MEASURING TEXTURAL CHANGES IN FROZEN MINCED COD FLESH

Textural deterioration in frozen cod fillet and frame minces were monitored for up to 35 days of storage at —7C and —40 C. Changes during storage were followed by measuring expressible moisture (EM), dimethylamine (DMA) production, springiness and cohesiveness with a raw texture panel, and relaxation time during a 50% compression on the Instron. Results indicate that EM, texture panel perceptions and the Instron follow changes during the early 35 days of frozen storage that occur with a different time course better than the DMA changes. The higher storage temperature showed a more rapid change in the properties measured as did the frames in comparison to the fillets.     

Deterioration of Fresh-Water Whitefish Muscle During Frozen Storage at −10°C

SUMMARY— Organoleptic and chemical deterioration of freshwater whitefish muscle frozen at −10°C for periods up to 16 weeks was assessed. As frozen storage of muscle progressed, the toughness and rancidity of baked muscle increased. The solubility of the myofibrillar protein fraction, "actomyosin," dropped from about 72 to 22% over the 16 week storage period of whitefish muscle. No change in the solubility of sarcoplasmic protein in frozen stored muscle was observed. However, with polyacrylamide disc electrophoresis, two new sarcoplasmic protein bands were detected after 16 weeks of storage. With storage of frozen muscle, water-binding capacity diminished. Although the total lipid and cholesterol contents of muscle remained constant throughout frozen storage, the phospholipid content decreased as the free fatty acid content increased. Oxidative deterioration of lipid in frozen muscle was estimated.     

骨架蛋白降解对冰鲜草鱼质构的影响

利用免疫组化技术检测草鱼背肌白肉中骨架蛋白在冰藏条件下的变化,同时通过超微结构、剪切力、滴水损失率分析草鱼背肌组织精微结构和质构特性的变化,以期阐明草鱼骨架蛋白降解与鱼肉质构劣化之间的关系,从而为调控冰鲜淡水鱼品质提供理论依据。结果显示：冰藏21 d内伴肌球蛋白、伴肌动蛋白、抗肌营养不良蛋白分别降解了76.10%、78.21%、71.14%;冰藏14 d后草鱼肌纤维明暗带模糊,Z带、M带被破坏,肌纤维结构出现严重断裂松散现象。冰藏10 d内剪切力由81 N快速下降至32 N,滴水损失率由1.6%增加至7.8%;将骨架蛋白的灰度与剪切力及滴水损失率进行相关性分析发现,剪切力与伴肌球蛋白、抗肌营养不良蛋白的灰度呈极显著正相关（P＜0.01）;滴水损失率与伴肌球蛋白、抗肌营养不良蛋白的灰度值呈极显著负相关（P＜0.01）。综上所述,骨架蛋白降解可能是草鱼在冰藏期间肌纤维结构破坏以及质构劣化的重要原因。     

Physicochemical,textural and sensory properties of white soft cheese made from buffalo and cow milk mixtures

The physicochemical, textural and sensory properties of white soft cheeses made from three different buffalo and cow milk mixtures (100:0, 70:30 and 30:70) during 3‐month storage were studied. The increase in buffalo milk concentration resulted in increasing total cheese yield, dry matter (DM) and fat retention and fat in DM content. However, it caused reductions in moisture content, salt intake, hardness, chewiness, elasticity, sensory hardness and sensory cohesiveness of the samples. The percentage of water‐soluble nitrogen to total nitrogen increased during storage resulting in decreased fracturability, hardness (textural and sensory), cohesiveness (textural and sensory), springiness, chewiness and elasticity. The panellists evaluated the white soft cheese made with buffalo milk as the most acceptable.     

TEMPERATURE ACCLIMATION OF ATLANTIC COD (GADUS MORHUA) AND ITS INFLUENCE ON FREEZING POINT AND BIOCHEMICAL DAMAGE OF POSTMORTEM MUSCLE DURING STORAGE AT 0° and -3°C

The freezing point of muscle fluid from Newfoundland Atlantic cod held at ambient sea water temperature was as low as - 1.30°C in March and as high as - 0.80°C in July. Muscle fluid from cod held live at 0°C for 3 weeks had a freezing point of - 1.02°C in contrast to a muscle fluid freezing point of - 0.90°C for cod acclimated at 10°C prior to sacrifice. Muscle fluid from cold acclimated cod exhibited 0.40°C thermal hysteresis indicating freezing point depression was influenced by antifreeze substances. The following indices of deterioration were measured in muscle sections stored at 0°C or - 3°C for 21 days: extractable protein (EP), free drip (FD), extracellular area (EA), trimethylamineoxide (TMAO), trimethylamine (TMA), dimethylamine (DMA), free amino acids (AA), and pH. Muscle sections at the anterior end of fillets, from myotomes 9–20, prepared using aseptic technique and treated with antibiotic showed less evidence of biochemical deterioration: (a) when stored at - 3°C compared to 0°C with respect to EP, AA, EA; (b) when prepared from fish acclimated at 0°C compared to at 10°C and stored at 0°C or - 3°C with respect to EP, EA, FD, AA. Negligible changes in pH, TMA and DMA occurred during 21 days storage at either temperature. TMAO decreased more during storage at-3°C than at 0°C.     

