DEGRADATION OF PROTEOGLYCANS IN THE SKELETAL MUSCLE OF PACIFIC ROCKFISH (SEBASTES SP.) DURING ICE STORAGE

Soluble collagen, proteoglycans and two lysosomal enzymes known to degrade proteoglycans were studied during ice storage of skeletal muscle from Pacific rockfish. The solubility of muscle collagen progressively increased during storage in ice for 7 days. Proteoglycans isolated from prerigor muscle by extraction with guanidine HCl and density gradient ultracentrifugation contained only 43 μg hexuronic acid/100 g of wet tissue. The sulfated glycosaminoglycans portion of proteoglycans were isolated by trypsin digestion of an extract from muscle acetone powder and contained 58 μg hexuronic acid/20 g of acetone-dried muscle tissue. Sulfated glycosaminoglycans had several components which separated by sodium dodecylsulfate polyacrylamide gel electrophoresis. Electrophoresis of sulfated glycosaminoglycans from stored rockfish revealed disappearance/decrease of specific zones after 5 days at 0C. The degradation of proteoglycans occurs in postmortem fish muscle and this may contribute to the destabilization of the extracellular matrix and texture softening during postharvest storage of fish.     

鲈鱼在4℃冷藏过程中的肌肉品质变化

目的：探究4℃冷藏过程中鲈鱼肌肉品质的变化。方法：测定4℃冷藏过程中鲈鱼肌肉pH值、菌落总数、总挥发性盐基氮（total volatile base nitrogen,TVB-N）含量、K值和质构等指标,综合评价鲈鱼生理生化品质的变化,采用Masson染色和免疫组化分析评价组织形态学变化,利用酶解荧光肽底物测定特异性酶解胶原蛋白的基质金属蛋白酶（matrix metalloproteinases,MMPs）活力变化。结果：鲈鱼在贮藏期间pH值呈先下降后升高趋势,菌落总数、TVB-N含量和K值随贮藏时间的延长而增加,并在第8天超过临界值。十二烷基硫酸钠-聚丙烯酰胺凝胶电泳分析结果显示,贮藏至6 d鲈鱼肌肉蛋白组成没有明显变化,而在第8天肌球蛋白重链降解明显。Masson染色和I型胶原免疫组化分析结果显示,随贮藏时间的延长,肌内膜逐渐被降解,至第12天,肌膜I型胶原蛋白和肌纤维之间出现明显间隙。MMPs活力随贮藏时间的延长而明显增加,而鱼肉硬度不断下降。结论：鱼类冷藏期间肌肉的软化与胶原蛋白分解密切相关,而MMPs对I型胶原蛋白的降解可能是鱼死后肌肉软化的主要原因。     

Effects of slaughtering methods on sensory,chemical and microbiological quality of rainbow trout (<Emphasis Type="Italic">Onchorynchus mykiss</Emphasis>) stored in ice and MAP

The effects of slaughtering methods (percussive stunning and death in ice slurry) on the quality of rainbow trout stored in ice and modified atmosphere packing (MAP) (40% CO₂, 30% N₂ and 30% O₂) were investigated in terms of sensory, chemical and microbiological analysis. Sensory analysis showed that the demerit points of fish slaughtered by percussive stunning were higher than those slaughtered by the ice slurry method, but there were no significant differences in demerit points (P>0.05). In addition, the rate of increase in demerit points in fish in MAP was significantly (P>0.05) higher at 6 and 10 days of storage than that in fish in ice for each slaughter method, which was due to increased drip, the appearance of slime and the odour of the fish in MAP packing. The mean K values of rainbow trout slaughtered by percussive stunning in this study were significantly lower (P<0.05) than those of trout slaughtered according to the ice slurry method. The level of biogenic amines, regardless of the slaughter method, showed a similar trend (P>0.05), but higher concentrations of biogenic amines were found for the ice slurry slaughter method and for fish stored in ice. There were no significant differences (P>0.05) in total viable count of fish stored in ice and MAP, regardless of the different slaughter methods used. However, fish packed in MAP showed reduction in bacterial counts compared to fish held in ice throughout study. The results of this study showed that slaughter by percussive stunning improved the quality of trout compared to the ice slurry method.     

