不同冷冻方式下猪肉贮藏期持水力的变化

采用浸渍冷冻(-35℃)与风冷冷冻(-35℃)两种方法,将猪背长肌中心温度从10℃分别降到-5℃与-18℃,再置于相应温度的冰箱里保藏.在1个月贮藏期间,测定解冻汁液流失率、蒸煮损失率与加压失水率,同时利用低场核磁共振技术(LF-NMR)测定弛豫性质变化(T2),来反映贮藏期间猪肉持水力的变化,并探讨T2值与解冻汁液流失率、蒸煮损失率与加压失水率之间的相关性.结果表明:浸渍式冷冻肉块的各项指标均优于风冷式冷冻,在贮藏14 d之前,浸渍-5℃肉块的T21值(30～60 ms)、T22值(100～400 ms或200～500 ms)、解冻汁液流失率、蒸煮损失率与加压失水率都显著低于浸渍-18℃组,但贮藏14 d后反之.通过核磁共振技术测定出的T21值、T22值与蒸煮损失率、解冻汁液流失、加压失水率具有相同的变化趋势.     

解冻温度对冷冻鲐鱼品质、质构及超微结构的影响

研究6种解冻温度(4℃冰箱解冻、12℃流水解冻、16℃静止空气解冻、20℃水浴解冻、30℃水浴解冻及40℃水浴解冻)对冷冻鲐鱼的解冻汁液流失率、蒸煮损失率、p H、鱼肉颜色和鱼肉蛋白质溶解度及质构的影响,并对解冻后的鲐鱼肌肉组织进行横、纵切面的扫描电镜观察。结果显示:不同的解冻温度对解冻汁液流失率和鱼肉蛋白的溶解性的影响呈非线性关系。在一定的范围内,最佳解冻温度使解冻汁液流失率最低;蒸煮损失率及鱼肉的白度随着解冻温度的增高而增大;鱼肉黏聚性、弹性、咀嚼度及硬度随着解冻温度的升高而减小;解冻温度对鱼肉的超微结构也有一定的影响,解冻温度越高对鱼肉超微结构的破坏作用越大。结论:解冻温度对冷冻鲐鱼鱼肉品质影响大,控制解冻温度对保护鲐鱼鱼制品品质非常重要。     

警示

警惕!冻肉时操作不正确也会出现食品安全问题肉买回家放入冷冻室保存,随吃随取,非常方便。但这个冷冻过程也涉及食品安全问题,中国疾病预防控制中心营养与健康所研究员张双庆说,遵循以下几个原则,才能让冻肉吃得放心。1.不要先洗再冻。我们从超市或菜市场买回来的肉通常都很干净,可直接放入冰箱冷冻。如果在冷冻前就清洗,肉的表面会浸入一定量的水,这些水分在冷冻时会凝结成大小不一的冰晶。由于冰的体积比水大,冰晶会膨胀挤压周围的肌肉细胞及肌纤维结构,造成机械性损伤,等解冻时,可能会有更多的汁液流失,影响肉的色泽和口感。不过,如果肉表面有明显脏污或过多血水,建议先用水洗一下,控干水或用洁净的吸水纸吸干表面水分后,再放冷冻室。     

不同解冻处理对猪肉理化特性及微生物数量的影响

以空气解冻、4 ℃冰箱解冻、静水解冻和微波解冻4 种不同解冻方式处理猪肉,分别测定处理后猪肉的汁 液流失率、蒸煮损失率、剪切力值、色泽、pH值、总挥发性盐基氮（total volatile basic nitrogen,TVB-N）含量、 硫代巴比妥酸反应物（thiobarbituric acid reactive substance,TBARs）值、菌落总数及乳酸菌数量,研究解冻方式 对猪肉品质的影响。结果表明：静水解冻后猪肉的解冻汁液流失率（2.74%）、蒸煮损失率（16.60%）、亮度值 （57.12）、红度值（13.94）、TVB-N含量（12.95 mg/100 g）和TBARs值（0.10 mg/100 g）低于其他3 种解冻方 式,pH值接近鲜肉,菌落总数及乳酸菌数量较低,因此静水解冻对猪肉的理化性质具有较好的保持作用;4 ℃冰箱 解冻后猪肉的剪切力值（25.41 N）最低,对猪肉嫩度的保持效果较好;微波解冻猪肉的黄度值（11.06）最低;随 着肉样冻结时间的延长,解冻肉中的菌落总数与乳酸菌数量均呈波动变化趋势;肉中的微生物数量对其理化性质具 有显著或极显著影响。在4 种解冻方式中,静水解冻能更好地保持猪肉品质。     

