反复冻结-解冻对黄鳍金枪鱼肉品质的影响

为了研究反复冻结-解冻对金枪鱼品质的影响,对金枪鱼(分别贮藏于-60℃和-18℃)做4次冻结-解冻处理后测定理化指标[解冻汁液流失,红度值a*,质构特性(包括硬度,咀嚼性,黏着性和弹性)],挥发性气味成分(电子鼻),菌落总数。结果表明:随着冻结-解冻次数增加,解冻汁液流失增加,-60℃下汁液流失更多;-18℃贮藏a*值显著降低,-60℃下降趋势不明显;硬度,咀嚼性和弹性都显著降低,然而黏着性变化不大;-60℃相对-18℃贮藏下反复冻结-解冻后挥发性气味差异较显著;菌落总数变化不明显,且在安全范围内。因此,金枪鱼贮藏加工、运输和贮藏过程中保持温度的稳定要避免温度反复波动,且-60℃是作为维持品质的较佳贮藏温度。     

黄鳍金枪鱼块常用解冻方法的比较

为获得金枪鱼块的较适解冻方法。比较常用解冻方法对金枪鱼块的影响,包括自然空气解冻、冷藏库解冻、温盐水组合解冻、静水解冻。测定解冻时间以及解冻后72h 内鱼肉色泽、剪切力、pH 值、菌落总数和感官指标的变化。综合这5 个指标得出,温盐水组合解冻能更好地保持金枪鱼的品质,解冻后得到的鱼块a* 值为12.30,剪切力为342.48g,感官得分12.80,且在贮藏48h 内卫生指标均在行业标准范围之内。其中,色泽和剪切力能更好地表征金枪鱼肉品质的变化。     

冰鲜法对黄鳍金枪鱼片品质的影响

取斐济岛黄鳍金枪鱼背部肌肉,模拟寿司店保存生鱼片的方法,定时观察鱼片物理(色泽、失重率)、生化(pH 值、TVB-N 值、鲜度指标K 值)、感官及微生物等各项指标的变化。结果表明,冰鲜法能在0～4h 内较好地保持黄鳍金枪鱼片的品质。0～1h 内色泽鲜红、气味芳香、滋味鲜美,处于理想的食用状态,1～4h 内色泽由亮变暗,鱼香味和鲜味随汁液流失,品质逐步下降。超过4h 金枪鱼不再新鲜,失去固有的口感、色泽,不具备商业价值。     

电子鼻结合气相色谱- 质谱联用技术分析黄鳍金枪鱼肉的挥发性成分

目的：探索黄鳍金枪鱼肉挥发性成分与加工温度的关系。方法：利用电子鼻分别检测不同温度(70、80、90、100、120、150℃)加热条件下的黄鳍金枪鱼肉及其生肉样品,并对所获数据进行主成分分析,在此基础上进一步采用顶空固相微萃取和气相色谱-质谱联用技术对新鲜和分别加热到95、150℃的黄鳍金枪鱼肉样品进行分析。结果：不同条件下的样品电子鼻信号表现出很强的聚类特性。经气相色谱-质谱联用技术测定3种样品,分别检出52、50、53种成分,主要为醛类、烃类、醇类、酮类、呋喃类,它们的协同作用构成了黄鳍金枪鱼肉特有的特征气味。结论：黄鳍金枪鱼生肉中含有较多的腥味成分--1-戊烯-3-醇、1,5-辛二烯-3-醇,通过加热处理后这两种成分的相对含量明显减少;加热处理后,具有特殊香气的长链醛以及呋喃类物质相对含量明显增多,2-乙基呋喃、2-戊基呋喃是烤制肉品重要的香味呈味物,是加热后黄鳍金枪鱼的特征气味。     

