EFFECT OF HIGH PRESSURE TREATMENT ON CYTOPLASMIC 5'-NUCLEOTIDASE FROM RABBIT SKELETAL MUSCLE

We investigated the effect of high‐pressure treatment on the properties of cytoplasmic 5′‐nucleotidase (NT), which converts inosine monophosphate (IMP) into inosine. After pressure treatment at 400 MPa, the activity of purified IMP‐NT remained at almost 100%, but the activity of partially purified adenosine monophosphate (AMP)‐NT decreased to about 40%. These data suggest that there is a difference in the pressure stability between the enzymes. In situ fluorescence spectroscopy of IMP‐NT under pressure showed that its pressure‐induced denaturation was reversible. When the pressure was reduced from the highest pressure to ambient pressure, hysteresis was observed. This suggests that high pressure treatment may lead to a partial change in the affinity of the subunits for each other once they have dissociated. The activities of IMP‐NT and AMP‐NT extracted from pressure‐treated muscles decreased remarkably between 250 and 450 MPa, but IMP‐NT was more stable than AMP‐NT.     

POSTMORTEM CHANGES IN QUALITY INDICES OF ICE-STORED FLOUNDER (PARALICHTHYS PATAGONICUS)

The characteristics of flounder (Paralichthys patagonicus) were evaluated during a 12‐day period of storage in ice by monitoring the biochemical, microbiological and sensory parameters. The adenosine‐5′‐triphosphate and adenosine‐5′‐diphosphate were not detected, and the initial content of adenosine‐5′‐monophosphate (AMP) rapidly decreased to zero. Inosine‐5′‐monophosphate (IMP) but not adenosine (Ado) was present in muscle extracts. The AMP deaminase activity was found in the muscle. Conversely, the Ado deaminase activity was not detected. A 55% decrease in IMP concentration occurred during the first 2 days of storage. The inosine content was barely detectable (<0.1 μmol/g), probably because of the high nucleoside phosphorylase activity in the muscle. Hypoxanthine significantly (P < 0.01) increased up to the seventh day and then remained approximately constant. The muscle pH fluctuated between 6.6 and 7.0. The iced flounder was microbiologically acceptable for up to 7 days with aerobic plate counts reaching <10⁷ cfu/g. The sensory score, determined by the Quality Index Method, linearly increased (r² = 0.96) with the keeping time. All the parameters, including the K‐value, indicated that the shelf life of iced flounder was 7 days.     

超高压处理对草鱼鱼肉风味物质的影响

以草鱼为原料,研究了不同超高压(0.1、100、200、300、400、500 MPa,保压10 min)条件处理后草鱼鱼肉的呈味核苷酸类物质、游离氨基酸以及挥发性物质的含量变化。结果表明:100、400和500 MPa压力处理后草鱼鱼肉的AMP含量显著增加(p0.05),200和300 MPa处理后则显著减少,100和300 MPa条件下IMP含量得到显著增加,而200、400和500 MPa条件下显著减少;不同压力条件对游离氨基酸的影响不一,100、300和400 MPa处理对草鱼鱼肉的游离氨基酸含量影响较小,而200和500 MPa压力则使得游离氨基酸总量显著减少;六组样品中分别检测到32、31、35、41、44和40种挥发性物质,其中以醛酮类和醇类为主,超高压处理后醇类的相对含量显著减少,醛酮类的相对含量则显著增加,并且200 MPa及以上的压力条件下醛酮类物质的种类也有所增加。     

5'-Adenylic Acid Deaminase in Porcine Muscle

SUMMARY— The 5'-adenylic deaminase activity and AMP and IMP levels of several porcine skeletal muscles were determined on samples from 14 Poland China pigs excised immediately following exsanguination. There were no significant (P > .0.5) differences in adenylic acid deaminase activity within or between the longissimus dorsi, gluteus medius or rectus femoris muscles even though muscle morphology varied from dark, firm and dry to pale, soft and exudative. Likewise no significant (P > .05 differences in AMP or IMP levels were observed in the longissimus dorsi and gluteus medius muscles. Simple correlation coefficients between muscle pH and adenylic acid deaminase activity indicated positive relationships between enzyme activity and muscle pH at 15 and 45 min post-mortem in all muscles studied. IMP concentration was negatively related to pH of the muscle.     

