进行冻结,冻品在-26℃冰箱中贮藏9个月后,解冻时的汁液流失率低于4.9%.     

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.     

葡萄酒冷冻过程的管理

葡萄酒的冷冻处理过程是通过冷冻机组和冷冻罐来实现的,通过冷冻处理,可以除去葡萄酒的一部分酒石酸盐和色素等物质,使葡萄酒更加稳定,并改善葡萄酒的感官质量.在冷冻处理过程中,首先是使酒温尽快达到冷冻温度(约-5℃),而酒温降低的速度与待冷冻酒的数量与酒温、冷冻机组的制冷量、冷冻罐的结构等有关,采用相同的冷冻设备,酒温降低的速度由待冷冻酒的数量与酒温决定.     

One-stage model of foods freezing

The freezing process in a NaCl eutectic solution is discussed taking into account both a non-constant specific heat and a non-constant thermal conductivity as potential functions of temperature. The non-linearity of the problem is introduced in the heat diffusion equation and in its boundary conditions. A strictly exact solution is used to solve it. By considering only conduction heat transfer mechanisms with phase-change, the simple analytical solutions common to these types of substances are obtained. Different characteristic parameters related to the freezing process are included, such as the movement of the interface boundary and the freezing time. Furthermore, some experiments were carried out for comparison with the theoretical model.     

Large batch freezing of bull semen: effect of time of freezing and fructose on fertility

Large-scale batch freezing of bull semen should be done in a processing schedule that yields the highest fertility and when it can be fitted efficiently into the work schedule. Conflicting reports have appeared on survival and fertility of bull sperm frozen within a few hours of semen collection or on the next day. To study this problem, a factorially arranged experiment with semen from 10 bulls was conducted, comparing whole milk-glycerol semen extender with and without fructose, and semen frozen in 0.5-ml straws after 4 versus 18 h of equilibration at 5 degrees C. Both fructose and 18 h of equilibration resulted in a small but significant improvement in freeze-thaw survival of sperm. A field trial followed with replicated semen collections from nine bulls processed in a whole milk-glycerol control extender frozen after 4 h of equilibration versus the addition of 1.25% (wt/vol) fructose to whole milk glycerol divided to freeze sperm after 4 and 28 h of equilibration. Semen from these bulls was used to inseminate 14,775 first-service cows. The 56-d nonreturn rates obtained for these three treatments were 74.7, 74.3, and 73.9%, respectively. As there was no difference in fertility, it would appear that programs to freeze sperm in whole milk extenders the same day of collection or the day after semen collection should yield equivalent results.     

新式冰淇淋凝冻和包装系统

<正> 冰淇淋的冻结凝固过程决定了制品应有的型态和膨松程度。配料混合物经过搅拌均质和杀菌后,随即进行快速的凝冻,使其所含水分结成细微的结晶,形成冰淇淋应有的状态。与此同时,随着黏度的提高,与搅入的空气相混合,制品的容积会不断增大,达到膨松的效果。     

冷冻酸奶生产工艺的研制

冷冻酸奶又称酸奶冰淇淋,是当今社会发展最快的一种具有保健作用的冷饮品。论述了冷冻酸奶的生产工艺及两种冷冻酸奶的生产配方与要求,以适应冷饮市场上升的趋势与活力,满足人们的消费需求。