肉类冷冻解冻技术研究进展

冷冻肉因具有易贮藏、易运输、安全性高的优势而被肉类加工企业广泛使用,是肉类加工的主要原料,但是肉类在冷冻解冻过程中会发生一系列品质下降和损耗的现象,如重结晶、油烧、汁液流失和干耗等。因此在肉类加工中为了防止冷冻解冻时品质劣变有必要采用高效的冷冻解冻技术。本文综述了不同冷冻解冻技术(传统技术、高新技术)在肉类加工中的应用,为肉类的高效冷冻解冻技术的研究提供参考。     

冰晶形貌对反复冻融肉体系稳定性影响的研究进展

冷冻是保持肉及肉制品品质和安全的重要方式,但在长期加工、运输和销售过程中冷冻肉及肉制品会不断经历冷冻-解冻过程。冻融期间冰晶的反复形成会导致肉及肉制品氧化变性、保水性降低、功能品质下降和营养物质损失等系列问题,严重影响了体系的稳定性,由此引起的品质劣变已成为肉品学科领域关注的热点。本文从冰晶的形成过程以及冰晶对肉体系微观结构、汁液流失、品质和氧化稳定性影响等方面进行综述,旨在为改善冻融肉体系稳定性研究提供参考,并为提高冷冻肉品质研究开拓新思路。     

静电场辅助冻结-解冻对肌肉保水性及蛋白理化特性的影响

以牛背最长肌（Longissmus dorsi）为研究对象,探讨静电场辅助冻结-解冻、自然冻结-解冻（对照组）、 自然冻结-静电场辅助解冻、静电场辅助冻结-自然解冻4 个处理对肌肉保水性及蛋白理化特性的影响,为冷冻肉 品质控制技术开发提供理论依据。采用差示扫描量热、核磁共振质子成像等技术,对比分析了冻结-解冻速率、解 冻汁液流失、蛋白表面疏水性、热稳定性、水分迁移等指标。结果表明：静电场辅助冻结-解冻实验组牛肉冻结、 解冻时间较对照组分别缩短16.290、8.920 h;通过最大冰晶生成带用时较对照组缩短3.41 h;解冻汁液流失率显著 低于对照组（P＜0.05）,为4.19%;冻结蛋白质表面疏水性显著降低,为16.16 μg,解冻后显著升高,为9.45 μg （P＜0.05）;蛋白质变性程度显著低于对照组（P＜0.05）,变性温度分别为55.130、63.940、78.350 ℃。静电场 辅助冻结-解冻可有效提高牛肉冻结-解冻速率,降低肌原纤维蛋白变性程度,减少解冻汁液损失。     

冷却与速冻对猪肉贮藏期品质影响的对比研究

本文运用风冷冷却与浸渍式冷冻两种方式对猪背长肌进行处理,使预冷12h后,温度约为10℃的猪背长肌中心温度降为0~4℃(风冷冷却),-5℃与-18℃(浸渍式冷冻)。然后把0~4℃与-18℃的肉块放入相应温度的冰箱保藏,-5℃的肉块则分别放入-5℃(一段式)与-18℃(二段式)的冰箱保藏。并对四种保藏处理下的猪肉在一定贮藏期内(冷却肉7d,浸渍冷冻肉7周)的导电率、保水性、滴水损失、蒸煮损失、质构特性、TVB-N、菌落总数、pH、色泽(L*、a*、b*)进行了对比研究。研究表明:浸渍式冷冻工艺中,二段式冷冻没有一段式冷冻品质好。浸渍式冷冻肉-18℃贮藏4周内的品质与冷却肉贮藏4d内的品质相当。冷却肉在保水性、质构特性、色泽方面要优于浸渍式冷冻组,但在TVB-N、菌落总数方面则不如浸渍式冷冻肉。     

不同解冻方法及添加抗冻剂处理对冷冻海鲈鱼鱼片解冻品质的影响

为探究不同解冻方法及添加抗冻剂处理条件对冷冻海鲈鱼鱼片解冻品质影响规律,以新鲜海鲈鱼(Perca fluviatilis)为主要材料,将鱼片(添加0. 4%复合磷酸盐为处理组A,4%海藻糖+0. 4%复合磷酸盐为处理组B)冻结后进行冻藏处理,设立对照组(-30℃,72 h)。采用空气解冻、冰箱解冻、静水解冻及微波解冻对冷冻海鲈鱼鱼片进行解冻处理。研究结果表明,与其他解冻方法比较,微波解冻及静水解冻可以显著提高海鲈鱼鱼片解冻速率(P <0. 05),而微波解冻及冰箱解冻可以显著降低其解冻汁液流失率、蒸煮损失率、菌落总数,并延缓其盐溶性蛋白含量、弹性、Ca²⁺-ATPase活性、白度值下降,且差异显著(P <0. 05)。对于空气解冻、冰箱解冻、静水解冻而言,与对照组比较,处理组B及处理组A均可显著降低其解冻汁液流失率、蒸煮损失率、菌落总数,并抑制盐溶性蛋白含量、弹性、Ca²⁺-ATPase活性下降(P <0. 05),且对于采用空气解冻及静水解冻法而言,处理组B效果较处理组A显著(P <0. 05)。9个检测指标可简化为...     