Assessment of the residual immunoreactivity of soybean whey hydrolysates obtained by combined enzymatic proteolysis and high pressure

Soybean (Glycine max) whey was hydrolyzed for 15 min using three food-grade proteases (Alcalase, Neutrase, Corolase PN-L) at atmospheric pressure (0.1 MPa) and under high pressure (HP) at 100, 200, and 300 MPa. All hydrolysates were analyzed by SDS-PAGE and their residual immunoreactivity was assessed by immunoblotting using the sera from children allergic to soybean. As shown in SDS-PAGE, Alcalase, Neutrase, and Corolase PN-L produced different patterns of hydrolysis. Each enzyme showed a similar proteolytic activity at atmospheric pressure and at 100 MPa, while an increased degree of hydrolysis was observed at 200 and 300 MPa. No residual antigenicity was observed in the hydrolysates obtained by Alcalase and Corolase PN-L in all considered conditions of hydrolysis. A positive reaction associated with a band having molecular weight of about 70 kDa was observed in the immunoblotting of the hydrolysates obtained with Neutrase at 0.1, 100, and 200 MPa, while no antigenicity was detected for those samples obtained under high pressure, at 300 MPa. These results suggest that high pressure combined with suitable enzymatic activity could be a useful tool for obtaining hydrolysates with low immunoreactivity to be used in special foods (hypoallergenic foods).     

Extractive components of boiled–dried scallop adductor muscle and effect on the taste of soup after mixing with chicken leg meat

The extractive components of raw and boiled–dried scallop adductor muscle were examined. On a dry weight basis the levels of total free amino acids, total adenosine triphosphate (ATP) and related compounds, and betaines in the boiled–dried sample were lower than those in the raw muscle, which may have been due to the outflow of these compounds during boiling. Soup prepared from the boiled–dried scallop and chicken leg meat was assessed by sensory evaluation. This soup cooked with the scallop and chicken was stronger in sweetness, umami and body and rated higher in overall preference than the soup containing these ingredients after cooking separately. The inosine monophosphate (IMP) level in the former soup was 4.4 times higher than that in the latter. The adenosine monophosphate (AMP) deaminase (EC 3.5.4.6) activity in the crude extract from the chicken meat was 9.16 units l^?1, whereas no activity could be detected in the crude extract from the boiled–dried scallop. It is concluded that AMP, which was mainly derived from the boiled–dried scallop, was converted to IMP by AMP deaminase from the chicken meat during the preparation of the soup, resulting in an improvement in the taste. Copyright © 2004 Society of Chemical Industry     

高压腌制对鸡胸肉微观结构的影响

采用食盐质量浓度为40 g/L的腌制液,在不同压力条件下（0.1、50、100、150、200、300 MPa,保压时间20 min）腌制鸡胸肉,应用低场核磁共振、明场相差显微镜和透射电镜研究鸡胸肉在不同压力条件下微观结构的变化。结果表明：高压腌制处理对鸡胸肉的水分存在状态具有显著的影响（P＜0.05）,300 MPa时的T22向慢弛豫方向移动,150 MPa时的不易流动水占总水分的百分含量最高。150 MPa以下处理组的肌肉组织结构无显著差异,肌细胞形状规则,排列有序;200 MPa处理下鸡胸肉的肌纤维排列疏松,肌纤维之间肌束膜开始破裂;300 MPa处理下鸡胸肉的肌束膜发生大量断裂和崩解,鸡胸肉的肌原纤维结构也发生明显变化,Z线和I带被彻底破坏,在Z线和M线附近形成了重聚体,肌纤维丝发生消融。150 MPa处理组的鸡胸肉肌肉结构保持良好。     

