Rapid Multiparameters Approach to Differentiate Fresh Skinless Sea Bass (Dicentrarchus labrax) Fillets from Frozen-Thawed Ones

Food authenticity is one of the major issues in the mind of today’s consumers. The sale of frozen-thawed fish fillets under the “fresh fillet” label is considered as a commercial fraud. However, their close sensory properties complicate the differentiation. This study focused on analyzing the composition of exudate (pressured flesh juice) in order to rapidly differentiate between fresh and frozen-thawed skinless fillets of sea bass (Dicentrarchus labrax). Protein concentration, α-D-glucosidase specific activity, nucleotides and related compounds (NRCs) concentration, and free calcium concentration were measured in exudates corresponding to fresh or frozen-thawed sea bass fillets. Significant increases of these four parameters were observed in exudates from frozen-thawed fillets, especially with a twofold increase in NRCs and free calcium concentrations. These results suggest that NRCs and free calcium concentrations can be promising indicators to rapidly detect mislabeling of fresh fillets.     

琼胶寡糖对冻虾仁和罗非鱼片品质的影响

以干耗率、解冻流失率、蒸煮流失率、质构特性、盐溶性蛋白质量分数和钙激活三磷酸腺苷（Ca2＋-ATP）酶活力为指标,研究了琼胶寡糖对虾仁和罗非鱼片在冻藏过程中品质的影响,同时对以海藻糖、水溶液浸泡处理的样品进行了比较。结果显示,经琼胶寡糖和海藻糖处理后的虾仁和罗非鱼片在冻藏过程中的干耗率、解冻流失率和蒸煮流失率均显著低于蒸馏水组和空白对照组（P〈0．05）;质构特性（硬度、胶黏性、凝聚性、弹性、咀嚼性和破断力）均优于蒸馏水和空白对照组;盐溶性蛋白质量分数和Ca2＋-ATP酶活力均高于蒸馏水和空白对照组;经琼胶寡糖处理后的样品指标略优于海藻糖组。这表明琼胶寡糖能显著提高冷冻虾仁和罗非鱼片的品质,在冷冻水产品的保水、抗冻等方面具有一定的应用前景。     

Comparison of Stunning Methods on the Physicochemical Properties of Frozen Nile Tilapia (Oreochromis niloticus) Fillets

This study compares how CO₂ narcosis and thermal shock affect the physicochemical aspects of Nile tilapia fillets held frozen (?18°C) for up to 6 months. The characteristics of tilapia fillets subjected to CO₂ narcosis were those of higher lightness and whiteness and lower redness. The hardness values of fillets of tilapia subjected to thermal shock were lower than those subjected to CO₂ narcosis. During frozen storage to both treatments, the drip loss, denaturation of myosin, and lipid oxidation increased, while fillet water holding capacity and hardness decreased. The physicochemical properties of frozen fillets of tilapia stunned by CO₂ narcosis were considered more desirable; therefore, the method can be a potential replacement to thermal shock.     

Stability of Krill Meal,Astaxanthin, and Canthaxanthin Color in Cultured Rainbow Trout (Oncorthynchus mykiss) Fillets During Frozen Storage and Cooking

Rainbow trout were pigmented with diets containing synthetic astaxanthin, canthaxanthin, or dried krill meal to 6 mg carotenoid/Kg (wwb) flesh. Vacuum packaged frozen fillets were held at -18°C, -28°C or -80°C for 90 d, 180 d, or 90 d, thawed, and refrozen for an additional 90 d. Tristimulus color (L*,a*,b*), carotenoid concentration, fatty acid composition and TBARS were measured for raw and cooked fillets. We observed no change in pigment content or in a* values after 180 d frozen storage or following a thaw/refreeze cycle compared to fresh fish, even though a higher a* values were seen in fillets from fish fed synthetic astaxanthin or canthaxanthin after 90 d frozen storage suggesting that care should be used when interpreting tristimulus color values for grading programs.     

