Phenoloxidase from the Cuticle of Florida Spiny Lobster (Panulirus argus): Mode of Activation and Characterization

Phenoloxidase (PO) from lobster cuticle existed as a large inert enzyme (IPO1) which became active (15-fold increase) upon incubation at 4°C and 3 days storage. Electrophorcsis of day 3 extracts showed that the large enzyme disappeared gradually while a new PO (EAPO) developed (Mw of 62.5 kDA). Trypsin treatment yielded a similar enzyme (TAPO2; 64 kDA). Kinetic properties such as Km and E_a indicated that dihydroxyphenylalanine (DOPA) appeared to be a more physiologically important substrate for the trypsin treated PO than EAPO. In addition, temperature and pH properties indicated that different structural and functional properties existed between the three forms (IPO1, EAPO, TAPO2).     

Heat-induced Activation of Polyphenoloxidase in Western Rock Lobster (Panulirus cygnus) Hemolymph: Implications for Heat Processing

ABSTRACT: Polyphenoloxidase (PPO) activity in western rock lobster (WRL) hemolymph results in blackening, or melanosis , of the tissues after processing. The impact of processing temperatures on WRL PPO activity was evaluated under steady state and non-steady state temperature conditions. Baseline PPO activity and total PPO activity were determined spectrophotometrically. PPO activity showed a heat-induced net activation effect between 60 and 80 °C. Deactivation of the enzyme was not significant until temperatures reached 90 °C. During heating, a balance existed between heat-induced activation and deactivation of PPO. Therefore, maximization of PPO deactivation and minimization of melanosis formation in processed WRL would require the internal temperature of processed lobsters to exceed 90 °C.     

Effectiveness of Onboard Application of 4-Hexylresorcinol in Inhibiting Melanosis in Shrimp (Parapenaeus longirostris)

ABSTRACT: Inhibition of melanosis in shrimp ( Parapenaeus longirostris ) captured at different times of year and treated with different 4-hexylresorcinol-based formulations onboard ship was studied. Melanosis inhibition increased with inhibitor concentration. The 4-hexylresorcinol proved effective at extending shelf life over that of untreated shrimp at all the concentrations tested. Combining the inhibitor with citric acid, ascorbic acid, and acetic acid did not increase the extent of melanosis inhibition but did noticeably improve shrimp appearance. Adding ethylenediaminetetraacetic acid (EDTA) and sodium pyrophosphate to the formulation enhanced melanosis inhibition at all times of year. Spray application of the inhibitor formulation extended shelf life compared with dipping and dusting, but dusting resulted in the lowest melanosis levels for a given formulation composition and concentration.     

Lactic Acid/Melanosis Inhibitors to Improve Shelf Life of Brown Shrimp (Penaeus aztecus)

l-Lactic acid, sodium bisulfite, and 4-hexylresorcinol were evaluated, alone and in combination, as melanosis and microbial spoilage inhibitors on brown shrimp (Penaeus aztecus). No effect on the microbiological shelf life of treated shrimp was observed. 4-Hexylresorcinol functioned exceptionally well as a melanosis inhibitor, alone and in combination with. l-lactic acid. However, extensive bacterial growth was demonstrated in the 4-hexylresorcinol dip solution during normal storage on deck, creating the potential for a heavy bacterial inoculation of shrimp during a typical dipping process. Addition of l-lactic acid to the 4-hexylresorcinol dip solution prevented bacterial growth in the dip solution and did not diminish melanosis inhibition.     

