Emulsifying capacity of fish mince from several species during frozen storage

Abstract : As a functional property of protein, emulsifying capacity (EC) is of great technological interest. This article examines EC in fish mince from three species differing in fat content and in the pattern of deterioration during frozen storage—blue whiting (Micromesistius poutassou R), horse mackerel (Trachurus trachurus L) and mackerel (Scomber scombrus L)—caught during two seasons of the year in which physiological behaviour is expected to be different (winter and summer). EC and protein solubility were determined periodically. The results indicate the existence of a direct relationship between the fat content of the species used and its EC. Furthermore, in the species studied EC was independent of protein solubility and the amount of protein in the medium, both of which decline as a result of the formation of aggregates during frozen storage. This is not therefore a suitable method for determining protein quality during frozen storage.     

Alteration of the electrophoretic pattern of myofibrillar proteins in fish mince during frozen storage

A study was made of the variations in the electrophoretic profile of myofibrillar proteins in the muscles of blue whiting (Micromesistius poutassou R.), horse mackerel (Trachurus trachurus L.) and mackerel (Scomber scombrus L.). It was shown that all species presented different deterioration patterns during frozen storage. The fish were caught at two separate times of the year (winter and summer) and were stored frozen at -18°C for 1 year. The results indicate that during frozen storage, electrophoretic patterns varied according to species. Comparison of myosin heavy chain/actin (MHC/A) ratios indicates that blue whiting is the species that undergoes most alteration, and that this is more intense in fish caught in the summer than in the winter. Alteration of the MHC/A ratio was similar in horse mackerel and mackerel caught in the winter, whereas in the summer horse mackerel proved to be the most stable species. In all cases, the reduction of the MHC/A ratio was due essentially to alteration of the MHC, an effect which was particularly marked in blue whiting. Tropomyosin remained stable throughout the storage period in all three species.     

Rheological and microstructural changes in gels made from high and low quality sardine mince with added egg white during frozen storage

 This paper examines the influence of freezing temperature (–40°C or –18°C) and frozen storage temperature (–18°C or –12°C) on gels made from two different sardine minces (M1, high functional quality; M2, low functional quality), with the addition of egg white as a gel enhancing ingredient. To characterize the washed mince, proximate analyses and protein functionality were determined. Freezing at either –40°C or –18°C caused no drastic changes in gel structure. Throughout the course of frozen storage of all samples, a decrease in the water holding capacity (WHC) was detected, along with an increase in the amount of protein soluble in 8 M urea. At 90 days the gels frozen at –40°C exhibited numerous ice micro-crystals; however, they did not affect the external appearance of the gel and had hardly any effect on gel strength, shear strength, hardness, cohesiveness or elasticity. On the other hand, at 90 days the gels frozen at –18°C and stored at either temperature exhibited large, macroscopically visible ice crystals. In these samples, gel strength and shear strength increased while hardness decreased. No definite changes attributable to mince quality were detected during frozen storage. Received: 23 June 1997     

熟制小龙虾冷冻贮藏期间的品质变化研究

目的研究熟制小龙虾冷冻贮藏期间的品质变化。方法以熟制的带壳和去壳小龙虾为原料,将其在-18℃下贮藏1个月,通过检测虾肉的脂肪氧化程度、pH值、挥发性盐基氮(total volatile base nitrogen,TVB-N)值、盐溶性蛋白含量、色泽、质构特性等指标,考察小龙虾在冷冻贮藏期间的品质变化。结果在贮藏期间,带壳和去壳小龙虾虾肉的脂质氧化程度、pH值、TVB-N均呈上升趋势,总巯基含量和盐溶性蛋白含量持续下降,去壳虾肉颜色变化不显著,而带壳虾肉的色泽参数L*值和白度值W显著降低,硬度、弹性、咀嚼度和回复力在贮藏前期下降显著,之后下降趋势较为平缓。结论带壳和去壳的虾肉在贮藏前期(0～2周)的各指标无显著差异,而冷冻贮藏3周之后,带壳虾肉的品质优于去壳虾肉,冷冻贮藏一个月后,带壳虾肉和去壳虾肉均可正常食用。     

鲢鱼滑在冻藏过程中的结构变化

为研究鲢鱼滑在-20℃冻藏过程中的结构变化,测定了鲢鱼滑盐溶性蛋白含量、活性巯基含量和Ca²⁺-ATPase活性,并结合圆二色光谱（CD）、扫描电镜（SEM）和低场核磁（LF-NMR）进行分析。结果发现,三个指标随冻藏时间延长逐渐下降,其中盐溶性蛋白含量从新鲜状态的58.2 mg/g降至17.3 mg/g,活性巯基含量从0.598 mol/105g降至0.204 mol/10⁵g,Ca²⁺-ATPase活性从0.214μmol/min·g降至0.051μmol/min·g;CD扫描结果显示,冻藏初期α-螺旋主要向β-折叠转化,后主要转化为无规则结构;SEM结果显示,鲢鱼滑凝胶结构由于失水而逐渐收缩,表面光滑度降低,凝胶网络结构受损;LF-NMR的T₂谱显示-20℃环境下有两种结合水的横向弛豫时间,分别为T₂₁（0.09¹ ms）和T₂₂（1¹0 ms）,随着冻藏时间的延长,T₂₁无明显变化,T₂₂总体呈现下降趋势,可知蛋白内部对水分的束缚力增强。从结构变化角度探究了鲢鱼滑在冻藏过程的品质变化。      