Superchilled,chilled and frozen storage of Atlantic mackerel (Scomber scombrus) fillets – changes in texture,drip loss,protein solubility and oxidation

Changes in quality characteristics in relation to protease activity and protein oxidation in chilled, superchilled and frozen mackerel fillets during storage were studied. The solubility of sarcoplasmic proteins was quite stable in mackerel samples for all storage experiments, whereas the solubility of myofibrillar proteins decreased in both superchilled and frozen samples. A significant correlation (r = 0.983, P < 0.05) between the increased activity of cathepsin B+L in chilled fillets and softening of the fish flesh during storage was revealed. Contrary with chilled samples, the texture of superchilled mackerel fillets became tougher along the storage period, which can be explained by a higher rate of myofibrillar oxidation (r = 0.940, P < 0.05). The hardness and drip loss decreased slightly at the end of frozen storage. Superchilling preserved the quality of mackerel fillets with the least side effects in relation to protein solubility, drip loss and softening of the fish tissue as compared to chilled and frozen storage.     

The impact of collagen on softening of grass carp (Ctenopharyngodon idella) fillets stored under superchilled and ice storage

The objective of this work was to study the impact of collagen on softening of grass carp (Ctenopharyngodon idella) fillets during chilled storage. The fillets were stored under superchilling (?1.5 ± 0.2 °C) and with ice (0.2 ± 0.1 °C) for 21 days, and texture properties, collagen and the related enzyme activities were measured. Results showed that firmness and collagen content were strongly influenced by storage temperature and time. Fillet firmness decreased by 32.3% (superchilling) and 49.6% (ice stored) of the initial values after 3 days of storage, respectively. Total collagen content decreased with time, but different collagen fractions showed variations. Collagen degraded to different extents depending on storage conditions as indicated by SDS‐PAGE and amino acid analysis. In addition, collagenase activity declined significantly during the first 3 days, followed by a slow increase. This study demonstrated that collagen degradation was involved in grass carp fillet softening and provided useful information for fillet quality improvement.     

中性氧化电解水对冷鲜草鱼肉品质及质构的影响

为探讨中性氧化电解水对冷鲜草鱼肉的保鲜效果,对冷藏条件下(4℃)冷鲜草鱼肉的品质指标及质构进行检测,并对比贮藏开始和结束后草鱼的肌原纤维组织结构的变化。结果表明:中性氧化电解水能够降低冷鲜鱼肉贮藏过程中菌落总数、假单胞菌数、挥发性盐基氮及硫代巴比妥酸值等品质指标的变化,可将货架期延长4 d左右;与对照组及减菌剂Ⅰ组相比,电解水处理可以减缓冷藏过程中鱼肉肌原纤维的分解,进而减少冷鲜草鱼的硬度、弹性和回复性等质构的变化。在贮藏至第6天,中性氧化电解水处理的冷鲜鱼肉硬度、弹性及回复性分别为对照组的1.23、2.13、1.83倍,且电解水组的肌原纤维相对较长且排布较规整。利用中性氧化电解水可以有效减轻冷鲜草鱼肉贮藏过程中品质及质构的变化,可为淡水鱼冷鲜鱼肉产品的贮藏保鲜技术开发提供参考。     

Relevance of collagen solubility and gelatinolytic proteinase activity for texture softening in chilled grass carp (Ctenopharyngodon idellus) fillets