超高压结合温热处理对脱脂乳透光率和粒径及蛋白溶解性的影响

目的：研究高压结合温热（≤50 ℃）处理对脱脂乳粒径、透光率及蛋白溶解性的影响。方法：采用不同温度（常温、30、40、50 ℃）和压力（0.1～700 MPa）分别处理脱脂乳10～30 min,利用激光纳米粒度仪检测脱脂乳粒径变化,分光光度法检测透光率变化,考马斯亮蓝法测定可溶性蛋白质量浓度变化。结果表明,脱脂乳透光率在压力不高于100 MPa范围内不受温度、压力和处理时间的影响;在200～700 MPa范围内,常温条件下处理的脱脂乳透光率随压力的升高和处理时间的延长而增大,在700 MPa下处理20 min时透光率最大,增幅为1 011%;在30～50 ℃范围内,透光率随压力增大（200～700 MPa）呈现先升高后降低的趋势,在40 ℃、500 MPa下处理10 min时透光率增幅最大（537%）,透光率受温度和保压时间的影响,且超高压结合温热处理脱脂乳透光率均高于未处理脱脂乳。在常温、0.1～400 MPa范围内,脱脂乳的中位径（Dx(50)）随压力的增大而总体降低,在400～700 MPa范围内变化趋势平稳,但均小于未处理脱脂乳的Dx(50);30、40、50 ℃下,脱脂乳Dx(50)随压力增大呈现先升高后降低的趋势,分别在400～700、300～500、200～400 MPa范围内变化趋势平稳,且受时间影响较小。经高压处理的脱脂乳中可溶性乳蛋白（soluble protein,S-Pro）质量浓度总体呈增加趋势,且受压力、时间和温度的影响,在30 ℃、500 MPa下处理30 min,S-Pro质量浓度增幅最大（83.55%）。pH 4.6下可溶性蛋白（S-Pro-pH 4.6）质量浓度在压力不高于100 MPa时不受温度、压力和时间的影响;在200～700 MPa范围内,不同温度下,随压力升高和处理时间的延长,S-Pro-pH 4.6质量浓度呈现下降趋势。对各指标间相关性进行分析发现,透光率与Dx(50)间的相关性随温度升高减弱;透光率与S-Pro质量浓度呈正相关,与S-Pro-pH 4.6质量浓度呈负相关。S-Pro与S-Pro-pH 4.6之间呈负相关。结论：经超高压结合温热处理,能够引发脱脂乳透光率、粒径及蛋白溶解性的变化,且这些变化存在一定的相关性。     

超高压辅助中华管鞭虾脱壳及对其肌肉品质的影响

为研究超高压处理对虾仁品质的影响,采取不同的压力(100~500 MPa)处理中华管鞭虾,通过测定虾仁肌原纤维蛋白盐溶性、巯基含量、表面疏水性、Ca~(2+)-ATPase活性及虾仁色泽、质构、肌肉超微结构,研究超高压处理在辅助脱去虾壳的同时对虾仁肌肉及其蛋白生化特性的影响。结果表明,与对照组相比,200、300 MPa处理中华管鞭虾,在保持虾仁结构完整性及其良好品质的同时能显著提高脱壳效果,400、500 MPa处理后虾肉发生熟化;200 MPa处理组虾肉硬度、弹性和咀嚼性比对照组分别提高35.37%、7.46%和24.93%,肌原纤维蛋白除表面疏水性上升外,其盐溶性、总巯基含量和Ca~(2+)-ATPase活性无明显变化;而300、400、500 MPa处理后肌原纤维蛋白盐溶性、巯基含量及Ca~(2+)-ATPase活性下降明显。结合脱壳效果和对虾仁肌肉及其肌原纤维蛋白生化特性的影响,选择200 MPa处理中华管鞭虾,可有效提高脱壳效果,还能保持虾仁良好品质。实验结果可为冻虾仁生产中利用超高压辅助中华管鞭虾脱壳技术的应用提供支持。     

Effect of high hydrostatic pressure on mortality and allergenicity of Anisakis simplex L3 and on muscle properties of infested hake