Melanosis inhibition and SO2 residual levels in shrimps (Parapenaeus longirostris) after different sulfite‐based treatments

The effectiveness of different sulfite‐based treatments to prevent melanosis in fresh deepwater pink shrimp (Parapenaeus longirostris) was evaluated. Increasing the concentration of sulfites, different methods of application (immersion and dust) and synergy with other compounds, such as citric acid and chelants, were investigated. The level of SO₂ residues in the muscle was determined in a selection of the most effective treatments. One‐hour dip treatment with 50 g kg^?1 sulfite, together with citric acid and chelants, was effective for melanosis prevention for at least one week. With this treatment, the statutory limit of 0.3 g kg^?1 SO₂ in edible part was not exceeded by the majority of samples analysed. Copyright © 2005 Society of Chemical Industry     

The Effect of Inhibitors and High Pressure Treatment to Prevent Melanosis and Microbial Growth on Chilled Prawns (Penaeus japonicus)

ABSTRACT: Ascorbic acid, citric acid, sodium benzoate, kojic acid, and 4-hexylresorcinol were evaluated alone and in combination as inhibitors of melanosis and microbial spoilage in prawns ( Penaeus japonicus ) under non-pressure and high-pressure conditions. Sodium benzoate and kojic acid was an effective combination for the inhibition of prawn melanosis. Alone and in combination with ascorbic or citric acid, 4-hexylresorcinol proved the most effective as inhibitors of melanosis and microbial spoilage in prawns. High-pressure treatment appeared to increase the melanosis process, but it did not alter the effect performed by inhibitors. Lower total count of microorganisms seemed to be obtained with the presence of ascorbic and citric acids under high-pressure treatment.     

Quality of Whole Lobster (Homarus americanus) Treated with Sodium Tripolyphosphate Before Cooking and Frozen Storage

ABSTRACT: The objective of this study was to determine the effects of pre-rigor treatment of lobster muscle with sodium tripolyphosphate (STP) before cooking, cryogenic freezing, and frozen storage. STP concentrations of 0.1% and 0.3% were prepared in 0.9% saline solution and injected into lobster before processing. Controls were injected with 0.9% saline solution. Lobsters were then steam-cooked, cryogenically frozen, and stored at −15 °C. Chemical and textural analyses were conducted on reheated samples at storage months 0, 2, 4, and 6, and sensory analyses were conducted at months 2 and 6. Cook loss results showed the 0.3% STP-treated lobsters had a 5% significantly ( P 0.05) lower cook loss than the 0.1% STP and control samples. Yield results revealed that STP-treated tails had a 0.7% to 0.8% significantly ( P 0.05) higher meat yield than control samples. Total moisture results showed that STP-treated lobster tail and claw meat had higher total moisture levels compared with control samples at month 6. Sensory results revealed that panelists rated both 0.1% and 0.3% STP-treated lobster tails significantly ( P 0.01) higher for flavor and texture, and significantly ( P 0.001) higher for overall acceptability than control samples at month 6. The results indicated that STP added at low concentrations may extend the shelf life of whole cooked cryogenically frozen lobster, decrease lipid oxidation over frozen storage time, maintain texture, color, and flavor attributes, increase yield, and decrease drip loss.     

A 4-Hexylresorcinol-based Formulation to Prevent Melanosis and Microbial Growth in Chilled Tiger Prawns (Marsupenaeus japonicus) from Aquaculture

ABSTRACT: A study was made of the effect on melanosis, biochemical indexes, and microbial growth in tiger prawns ( Marsupenaeus japonicus ) from aquaculture, using a formulation containing 4-hexylresorcinol (0.1% and 0.05%) in combination with organic acids (citric, ascorbic, and acetic) and chelating agents (ethylenediaminetetraacetic acid [EDTA] and disodium dihydrogen pyrophosphate [PPi]). In vivo and postmortem application of treatment was evaluated. Prawns with no additives or treated with 4% of a commercial formula based on sulfites were used to compare with 4-hexylresorcinol. The formulations based on 4-hexylresorcinol or sulfites inhibited the polyphenoloxidase (PPO) activity under 0.2 (Δoptical density [OD]/min/mL), instead of 1 (ΔOD/min/mL) achieved by prawns without additives, with the consequent delay in the appearance of melanosis during the 1st wk of storage. Prawns treated with sulfites showed initially better protection; however 4-hexylresorcinol proved to be more effective at the end of storage. The formulation based on 4-hexylresorcinol at 0.1% concentration, provided in vivo, inhibited the microbial growth (total bacteria count, H₂S-producer microorganisms, lactic acid bacteria, enterobacteria, and pseudomonads), whereas the commercial sulfites inhibited the luminescent bacteria growth.     