Muscle changes in hard and soft shell crabs during frozen storage

Chemical and physicochemical changes of muscles from hard and soft shell mud crabs (Scylla serrata) were monitored during 12 weeks of storage at −20 °C. Ca²⁺-ATPase activity of natural actomyosin (NAM) from both crabs decreased continuously during storage, regardless of muscle types. After 8 weeks of storage, Ca²⁺-ATPase activity of NAM from lump muscle of soft shell crab decreased to a greater extent than that of hard shell crab (P < 0.05). An increase in disulfide bonds was observed with the coincidental decrease in sulfhydryl group content during extended storage (P < 0.05). Surface hydrophobicity of all samples increased up to 8 weeks, being this sampling time followed by a gradual decrease. Formaldehyde content of all samples increased throughout the storage (P < 0.05). Slightly higher formaldehyde content was found in soft shell crab muscle, compared with hard shell counterpart (P < 0.05). Claw muscle generally contained a greater amount of formaldehyde than lump counterpart (P < 0.05). Protein solubility of all samples decreased continuously throughout the 12 weeks of frozen storage (P < 0.05). Lipid oxidation took place during the extended storage as evidenced by the increase in thiobarbituric acid reactive substances. The pH of all samples generally decreased during frozen storage. Cooking loss of all crab muscles increased as storage time increased (P < 0.05) and was more pronounced in claw muscle, particularly from soft shell crab.     

Quality changes during frozen storage and thawing of mixed bread

In the present work investigations of the dependence between frozen storage time, the method of thawing (air blast at 50 degrees C and microwave), organoleptic and physico-chemical changes in bread are reported. The quality of the thawed product was analysed directly after thawing and after two days of storage at room temperature. It was found that changes in quality of bread are more affected by frozen storage than by the employed thawing method. The thawing methods had a significant (p < or = 0.01) effect on the investigated physico-chemical parameters of the product, however, their statistically significant (p < or = 0.01) effect on the sensory quality could only be revealed after two days of storage of the previously thawed bread at room temperature rather than directly after thawing. The results obtained in the present study suggest that bread which underwent microwave thawing had generally better quality in comparison with air blast thawing.     

冷冻面团制作的面包在储存期间风味的变化

在冷冻甜面团的研究开发中,通过感官评价小组采用描述性分析对面包样品的风味剖析,同时采用固相微萃取(SPME)技术分别提取样品中的挥发性风味物质,并经气相色谱-质谱(GC-MS)联用法进行鉴定,重点研究了冷冻甜面团在不同冷冻储存阶段所制作的面包的风味变化问题。结果发现,用冷冻甜面团制作的面包与相同配方制得的新鲜面包相比,在冷冻期间21～28d内,烘焙风味的劣化即呈现出来并急速降级,如酸含量明显升高,醇类明显降低,醛类相对较高,酯类、呋喃类有所升高但芳香族化合物却较低,并在长达70d的冷冻储存期间趋于不可逆转的稳定状态。     

Texture changes in frozen cod mince measured by low-field nuclear magnetic resonance spectroscopy

Studies were carried out on changes in water proton relaxation, Instron parameters, dimethylamine (DMA) content and sensory texture scores during storage of cod mince at -10°C, -20°C and -70°C. The longest transverse proton relaxation time measured by pulsed low-resolution nuclear magnetic resonance (NMR) spectroscopy increased with temperature and duration of frozen storage. These variations in the NMR parameter paralleled changes observed with analytical methods commonly used for evaluating fish texture, ie Instron measurements, as well as dimethylamine and sensory analyses. It is concluded that the NMR method can be an alternative tool to study textural modifications of cod during frozen storage. © 1997 SCI.     

Changes in lipids,proteins and kamaboko forming ability of silver carp (Hypophthalmichthys molitrix) mince during frozen storage

Frozen storage of mechanically deboned silver carp (Hypophthalmichthys molitrix) mince for 180 days resulted in a significant (P⩽0.05) decrease in myofibrillar proteins. In contrast, peroxide value (PV), free fatty acids (FFA) and total volatile base nitrogen (TVBN) contents increased significantly (P⩽ 0.05) throughout the storage period. The kamaboko forming ability and the sensory scores of the silver carp mince decreased significantly (P⩽0.05) during the storage period. Texture of the mince was significantly (P ⩽ 0.001) correlated with the decrease in the myofibrillar proteins (salt-soluble proteins), jelly strength and folding test grades; and increase in expressible water percentage, PV, FFA and TVBN content. Based on ‘texture’ of the mince, the product was acceptable for 180 days at −18°C.     