BACKGROUND: High pressure (HP) ranging from 100 to 350 MPa (1–15 min) was applied to Anisakis simplex larvae and parasitised hake (Merluccius merluccius) muscle. The aim of the study was to kill the larvae to prevent human anisakidosis, to evaluate the effect on A. simplex allergens and to minimally alter fish muscle quality. RESULTS: The larvae were killed at pressures ≥ 200 MPa and times ≥ 1 min, producing alterations in the larva body and ruptures in the cuticle when observed by scanning electron microscopy. Nevertheless, Ani s 4 and A. simplex crude antigens were recognised by immunoblotting and immunohistochemistry at all HPs assayed. Small changes in colour and texture were observed in fish muscle under all pressure/time conditions. Major changes were observed visually at 300 MPa, where the muscle appeared as slightly cooked. Apparent viscosity of muscle homogenates decreased significantly at longer times or higher applied pressure. No changes were detected at 200 MPa in the electrophoretic pattern of proteins treated with or without β‐mercaptoethanol, suggesting that disulfide bonds were not formed. CONCLUSION: Application of HP at 200 MPa for up to 5 min would kill A. simplex larvae, avoiding infestation of the consumer and causing small changes in the hake muscle perceived sensorially. However, HP‐treated A. simplex‐parasitised fish would still be a potential hazard for consumers allergic to the larvae. Copyright © 2009 Society of Chemical Industry     

超高压对低盐海藻鸡肉糜品质的影响

为探究超高压对低盐海藻鸡胸肉糜的影响,考察了不同压力（0.1～500 MPa/10 min）和保压时间 （0～25 min/300 MPa）时肉糜的色泽、盐溶蛋白溶解度、蒸煮损失率、持水性、冻融损失率、质构以及流变特 性的变化规律。结果表明：随着压力的升高,肉糜亮度（L*）和白度（W）先降低后增加,在200 MPa时最低, 红度（a*）逐渐上升;100～300 MPa超高压处理对盐溶蛋白溶解度无显著影响（P＞0.05）,压力大于300 MPa 时盐溶蛋白溶解度显著降低（P＜0.05）;蒸煮损失率和冻融损失率随压力的升高呈先降低后增加趋势,在压力 为300 MPa时达到最低值;与0.1 MPa处理组相比,100～500 MPa压力处理使肉糜持水性显著升高（P＜0.05）; 硬度和弹性随着压力的增加先升高后降低,在200～300 MPa时达最大值,200、300 MPa处理组间无显著差异 （P＞0.05）;与0.1 MPa处理组相比,超高压处理能够改善海藻鸡胸肉糜的储能模量（G’）和相位角正切值 （tan δ）。保压时间对低盐海藻鸡胸肉糜色泽、盐溶蛋白溶解度、蒸煮损失率无显著影响（P＞0.05）;随着保压 时间的延长,肉糜的持水性、G’、tan δ值和质构得到改善,但保压时间过长（25 min）可破坏肉糜的硬度和弹性。 本研究表明超高压处理能够改善低盐海藻鸡胸肉糜的品质,为新型肉制品的开发提供了理论依据。     

Changes in purified tomato pectinmethylesterase activity during thermal and high pressure treatment

The enzymatic reaction of purified tomato pectinmethylesterase on pectin was investigated during a combined high pressure/temperature treatment (0.1–600 MPa/20–65 °C) at pH 8.0 and pH 4.4. The optimal temperature for tomato pectinmethylesterase activity at atmospheric pressure is situated around 45 °C at pH 8.0, and around 35 °C at pH 4.4. At both pH 8.0 and pH 4.4, the optimal temperature shifted to higher values at elevated pressure compared with atmospheric pressure. At both pH values, the catalytic activity of tomato pectinmethylesterase was higher at elevated pressure than at atmospheric pressure, creating possibilities for rheology improvements by pressure processing. Maximal tomato pectinmethylesterase activity in the pressure–temperature domain investigated was observed at 55 °C and 300 MPa for pH 8.0 and at 57 °C and 450 MPa for pH 4.4. However, under all pressure–temperature conditions tested the catalytic activity of tomato pectinmethylesterase at pH 4.4 was much lower than at pH 8.0. The chemical de‐esterification of pectin at pH 8.0 was accelerated by increasing pressure and temperature, whereas no chemical deesterification of pectin was observed at pH 4.4. Copyright © 2004 Society of Chemical Industry     

