Compositions and yield of lipids extracted from hepatopancreas of Pacific white shrimp (Litopenaeus vannamei) as affected by prior autolysis

Compositions and yield of lipids extracted from hepatopancreas of Pacific white shrimp (Litopenaeus vannamei) subjected to autolysis at 60 °C for different times (0, 30, 60, 90 120 and 150 min) were investigated. Extraction yield increased from 7.4% to 8.8% as autolysis time increased from 0 to 150 min. Coincidental increase in total carotenoid content was obtained with increasing autolysis time (p < 0.05). The increases in thiobarbituric acid-reactive substances (TBARS) and p-anisidine value (AV) of lipids were noticeable when autolysis time increased (p < 0.05). However, no changes in free fatty acid (FFA) content were observed within the first 60 min of autolysis (p > 0.05), but subsequently increased up to 150 min. (p < 0.05). No differences in fatty acid profiles of lipids extracted from hepatopancreas without and with 60 min prior autolysis were observed. Lipids extracted contained docosahexaenoic acid (DHA; C22:6(n − 3)) as the most abundant fatty acid, followed by eicosapentaenoic acid (EPA; C20:5(n − 3)). Therefore, prior autolysis at 60 °C for 60 min increased the extraction yield without negative effect on lipid quality.     

Impact of a pulsed electric field on damage of plant tissues: effects of cell size and tissue electrical conductivity

Efficiency of pulsed electric field (PEF) induced permeabilization at 293 K in selected fruit and vegetable plant tissues (apple, potato, carrot, courgette, orange, and banana) at electric field strength (E) of 400 V·cm(-1), 1000 V·cm(-1) and pulse duration (t(p)) of 1000 μs was studied experimentally. The mean cell radius (〈r〉) was within 30 to 60 μm, and the ratio of electrical conductivities of the intact and damaged tissues (σ(i)/σ(d)) was within 0.07 to 0.79 for the studied tissues. Electroporation theory predicts higher damage for tissue with larger cells; however, the direct correlation between PEF damage efficiency and size of cell was not always observed. To explain this anomaly, a theoretical Monte Carlo model was developed and checked for parameters typical for potato tissue. The model showed a strong dependence of PEF damage efficiency and power consumption (W) on σ(i)/σ(d) ratio. The optimum value of electric field strength (E(opt)) was an increasing function of σ(i)/σ(d), and plant tissues with high σ(i)/σ(d) ratio (σ(i)/σ(d) ≈ 1) required application of a rather strong field (for example, E(opt) ≈ 3000 V·cm(-1) for σ(i)/σ(d) ≈ 0.8). However, the PEF treatment at a lower field (E ≈ 400 V·cm(-1)) allowed regulation of the selectivity of damage of cells in dependence of their size. A good qualitative correspondence between experimental data and simulation results were observed.     

Effect of cinnamaldehyde on melanosis and spoilage of Pacific white shrimp (Litopenaeus vannamei) during storage

BACKGROUND: Shrimp is a very perishable product and postmortem changes occur rapidly. Sulfiting agents were once and are still widely used as a preservative in the shrimp industry. However, the application of sulfite in shrimp may pose a risk to human health. Thus development of a natural preservative as a sulfite alternative to extend the shelf life of Pacific white shrimp is urgently needed. RESULTS: The effects of cinnamaldehyde essential oil (1 and 5 g kg^?1) on the shelf life of Pacific white shrimp stored at 4 °C were investigated. As the concentration of cinnamaldehyde increased, residual polyphenoloxidase (PPO) enzyme activity decreased. Kinetic analysis showed that cinnamaldehyde was a noncompetitive inhibitor for the oxidation of L ‐DOPA (L ‐3,4‐dihydroxyphenylalanine) by PPO of Pacific white shrimp. Based on this study, shrimp treated with 5 g kg^?1 cinnamaldehyde possessed the lowest aerobic plate count, total volatile basic nitrogen, and pH values in all treatments after 10 days of storage. According to the results of L*, cinnamaldehyde showed inhibitory activity toward the formation of melanosis. CONCLUSION: Treatment with cinnamaldehyde could improve the sensory properties and extend the shelf life of Pacific white shrimp to 8 days. Therefore, cinnamaldehyde could be used as a promising natural preservative for inhibiting melanosis and preventing the growth of microbes during the chilled storage of Pacific white shrimp. Copyright © 2012 Society of Chemical Industry     