The aim of the present study was to investigate the underlying mechanisms of softening texture in chilled grass carp filletsunderpinning collagen solubility, gelatinolytic proteinase activity and physicochemical parameters. Acid-soluble collagen (ASC) and heat soluble collagen (HSC) increased markedly, while a significant decline was detected in total collagen and insoluble collagen (ISC) during the first 3 days of storage, coinciding with a loss of shear force and water-holding capacity (WHC) (P < 0.05). Moreover, the activity of gelatinolytic proteinases was gradually activated and reached the peak at day 3 (P < 0.05). Pearson coefficient analysis showed that gelatinolytic proteinase activity revealed a significant correlation with collagen solubility. Total collagen, ASC, ISC and HSC were significantly correlated with shear force and WHC. Our study clarified that the increase of collagen solubility by gelatinolytic proteinases played an important role for texture softening in the early stage of chilled grass carp fillets.     

EFFECT OF CHILLING AND FREEZING ON SURVIVAL OF VIBRIO PARAHAEMOLYTICUS ON FISH FILLETS1

Vibrio parahaemolyticus is a foodborne pathogen isolated from coastal waters of the United States, and from seafoods including fish. No information is available on the viability of V. parahaemolyticus on raw, chilled and frozen fish. A three‐strain mixture of V. parahaemolyticus was inoculated on fish fillets (pH 6.4) to obtain a bacterial load of 10⁴ (high) or 10³ (low) CFU/fillet, and stored at 4C or 8C for 9 days or at – 18C for seven weeks. At 4C and 8C, and at both levels of inoculation, V. parahaemolyticus survived on the fillets for the entire duration of the study. However, there was a significant reduction (P < 0.01) in V. parahaemolyticus population on the fillets by 9 days of storage. In the frozen fillets, there was a sharp decline (P < 0.01) in the population of V. parahaemolyticus by day 5 of storage. Although chilling and freezing significantly (P < 0.01) inactivated high numbers of V. parahaemolyticus on fish, they cannot be relied upon as a method to reduce V. parahaemolyticus on fish, since the time and magnitude of reduction depends on the initial load of the pathogen and the storage temperature.     

1-MCP suppresses ethylene biosynthesis and delays softening of 'Hami' melon during storage at ambient temperature

BACKGROUND: ‘Hami’ melon is susceptible to softening during postharvest storage at ambient temperature, which enhances postharvest deterioration and limits transportation and storage. To look for a method of softening control, the effect of 1‐methylcyclopropene (1‐MCP) on regulating postharvest softening of ‘Hami’ melon fruit was investigated. RESULTS: 1‐MCP treatment at 1 µL L^?1 significantly reduced ethylene production and maintained higher levels of fruit firmness. It also markedly inhibited the accumulation of 1‐aminocyclopropane‐1‐carboxylic acid (ACC) and maintained lower activities of ACC synthase and ACC oxidase. In addition, 1‐MCP treatment reduced the activities of fruit‐softening enzymes such as pectin methyl esterase, polygalacturonase, endo‐1,4‐β‐glucanase and β‐galactosidase. CONCLUSION: 1‐MCP was effective in suppressing ethylene production and delaying fruit softening in ‘Hami’ melon by decreasing the activities of ethylene biosynthesis enzymes and inhibiting fruit‐softening enzymes. Copyright © 2011 Society of Chemical Industry     

不同宰杀方式对草鱼肉呈味水溶性成分的影响

以不同宰杀方式草鱼的背部肉为对象,采用高效液相色谱法和氨基酸自动分析法研究不同宰杀方式（自然、急杀、去鳃）对草鱼背部肉核苷酸类化合物和游离氨基酸含量的变化,并测定背部肉pH值、糖原和乳酸的含量。结果表明：自然、急杀、去鳃3 种宰杀方式的草鱼背肉苦味氨基酸含量占总游离氨基酸含量分别为78.95%、68.60%、69.44%,部肉的鲜度K值分别为20.28%、15.49%、12.13%,自然死亡组腺嘌呤核苷三磷酸含量最低,肌苷酸含量最低,鲜度最差。草鱼背肉中pH值的变化与乳酸含量的变化呈负相关,乳酸含量的变化与糖原含量的变化呈负相关,自然死亡的草鱼肉乳酸含量最高,pH值最低。不同宰杀方式对草鱼背肉呈味水溶性成分影响较大,自然死亡的草鱼肉滋味最差,急杀致死和去鳃致死组滋味差别不明显。因此,在加工过程中,要避免鱼血渗入肌肉,造成鱼肉土腥味产生。     