Identification of Irradiated Norway Lobster (Nephrops norvegicus) Using Electron Spin Resonance (ESR) Spectroscopy and Estimation of Applied Dose Using Re-irradiation: Results of an In-House Blind Trial

An in-house blind trial on Norway lobster (Nephrops norvegicus) was carried out in which 72 coded samples were correctly identified. The samples were either left unirradiated or had been given doses of 1·03, 2·39 or 3·40 kGy and stored for 0, 7 or 14 days at 1°C. Using re-irradiation, the doses received by the samples identified as irradiated were determined with either linear, quadratic or asymptotic equations being fitted to the data. The most successful estimates of absorbed dose were obtained using a quadratic fit, with average values of 1·71, 2·98 and 3·45 kGy being calculated. © 1997 SCI.     

Development of different damage pathways in Norway lobster (Nephrops norvegicus) stored under different chilling systems

Slurry ice is a biphasic system that has recently shown a number of advantages when employed as a chilling medium for fish species. Its use for a crustacean species of high commercial value, Norway lobster (Nephrops norvegicus), was evaluated in parallel with traditional flake icing. Quality parameters related to microbial spoilage and biochemical breakdown (aerobe and psychrotroph counts, pH, K value, total volatile amines, trimethylamine, free fatty acids and non‐enzymatic browning reactions) were assessed and compared with sensory (carapace, eyes, gills, odour and flesh) acceptability. Storage in slurry ice produced a significant (P < 0.05) inhibitory effect on both microbial growth (as determined by aerobes, psychrotrophs and volatile amines) and autolysis breakdown (as determined by K values and the release of free fatty acids) in comparison with the flake ice batch. In contrast, an enhancement effect of slurry ice on carapace browning was observed as a result of enzymatic browning development. Slurry ice batch also showed a more intense non‐enzymatic browning reaction in the lipid extract of the edible flesh. With a view to limiting both browning effects, the incorporation of an anti‐melanosis agent in the liquid phase of the slurry ice system is envisaged. Copyright © 2006 Society of Chemical Industry     

稻草皮层硅化物的XPS研究(Ⅰ)

对稻草茎部和叶鞘的外表面及穗轴等进行了皮层硅化物的X射线光电子能谱(XPS)研究.结果表明,所研究的几个部位皮层中,自外至里,硅化物的含量及分布具有相同的规律性;茎部皮层外表面硅化物的含量(面积)最低,但半峰宽则比皮层内部高;叶鞘及穗轴的皮层外表面硅化物的含量及半峰宽均比其皮层内部低.初步测定表明,所有部位中的硅化物均为无机硅化物,不同部位硅化物的组成不同;但各测定点的半峰宽都明显高于基准值1.57,说明在测定范围内的硅化物均是由两种或两种以上的硅化物组成的.因此,对各部位的Si2P峰均需进行分峰拟合分析才能得到正确的结果.     

竹茎皮层SEM-EDXA研究(Ⅰ)

利用SEM-EDXA研究了竹茎外表面皮层的形态及Si等矿质元素的分布。结果表明,同一竹茎不同高度处皮层外表面的形态相似,不同种类竹子竹茎的皮层形态则有明显差异。五月季竹竹茎的皮层中,较低部位测定的元素种类较多,较高处所测定的元素种类较少;皮层外表面的颗粒物组有双颗粒、三颗粒及单颗粒3种类型:每个颗粒物组中各颗粒物的粒度及C、O、Si等元素含量的均一性较差。竹茎的纵切面中,皮层是Si含量最高的部位,与皮层相邻的薄壁细胞中Si含量也高些,远离皮层的组织结构中Si的含量极低。竹茎皮层不同的部位和结构物中硅化物的含量及组成有明显差异。     

Effects of Plant Extract-Sulphide Combinations on Melanosis Inhibition and Quality in Shrimp (Aristeus Antennatus)

In this study, shrimp (Aristeus antennatus) immediately after trawling was treated with plant extracts (rosemary and green tea), sodium metabisulphite solution, and their combinations. After dipping into the solutions, melanosis and selected quality changes of shrimp were investigated during the storage at 4°C. Plant extracts were found effective in delaying melanosis in shrimp. Combinations of sodium metabisulphite and plant extracts were found more effective than those groups separately treated with plant extracts. Plant extracts, sodium metabisulphite, and combinations showed lower trimethylamine and total volatile nitrogen values as compared to the control group. It is concluded that use of plant extracts decreased the need for sodium metabisulphite.     

