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.     

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.     

几种冷冻新技术对食品冻结过程中冰晶形成的影响

冷冻技术在现代食品加工工业中起着十分重要的作用,水结晶是冷冻过程的关键步骤。文章介绍几种冷冻新技术对食品冻结过程中水结晶的影响的研究进展,包括高压冷冻、超声波冷冻、渗透脱水冷冻、抗冻蛋白、冰核活性蛋白以及其它冷冻新技术。并阐述这些新技术对冰晶的影响机制,旨在能够更好地了解、预测及控制水结晶的过程,并进一步改进冷冻过程和提高冷冻食品的品质。     

High-pressure calorimetric evaluation of ice crystal ratio formed by rapid depressurization during pressure-shift freezing of water and pork muscle

The amount of ice nuclei formed during the pressure release is important for the final formation and development of ice crystals in pressure shift freezing (PSF) frozen products. In this study, a high-pressure (HP) calorimeter was used to evaluate the ratio of ice crystals instantaneously formed by rapid depressurization during PSF of pure water and pork muscle tissue. Experiments were carried out initial pressure levels of 62, 115, 157 and 199 MPa, with corresponding phase change temperatures of −5, −10, −15 and −20 °C, respectively (slightly higher than phase change point of water–ice I). The ice crystal ratio was determined based on calorimetric peak measured and heat balance. The evaluated regression relationship between observed ice crystal ratio (R_ice in %) and pressure (P, MPa) was R_ice–water = 0.115P + 0.00013P² (R² = 0.96, n = 9) for pure water, and R_ice–pork = 0.080P + 0.00012P² (R² = 0.95, n = 11) for pork muscle. Compared to other methods, the calorimetric evaluation does not require any of the pressure-related properties of the test sample. HP calorimetry can thus be used to evaluate ice crystal ratio for PSF of foods even though their pressure related properties may be unknown.     

冷冻贮藏对冻猪肉冰晶形态、TVB-N及TBARS的影响

研究了冻藏(-10、-15、-19、-22℃,150d)对猪肉品质的影响.结果显示:冷冻温度越低,形成的冰晶越小,冷冻结束时,各处理的冰晶面积的分布范围为4045.855～ 5509.739μm2,相当直径分布范围为69.381～ 81.439μm;经150d贮藏后,尽管温度越低,冰晶重结晶速度越慢,冰晶的体积仍显著增大(p<0.01),面积为7546.855～ 11273.890μm2,相当直径为98.945～ 106.670μm;而圆度和长度则没有显著变化(p>0.05).挥发性盐基氮含量(TVB-N含量)和硫代巴比妥酸还原值(TBARS值)同样也显著增大(p<0.05).冰晶体积、TVB-N含量和TBARS值变化显示了很好的时间相关性.实验说明冰晶形态也可用于反应猪肉的新鲜程度.     

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.     

Microwave assisted freezing part 2: Impact of microwave energy and duty cycle on ice crystal size distribution

Among innovative freezing processes, electromagnetic wave assistance during freezing has received great attention in recent years. The literature provides interesting studies indicating that smaller ice crystals may be obtained during freezing with the assistance of microwaves. In the companion paper, we designed a laboratory scale prototype to perform experiments of this type in well controlled conditions at 2.45 GHz. In the current study, we performed freezing experiments using this prototype and developed a protocol to measure ice crystal sizes using X-ray micro-tomography. The methodology was first validated by measuring ice crystal distribution in unidirectional conventional freezing. Then several microwave assisted freezing modalities were studied. Experiments were conducted with pulsed and continuously applied microwaves. The impact of microwave irradiation time was studied at a constant incident microwave power, and then at constant energy supplied to the system. We observed a significant reduction of up to 25% in ice crystal size when microwave assistance was used during freezing with both pulsed and continuously applied microwaves. These observations tend to disconfirm the hypothesis in the literature according to which ice crystal size reduction is due to temperature oscillations. The only remaining hypothesis in the literature is that ice crystal size reduction may be due to the perturbation of the H-bond network in water, which could be a precursor to crystalline structure. It appeared that at constant incident microwave power, the increase in irradiation time tended to decrease ice crystal size. No significant difference in ice crystal size reduction was observed for a constant energy supplied to the system. The amount of energy supplied by microwaves seems to be a factor influencing ice crystal size.Industrial relevanceMicrowave assisted freezing is an emerging process which permits reducing ice crystal size, and thus improving frozen product quality. The measurement of ice crystals in samples frozen in controlled conditions of both freezing and microwave irradiation allows studying the main parameters that induce the reduction of their size. Better understanding of the relevant factors influencing nucleation and/or crystal growth can help to optimize the process.     