Investigation of colour changes of some tomato products during frozen storage

The colour changes of frozen tomato pulp were investigated under different conditions of frozen storage (?25°C; in open bags with presence of O₂ and in artificial light or darkness; in closed bags also in artificial light or darkness). In addition the antioxidative effect of tomato seeds and spices (sage, thyme, rosemary, oregano, majoram) was studied. The colour change of tomato pulp was determined with instrumental colour measurement, the carotenoid pigments loss was measured with UV/VIS spectrophotometry. It was found that exposure to light and oxygen accelerated the colour loss and oppositely packaging and storage in darkness had a colour saving effect. The ground tomato seeds (5%) could stabilize the carotenoid pigments after longer time frozen storage (min. 10 weeks). The commercial spices (0.2%), mainly rosemary and marjoram significantly reduced the pigment degradation. The tomato seeds and the spices did not change significantly the taste of tomato pulp.     

Effect of ice storage on the functional properties of pink perch and oil sardine meat

Ice storage of dressed pink perch (Nemipterus japonicus) and Indian oil sardine (Sardinella longiceps) for 16 and 20 days, respectively, resulted in a decrease in emulsifying capacity (EC), protein solubility (PS), relative viscosity (RV) of salt‐soluble proteins (SSP) and water‐soluble proteins (WSP), water binding capacity (WBC) in terms of absorbed moisture in water (AM_w), absorbed moisture in brine lpar;AM_b), retained moisture in water (RM_w) and retained moisture in brine (RM_b), WSP and SSP, and increase in cook loss (CL). Decrease in protein solubility influenced the EC, RV, CL and WBC in both the species of fish. Significant (P<0.05) correlations existed among various functional properties analysed, in both the fishes during the ice storage. © 1999 Society of Chemical Industry     

不漂洗鲢鱼鱼糜浸渍冻藏及其品质变化

目的:研究浸渍冻藏(IFS)对不漂洗鲢鱼鱼糜品质变化的影响。方法:将鱼糜样品非接触浸入过冷液(-20±2)℃冻藏60 d,以传统空气冻藏(TFS)为对照,分析不漂洗鲢鱼鱼糜Ca²⁺-ATP酶活性、羰基含量、硫代巴比妥酸值(TBA)以及凝胶强度、持水力和凝胶结构在冻藏过程中的变化规律。结果:IFS组鱼糜冻结过程中通过最大冰晶生成带时间仅为10 min,冻藏过程中温度波动幅度为0.72℃,显著低于TFS组(分别为78 min和1.43℃);冻藏过程中,鱼糜Ca²⁺-ATPase活性、凝胶强度和持水力逐渐下降,蛋白质羰基含量、TBA值逐渐上升,凝胶网络结构逐渐被破坏;但与TFS组相比,IFS能明显减小这些指标的变化幅度。结论:浸渍冻藏能有效延缓鱼糜冻藏过程中的品质劣变,是一种有潜力的食品冷链技术。     

鳙鱼鱼糜在冻藏过程中理化性质变化的研究

研究了不同温度冻藏条件下鳙鱼(Aristichthysnobilis)鱼糜的品质变化。鳙鱼鱼糜分别冻藏于-10℃、-20℃和-30℃条件下,冻藏过程中肌原纤维蛋白质Ca2 -ATPase活性和总-SH含量不断下降,冻藏20周后分别下降至新鲜样品的16.9%、64.1%、77.4%和53.1%、60.2%、66.1%,凝胶强度也呈现下降趋势,同Ca2 -ATPase活性和总-SH含量变化相一致。鱼糜微结构表明,不同温度冻藏条件下,鱼肉蛋白质中冰结晶大小有很大差异,冰晶的影响是导致蛋白质变性的主要原因。     

广西北部湾主要贝类在冻藏过程中品质变化的研究

测定冻藏过程中牡蛎(Crassostrea rivularis)、文蛤(Meretrix meretrix Linnaeus)和波纹巴非蛤(Paphia Undulata)的水分含量、pH、氨基态氮含量、挥发性盐基氮含量和色差。研究不同的冻藏温度(-18℃和-60℃)和预处理方式(新鲜的和预煮的)对贝肉冻藏品质的影响。结果表明,新鲜的牡蛎、文蛤和波纹巴非蛤在-18℃和-60℃下冻藏3个月,肌肉的水分含量在总体上均呈现下降的趋势;pH的变化起伏不定;氨基态氮和挥发性盐基氮的含量随着冻藏时间的延长而逐渐升高;肌肉亮度降低,总体颜色变暗淡。经过预煮的牡蛎、文蛤和波纹巴非蛤在-18℃或-60℃下冻藏3个月,贝肉的水分含量、pH、氨基态氮和挥发性盐基氮以及亮度变化不大,其品质变化小于未经预煮处理的样品。