Prediction of Quality in Frozen Cod (Gadus morhua) Fillets

Physical and chemical indices were determined on frozen cod (Gadus morhua) fillets stored for ca. 90 days at either - 12°C, - 15°C, - 22°C, - 30°C or under a set of simulated industrial fluctuating temperature conditions (SIFTC). Univariate and multivariate statistics on the quality indices gave a relationship between frozen storage textural deterioration and the chemical parameters as influenced by storage temperature. Results on the SIFTC resembled the - 12°C and - 15°C storage treatments. Chemical indices had lower activation energy values than those for the physical parameters. Ammonia, determined enzymatically, can be used as an index of frozen fish quality. The quadratic equations developed using the dependent variable of Instron raw peak force, independent of time and temperature, can predict the textural quality of frozen cod fillets.     

薏仁米储藏过程中蒸煮品质及质构特性的研究

以贵州兴仁薏仁米作为实验材料,研究了薏仁米储藏一年(储藏温度25 ℃,相对湿度40%)过程中蒸煮品质及质构特性的变化。结果表明:随着储藏时间的延长,薏仁米质构特性中的硬度、压缩功、胶着性和咀嚼性变化明显,均呈先升后降的趋势;弹性、弹力和内聚性在储藏过程中无明显变化规律且变化幅度较小。薏仁米蒸煮指标中的加热吸水率、浸渍吸水率、透光率随储藏时间的延长呈上升趋势,碘蓝值和pH呈下降趋势。对薏仁米质构特性和蒸煮指标的相关性分析表明,薏仁米的部分质构特性与蒸煮指标间具有显著的相关性,反映随着储藏时间的延长,薏仁米蒸煮品质及耐储性的逐渐下降。因此,部分质构指标(硬度、压缩功、胶着性和咀嚼性)和蒸煮指标可对薏仁米的储藏品质进行评价。     

不同冷藏时间的鳝鱼肉经熟化后质构特性变化及其机理

通过测定不同冷藏时间的鳝鱼肉经熟化后（100 ℃、5 min）的蒸煮失水率、质构特性、化学作用力、蛋白质电泳和拉曼光谱等指标变化规律,探讨冷藏对鳝鱼肉熟化后质构特性变化的影响及机理。结果表明,随着冷藏时间的延长,其蒸煮失水率逐渐增加,硬度和弹性无显著性变化（P＞0.05）,内聚性和胶黏性分别在第2天和第3天显著增加（P＜0.05）,咀嚼性和回复性呈现先增加后降低的趋势（P＜0.05）。价键分析表明,疏水作用和二硫键是熟化鳝鱼肉蛋白间的最主要作用力,贮藏时间越长的鳝鱼肉,经熟化后其疏水作用越低,二硫键含量则呈先增加后降低的趋势。相关性分析表明不同冷藏时间的鳝鱼肉经熟化后二硫键含量与弹性、咀嚼性、回复性之间呈显著正相关（P＜0.05）。十二烷基硫酸钠-聚丙烯酰胺凝胶电泳分析表明分子质量低于30 kDa及分子质量约30、37、60 kDa的蛋白组分可能参与二硫键的形成,进而对熟化鳝鱼肉的相关质构特性产生影响。拉曼光谱结果显示,色氨酸、酪氨酸残基的疏水性降低,这与疏水作用变化趋势一致。二级结构分析结果表明,冷藏前3 d主要是α-螺旋和无规卷曲向β-转角和β-折叠结构转化,后期则由α-螺旋和β-折叠结构转化为β-转角和无规卷曲,蛋白无序化程度增加。综合各项指标表明二硫键和疏水作用成为熟化鳝鱼肉蛋白间的主要作用力,其变化导致蛋白构象趋于无序,进而造成不同冷藏时间的鳝鱼肉经熟化后相关质构特性变化。     

Concentration of soy protein isolate affects starch-based confections' texture, sensory, and storage properties