冷鲜肉保鲜过程中的微生物污染及其预防措施

随着人们生活质量的不断提高,对肉类的需求逐渐由量向质转变,肉品质越来越受到重视。冷鲜肉是一种低温生鲜肉类制品,从屠宰到上市在低温的环境中经历了僵直、解僵和成熟的过程,具有鲜嫩多汁、汤清肉鲜、易咀嚼以及易被消化等特点。冷鲜肉的水分含量高且营养较丰富,动物体内携带的微生物以及在屠宰、加工、储存和运输环境中的微生物都极易在其中生长繁殖,从而引发冷鲜肉腐败变质,货架期缩短。本文概述了冷鲜肉污染的几种主要途径,并介绍了产品包装、保鲜剂、物理处理及宰前饲喂等预防腐败、延长冷鲜肉货架期的措施,为进一步探索更加高效的冷鲜肉保鲜方式提供参考依据。     

Psychrophilic and psychrotrophic clostridia: sporulation and germination processes and their role in the spoilage of chilled,vacuum‐packaged beef,lamb and venison

Spoilage of beef, lamb and venison by psychrophilic and psychrotrophic clostridial species renders meat unacceptable resulting in financial losses and reduced consumer confidence. A number of clostridial strains, including Clostridium algidicarnis, Clostridium algidixylanolyticum, Clostridium estertheticum, Clostridium frigidicarnis and Clostridium gasigenes, have been implicated in red meat spoilage. Unlike other spoilers, these clostridia are able to grow in anaerobic conditions and at chilled temperatures (some at ?1.5 °C the optimal storage temperature for chilled red meat). The spoilage they cause is characterised by softening of the meat, production of large amounts of drip (exudates), offensive odours and in the case of C. estertheticum and C. gasigenes production of gas. Spoilage occurs following the introduction of clostridial spores into vacuum packages during processing. Germination of spores is necessary for the growth of vegetative cells, which cause spoilage. Current mitigation strategies focus on good management practice within meat processing plants. However, this is not always sufficient to prevent spoilage. This review summarises the issues associated with meat spoilage because of psychrotolerant clostridia and discusses areas that require further study.     

肌肽联合超高压对黑鱼肉脂质氧化及肌原纤维蛋白的影响

为研究肌肽联合超高压(CUH)对黑鱼肉脂质氧化及肌原纤维蛋白(myofibrillar protein,MP)的影响,以新鲜宰后黑鱼肉为材料,比较分析CUH(肌肽浓度25 mmol/L,超高压压力300 MPa,保压时间900 s)处理对黑鱼肉在冷藏期间的脂质氧化、蛋白氧化、蛋白降解、蛋白结构等的影响.通过测定超高压后...     

The chilled storage life and retail display performance of vacuum and carbon dioxide packed hot deboned beef striploins

Two cooling regimes that complied with the New Zealand meat hygiene requirement that hot deboned meat be chilled to +7 °C or less within 24 hr of leaving the slaughter floor were evaluated for the production of chilled table meats. Electrically stimulated hot deboned bull beef half striploins were either vacuum or carbon dioxide packed before being cooled in accordance with either Regime 1 (cool at +5 °C for 24 hr, transfer to chiller operating at −1.0 ± 0.5 °C) or Regime 2 (cool at +5 °C for 24 hr, hold at 5 °C for 6 days, transfer to chiller operating at −1.0 ± 0.5 °C). Striploins were removed from −1.0 °C storage 8, 28, 42, 56, 70, 84 and 98 days after slaughter and subjected to microbiological, tenderness, sensory and retail display performance evaluations.