高压脉冲电场和热处理对蓝莓汁品质的影响

以蓝莓汁为原料,比较了高压脉冲电场(PEF)杀菌和热力杀菌处理对蓝莓汁中微生物和理化指标的影响,以及不同处理的蓝莓汁在贮藏期间的品质变化规律。结果表明:PEF可以有效杀灭蓝莓汁中的微生物;PEF杀菌对蓝莓汁色泽参数影响程度小;杀菌处理后,贮藏期内PEF处理和热处理对蓝莓汁的还原糖、总酸、可溶性固形物含量、总酚含量影响较小,PEF处理较热处理能更好地保持蓝莓汁中的VC和花青素含量。      

Effects of freeze-thaw cycles of Pacific white shrimp (Litopenaeus vannamei) subjected to radio frequency tempering on melanosis and quality

This study was conducted to investigate the effects of different tempering methods and freeze-thaw cycles on melanosis and quality parameters of pacific white shrimp. Frozen pacific white shrimps tempered with radio frequency tempering (RFT) were compared to that in water tempering (WT) and refrigerator tempering (RT) in terms of temper loss, total volatile base nitrogen (TVBN), polyphenol oxidase (PPO) activity, melanosis, total sulfhydryl contents, differential scanning calorimetry (DSC), and texture properties after 0, 1, 3, 5 freeze-thaw cycles. Results showed that crushed ice was effective as an effective surrounding medium for six layers of frozen shrimp reaching −2 °C within 6 min in RFT. For quality attributes, the temper loss of samples tempered with radio frequency is lower than that of RT and WT after all freeze-thaw cycles, and RFT resulted in the lowest TVBN value (9.17 mgN/100 g) of shrimps after the 5th freeze-thaw cycle. The PPO activity and melanosis of samples increased as the number of freeze-thaw cycles increased, and RFT effectively inhibited the development of melanosis. After the 3rd freeze-thaw cycle, the enthalpy change (△H) and the sulfhydryl content (0.16 mmol/gprot) of radio frequency tempered samples was significantly higher (p < 0.05) than that of WT and RT. RFT retained the hardness and chewiness of shrimp samples in all freeze-thaw cycles. Therefore, RFT effectively inhibited melanosis and reduce protein oxidation in Pacific white shrimp during freeze-thaw cycles with its fast and uniform heating characteristics.     

Effect of pyrophosphate and 4-hexylresorcinol pretreatment on quality of refrigerated white shrimp (Litopenaeus vannamei) kept under modified atmosphere packaging

ABSTRACT:  The effect of pretreatment with pyrophosphate and 4-hexylresorcinol in combination with modified atmosphere packaging (MAP) (80% CO₂, 10% O₂, 10% N₂, or 80% CO₂, 20% N₂) on the quality of white shrimp during storage at 4 °C was investigated. Shrimp pretreated with 2% pyrophosphate and 0.25% 4-hexylresorcinol and stored under MAP showed the lower microbiological and chemical deteriorations as evidenced by delayed microbial growth as well as lower trimethylamine (TMA) and total volatile base nitrogen (TVB) production ( P < 0.05). Additionally, the growth of coliforms was inhibited effectively. White shrimp pretreated with 4-hexylresorcinol had the lower melanosis throughout the storage compared with those without treatment ( P < 0.05). This was associated with the lowered polyphenol oxidase (PPO) activity in shrimp treated with 4-hexylresorcinol. Therefore, the effective retardation of microbiological and chemical deterioration of white shrimp stored under MAP with the decrease in melanosis could be achieved by pretreatment of the shrimp with pyrophosphate and 4-hexylresorcinol. Furthermore, decapitation could be another means to lower the microbial load and melanosis in white shrimp, particularly those stored under MAP.     