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     

芒秆皮层的SEM-EDXA研究(Ⅰ)

用SEM-EDXA法研究芒秆茎部皮层的形态、超微结构及矿质元素分布.结果表明,芒茎皮层外表面由纵向的条纹区和非条纹区交替排列而成;皮层纵切面中存在多孔结构及具层状细胞壁的横向管孔;皮层中存在不同结晶形态的Si化合物.芒茎皮层的形态及超微结构明显与甘蔗、麦草等的茎部皮层不同.芒茎皮层主要含C、O、Si、K等元素,Si元素含量高于50%,C元素含量低于4.0%;皮层中部的Si元素含量最高,外部及内部的Si元素含量稍低;皮下纤维及芒茎内部组织结构中的Si元素含量均为0.00%.皮层中的Si化合物主要是无机物.     

芒秆皮层的SEM-EDXA研究(Ⅱ)

用SEM-EDXA法研究芒秆叶鞘皮层的形态、超微结构及Si等矿质元素的分布.结果表明,叶鞘外表面皮层由颗粒物纵向规则排列区域和分散分布区域交替排列而成;每个颗粒物组由两个相对的"肾型"颗粒物纵向排列而成.与外表面皮层两种形态区域对应,皮层横切面由致密区域和疏松区域交替排列而成;致密区域的厚度大且质地较均一,Si元素的含量低,其内部主要是维管束组织;疏松区域的厚度小,Si元素的含量高,其内部则主要是近乎圆形的空腔.叶鞘皮层主要含C、O、Si、Cl、K、Ca等元素,C元素的含量低;外表面皮层的Si含量约为50%,内表面皮层的Si元素含量仅4%左右;叶鞘外表面皮层中的Si化合物主要是无机物.     

稻草皮层的SEM-EDXA研究(Ⅰ)

用SEM-EDXA法研究粤晶丝苗水稻茎部皮层的超微结构及硅等矿质元素的分布.结果表明,稻草茎部外表面皮层由颗粒物区和非颗粒物区交替排列而成;气孔主要分布在颗粒物区.颗粒物区中每一颗粒物行都被硅含量极高的颗粒物团所加强;每一颗粒物组主要由2个横向相对的颗粒物组成.非颗粒物区的Si元素含量为21.04%,明显低于颗粒物区,但K元素含量则明显高于颗粒物区.稻草茎皮层结构紧密：表皮细胞璧呈多层结构,不同层次方向不同,细胞壁上分布着较多孔洞.切面中,皮层中的Si元素含量明显低于皮层的外表面,内部组织中的Si元素含量极低,但K元素含量高.粤晶丝苗稻草茎的Si元素含量较低、K元素含量较高,这些特点将对稻草浆黑液碱回收产生一定的影响.     

麦秆皮层硅化物的XPS研究(Ⅰ)

进行麦秆皮层硅化物的XPS测定及分峰拟合分析.结果表明,麦秆不同部位皮层中的硅化物都是由有机硅化物和无机硅化物组成的.有机硅化物主要有线状p-MethylSil、树脂p-PlnenylSil、Ph_3 SiOSiPh_3、Ph_4Si、Et_3SiCl、Et_2 SiCl_2等.无机硅化物的种类更复杂,主要有硅灰石、云母、钠长石、硅线石、高岭土、分子筛A型及x型物质以及5种结晶形式的SiO_2等.不同部位硅化物的组成、含量不同,将影响其在制浆等处理过程中的稳定性.