The effects of increasing soy protein isolate concentration on the physico-chemical properties of starch-based grape confectionery gels were investigated using thermal, textural, and sensory analyses. Soy protein isolate decreased hardness, cohesiveness, and gumminess, demonstrating potential as a texture modifier. Increasing soy protein concentration progressively decreased the elastic properties of the starch network demonstrated by a lower G'-G" crossover frequency. High levels of soy protein also created a more homogeneous water population, one which was lost at lower temperatures compared to standard confections. An improvement in taste and texture acceptability of the confections upon addition of soy protein isolate was found by sensory analysis. Finally, physico-chemical properties were compared up to 20 d of storage at ambient temperature. Soy-containing confections demonstrated lower gumminess and cohesiveness during the entire storage period but a significant increase in hardness after 20 d of storage. PRACTICAL APPLICATION: Soy protein isolate imparted soft texture to starch-based confections on a concentration-dependent basis. Increasing soy protein isolate concentration decreased elastic properties of the starch network in starch confections and significantly improved flavor and texture. Gumminess and cohesiveness of soy protein isolate confection was lower during 20 d of storage.     

Instrumental Textural Characteristics of Restructured Carrot Cubes

Studies were carried out on the instrumental textural evaluation of restructured carrot cubes. The experiment was conducted by incorporating different levels of alginate, glucono delta lactone (GDL), and calcium salt to the carrot pulp. Investigations showed that as pulp level increased from 0 to 90%, there was a corresponding decrease in failure stress, failure strain, and deformability modulus. Instrumental textural profile analysis (TPA) parameters viz. hardness, springiness, gumminess, cohesiveness, chewiness, and resilience also showed a similar trend. Effect of formulation variables, i.e., alginate, GDL, and calcium salt on hardness (response variable) were evaluated by the application of response surface methodology. All the three ingredients showed a significant (P < 0.05) influence on hardness of carrot gel. Heat treatment of restructured carrot samples resulted in an increased hardness, cohesiveness, gumminess, and chewiness while springiness, cohesiveness, and resilience decreased. The data indicated that the shrinkage during thermal treatment may be responsible for the change in textural attributes. The authors concluded that a thermally stable restructured product with appreciable textural integrity can be obtained from carrot pulp.     

Physicochemical and textural properties of ultrasound-degraded konjac flour and their influences on the quality of low-fat Chinese-style sausage

Physical and textural properties of varying molecular-weight konjac gels made by ultrasonic degradation were compared and gels were processed into low-fat Chinese-style sausages for the evaluation of textural and sensory characteristics. Results showed that as molecular weights decreased, storage modulus and loss modulus of konjac gels of varying molecular weights declined, indicating more elastic and viscous konjac gels. Shear values and textural springiness and cohesiveness of Chinese sausage were similar among all treatments. All treatments were found to have similar juiciness and overall acceptability scores. Results indicated that konjac gels with varying molecular weights could be used to partially replace pork fat to achieve similar textural properties. Incorporation of konjac gels with varying molecular weights at the current levels showed similar textural and sensory quality characteristics to the high-fat control, and contained less fat than traditional Chinese sausage.     

Low-temperature transitions in cod and tuna determined by differential scanning calorimetry

Differential scanning calorimetry measurements have revealed different thermal transitions in cod and tuna samples. Transition temperatures detected at −11°C, −15°C and −21°C were highly dependent on the annealing temperature. In tuna muscle an additional transition was observed at −72°C. This transition appeared differently than the thermal events observed at higher temperatures, as it spanned a broad temperature interval of 25°C. The transition was comparable to low-temperature glass transitions reported in protein-rich systems. No transition at this low temperature was detected in cod samples. The transitions observed at higher temperatures (−11°C to −21°C) may possibly stem from a glassy matrix containing muscle proteins. However, the presence of a glass transition at −11°C was in disagreement with the low storage stability at −18°C during practical time scales. It was proposed that freezing of cod could be associated with more than one glass transition, with a glass transition at a temperature lower than −11°C being too small to be detectable with instrument, yet governing important deterioration processes. In order to optimize frozen storage conditions, the relationship between deterioration processes important for preservation of quality and glass transition temperatures still needs to be established.     

CONTRACTIBILITY OF MUSCLE FIBRES AS A POSSIBLE AID TO JUDGING TEXTURAL CHANGES IN FROZEN MEATS AND FISH

Abstract Following addition of ATP, the contractibility of muscle fibres in suspension (obtained by muscle homogenization) changes during frozen storage of the muscle. These changes were detected by turbidity measurements. In beef, there were no significant changes up to 6 months storage at— 8°C or lower. Considerable loss in contractibility occurred in chicken white muscle. Losses were rapid in cod and carp muscle, contractibility being completely lost in one month at— 3°C. The method is proposed as one criterion for judging textural changes in lean fish during frozen storage.     