Impact of apple processing modes on extracted juice quality: Pressing assisted by pulsed electric fields

The purpose of this study was to compare the effects of pulsed electric field (PEF) on apple juice characteristics (turbidity, polyphenolic content and antioxidant capacities). The pressing was used as a standard method for juice extraction. Experiments were carried out at a constant pressure (P = 3 bar) using a laboratory press cell. Two different methods for PEF application at 400 V/cm were investigated (PEF treatment of whole samples before cutting and PEF treatment of apple slices after cutting). PEF treatment resulted in increase of the juice yield from 44 g/100 g apple (untreated samples) to 58 g/100 g apple (treatment of whole apples) and 64 g/100 g apple (treatment of slices) after 30 min of pressing. The analysis of pH and conductivity showed no significant difference between untreated and PEF-treated samples. However, the total soluble matter content of juice increased after PEF treatment. The obtained turbidity and transmittance data evidence a noticeable improvement of juice clarity for PEF-treated samples. The PEF pre-treatment was accompanied by an increase of the content of polyphenols and intensification of the antioxidant capacities of juice. Most of these effects (juice clarity and content of antioxidants) were more pronounced for the whole treated apples as compared to untreated apples and PEF-treated apple slices. The evolution of apple browning before and after PEF treatment was more pronounced for whole samples. PEF treatment accelerates browning. The obtained data can contribute to the determination of an optimum time for PEF application. The results evidence that PEF-enhanced expression is promising for production of higher quality juices. PEF treatment of whole apples reduces the energy consumption and is advantageous for industrial applications as compared to the treatment of apple slices. PEF combined with pressing can become a good alternative to traditional process.     

Changing in processing yield and physical properties of frozen white shrimp (Penaeus vannamei) treated with lysine and sodium bicarbonate

The objective of this research was to investigate the phosphate alternative use of natural compound, lysine with sodium bicarbonate (NaHCO₃), at low concentration for freezing of white shrimp (Penaeus vannamei). Shrimp were treated with lysine, NaHCO₃ and lysine with NaHCO₃ at various concentrations and frozen in an air‐blast freezer. Thawing yield, cooking yield, colour, texture and nanostructure of the sample were studied compared to the control (nontreated sample) and sodium tri‐polyphosphate (STPP) treated one. Use of lysine/NaHCO₃ each at 1% (w/v) could improve water holding capacity (WHC) of the frozen shrimp, increasing cooking yield to 100.45% (w/w), comparable to the 101.73% (w/w) of STPP‐treated sample. The colour of the noncook‐thawed shrimp was also improved. Microstructure and lipid oxidation of the treated samples were also studied. The combination of lysine and NaHCO₃ indicated high potential use as phosphate alternative for frozen white shrimps.     

Laundry detergent-stable lipase from Pacific white shrimp (Litopenaeus vannamei) hepatopancreas: Effect of extraction media and biochemical characterization

Extraction and biochemical properties of a new lipase from the hepatopancreas of Pacific white shrimp were studied. Recovery of the hepatopancreas powder with 50 mM Tris-HCl, pH 7.0 containing 0.2% (v/v) Brij35 gave a higher recovery of lipase activity than other extractants tested (p < 0.05). The optimal pH and temperature for lipase activity were 8.5 and 60°C, respectively, when p-nitrophenyl palmitate was used as a substrate. The enzyme was stable to heat treatment up to 40°C and over a pH range of 7.0–10.0 for 30–120 min. Lipase activities continuously decreased as the sodium deoxycholate (NaDC) concentration increased, but activities increased as NaCl concentration increased up to 3.0 M. Hydrolytic activity was enhanced by NaN₃, but strongly inhibited by Hg²⁺, Cu²⁺, Al³⁺, and phenylmethanesulfonyl fluoride. The lipase was evaluated as highly stable against surfactants (Tween 20, Tween 80, Triton X-100, and gum arabic). However, the enzyme was unstable against sodium dodecyl sulphate. Stability of the lipase with commercial liquid and solid detergents (Attack^®, Bres^®, Omo^®, and Pao^®) was also investigated. The lipase exhibited substantial stability and compatibility with tested commercial liquid and solid laundry detergents for 30–60 min. The overall properties of the lipase from Pacific white shrimp hepatopancreas, thus leading us to propose that it is an excellent candidate for use as biocatalysts for better detergent formulation.     

