Enzymatic extraction of oil from yellowfin tuna (Thunnus albacares) by‐products: a comparison with other extraction methods

This study evaluated the quality of oil extracted from yellowfin tuna (Thunnus albacares) by enzymatic hydrolysis (EHO) compared with oil extracted by traditional methods, such as the physical method of cooking and pressing after fishmeal production and the chemical solvent method. The oil extracted by EHO presented the lowest acidity (1.96% oleic acid) and peroxide indexes (5.14 mEq O₂ kg^?1 of oil) and the highest levels of eicosapentaenoic acid (6.05g 100 g^?1) and docosahexaenoic acid (27.15 g 100 g^?1), two omega‐3 fatty acids with high nutritional value. Importantly, oil extraction from yellowfin tuna heads using EHO produced oil rich in omega‐3s with no oxidation. This study shows that this extraction method greatly increases the value of fish by‐products and increases the competitiveness of the fishing industry.     

Radical scavenging properties of protein hydrolysates from Jumbo flying squid (Dosidicus eschrichitii Steenstrup) skin gelatin

Gelatin extracted from Jumbo flying squid skin was hydrolyzed with serials of protease. The scavenging effects of gelatin hydrolysates on superoxide and hydroxyl radical were assessed by chemiluminescence analysis. Properase E and pepsin have shown efficient hydrolysis of squid skin gelatin to obtain high radical scavenging activity peptides. The conditions chosen for enzymic hydrolysis of squid skin gelatin with properase E were pH 9.0, 45 °C, 3 h reaction time, and enzyme‐to‐substrate ratio of 1:50. Hydrolysates combining properase E and pepsin showed the best radical scavenging activity. For fragmented hydrolysates by ultrafiltration, fractions UF‐2 (M_w < 2000 Da) had high yield and radical scavenging activity. Copyright © 2006 Society of Chemical Industry     

Quality assessment of filtered smoked yellowfin tuna (Thunnus albacares) steaks

Abstract: Filtered smoke (FS) has been used to preserve taste, texture, and/or color in tuna and other fish species. This treatment is particularly important in color preservation during frozen storage. The objective of this study was to compare changes in the quality profiles of FS‐treated and untreated (UT) yellowfin tuna (Thunnus albacares) steaks stored in 3 ways: room temperature (21 to 22 °C), refrigerated (4 to 5 °C), and iced (0 °C). FS and UT steaks were processed from the same lot of fish and analyzed for chemical, microbiological, lipid oxidation, color, and sensory profiles. Similar trends were seen for microbial proliferation and accumulation of apparent ammonia and total volatile base nitrogen (TVB‐N) during the storage temperatures evaluated. Notable exception in quality profile was found in lipid oxidation which was, as expected, lower for treated samples at all storage temperatures for TBARS (P < 0.05) and lower or significantly (P < 0.05) lower for POV values. FS increased the initial redness value significantly (P < 0.05). Unlike UT product, there was no loss of color value concomitant with quality changes for FS‐treated tuna for all storage temperatures evaluated. Practical Application: The overall goal of this project was to evaluate filtered smoked tuna steaks as to the impact on the overall quality profile. As a color‐stabilizing technology, it could mask deteriorating quality.     

Endogenous level of acetic acid in yellowfin tuna (Thunnus albacares): a pilot study about a possible controversy on its residue nature

ABSTRACT

A method based on headspace solid-phase microextraction (HS-SPME) followed by GC-MS analysis was developed for the determination of underivatised acetic acid in fresh tuna fish muscle. Parameters such as the fibre selected and the extraction time and temperature were optimised and the linearity, detection limits and precision of the whole analytical procedure were assessed. The method was then applied to determine the acetic acid concentration in fresh yellowfin tuna muscles (Thunnus albacares) in order to evaluate the endogenous level and its variations during the shelf life under different storage conditions. A qualitative comparison was also made with variations in histamine levels to evaluate the possibility of the joint monitoring of acetic acid and histamine to identify fish stored in poor conditions. The caudal area always had a lower content of acetic acid than the ventral area, independent of the storage time and temperature. A difference was found between the 6- and 3-day time points and day 0 at a storage temperature of 8°C and between the 6-day time point and day 0 at a storage temperature of 0°C, independent of the anatomical area of the sampled tissue. The evaluation of acetic acid could represent an important approach in the field of food safety to detect the illicit use of acetic acid as an antibacterial preservative treatment or to eliminate the unpleasant smell of trimethylamine.     