空气解冻温度对猪里脊肉品质的影响

以冷冻猪里脊肉为研究对象,在4、12、20、30 ℃温度条件下对其进行空气解冻,测定猪里脊肉解冻时 间、汁液流失率、蒸煮损失率、保水性、pH值、色泽、水分分布、质构和微观结构等特性变化。结果表明：猪里 脊肉汁液流失率与解冻时间呈非线性关系;12、20 ℃空气解冻对猪里脊肉的保水性影响较小;不同空气解冻温 度对猪里脊肉pH值、亮度值和红度值无显著影响;30 ℃空气解冻对猪里脊肉中不易流动水影响最小,稳定性 最好,其次为20、4、12 ℃;与对照组鲜肉相比,不同温度空气解冻处理组猪里脊肉蒸煮后硬度存在显著差异 （P＜0.05）;12 ℃空气解冻后猪里脊肉中肌纤维间空隙变大。不同空气解冻温度对猪里脊肉品质的影响存在 差异性。     

Characterization of Ice Crystals in Pork Muscle Formed by Pressure-shift Freezing as Compared with Classical Freezing Methods

ABSTRACT: Cylindrical specimens of fresh pork muscle packed in plastic bags were frozen by air blaster freezing (ABF), liquid immersion freezing (LIF), and pressure-shift freezing (PSF) (100 to 200 MPa). Sample internal temperature and phase transformations were monitored at center, midway, and surface locations. ABF and LIF resulted in large irregular ice crystals, causing serious muscle structure deformation. PSF ice crystals were generally small and regular, but differed along the radial direction. Near the surface, there were many fine and regular intracellular ice crystals with well-preserved muscle tissue. From midway to the center, ice crystals were larger in size and located extracellularly. Ice crystal formation was affected by super-cooling during/after depressurization and subsequent freezing.     

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.     

Novel assistive technologies for efficient freezing of pork based on high voltage electric field and static magnetic field: A comparative study

To enhance the freezing rate and thawed product quality of pork tenderloin, an experimental study was conducted using the high voltage electric field and static magnetic field separately during freezing. Pork tenderloin pieces were frozen at −20 °C under several high voltage electric fields (10 kV/m (HVEF1), 30 kV/m (HVEF3), 50 kV/m (HVEF5)) and magnetic fields of 2 mT (MF2), 4 mT (MF4), 6 mT (MF6) and 8 mT (MF8). The effects of different methods on freezing rate, ice crystal size as well as the distribution, and product quality after thawing were investigated. The freezing time of pork tenderloin was reduced by 40.04% and 37.81% respectively, under the optimal electric and magnetic field conditions tested. The thawing loss decreased from 5.7% of conventional freezing to 1.7% of HVEF1 and 2.4% of MF2, respectively. In addition, both high-voltage electric field freezing and magnetic field freezing can better maintain the moisture state in the sample. The results for color and pH confirmed that the thawed product quality using HVEF1 and MF2 was superior to that obtained under other conditions. The myofibrillar protein in the thawed products obtained from HVEF1 and MF2 treatments was also found to be thermally more stable. It is noteworthy that the HVEF1 treated sample has the highest umami signal and the lowest salty signal. Considering the enhanced freezing efficiency and improved quality, application of HVEF1 is recommended as a viable strategy to produce high-quality frozen pork tenderloin.Industrial relevanceThe slow freezing rate of frozen meat products and serious deterioration of product quality are the key problems. Therefore, improving the efficiency of freezing is desirable. This study provides ideas for pork preservation. It caters to the need of industrial production of meat product where better efficiency freezing process is highly desirable, and the findings of this study is beneficial to the meat processing industry.     

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。     

不同冻藏时间的猪肉品质比较及其变化机制研究

为了解冷冻储藏期间猪肉品质变化的原因及其可能的机制,分别比较了冻藏4个月和冻藏8个月猪肉的持水性、质构、颜色等品质指标;并通过低场核磁（low-field nuclear magnetic resonance,LF-NMR）检测了猪肉样品中水分的种类和分布,探索了不同水分分布与持水性、质构间的相关性;通过电子鼻和基于高分辨质谱的脂质组学分析探讨了猪肉风味成分的变化以及引起变化的特征物质的种类。结果表明,与冻藏4个月的猪肉相比,冻藏8个月猪肉的品质明显劣变,而其肌纤维形貌更加松散、水分弛豫时间延后、峰面积减小。而猪肉的持水性和质构等品质指标与冻藏时间存在正相关性,与水分弛豫时间和面积之间存在负相关性,也说明经过长时间冻藏,猪肉中结合水和不易流动水的迁移与损失可能是引起猪肉质构品质发生劣变的主要原因。通过对猪肉电子鼻数据的偏最小二乘回归分析（PLS-DA）发现,经过长期冻藏后猪肉的风味成分也明显改变,发生变化的风味成分主要为烷烃、芳香类成分、弱极性化合物、甲烷和醇类化合物。而通过高分辨质谱鉴定出5种与脂质氧化相关的差异化合物,推测经过长时间冻藏后,猪肉风味物质发生的明显变化可能是由于肌肉组织中的脂类被氧化造成的。     