速冻温度对罗非鱼片品质的影响

通过测定不同冷冻方式冻罗非鱼片的理化指标,试图找到最优处理方式,并为冻罗非鱼片工厂化生产提供参考。通过设置双螺旋冷冻机不同的冷冻温度(-35℃、-38℃、-41℃、)冻结新鲜罗非鱼片,将冻结后的鱼片置于-18℃的冷库贮藏,每隔7 d对鱼片样品的pH、水分活度(Aw)、质构参数、挥发性盐基氮(TVB-N)等物理及化学指标进行检测并分析结果。数据表明,冷冻温度对鱼片色差值、失水率、硬度有较大影响,且冷冻温度越低,鱼片品质越好,对咀嚼性、弹性、TVB-N影响不大,对pH则无明显影响。综上,在现有加工工艺的冷冻温度波动范围内,选择较低冷冻温度,提高冻结速率可延缓冻罗非鱼片品质劣变速度,故建议企业加工时,将冷冻温度控制在-40℃,冷冻时间控制在40 min以尽可能保持鱼片品质。     

Changes During Chilled Storage of Whole Tilapia and Short-Term Frozen Storage of Tilapia Fillets

This study evaluated the physicochemical changes in Nile tilapia (n = 82, 373.71 ± 61.91 g) refrigerated for up to 92 h and in the frozen fillets. The tilapias were captured with nets, slaughtered by ice and water shock (1:1) in a temperature of approximately 2°C for 30 min, and stored refrigerated at 4°C in polystyrene boxes containing ice. The fish were filleted, and filets were weighed and frozen. The drip loss and protein were determined after 23 days of frozen storage. After 4 h of storage, all fish were in full rigor mortis. The pH of the muscles decreased for up to 45 h of the storage period. The fillets obtained from tilapia stored for more than 72 h lost more weight and protein. Thus, the filleting or processing of tilapia should be done before 72 h of cold storage, since deterioration of the fish starts to occur after this period.     

冻罗非鱼片的复配冰衣护色效果研究

针对冷冻罗非鱼片在贮运过程中色泽品质退化的问题开展试验,寻求一种防止冻鱼片贮藏期间变色的新方法。采用响应面试验设计,在发色罗非鱼片和不发色罗非鱼片的冰衣中加入不同添加剂,测定鱼片中高铁肌红蛋白含量,比较组氨酸、抗坏血酸钠、异抗坏血酸钠、山梨酸钾及烟酰胺对鱼片的冰衣护色效果。结果显示,山梨酸钾与异抗坏血酸钠为较优的添加剂组合。以高铁肌红蛋白含量拟合公式中变色系数为试验指标,得到未发色鱼片护色的优化配方为:异抗坏血酸钠0.32‰,山梨酸钾0.68‰,此时变色系数为13.79;发色罗非鱼片的最适护色组合为:异抗坏血酸钠0.32‰,山梨酸钾0.68‰,变色系数为10.42。研究表明,冰衣护色法对防止冷冻罗非鱼片的褪色及褐变是有效果的,可作为罗非鱼片出口加工和贮运的实用技术,能有效减缓冷冻罗非鱼片的褐变速度,延长其鲜红色或原色的保持时间。     

Preservation of Tilapia (Oreochromis aureus) Fillet by Isochoric (Constant Volume) Freezing

ABSTRACT

The aim of this work was to evaluate the effects of isochoric freezing on the quality of tilapia fillet. Isochoric freezing was compared to chilling, super-chilling, and freezing. Isochoric freezing showed muscle color alterations similar to the other preservation methods. All preservation methods resulted in softer fillets, with the isochoric frozen fillet having the most similar texture to that of the fresh sample. Thiobarbituric acid reactive substances (TBARS) for isochoric samples were similar to those of fresh samples. However, there was a 53%, 55%, and 34% increase in TBARS for chilled, super-chilled, and frozen samples, respectively. Total volatile basic nitrogen (TVB-N) content was 1.4 times higher for isochoric samples than for fresh samples. For chilled, super-chilled, and frozen samples, TVB-N content was 3.0, 1.9, and 1.3, respectively, times higher than for fresh samples. Microstructural analysis indicated that isochoric samples showed less cell damage compared to those using other methods. Subfreezing temperatures in conjunction with no ice formation during isochoric freezing contributed to improved quality of tilapia fillet. This study may find application in the commercial preservation of fish to increase shelf life and allow for expanded distribution of raw fish. This study might also be a potential solution to “food desert” areas, where residents have low access to fresh healthy foods.     