Characteristic and antioxidant activity of retorted gelatin hydrolysates from cobia (Rachycentron canadum) skin

Alkali-pretreated cobia (Rachycentron canadum) skin was extracted in a retort (121 °C) for 30 min to obtain a retorted skin gelatin hydrolysate (RSGH). The molecular mass distributions and antioxidant activities of cobia RSGH and enzyme-treated RSGHs (ET-RSGHs) derived from bromelain, papain, pancreatin, and trypsin digestion were then characterized. The molecular mass distribution of the RSGH ranged mainly between 20,000 and 700 Da and those of ET-RSGHs ranged between 6500 and 700 Da. The DPPH (α,α-diphenyl-β-picrylhydrazyl) radical scavenging effects (%) of 10 mg/ml of RSGH and 10 mg/ml of the four ET-RSGHs were 55% and 51–61%, respectively. The lipid peroxidation inhibition (%) of RSGH and ET-RSGHs (10 mg/ml) were 58% and 60–71% on the fifth day in a linoleic acid model system, respectively. The 3Kd-ET-RSGHs, obtained by using a series of centrifugal ultrafiltration filters (molecular weight cut-offs of 10, 5, and 3 kDa done sequentially with decreasing pore size), exhibited dramatically improved antioxidant activity, with most of the molecular mass ranging below 700 Da. Compared to 10 mg/ml of the RSGH, 10 mg/ml of 3Kd-ET-RSGHs exhibited 45–65% more scavenging of DPPH radical and 24–38% more inhibition of lipid peroxidation. The peptides with molecular masses below 700 Da in the ET-RSGHs or 3Kd-ET-RSGHs significantly affect the antioxidant properties. These peptides are composed of a small number of amino acids or free amino acids and have the potential to be added as antioxidants in foods.     

Protein hydrolysate from tilapia frame: antioxidant and angiotensin I converting enzyme inhibitor properties

The effect of varying the aminopeptidase concentration and hydrolysis time in the production of a protein hydrolysate from tilapia frame (TFPH) was evaluated in terms of the obtained antioxidant and angiotensin I converting enzyme (ACE) inhibitor activities. Minced tilapia frame was subjected to hydrolysis using three concentrations Flavourzyme^® 1000 L [Brenntag Ingredients (Thailand) Company Limited (Public), Bangkok, Thailand] [0%, 1% and 2% (w/w)] and two hydrolysis times (0 and 1 h). The enzyme concentration and hydrolysis time both significantly affected the antioxidant and ACE inhibitor properties. The use of 2% (w/w) Flavourzyme^® 1000 L for 1 h yielded the highest levels of 2,2‐diphenyl‐1‐picrylhydrazil free radical scavenging (90.4%), metal chelating (91.8%), thiobarbituric acid activity ratio (81.9%), and ACE inhibition (83.8%). In addition, this TFPH contained a higher net amount of amino acids and a larger peptide molecular weight distribution compared to the unhydrolysed tilapia frame supernatant. Thus, TFPH may be a suitable supplement to improve the functionality of food products.     

罗非鱼皮明胶酶解物及其模拟消化产物的抗氧化活性

以罗非鱼皮为原料提取罗非鱼皮明胶,选用风味蛋白酶和胰蛋白酶制备罗非鱼皮明胶酶解物,采用ABTS自由基、DPPH自由基、羟基自由基及亚油酸过氧化体系,初步评价罗非鱼皮明胶酶解物的抗氧化活性,再通过模拟体外胃肠道消化实验,结合分子质量分布测定,进一步考察罗非鱼皮明胶酶解物的抗氧化活性。结果显示,在酶解过程中,风味蛋白酶及胰蛋白酶酶解的水解度逐渐升高,在3 h时达到最高,分别达到5.8%和25.36%。在酶解60 min时其TCA可溶性肽得率最高,风味蛋白酶、胰蛋白酶酶解物分别达56.82%和54.44%。通过比较半抑制浓度（IC₅0）,确定了酶解60 min时风味蛋白酶酶解物的清除DPPH自由基及抑制亚油酸过氧化能力较胰蛋白酶酶解物强。模拟体外胃肠道消化后,酶解物羟基自由基清除活性均显著提高（p<0.05）,亚油酸脂质过氧化活性明显降低,消化前后样品分子量分布范围均主要集中于3000⁵000 Da,消化后风味蛋白酶及胰蛋白酶酶解物3000⁵000 Da组分的含量分别提高了45%及13%。以上研究结果表明,罗非鱼皮明胶酶解后制备的明胶水解物具有一定的抗氧化能力,具有潜在的开发价值。      

Antioxidant activity of bigeye tuna (Thunnus obesus) head protein hydrolysate prepared with Alcalase

The antioxidant activities of tuna head protein hydrolysate (THPH) prepared with Alcalase were evaluated. THPH showed evident radical scavenging activity in a dose‐dependent manner with the IC₅₀ values for 1,1‐diphenyl‐2‐pycrylhydrazyl (DPPH), superoxide and hydroxyl radicals being 1.34, 1.20 and 2.84 mg mL^?1, respectively, and its reducing power was 0.948 at 12.5 mg mL^?1. THPH showed good inhibitory activity in soybean oil peroxidation after accelerated oxidation at 60 °C, and the oils with 0.01%, 0.05% and 0.1% THPH had significantly (P < 0.05) lower peroxide values than the control, after storage at 60 °C. Moreover, the inhibited oxidation effect of 0.1% THPH was similar to that of 0.01% butylated hydroxytoluene (BHT). The molecular weight distribution of THPH revealed that 70.5% of the total amount was peptides with molecular weight lower than 5000 Da, composing mostly of low molecular weight peptides located at 1020–2585 Da (30.78%) and 241–1020 Da (37.15%).     