Oxymyoglobin and Lipid Oxidation in Yellowfin Tuna (Thunnus albacares) Loins

The present study characterized oxymyoglobin (OxyMb) and lipid oxidation in yellowfin tuna, and determined the influence of various aldehydes on tuna OxyMb stability in vitro. Surface metmyoglobin accumulation and lipid oxidation increased in tuna steaks with time (P < 0.05). In both tuna steaks and patties, a* values decreased (P < 0.05) and hue angle increased following 6 d storage (P < 0.05). Sensory evaluation demonstrated increased discoloration and decreased odor acceptability in refrigerated steaks and patties over time (P < 0.05). Hexanal, hexenal, and 4‐hydroxynonenal enhanced OxyMb oxidation relative to controls in vitro (P < 0.05). These results indicate a relationship between myoglobin and lipid oxidation in tuna, and that aldehydes known to be produced during lipid oxidation can accelerate tuna OxyMb oxidation in vitro. Keywords: yellowfin tuna, oxymyoglobin, lipid oxidation, discoloration, aldehydes     

Utilization of Yellowfin Tuna and Red Snapper Roe Protein Concentrate as Emulsifier in Mayonnaise

Roes of yellowfin tuna （Thunnus albacares） and red snapper （Lutjanus champecanus） are considered as abundant and underutilized by-product in Indonesia. The production of roe protein concentrate （RPC） is expected to increase the economic value and potency of their usage. Tuna and red snapper RPC was defatted using etano195% with one, two, three and four times of repetition. Both RPC made with four times repetition of defatting had the highest protein content （79.90% and 80.72%）, showed high emulsion activity （97.46% and 99.62%） and emulsion stability （97.10% and 99.48%）, and decreased the interfacial tension of 51% and 55.9%, respectively. Mayonnaise was made with 0, 25, 50, 75 and 100% substitution level of each RPC with four times repetition ofdefatting. The physical, chemical and organoleptic properties of mayonnaise were studied. The best mayonnaise formulation was obtained from 50% substitution level of tuna and red snapper RPC. Mayonnaise with tuna and red snapper RPC had good viscosity （5,920 cPs and 5,845 cPs）, high emulsion stability （90.5% and 91.73%） and small fat globule size （±2.5 lam and ± 2.25 lam）, respectively. These mayonnaises also showed high score of spreadability and low intense of fishy odor. However they still had quite strong of fishy flavor based on scoring test.     

Heat-Induced Textural and Histological Changes of Ordinary and Dark Muscles of Yellowfin Tuna

When a fresh specimen of yellowfin tuna Neothunnus albacora was analyzed, the cross-sectional area of ordinary (white) muscle fiber was 3.5 times larger than that of dark muscle. As heating temperature was raised, the shear force of dark muscle became progressively larger than that of ordinary muscle. Simultaneously, the A band in the ultrastructure of both muscles was stained more densely. While the Z line in I band of dark muscle still remained, that of ordinary muscle disappeared completely by heat treatment at 60°C for 30 min. Therefore, the differences in toughness change during heat treatment correlated well with that fiber sizes and ultrastructures of the two types of muscle.     

Fatty Acid Profile and Selected Chemical Contaminants in Yellowfin Tuna From the Arabian Sea

Fresh yellowfin tuna (n = 110) collected for a period of one year was analyzed for chemical composition, fatty acids, nutrients, and toxic metals. The mean values of investigated minerals were 892, 2834, 0.81, 6.61, 0.38, 11.0, 0.94, 0.59, 0.71, 0.53, and 0.29 mg kg^–1 for Na, K, Cu, Zn, Mn, Fe, Ni, Co, Cr, Sr, and V, respectively. Average Cd, Pb and Hg levels were 0.016, 0.029 and 0.137 mg kg^?1, respectively. The average concentrations of saturated, monounsaturated, and polyunsaturated fatty acids were 196.56, 84.8, and 218 mg 100g^–1, respectively. Yellowfin tuna contained higher DHA (148.2 mg 100g^–1) than EPA (29.3 mg 100 g^–1). A meal with 100 g of this species provides 48.6 and 71.05% of the required daily level of protein and EPA+DHA, respectively. Yellowfin tuna showed low thrombogenic (0.27) and atherogenic (0.43) potential and the value obtained for h/H index (1.97) indicates that regular intake of yellowfin tuna may bring hypocholesterolemic effect. All contaminants in the studied fish were either undetectable or present at very low levels when compared to the United States Food and Drug Administration (USFDA), Food and Agriculture Organization/World Health Organization (FAO/WHO), and European Union regulatory standards and yellowfin tuna would be one of the best options for people who frequently consume tuna fish to get sufficient EPA+DHA and essential elements.     