Both Regimes 1 and 2 produced meat of acceptable mean tenderness, 8 kgF (MIRINZ Tenderometer) in either vacuum or carbon dioxide packs within 28 and 8 days of slaughter, respectively. However, 70 days after slaughter the first signs of over-ageing became apparent. Steaks from Regimes 1 and 2 maintained acceptable visual appearance during retail display at 5 °C for 48 hr and 24 hr, respectively. After these times, the product was judged by the panel to be unacceptable because of its dull dark lean tissue and grey to green discoloration of the fat. Poor colour stability during retail display was mirrored by deterioration of sensory attributes, particularly aroma which is indicative of incipient spoilage. While carbon dioxide packaging in combination with Regime 1 offered an initial microbiological advantage over vacuum packaging, this advantage was not, however, carried over into retail display.

Poor colour and sensory stability during retail display suggest that chilled table cuts derived from hot deboned bull beef are more suited to the Hotel-Restaurant-Institutional (HRI) trade than supermarket retailing. To serve the HRI, vacuum packed hot deboned bull beef primal cuts processed by Regime 1 appear to be the combination of choice. This combination would enable commercial processors to produce quality table beef with a chilled storage life of up to 70 days.     

茄子果实采后软化过程中细胞壁组分及其降解酶活性的变化

研究了细胞壁组分及其降解酶活性的变化与茄子果实采后软化的关系。结果表明,采后茄子果肉硬度随贮藏时间的延长而不断下降。贮藏期间果肉水溶性果胶(WSP)含量在贮藏前12天不断增加,之后快速下降,而共价结合型果胶(CSP)、半纤维素和纤维素等细胞壁组分含量持续减少。果肉果胶甲酯酶(PME)、多聚半乳糖醛酸酶(PG)和纤维素酶(CX)活性均呈先升高后下降趋势,分别在贮藏至第6、9、12天达到最大值;β-半乳糖苷酶(β-Gal)活性始终保持较高水平,且在整个贮藏期间活性变化不明显。相关性分析结果表明,CSP、半纤维素和纤维素的降解与采后茄子果实软化密切相关,PG和CX在茄子果实采后软化过程中起着重要的作用。     

Effects of aluminium foil and cling film on biogenic amines and nucleotide degradation products in gutted sea bream stored at 2±1 °C

Biogenic amines and nucleotide degradation products of sea bream stored in ice, wrapped in aluminium foil (WAF) and in cling film (WCF) at 2±1 °C were investigated by using a rapid HPLC method. Results obtained from this study showed that for household purposes packing fish in different materials has a little effect on the biogenic amines formation and nucleotide degradation products. The highest decrease of IMP content was observed for sea bream in WAF, followed by WCF. INO values showed a fluctuation and remained below the levels of 5.5 μmol/g for all storage conditions. Hx value constantly increased with the storage time during chilled storage. For all of the storage condition, K and Ki value increased linearly with storage time. At the end of the storage period, K, Ki, H and G value reached 60–76%, 65–81%, 30–54% and 89–173%, respectively. Among biogenic amines, (trimetylamine) TMA, putrescine, cadaverine, spermidine, spermine, tryptamine, tyramine, β-phenylalanine and histamine were detected during storage period. TMA and putrescine were observed to increase linearly during storage period. Histamine production was only found at the end of storage period. The highest histamine values for fish wrapped in aluminium foil were 6.4 mg/100 g and fish wrapped in cling film was 4.6 mg/100 g.     