Improvement of the antioxidant properties of squid skin gelatin films by the addition of hydrolysates from squid gelatin

Gelatin hydrolysates (HG1 and HG2) were obtained from giant squid (Dosidicus gigas) gelatins (G1 and G2) by hydrolysis with Alcalase. Antioxidant properties of both gelatins were highly increased by hydrolysis, especially ABTS radical scavenging capacity, whereas no significant differences were found between HG1 and HG2. The amino acid composition of HG1 and HG2 closely resembled the amino acid composition of the parent proteins, gelatins G1 and G2. Both, HG1 and HG2 were composed by peptides below 30 kDa, although no clear protein bands were observed in HG2. Edible gelatin films with increasing percentages of HG1 (0–10%) were made from G1, giving rise to increasing values of FRAP and ABTS, as well as changes in mechanical properties (decrease puncture force and increase puncture deformation) and water vapour permeability (increase). HG1 gelatin hydrolysate showed lower antioxidant capacity in the gelatin films than in the free form at the same amount added into the filmogenic solution, probably due to interactions with protein matrix.     

黄鳍金枪鱼鱼皮热泵干燥特性研究

以黄鳍金枪鱼鱼皮为研究对象,采用热泵干燥技术,分别研究了热泵干燥温度和鱼皮干燥终点含水率对鱼皮复水率、胶原蛋白、蛋白质稳定性、脂肪氧化、色泽的影响。结果表明,热泵干燥温度为55℃,鱼皮干燥终点含水率为10%时,其色差变化、脂肪氧化程度最小,胶原蛋白含量与干燥前鱼皮最为接近,蛋白质热稳定性较好。      

Optimum extraction and recovery of trypsin inhibitor from yellowfin tuna (Thunnus albacores) roe and its biochemical properties

Effect of lipid removal, extraction medium and extraction time on the isolation and recovery of trypsin inhibitor from yellowfin tuna (Thunnus albacores) roe was investigated. Trypsin inhibitor extracted from defatted tuna roe showed the higher specific inhibitory activity than extracted from origin tuna roe. Optimal extraction medium was attained by shaking the defatted yellowfin tuna roe powder in 10 mm Na phosphate buffer (pH 7.0) containing 0.5 m NaCl (P < 0.05). The extraction time affected the inhibitor recovery significantly (P < 0.05). The extraction time of 30 min was optimum for recovery of trypsin inhibitor from yellowfin tuna roe. The biochemical properties of trypsin inhibitor from yellowfin tuna roes were also determined. The inhibitor was stable to heat treatment up to 60C and over a broad pH range (5‐8). Increasing the concentration of salt (up to 3%, w/v) did not significantly decrease the trypsin inhibitory activity. However, the activity decreased when trypsin inhibitor was incubated with metal ions at ambient temperature for 30 min.     

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。     

Angiotensin I‐converting enzyme inhibitory and Ca‐binding activities of peptides prepared from tuna cooking juice and spleen proteases

Tuna cooking juice is a by‐product from the tuna canning industry. In this study, tuna cooking juice was hydrolysed by proteases extracted from the spleen. Tuna cooking juice showed the highest ACE inhibitory and Ca‐binding activities after hydrolysis for 270 and 180 min, respectively. The hydrolysate was further fractionated by ultrafiltration. The permeate exhibited highest ACE inhibitory and Ca‐binding activities when passed through 1 and 5 kDa cut‐off membranes, respectively. Gel filtration chromatography was used to determine the MW of bioactive peptides that exhibited highest ACE inhibitory and Ca‐binding activities. Those peptides that exhibited highest ACE inhibitory and Ca‐binding activities were the MW range of 238–829 Da and 1355–1880 Da, respectively. These results suggest that the tuna cooking juice and the spleen protease extract are a potential source of bioactive peptides that can be utilised as bioactive ingredients in functional food and nutraceuticals.     

Chemical compositions and functional properties of gelatin from pre-cooked tuna fin

Gelatin was extracted from pre-cooked tuna caudal fin with the yield of 1.99%. Tuna fin gelatin (TFG) contained high protein content (89.54%) with hydroxyproline content of 14.12 mg g⁻¹. TFG comprised a lower content of high-molecular-weight cross-links and hydroxyproline content than porcine skin gelatin (PSG). However, proline content in TFG was twofold higher than that of PSG. The highest bloom strength and turbidity of TFG were observed at pH 6, while the lowest solubility was noticeable at the same pH. The bloom strength of TFG gel was lower than that of PSG gel at all pHs. TFG exhibited the lower emulsifying activity but greater emulsifying stability than PSG (P < 0.05). TFG showed poor foaming properties than PSG. The tensile strength, elongation at break, water vapour permeability of film from PSG was greater than those of TFG (P < 0.05). The study revealed that gelatin of good quality can be prepared from tuna processing discards.