Optimization of Enzymatic Hydrolysis of Visceral Waste Proteins of Yellowfin Tuna (Thunnus albacares)

Fish protein hydrolysate was produced from the viscera of yellowfin tuna (Thunnus albacares). Hydrolysis conditions (enzyme activity, temperature, and time) were optimized using response surface methodology. A factorial design was applied to minimize enzyme utilization and modeling of degree of hydrolysis (r ² = 0.94). Lack-of-fit test revealed a non-significant value for the model, indicating that the regression equation was adequate for predicting the degree of hydrolysis under any combination of the variables (P < 0.05). The optimum conditions to reach the highest degree of hydrolysis were: 60.4 °C, 90.25 min, and a protease (Alcalase 2.4 L) activity of 70.22 AU/kg protein. The spray-dried tuna visceral protein hydrolysates had relatively high protein (72.34%) and low lipid (1.43%) content. The chemical score of the hydrolysate indicated that it fulfils adult human nutritional requirements except for methionine. Lysine and methionine were the first and the second limiting amino acids in that order. Phenylalanine was the predominant amino acid in the hydrolysates with respect to common carp requirement. In addition, the protein efficiency ratio of tuna visceral hydrolysate was 2.85–5.35.     

金枪鱼暗色肉酶解工艺及其水解物营养价值评价

利用胰蛋白酶,以金枪鱼暗色肉为原料、水解度和氮回收率为指标,制备蛋白水解液。通过正交试验得到最佳酶解条件为：加酶量2 400 U/g原料、初始pH 8.0、酶解温度55 ℃、酶解时间6 h,在此条件下制得酶解液水解度（19.89±0.10）%、氮回收率（64.88±0.72）%。通过高效液相色谱分析酶解液分子质量分布,结果表明酶解对大分子蛋白质有明显的降解作用,酶解液主要由寡肽组成,降解生成的物质分子质量以3 kD以下为主,1 kD以下占大部分（质量分数79.23%）。通过对酶解液氨基酸组成的分析表明,产物酶解液各种氨基酸种类齐全,必需氨基酸含量丰富（质量分数42.38%）,可用作食品的营养补充剂。     

在不同冻藏温度下黄鳍金枪鱼腹部肌肉的脂质氧化和肌红蛋白氧化的动力学研究

以冻藏在-18、-25和-30℃,并贮藏310d的黄鳍金枪鱼腹部肌肉为研究对象,理化指标分析发现,脂质氧化值和肌红蛋白氧化值随贮藏温度的升高,贮藏时间的增加呈现上升趋势。利用相应的反应函数,确立脂质氧化和肌红蛋白氧化反应级数为0级。化学品质动力学研究显示,脂质氧化值和肌红蛋白氧化值的增加随贮藏温度的变化对Arrhenius关系有很高的拟合精度,其拟合方程分别为:y=4.35×10-9exp(0.057t)、y=2.01×10-5exp(0.037t)。     

Burnt Tuna: An Ultrastructural Study of Postmortem Changes in Muscle of Yellowfin Tuna (Thunnus albacares) Caught on Rod and Reel and Southern Bluefin Tuna (Thunnus maccoyii) Caught on Handline or Longline