Effect of Zataria multiflora Boiss (Avishan Shirazi) Essential Oil on Oxidative Progress in Frozen Cobia Fish Fillets During Storage

Antioxidants have been widely used as additives to provide protection against oxidative degradation of foods by free radicals. The effect of thyme essence (Zataria multiflora Boiss) on the rancidity development in cobia (Rachycentron canadum) fillets during frozen storage was studied. Cobia fillets were treated with thyme essence (250 and 500 ppm) and then stored at??18°C for up to 6 months. Rancidity development was measured by several biochemical indices including free fatty acids (FFA), peroxide value (PV), thiobarbituric acid (TBA), and complemented by sensory analysis (flesh odor, consistency, and appearance). Also, pH and expressible moisture were measured during 6-month storage. Proximate composition was also determined in the first day. TBA, PV, and FFA levels increased in all treatments due to lipid oxidation. Thyme essence showed an antioxidative effect in cobia fillets during frozen storage as indicated by TBA, PV, and FFA levels. Results showed that FFA, primary and secondary oxidation products, expressible moisture (EM), and pH of thyme essence treated samples were significantly lower than those of the control samples (p < 0.05). Thyme essence retarded oxidative changes in frozen cobia fillets, and the best oxidation inhibition was obtained using thyme essence at 500 ppm.     

不同致死方式对罗非鱼鱼片品质的影响

为了改善鱼肉的品质,文章通过测定样品的挥发性盐基氮（TVB—N）、Ca^2＋-ATP酶活性以及鱼片色泽和质构指标随时间的变化情况分别评价了4种不同致死方式（I．鳃部放血;II．冰激致死;Ⅲ．敲击头部致死;Ⅳ．敲击头部后放血）对罗非鱼（Oreochromissp．）鱼肉品质的影响。结果显示,贮藏期间4个组的TVB—N显著增大,但Ⅱ组和Ⅲ组的TVB—N显著低于I组和Ⅳ组,有利于鱼片冰藏期的保鲜;4个组鱼片的Ca^2＋-ATP酶活性显著下降,Ⅲ和IV2种宰杀方式有利于保持Ca^2＋-ATP酶活性;4个组的亮度（L^＊）、红绿色值（a^＊）和黄蓝色值（b^＊）都随着贮藏时间的延长而增加,I和Ⅳ2种宰杀方法使鱼片L^＊较大而a^＊较小,但4组之间b^＊无显著差异;鱼片的硬度、咀嚼性和胶着性随贮藏时间的延长呈下降的趋势,其中Ⅲ组的质构品质保持得最好。综合以上所有指标,可以认为Ⅲ组最有利于罗非鱼片的保鲜,其次为Ⅱ组。     

冷藏大西洋鲑背腹部鱼片脂肪氧化变化规律及货架期模型的建立

以冷藏三文鱼背腹部鱼片为研究对象,定期取样测定其在冷藏过程中与脂肪氧化相关的酸价(Acid Value, AV)值、过氧化值(Peroxide Value, POV)和硫代巴比妥酸值(Thiobarbituric Acid Value, TBA),结合感官评价,探究冷藏三文鱼背部、腹部鱼片在贮藏过程中的脂肪氧化变化规律并建立基于脂肪氧化指标的货架期预测模型并进行验证。结果表明：三文鱼背部、腹部鱼片的AV值、POV值以及TBA值都随贮藏时间延长而呈现增加的趋势,感官评价得分一直降低,腹部鱼片比背部鱼片变化更加明显,且温度越高脂肪氧化指标变化越显著。将冷藏三文鱼背部、腹部鱼片的脂肪氧化指标用一级化学反应动力学模型拟合后发现：POV值、TBA值与一级化学反应动力学模型有很好的拟合效果(R2>0.90);AV值与一级化学反应动力学模型有较好的拟合效果(R2>0.82)。用Arrhenius方程建立冷藏温度下三文鱼背部、腹部鱼片AV值、POV值、TBA值与贮藏时间、贮藏温度的动力学模型具有很高的拟合精度(R2>0.90)。建立的动力学方程中背部AV值、POV值和TBA值的活化能EA分别为：47.309 KJ/mol、81.611 KJ/mol、35.560 KJ/mol,腹部的活化能EA分别为：77.628 KJ/mol、55.686 KJ/mol、19.399 KJ/mol。建立的三文鱼背部、腹部鱼片的预测货架期模型经验证后发现,脂肪氧化指标的预测值与实际值相对误差在(±10.60)%内,因此该模型能很好的预测冷藏温度下三文鱼片的货架期。     