对虾低频电场冰温贮藏期间品质的变化

目的:探究低频电场辅助冰温保鲜提高虾肉品质的可行性。方法:在冰温基础上施加低频电场(LFEF+冰温)保鲜对虾,监测贮藏期间对虾的丙二醛含量、盐溶性蛋白含量、Ca²⁺-ATPase活性、pH值、剪切力、色差和蛋白质分子量变化规律,并与常规冰温保鲜作对照。结果:相对于常规冰温保鲜处理,LFEF+冰温保鲜处理对虾肉的丙二醛含量、盐溶性蛋白含量、pH值、剪切力、色泽无显著影响,但贮藏3 d后,低频电场辅助冰温保鲜可显著抑制虾肉Ca²⁺-ATPase活性的下降,其中贮藏第15天时LFEF+冰温处理组的Ca²⁺-ATPase活性是常规冰温保鲜处理组的2.20倍。此外,低频电场辅助冰温保鲜可明显抑制肌球蛋白重链、肌动蛋白和原肌球蛋白条带密度的下降。结论:与常规冰温保鲜相比,低频电场冰温保鲜处理可显著抑制Ca²⁺-ATPase活性下降和蛋白质降解,维持蛋白质结构和性质的稳定,减缓虾肉品质劣变。     

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 electric field and osmotic pre-treatments on quality of apples after freezing–thawing

This work discusses the effects of pulsed electric field (PEF), ohmic heating (OH), and osmotic (O) treatments on the structure of apple tissue and its freezing/thawing behaviour. Apple discs were treated at electric field strength E = 800 V/cm (PEF, isothermal regime) and E = 40 V/cm (OH, non-isothermal regime) to a high level of tissue disintegration (conductivity disintegration index Z was ≈ 0.98) and then were subjected to osmotic (O) treatment in the aqueous solution of glycerol (20 wt.%). The distribution of osmotic solution was practically homogeneous inside the disc of PEF-treated tissue and highly inhomogeneous in untreated and OH-treated samples. The freezing–thawing (FT) experiments (+ 20 °C → − 40 °C → + 20 °C) were done in order to reveal the effects of combined modes of treatment on the structure of apple tissue. The most pronounced reducing of both freezing and thawing times and strengthening of the apple texture were observed for PEF treatment.Industrial relevanceFreezing-assisted preservation of plant materials in the most natural-looking state with near-original texture and colours requires thorough optimization of freezing operation. In this study, the research of the impact of pulsed electrotechnologies combined with osmotic pre-treatment on the structure of apple tissue, its freezing/thawing behaviour and texture quality, is provided.     

Online ice crystal size measurements during sorbet freezing by means of the focused beam reflectance measurement (FBRM) technology. Influence of operating conditions

In ice cream and sorbet manufacturing small ice crystals are desired to deliver a product with a smooth texture and good palatability. This research studied the influence of the operating conditions on the ice crystal size and the draw temperature of the sorbet during the freezing process. The evolution of ice crystal size was tracked with the focused beam reflectance measurement (FBRM) technique, which uses an in situ sensor that makes it possible to monitor online the chord length distribution (CLD) of ice crystals in sorbets containing up to 40% of ice. The refrigerant fluid temperature had the most significant influence on the mean ice crystal chord length, followed by the dasher speed, whereas the mix flow rate had no significant influence. A decrease in the refrigerant fluid temperature led to a reduction in ice crystal size, due to the growth of more small ice crystals left behind on the scraped wall from previous scrapings. Increasing the dasher speed slightly reduced the mean ice crystal chord length, due to the production of new small ice nuclei by secondary nucleation. For a given refrigerant fluid temperature and dasher speed, low mix flow rates resulted in lower draw temperatures, due to the fact that the product remains in contact with the freezer wall longer. High dasher speeds warmed the product slightly, due to the dissipation of frictional energy in the product, the effect of which was in part moderated by the improvement in the heat transfer coefficient between the product and the freezer wall.     