Ultrastructure of muscle from yellowfm tuna (Thunnus elbacares) caught by rod and reel, and southern bluefin tuna (Thunnus maccoyii) caught by longline or handline was examined at various postmortem times. The pattern of degeneration after death was similar to that of other vertebrates. Burnt tuna meat, which is pale or brown in color, and soft, occurred in carcasses showing a greatly accelerated rate of postmortem degeneration. Burnt tuna had no ultrastructural features which made it different from normal degenerated meat. Ultrastructural quality of muscle was best in samples from longline tuna, and poorest in samples from handline tuna. Longer capture times (hooking to boating) are correlated with better ultrastructural quality of tuna meat, and less burning.     

Development of Biogenic Amines in Yellowfin Tuna (Thunnus albacares): Effect of Storage and Correlation with Decarboxylase-Positive Bacterial Flora

ABSTRACT: The effects of storage at 0,4,10, and 22°C for 0,1,3,5, and 9 d on the quality of yellowfin tuna fillets as determined by microbiological assessment, development of some biogenic amines, and sensory analysis were studied. Tuna fillets stored at 22 °C for 3 d, 10 °C for 5 d, and 4 °C for 9 d were rated unacceptable for consumption. Those stored at 22 °C for 3 d had total aerobic bacterial count of > 8 log₁₀ CFU/g, a histamine-producing bacterial population of 7 log₁₀ CFU/g, and 832 ppm of histamine, 35.8 ppm of putrescine, and 147 ppm of cadaverine. A comparison of the capillary electrophoresis, AOAC fluorometric method, and gas chromatography showed a very good correlation (r² > 0.99) among these 3 methods for histamine quantitation in tuna samples. Morganella morganii, Enterobacter agglomerans, Enterobacter intermedium, Pseudomonas fluorescens, Proteins vulgaris , and Serratia liquefaciens were the decarboxylase-positive bacterial species isolated by using the Niven's medium and identified during storage, which were responsible for histamine production in test tuna fillets.     

Tuna Protein Nutritional Quality Changes after Canning

Albacore tuna (Thunnus alalunga) was steamed and canned in soy bean oil and sterilized at 115°C for 55 or 90 min. Proximate composition, total amino acid and available lysine content were determined during different phases of the process. Water and protein were lost in all phases and fat content increased. There was a decrease in available lysine during cooking but no loss in total amino acids. Nutritional evaluation of the protein showed differences in biological value and net protein utilization when the canned tuna was mixed with bread flour.     

Use of Hydrolysates from Yellowfin Tuna (Thunnus albacares) Heads as a Complex Nitrogen Source for Lactic Acid Bacteria

Two different peptones obtained by enzymatic hydrolysis of yellowfin tuna (Thunnus albacares) head waste have been shown to be effective in promoting the growth of lactic acid bacteria (Lactobacillus bulgaricus Persian Type Culture Collection (PTCC) 1332, Lactobacillus acidophilus PTCC 1643, Lactobacillus casei PTCC 1608, Lactobacillus delbrukii PTCC 1333, Lactobacillus plantarum PTCC 1058, Lactococcus lactis PTCC 1336, and Lactobacillus sakei PTCC 1712). Peptones obtained from the enzymatic hydrolysis with Alcalase or Protamex were used instead of the standard peptones used in commercial MRS media. Peptones produced by Alcalase and Protamex had a 34% and 19% degree of hydrolysis, respectively. The results showed that the peptones from Alcalase and Protamex were better at promoting lactic acid bacteria (LAB) growth than the commercial MRS media (P < 0.05). The choice of proteolytic enzyme used to produce the fish hydrolysate had a considerable impact on the performance of the resulting hydrolysate, both in terms of maximum growth rate and biomass production. Peptones produced using Alcalase, with a higher degree of hydrolysis, induced better growth and performed better overall as an LAB substrate than those using Protamex. Current study revealed that enzymatic-modified fish by-products can be used as low cast nitrogen source for bacterial growth.