EFFECT OF HIGH-PRESSURE TREATMENT OF MILK ON LIPASE AND γ-GLUTAMYL TRANSFERASE ACTIVITY

High‐pressure (HP) treatment (0–180 min at 300–400 MPa) was applied to milk to evaluate the pressure effects on the activities of lipoprotein lipase and γ‐glutamyl transferase. Short time pressure exposure resulted in some enhancement in the activity of both enzymes, and for lipase, there was no inactivation during the entire pressure hold time (up to 100 min). With γ‐glutamyl transferase, the extent of enhancement in activity was pressure level dependent, with lower pressure resulting in a greater enhancement. Furthermore, longer pressure treatment times resulted in inactivation of γ‐glutamyl transferase, following a first order kinetic model. The pressure sensitivity of the inactivation parameters (k and D‐values) for γ‐glutamyl transferase was adequately described by the pressure death time and Arrhenius models with a z_pof 543 MPa and an associated volume of activation, ΔV^≠, of ?3.28 × 10^?8 m³/mole.     

超高压处理对三疣梭子蟹感官及其肌原纤维蛋白生化特性的影响

以不同的压力处理三疣梭子蟹,通过考察其感官、pH值、色泽、肌原纤维蛋白含量、巯基含量、表面疏水性和Ca~(2+)-ATPase活力的变化,研究超高压处理对梭子蟹品质的影响。结果表明,150、200 MPa以及250 MPa处理后的梭子蟹,其感官评分、pH值和白度无显著变化(P0.05),而300 MPa和350 MPa组均出现显著性变化(P0.05),且蟹肉出现熟化,产生了微弱的熟蟹肉特有风味;与对照组相比,250 MPa组的肌原纤维蛋白含量和150、200 MPa组的Ca~(2+)-ATPase活力变化不显著(P0.05),其余处理组均发生显著性变化(P0.05);150 MPa和200 MPa组蟹肉肌原纤维蛋白的巯基含量没有显著性变化(P0.05);而表面疏水性与对照组相比均显著升高(P0.05)。综合梭子蟹感官评分及其肌原纤维蛋白生化特性指标,150、200 MPa和250 MPa的压力不会引起梭子蟹品质显著改变,这为后续研究超高压对梭子蟹贮藏品质的影响提供了理论依据。     

EFFECT OF SODIUM CHLORIDE ON THE ACTIVITY AND STABILITY OF POLYPHENOL OXIDASE FROM FUJI APPLE

The effect of sodium chloride on activity and stability of polyphenol oxidase (PPO, EC1.14.18.1) from Fuji apple was investigated. Partially purified PPO was activated with 0.17–3.4 M NaCl. Purified PPO stored with NaCl was stable for 2 months at 4C. PPO in the presence of NaCl (0–5.1 M) was scanned by Differential UV from 240 to 300 nm and spectral analysis showed that there were conformational changes as a function of NaCl concentration.     

高压处理对牛骨骼肌G-肌动蛋白结构的影响

从牛骨骼肌中提取G- 肌动蛋白,并用0.1～400MPa 高压处理,对G- 肌动蛋白的荧光光谱、质量中心、表面巯基含量、芳香族表面疏水性残基的变化进行分析,探讨G- 肌动蛋白的结构变化。在0.1～100MPa 处理时G- 肌动蛋白荧光强度呈下降趋势,在200～400MPa 处理时荧光强度呈上升趋势,荧光强度峰值的极大波长发生蓝移。100MPa 压力下G- 肌动蛋白质量中心稍微下降,但压力在100～300MPa 时质量中心呈上升趋势。表面巯基含量随着压力的增高有明显上升趋势。随着压力的升高芳香族表面疏水性残基的荧光强度升高,压力为300MPa 时显示最高值。从此结果可推测超高压处理引起的G- 肌动蛋白三级结构变化是不可逆变化。     

Effect of Osmotic Dehydration Under High Hydrostatic Pressure on Microstructure, Functional Properties and Bioactive Compounds of Strawberry (Fragaria Vesca)