Effect of high voltage electrostatic field treatment on thawing characteristics and post-thawing quality of frozen pork tenderloin meat

The thawing characteristics and post-thawing quality of frozen pork treated with high voltage electrostatic fields (HVEF) were compared with those of an air-thawed control. A multiple points-to-plate electrode operating at voltages above 6 kV significantly shortened the thawing time. Under electrode voltages 4, 6, 8, and 10 kV, thawing times were 70, 52, 46, and 40 min respectively, versus 64 min in the control. HVEF treatment was particularly effective in the temperature range −5–0 °C. HVEF treatment reduced the total microbial counts in thawed frozen meat by 0.5–1 log CFU/g, without affecting meat quality. During five days of post-thawing storage, the volatile basic nitrogen (VBN) levels increased from 10.64 to 16.38 mg/100 g under 10 kV applied voltage, while the control VBNs increased from 10.66 to 19.87 mg/100 g. This suggests an application potential for HVEF treatment in the thawing and storage of frozen meat.     

Effect of freezing conditions and storage on ice crystal and drip volume in turbot (Scophthalmus maximus): Evaluation of pressure shift freezing vs. air-blast freezing

Turbot fillets were frozen either by pressure shift freezing (PSF, 140 MPa, −14°C) or by air-blast freezing (ABF), and then stored at −20°C for 75 days. Smaller and more regular intracellular ice crystals were observed in fillets frozen by PSF compared with air-blast frozen ones. Ice crystals area in PSF samples was approximately 10 times smaller than that of ABF samples, on average. The PSF process reduced thawing drip compared with air-blast freezing. Conversely to this classical freezing process, the storage time did not adversely influence the thawing drip of PSF samples. In addition, PSF appeared to reduce cooking drip after 45 days of storage at −20°C. Differential scanning calorimetry analysis showed a significant reduction of the total enthalpy of denaturation for the pressure shift frozen samples compared to fresh and conventional frozen samples. Besides, a new melting transition appeared on the thermogram of PSF samples at approximately +40°C.     

Effect of pork meat proteins on the binding of volatile compounds

The binding ability of pork meat proteins (sarcoplasmic, myofibrillar and isolated actin and actomyosin) was determined by measuring the relative headspace concentration of the volatile compounds in the presence of each protein (expressed as percentages of the free volatiles relative to a standard solution without protein) using solid-phase microextraction (SPME) and gas chromatography analysis. The sarcoplasmic homogenates bound higher quantities of the volatile compounds assayed (3-methylbutanal, 2-methylbutanal, 2-pentanone, hexanal, methional and octanal) than myofibrillar homogenates. The addition of salts also affected the binding ability of sarcoplasmic and myofibrillar proteins. Actomyosin was able to bind all the assayed volatile compounds although the binding depended on protein concentration and conformation, and it was highly affected by frozen storage. On the other hand, G-actin was unable to bind any of the assayed volatile compounds although the polymerized form (F-actin) bound higher quantities of the volatile compounds.     

欧姆加热技术对肉块品质的影响

自主设计的欧姆加热装置被用来进行研究。研究了不同电场强度(3、6、9V/cm),不同保温时间(7、9、11min)欧姆加热处理对肉块品质(加热程度值,微生物杀灭效果,质构)的影响,并与改进的水浴加热方式处理的肉块进行了品质上的比较。     

高压静电场处理对几种呼吸跃变型果实呼吸强度的影响

以苹果等几种呼吸跃变型果实为试材,研究了100kV/m的高压静电场每天处理2h对其呼吸强度变化规律的影响并与相同条件下的对照果进行了比较,发现高压静电场处理能够有效地降低这几种果实呼吸强度的最大值,并不影响它们呼吸高峰出现的时间。     

Effect of heating time on volatile composition of canned pork meat

Volatiles from samples of ground pork meat, subject to 10, 20, 30 and 40 min heating at 121°C, were isolated by trapping on Tenax GC and Porapak Q. Essences were compared on wall-coated open-tubular glass capillary columns and analysed by glass capillary gas chromatography-mass spectrometry. Low molecular weight alcohols, many with branched-chain skeletons, mercaptans and cyclic products, were among the compounds identified. The amount of volatiles present appeared to correlate well with the heating time to which the sample had been subjected.