Evaluation of slaughtering methods for turbot with respect to animal welfare and flesh quality

After elaborating a suitable scheme to assess consciousness/unconsciousness of turbot, the effects on fish welfare of commercial and experimental slaughtering techniques were evaluated. Strong adverse reactions and slow loss of clinical reflexes were observed when fish were slaughtered by bleeding without prior anaesthesia. The efficiency of electricity (150 V for 2 s followed by 25 V for 5 min) as a stunning and killing technique was dependent on the current frequency and mode of administration, ie whether the electrical discharge was applied to the head only or throughout the whole body. Finally, percussion of the head with a mechanical device resulted in immediate and permanent loss of all responses and reflexes in all fish tested. Three methods were selected as a result of the preliminary tests (bleeding in ice slurry, whole‐body electrical treatment and percussion), and their influence on flesh quality was studied over a 9 day period. Fish killed by percussion were characterised by a higher pH and higher water content in the very early stage of post mortem storage, but also by a much delayed rigor mortis. In contrast, fish killed by electricity entered most rapidly into rigor mortis; their flesh was significantly softer (p < 0.05) throughout the entire storage time and was also redder and darker, as indicated by higher a* values (p < 0.001) and lower L* values (p < 0.01) respectively. It is suggested that automated percussion is a suitably humane method for the slaughter of farmed turbot. © 2002 Society of Chemical Industry     

Biochemical, sensory and microbiological attributes of bream (Megalobrama amblycephala) during partial freezing and chilled storage

BACKGROUND: Bream is one of the main farmed freshwater fish species in China. This study aimed to examine the nucleotide degradation of bream during partial freezing and chilled storage and to assess the possible usefulness of nucleotide ratios (K, Ki, H, P, Fr and G values) as freshness indices in comparison with sensory assessment and total viable counts. RESULTS: Total viable counts were 5.74 and 4.66 log(colony‐forming units g^?1) on the day of sensory rejection under chilled storage and partial freezing storage respectively. The inosine 5‐monophosphate decrease and inosine increase were faster in chilled storage than in partial freezing storage. Hypoxanthine levels increased continuously with time under both storage regimes. Among the nucleotide ratios, the K, Ki, P, G and Fr values were superior to the H value and provided useful freshness indicators for both storage conditions. CONCLUSION: Bream in chilled storage were sensorially acceptable only up to 10 days, compared with 33 days for bream in partial freezing storage. Partial freezing delayed the nucleotide degradation of bream. Copyright © 2011 Society of Chemical Industry     

出口冰鲜鸡肉保质期限的研究

在检疫卫生注册的出口鸡肉加工厂,在正常的生产卫生条件下,将加工的鸡肉产品速冻,使其中心温度达到-1±0.5℃后,在-1℃、0℃、4℃、10℃五种不同保存温度下,对冰鲜肉进行保质期限试验研究。通过感官检查和实验室检查冰鲜肉的品质变化,确定了不同保存温度下冰鲜鸡肉的最佳保质期限。     

Animal welfare at markets and during transport and slaughter

This review highlights some recent developments in our understanding of stress and physical injuries that occur before and during transport to slaughter, during handling at livestock markets, and at the time animals are put-up for slaughter within abattoirs. Stress in pigs during transfer to the stunning point within the abattoir has important effects on meat quality, and there is growing evidence that strenuous exercise or CO(2) stunning can contribute to oxidative rancidity in pigs, poultry and fish. In the EU, putting cattle through a crush in order to check that their eartag numbers correspond to their passport numbers is imposing additional stress, and there are reports that it is leading to greater hide contamination with Escherichia coli O157. Recent developments in stunning and slaughter include a better understanding of the causes of variation in captive bolt gun performance, the effectiveness of poll instead of frontal shooting in water buffalo, the prevalence of false aneurysms in carotid arteries during shechita and halal slaughter, and the stress effects of CO(2) stunning in fish. Stunning pigs with 90% CO(2) leads to less PSE meat than 80% CO(2). There have been concerns about the physical activity that cattle show following electrical stunning with an electrically induced cardiac arrest, and with electrical stunning using DC waveforms in broiler chickens. There is also growing concern about the hygiene problems that exist in wet markets, where animals are slaughtered alongside meat that is on display to customers.