Size and location of ice crystals in pork frozen by high-pressure-assisted freezing as compared to classical methods

In high-pressure-assisted freezing, samples are cooled under pressure (200 MPa) to - 20 °C without ice formation then pressure is released (0.1 MPa) and the high super-cooling reached (approx. 20 °C), promotes uniform and rapid ice nucleation. The size and location of ice crystals in large meat pieces (Longissimus dorsi pork muscle) as a result of high-pressure-assisted freezing were compared to those obtained by air-blast and liquid N(2). Samples from the surface and centre of the frozen muscle were histologically analysed using an indirect technique (isothermal-freeze fixation). Air-blast and cryogenic fluid freezing, having thermal gradients, showed non-uniform ice crystal distributions. High-pressure-assisted frozen samples, both at the surface and at the central zones, showed similar, small-sized ice crystals. This technique is particularly useful for freezing large pieces of food when uniform ice crystal sizes are required.     

Freezing rate simulation as an aid to reducing crystallization damage in foods

In food freezing processes the presence of large ice crystals is a serious drawback when a good final quality of the product is desired. To study the size and distribution of those crystals, a large piece of pork muscle has been frozen by liquid nitrogen evaporation. A mathematical model to simulate different cooling rates at the surface of the product was solved using a finite element method; this model satisfactorily fitted experimental data and predicted local freezing rates at different locations in the meat tissue. The model was applied to find the freezing rates that led to a good quality product, related to an optimum distribution of small ice crystals located inside and outside the tissue fibres.     

4种保鲜技术在冰箱内软冷冻猪肉保鲜中的应用

为寻找能有效延长冰箱软冷冻区(-8℃)猪肉货架期的保鲜技术,比较臭氧(15ppm)、紫外线(4.87μW/cm2)、芥末提取物(AIT)、硅窗膜(联合气调包装)4种保鲜技术,并与-18℃条件下猪肉各项理化指标进行对比.实验设计了6组:对照组Ⅰ(-8℃)、对照组Ⅱ(-18℃)、臭氧组、紫外线组、AIT组和硅窗膜组;比较不同时期的软冷冻猪肉感官指标、色差值、pH值、菌落总数、汁液流失率、TVB-N值.结果表明:硅窗膜组的猪肉在15d失水严重,猪肉表现出现干裂现象;AIT组的杀菌效果最好;臭氧和紫外线技术虽然杀菌效果明显,但加速软冷冻猪肉的脂肪氧化,对猪肉的气味产生不好的影响;AIT条件下的软冷冻猪肉与-18℃条件下猪肉的气味变化基本吻合.综合考虑,AIT组好于臭氧组和紫外线组,硅窗膜组应在猪肉保水性上改进,需要进一步探索.     

Physico-chemical and processing quality of porcine M. longissimus dorsi frozen at different temperatures

Longissimus dorsi muscle from six pigs (24 h post-mortem) was cut into portions of similar size and shape (c. 700 g) and vacuum-packed in polyfilm. The muscle specimens were divided into three samples, one frozen at -20°C, another at -80°C and the third served as the control (not frozen). The meat sample frozen at -80°C was transferred to the -20°C freezer. After one month, both frozen pork samples were thawed at -2°C and drip loss (%) was measured. Hunter colour, metmyoglobin (MetMb) formation (%), water-holding capacity (WHC), TBA value, transmission value (TM) and myofibril fragmentation were also determined. There was no significant difference in drip loss for the two frozen samples. No MetMb formation could be detected and Hunter values were basically the same for all three samples. WHC, TBA value and TM were essentially the same for all three samples. TBA value was quite low for each frozen sample, indicating that lipid oxidation did not occur during freezing. Histological examination of both frozen samples indicated inter- and intracellular ice crystal formation at -20°C, and intracellular ice at -80°C, the extent being less than at -20°C. At -20°C, ice crystals were larger and muscle fibre diameter smaller than for the control or -80°C sample. Myofibril fragmentation in both frozen samples was significantly higher than in the control. Pork sausage was prepared from all three samples by adding 2% NaCl and 100 ppm NaNO(2). Cooking loss and colour forming ratios were essentially the same. The sausage sample made from the -20°C frozen meat was harder than that of the other two samples according to rheological measurement.