响应面法优化复合咸味剂腌制罗非鱼片的工艺

为开发一种低盐健康新型的使用复合咸味剂腌制罗非鱼片的加工技术,本研究以罗非鱼片为原料,通过单因素实验,考察氯化钠分别与氯化钾、苹果酸钠、白砂糖不同添加量组合对腌制罗非鱼片的感官品质、含盐量、水分含量、蛋白水解指数和质构的影响,采用Box-Behnken响应面法优化复合咸味剂的最佳配比参数。结果显示,氯化钾、苹果酸钠、氯化钠添加量对罗非鱼片品质影响显著,白砂糖添加量对罗非鱼片品质影响不显著;通过Box-Behnken响应面法优化得到复合咸味剂腌制罗非鱼片的最佳工艺条件:氯化钾添加量为2.6%、苹果酸钠添加量为1.3%、氯化钠添加量为9.1%、白砂糖添加量为0.5%。优化后产品的感官评分为89,含盐量为2.81%,表明实验模型可以用于预测实际值。研究表明,与对照组相比,产品的钠含量降低了22.92%,从而为罗非鱼的加工提供了一种低盐低钠快速腌制的加工新技术。     

脆化专用饲料对罗非鱼生长和肌肉品质的影响

为考察脆化饲料对罗非鱼(Tilapia)生长和肌肉品质的影响,实验分别以配合饲料(对照组)、脆化饲料(试验组)喂养体质量为(115.30±23.69)g的罗非鱼99 d。结果显示:配合饲料组和脆化饲料组罗非鱼的增重率分别为185.25%、94.96%;饲料系数为1.87、2.94;肥满度为15.23、12.50;肌肉粗蛋白含量为19.40%、18.26%;粗脂肪含量为0.75%、1.32%;胶原蛋白为2.03、2.91;肌原纤维耐折力为33.93μm、64.84μm;滴水损失为2.59%、1.82%。与对照组相比,在生长方面,脆化饲料组罗非鱼增重率、肥满度显著降低,饲料系数显著增加(P<0.05);在肌肉品质方面,肌肉的粗蛋白含量和滴水损失显著降低,而粗脂肪含量、胶原蛋白含量和肌原纤维耐折力显著提高(P<0.05)。结果表明,脆化饲料在一定程度上改善了罗非鱼的肌肉品质。     

一氧化碳发色处理对罗非鱼鱼片暗色肉贮藏过程色泽影响分析

以罗非鱼（Orochromis niloticus♀×0．aureus♂）为研究对象,分析了一氧化碳（CO）发色处理对鱼片背部暗色肉贮藏过程中色泽的影响。结果表明,CO发色处理可以明显提高鱼片的红绿色值（a^＊）,并影响贮藏过程中色泽变化,特别是表征鱼片色泽的a^＊。冷藏初期发色鱼片a^＊略有上升,而后缓慢下降,但未发色鱼片则始终呈缓慢下降的趋势,冻藏期间3种处理鱼片a^＊均缓慢下降;发色鱼片冷藏期间保持鲜红色泽达13d,冻藏达半年。其他2项色泽指标亮度（L^＊）和黄蓝色值（b^＊）贮藏过程中变化趋势基本一致。贮藏过程中a^＊的变化情况与肌肉组织对CO的结合程度及稳定性密切相关,一般经CO发色处理的鱼片贮藏1～2d后鱼片的a^＊会进一步提高,这在冷藏过程中表现尤为明显。CO发色处理对鱼肉中的色素成分肌红蛋白（Mb）起到一定的保护作用,在某种程度上抑制或减缓了Mb氧化反应的发生,阻止高铁肌红蛋白（met—Mb）的生成。     

Sensory Evaluation and Composition of Tilapia (Oreochromus niloticus) Fed Diets Containing Protein-Rich Ethanol By-Products from Corn

Fish rations containing 16 to 29% of corn gluten meal, corn gluten feed, or corn distillers' grains with solubles and a control commercial feed were fed to tilapia. A trained, 10-member sensory panel evaluated the flavor characteristics of harvested, cooked tilapia fillets. The intensities of flavor characteristics of cooked fillets from tilapia raised on pellets containing 16% of corn gluten meal or corn gluten feed, as well as 19% of corn distillers' grains with solubles, were not significantly different than fish fed commercial fish feed. In general, the commercial feed resulted in similar protein and ash contents but higher total fat in the fillets compared with those containing ethanol by-products.     