空心面品质评价方法的研究

以实验室制作的5种手工空心面为研究对象,用质构仪和色差仪分别测定面条的质构指标和色泽指标分析了空心面质构指标、色泽指标与感官指标之间的相关关系,建立了质构、色泽指标与感官指标的逐步回归模型。结果表明:质构仪的9个测量指标最大剪切力、韧性、硬度、黏附性、内聚性、胶着性、咀嚼性、回复性以及色差仪的3个测量指标亮度参数L*、红绿参数A*、黄蓝参数B*与感官评价所有6个单项指标以及总分都存在着极显著的相关关系。逐步回归分析发现,可以仅使用黏附性、内聚性、亮度L*和黄蓝参数B*这2个仪器测量值来代替感官评价总分。     

不同贮藏条件下东海马鲛鱼鱼肉质构变化研究

以鲜活马鲛鱼为研究对象,在鱼体TVBN含量变化基础上,应用质构仪质地多面分析(TPA)试验法,采集不同贮藏温度下样品的质构特性。结果表明:马鲛鱼TVBN含量在贮藏期间不断升高,5℃和0℃贮藏组分别贮藏5d和7d后,肌肉TVBN含量超过国家标准限量;马鲛鱼各质构参数(硬度、弹性、黏聚性及咀嚼度)随贮藏时间延长总体呈下降趋势;-55℃和-20℃冻藏样品质构特性变化相对缓慢,且-55℃保鲜效果优于-20℃贮藏。     

Collagenase activity and protein hydrolysis as related to spoilage of iced cod (Gadus morhua)

Collagenase activity and changes in muscular protein of iced Atlantic cod stored for 9 days were studied. The crude fish muscle extract showed maximum collagenase-like activity against bovine insoluble tendon collagen at 48 h of incubation at 37 °C. Collagenase activity against synthetic substrate increased (P<0.05), especially for fish in initial and advanced stages of decomposition. These results suggest that endogenous collagenases and other proteases may be responsible for the destruction of fine collagenous fibrils in the skeletal muscle of cod. The content of titin 1 decreased when decomposition was advanced. Moreover, a progressive degradation of sarcoplasmic proteins with a molecular weight of 100, 94, 85 and 80 kDa was observed. Results suggest that softening of cod muscle during iced storage is caused more by collagenase activity than by proteolysis of myofibrils.     

MODELING OF TEXTURE EVOLUTION OF CAKES DURING STORAGE

The aim of this work is to model the variation of texture parameters in cakes during staling. The evolution was studied in layer cakes (cake A) and sponge cakes (cake B). The effect of storage temperature and the addition of fiber, xanthan gum (cake A) and emulsifier (cake B) were also studied. The best model to adjust the texture parameters variation during storage in both kinds of cakes was square root x ( y = a + b * x^1/2 ), except for firmness and springiness in cakes B. Firmness and springiness were adjusted the best to the linear model. In the model, y stood for the textural parameters and x for the time. a and b were related to the initial value of the studied parameter and with its change over time respectively. In both kinds of cakes, A and B, the firmness and gumminess increased, and the cohesiveness, springiness and resilience decreased, as the storage time increased. The increase in the storage temperature and the addition of fiber minimized the firmness changes in both kinds of cakes.

PRACTICAL APPLICATIONS

This methodology simplifies the study of cake textural parameters during storage and the result interpretation. Moreover, the correlation analysis has demonstrated that the number of textural parameters of cakes to study can be reduced.     

HYDROTHERMAL PROCESSING OF PACIFIC CHUM SALMON: EFFECTS ON TEXTURE AND IN-VITRO DIGESTIBILITY

Pacific chum salmon (Oncorhynchus keta) muscle was subjected to hydrothermal treatment (60–100C) for different time intervals (0–40 min). The texture of raw and heat treated muscles were determined using texture profile analysis. Hardness, cohesiveness, springiness (or elasticity), and chewiness of heat treated fish muscle were higher than those for raw muscle. Increase in time or temperature of treatment increased these textural attributes. However, softening of muscle, as indicated by the decrease in hardness, springiness and chewiness values, occurred with prolonged heating at higher temperatures (90–100C). Muscle cohesiveness was fairly unaffected by processing temperatures. In-vitro digestibility of chum salmon muscle protein remained unaltered by thermal processing for the time-temperature combinations studied.     

Time-dependent characteristics of Herschel–Bulkley fluids from edible powders

Herschel–Bulkley shear thinning fluids were produced by blending saturated aqueous solutions of sucrose with one of the following edible powders: potato starch, wheat flour, maize flour, cocoa powder and milk powder. In each case, plasticity only occurred over a narrow range of proportions of saturated sucrose solution to edible powder. This proportion was crucial in controlling storage changes and textural properties. Bingham yield stresses increased with storage time and this was attributed to the competition for water between saccharides in the saturated solutions and components of the admixed powders. Dissolution of the components of the admixed powders was thought to be a key factor in determining the rate of change of textural properties such as hardness, fracturability, adhesiveness, springiness, cohesiveness, resilience and stringiness.