Sliced strawberries were subjected to combined osmotic dehydration (40 °Brix) and high hydrostatic pressure (HHP) at 100, 200, 300, 400 and 500 MPa for 10 min. This research was carried out to study the effects of pressure on firmness, polysaccharides, total dietary fibre and microstructure, functional properties (rehydration ratio and water holding capacity) and bioactive compounds (anthocyanins, flavonoid and total phenolic). HHP affected the texture of the fruits leading to soft fruits due to increasing pressure. Fruit microstructure evidenced influence of pressure presenting the pressurised samples irregular matrices compared to samples treated at 0.1 MPa (control samples). Polysaccharides increased with pressure. Total dietary fibre, anthocyanins, flavonoids and total phenolic content showed a decrease with pressure when compared to control samples. Based on results, minor alterations of the mentioned quality parameters were evidenced when working in the range of 300–500 MPa.     

High-pressure/temperature treatment effect on the characteristics of octopus (Octopus vulgaris) arm muscle

Octopus muscle was pressurized at 200, 300 and 400 MPa for 15 min at 7 °C and 40 °C; treatments at 400 MPa continuously for 15 min and in three 5 min pulses at 7 °C and 40 °C were also carried out. Total viable counts of Enterobacteriaceae, Staphylococcus aureus and lactic bacteria, shear strength and autolytic activities were studied. High-pressure treatments reduced colony-forming units (cfu) for all groups tested, especially when applied in pulses at 40 °C, and caused a change of the predominant flora. Autolytic activity clearly decreased when pressure was over 200 MPa. When muscle is pressurized, shear strength increases although it is higher at lower pressures (200 MPa) than at higher pressure (400 MPa). When pressure was applied, morphological and ultrastructural changes were observed, mainly in the variation of fibrillar compacting, destruction of the sarcomere pattern, ultrastructural alteration of the myofibrils and gradual disappearance of the cell nucleus. The connective tissue was virtually unaffected by pressure despite the temperature applied.     

Levels of calpain and calpastatin in meat subjected to high pressure

The levels of μ-, m-calpain and calpastatin were assayed in pressurized rabbit muscle.

The crude calpain level from the pressurized muscle at 100 MPa was almost the same with that of control. Above 100 MPa, the level of calpain decreased rapidly with increased pressure. At 300 MPa, the calpain level was almost inactivated. When the crude extract was pressurized, the calpain level followed the same tendency as that in the pressurized muscle.

When the extracts from control or pressurized muscle were subjected to DEAE-Sephacel column chromatography, μ- and m-calpains and calpastatin lost their activity with increasing pressure, but the degree of loss was different for each.

Calpains resisted changes in pressurization at 200 MPa and were inactivated over 200 MPa. Inactivation of calpastatin at 100 MPa was faster than that of calpains.

From the results, it was concluded that calpain levels remained in muscle pressurized up to 200 MPa, whereas calpastatin levels were decreased by the pressurization. Thus the total activities of calpains in pressurized muscle appear to have been increased by the pressure treatment and this may result in tenderization of meat.     

THERMAL AND HIGH-PRESSURE STABILITY OF PURIFIED PECTIN METHYLESTERASE FROM PLUMS (PRUNUS DOMESTICA)

Pectin methylesterase (PME) from greengage plums (Prunus domestica) has been extracted and purified using affinity chromatography. Only one band on sodium dodecyl sulfate–polyacrylamide gel electrophoresis was obtained, with an estimated molecular weight of 31 kDa. On isoelectric focusing electrophoresis, two bands with neutral isoelectric points (6.8 and 7.0) were detected. The optimal pH and temperature for plum PME activity were 7.5 and 65C, respectively. A study of purified plum PME thermostability was performed at pH 7.5 and 4.0, indicating a higher thermostability at pH 7.5 than at pH 4.0. A biphasic inactivation behavior was observed for thermal treatments (54–70C), whereas its pressure inactivation could be described by a first‐order kinetic model in a pressure range of 650–800 MPa at 25C. Purified plum PME was found to be relatively stable to thermal and pressure (≤600 MPa) treatments, compared to PME from other fruits.