Pre-rigor filleting and drip loss from fillets of farmed Atlantic cod (Gadus morhua L.)

Improved slaughtering procedures of farmed fish may provide sufficient time so that filleting can be performed pre‐rigor while the muscle pH is still high. Such filleting not only reduces fillet gaping but also lowers the transportation costs and makes fresh fillets available to the markets at an earlier stage. The aim of our work was to determine the weight reduction of the fillets due to liquid loss and to study the proteins and enzymes in the drip. After 11 days of cold storage, fillets of farmed Atlantic cod produced pre‐rigor had a weight loss of 10% and a fillet contraction of 19% while for fillets produced post‐rigor the values were 5% and 4% respectively. At the same time, approximately twice the amount of proteins had been lost from the pre‐rigor‐produced fillets. Sodium dodecyl sulphate polyacrylamide gel electrophoresis analysis showed that the proteins in the drip were similar to the sarcoplasmatic proteins extracted from the muscle. Specific analysis of proteolytic enzymes indicated that they are less stable in the expelled liquid than in the flesh during storage. The extensive loss of weight and proteins from pre‐rigor‐produced fillets during subsequent storage must be taken into account if such processing is considered for farmed cod.     

Bio-based Coating from Fish Gelatin,K-Carrageenan and Extract of Pomegranate Peels for Maintaining the Overall Qualities of Fish Fillet

ABSTRACT

To maintain the overall quality of fisheries products, functional edible coatings from natural ingredients including fish gelatin (Gf), k-carrageenan (Cr), and extract of pomegranate peels (PPE) were composed. The Gf was extracted from blue tilapia (Oreochromis aureus), microencapsulated with Cr, and then loaded with PPE (at concentrations of 0.5%, 1.0%, 1.5% and 2.0%). The Fourier transform infrared (FTIR) spectra of Gf/Cr composites verified their cross-linkage and functionality; the Gf/Cr microcapsules had a mean particle size of 36.2 µm with good distribution and homogeneity. The coating of Nile tilapia (Oreochromis niloticus) fillets, with constructed solutions from Gf/Cr/PPE, revealed their positive effects on fillet quality attributes; the effectiveness was dependent on the supplemented PPE concentration. The Gf/Cr/PPE solutions could effectively reduce the microbial counts of total aerobics, psychrotrophs, yeast and molds, and enterobacteriaceae groups throughout 30 days of refrigerated storage. Additionally, the analysis of spoilage chemical parameters (total volatile basic nitrogen, peroxide value, and thiobarbituric acid reactive substances) in coated samples indicated that formulated solutions could hinder the increase of their values during storage. The sensorial evaluation indicated the acceptability and validity of coated samples for up to 30 days of storage. Gf/Cr/PPE coating is recommended for overall quality maintenance of fish fillets and prolongation of storage using safe and healthy biopreservatives.     

Changes in Red Hake (Urophycis chuss) Muscle Induced by Different Freezing Strategies

The effect of single and double freezing at ?20°C on fresh and aged red hake with two different holding times of the thawed fillets between the first and second freezing treatments was determined. In addition, twice-frozen fresh red hake was treated with two antioxidation systems to assess their effectiveness in reducing lipid oxidation. Fresh, untreated red hake at 0 time was used for comparison. Significant dimethylamine (DMA) production occurred with all frozen samples, and the differences were not marked after 7-month storage. With a storage time of 3 months, however, there were differences between the treatments in both the fresh and aged samples with the once-frozen sample producing the least DMA, the twice-frozen sample with the 24-h holding time between freezings the most, and the twice-frozen sample with a 6-h holding time between freezings giving intermediate values. All samples showed a greater than 50% loss in protein solubility as determined by lithium chloride extraction after 3 months of storage, and the protein solubility declined further when samples were tested at 7 months. Samples with the best (once-frozen fresh) and worst (twice-frozen with 24-h holding time between freezings of 5-day aged muscle) treatments had the highest thiobarbituric acid-reactive substances (TBARS) values. Both antioxidant treatments were effective in reducing TBARS development.