Autolysis of Pacific white shrimp (Litopenaeus vannamei) meat: characterization and the effects of protein additives

ABSTRACT:  Autolytic activity of Pacific white shrimp ( Litopenaeus vannamei ) mince in the absence and in the presence of 2.5%NaCl was investigated. Pacific white shrimp mince exhibited the maximum autolytic activity at 35 and 40 °C in the absence and in the presence of 2.5%NaCl, respectively, as evidenced by the highest TCA-soluble peptide content and the greatest disappearance of myosin heavy chain (MHC). The autolysis was more pronounced in the acidic pH values, followed by alkaline pH ranges. Pepstatin A showed the highest inhibition toward autolysis in the acidic condition, revealing that aspartic proteinase was dominant in shrimp muscle. Nevertheless, soybean trypsin inhibitor effectively inhibited the autolysis at neutral and alkaline pH values, suggesting that serine proteinase was present in shrimp mince but contributed to autolysis at a lower extent in shrimp meat. Autolysis in shrimp meat could be inhibited partially by all protein additives, including bovine plasma protein (BPP), egg white (EW), and whey protein concentrate (WPC). The inhibition of autolysis increased when the level of protein additives increased with the concomitant increase in band intensity of MHC retained. WPC and BPP in the range of 2% to 3% exhibited the highest inhibition toward autolysis of shrimp mince.     

响应面法优化高压脉冲电场辅助提取海鲫鱼内脏油脂工艺

采用高压脉冲电场技术从海鲫鱼内脏提取油脂,以提取率为指标,在单因素实验基础上设计响应面法实验,考察了高压脉冲电场强度、脉冲频率、提取时间及液固比对海鲫鱼内脏油脂提取率的影响,得到最优提取工艺条件为:电场强度18 k V·cm-1,脉冲频率300 Hz,提取时间65 min,液固比1∶1,此时提取率为15.18%。通过回归方程拟合和响应曲面分析,得到二次多项式提取回归模型,经验证实验值与模型预测值拟合性良好,该模型可用于预测海鲫鱼内脏油脂提取率。      

脉冲电场处理油菜籽对菜籽油品质的影响

运用脉冲电场处理双低油菜籽种子,对出油率最优条件下所得菜籽油中主要功能性成分和理化性质等品质指标进行了研究。结果表明:经脉冲电场处理后的菜籽油中总酚以及α-、γ-生育酚含量均极显著增加(P0.01);酸值、过氧化值和p-茴香胺值均极显著增加(P0.01),碘值极显著降低(P0.01),皂化值变化不显著;菜籽油清除DPPH·的能力提高,清除·OH和O_2~-·的能力下降;脉冲电场对油菜籽处理可以提高菜籽油的稳定性。     

Temperature alters the structure of membrane lipids and pulsed electric field (PEF) resistance of Salmonella Typhimurium

The effect of culture temperature on the conformation of membrane lipid of Salmonella Typhimurium as well as their pulsed electric field (PEF) resistance was investigated. Results revealed that S. Typhimurium cells cultured at relatively lower temperature (10 and 25 °C) were more easily inactivated by PEF treatment than those cultured at relatively higher temperature (37 and 45 °C). Using a Weibull model, it was determined that the PEF treatment time to inactivate 90% S. Typhimurium cells cultured at 45 °C was almost fourfold compared to those cultured at 10 °C. Results of micro‐Raman spectroscopy indicated that as the culture temperature increased, the order degree of C–C and lateral packing order of membrane lipid chain also increased, resulting in a drop in the membrane fluidity. These results are important in considering the use of heat and PEF to inactivate microbe contaminants in food.     

高压脉冲电场处理对初榨橄榄油得率和品质的影响

为开发一种能提高初榨橄榄油(VOO)得率、对品质无不利影响且适用于工业化生产的新工艺,以甘肃陇南产区莱星、鄂植8号品种油橄榄鲜果为原料,采用高压脉冲电场(PEF)处理辅助传统工艺提取VOO,通过与传统提取工艺比较,研究PEF处理对VOO得率、理化性质、总多酚含量和脂肪酸组成及相对含量的影响。结果表明:与传统提取工艺相比,采用PEF处理VOO得率平均增幅为15.38%,果渣含油率平均降幅为22.28%,对VOO的色泽、酸值、过氧化值、总多酚含量和脂肪酸组成及相对含量等总体无显著性影响。研究认为,在VOO传统提取工艺的基础上,鲜果破碎之后增加PEF处理环节,可显著提高VOO得率,而且对VOO品质无不利影响,该技术在VOO工业化生产中有良好的应用潜力。