Impact of Ethanolic Thai Indigenous Leaf Extracts on Melanosis Prevention and Shelf-Life Extension of Refrigerated Pacific White Shrimp.

Shrimp has been known for its delicacy, but it undergoes rapid deterioration induced by biochemical and microbiological reactions. Melanosis is a major cause of discoloration associated with consumer rejection. All ethanolic extracts from different leaves including soursop, noni, and Jik leaves were dechlorophyllized via the "Green" sedimentation method before being used. The inhibitory activity against polyphenoloxidase (PPO) from Pacific white shrimp (Litopeneous vannamei) and the copper-chelating properties of varying extracts were compared. Soursop leaf extract (SLE) showed higher PPO inhibitory activity and copper-chelating ability than others (p < 0.05). Based on LC-MS, aempferol-3-O-rutinoside was identified as the most abundant compound, followed by catechin and neocholorigenic acid. The efficacy of SLE at different levels (0.25-1%) for inhibiting melanosis and preserving the quality of Pacific white shrimp was evaluated during refrigerated storage at 4 °C for 12 days in comparison with that of a 1.25% sodium metabisulfite (SMS)-treated sample. SLE at a level of 1% effectively retarded melanosis and bacterial growth, in which the total viable count did not exceed the microbial limit within 12 days. In addition, 1% SLE treatment impeded autolysis, reduced protein degradation and decomposition, and minimized lipid oxidation, as witnessed by the lower increases in pH, TVB-N, and TBARS values. Sensory evaluation indicated higher likeness scores and overall acceptability for SLE-1% and SMS-1.25% shrimps than those of the control and other samples. Therefore, SLE could be used as a natural alternative that effectively lowered the melanosis and quality loss of shrimp during refrigerated storage.

Impact of different ultrasound-assisted processes for preparation of collagen hydrolysates from Asian bullfrog skin on characteristics and antioxidative properties.

This study focused on impact of ultrasound-assisted process (UAP) at pre-treatment (UP) and simultaneous treatment (US) during papain hydrolysis for preparing collagen hydrolysate (CH) from Asian bullfrog skin. Ultrasonication times were varied (10, 20, 30 min), and CH prepared using papain hydrolysis without UAP was used as control. Different UAPs provided CH with various hydroxyproline contents, α-amino group contents, surface hydrophobicities, and antioxidative activities. UP at 20 min (UP-20) and US at 30 min (US-30) provided highly antioxidative CHs, which were selected for further studies on their Oxygen reactive absorbance capacity (ORAC) and molecular characteristics. CHs from UP-20 and US-30 had higher ORAC than that of control group (p ≤ 0.05). Slight difference in amino acid composition was detected between samples. Based on these results, molecular characteristic styles, molecular weight profile, antioxidative peptide content, and secondary structure of each sample were obtained. These results indicate that UP and US used varied enzymatic hydrolysis patterns and modified molecular conformation of CH, resulting in enhanced antioxidative activity. Therefore, different UAPs as UP and US could be effectively used in preparation of CH using papain hydrolysis from Asian bullfrog skin, which could improve production process efficiency by enhancing their bioactivity, particularly antioxidative activity.

Improved cholesterol depletion with enhanced astaxanthin and polyunsaturated fatty acids of lipid from Pacific white shrimp cephalothorax using prior ethanolic separation of polar lipid and ß-Cyclodextrin.

Shrimp lipid (SL) from Pacific white shrimp (Litopenaeus vannamei) cephalothorax was subjected to ethanol separation with subsequent cholesterol removal. Around 98.4% of cholesterol was removed from cholesterol rich polar lipid fraction (PLF), in which PLF/ß cyclodextrin (ß-CD)/mixed solvents (ethyl acetate/water,1:1) at the ratio of 1:10:20 (w/w/v) were used. Thereafter, PLF with lowered cholesterol was combined with non-polar fraction rich in triglycerides to obtain lowered cholesterol shrimp lipid (LC-SL). Astaxanthin content in LC-SL was augmented by three-fold, compared to that found in SL. Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) contents of LC-SL were also significantly increased, contrasted with SL. Peroxide value and phospholipids were decreased in LC-SL (4.56 ± 0.15 meq/kg and 9.94 ± 1.9%) compared to those of SL (4.80 ± 0.25 meq/kg and 49.11 ± 2.1%), while TBARS and p-Anisidine values remained unchanged. However, conjugated dienes and free fatty acids were augmented, plausibly due to hydrolysis. FTIR spectra confirmed the increased degree of unsaturation of lipids. Thus, the lowered cholesterol shrimp lipid could be used as functional foods or nutraceutical for health promotion.

Effect of hydrolyzed collagen from defatted Asian sea bass (Lates calcarifer) skin on fibroblast proliferation, migration and antioxidant activities.

Hydrolyzed collagen from the defatted Asian sea bass (Lates calcarifer) (Asbs-HC) had high hydrophobic amino acids and imino acids. When fibroblast cell was treated with Asbs-HC, there was no cytotoxicity at any concentrations (25-1000 µg/mL). Asbs-HC at 1000 µg/mL exhibited the highest cell proliferation and cell migration (p < 0.05), indicating wound healing ability. Antioxidative activities of Asbs-HC at different concentrations were determined. ABTS radical scavenging activity (ABTS-RSA) and oxygen radical absorbance capacity (ORAC) increased when Asbs-HC levels augmented up to 1 mg/mL (p < 0.05). Decreased activities in scavenging DPPH radical and chelating metal were found at higher levels of Asbs-HC (0.5 and 1 mg/mL) (p < 0.05). Molecular weight (MW) of peptides in Asbs-HC ranged from 406 to 16,120 Da. Peptide containing MW of 406 Da rendered the highest scavenging activity towards ABTS radical. Thus, Asbs-HC could be applied as antioxidant, skin nourishment and wound healing agents for food/drink fortification.

Distribution and Characteristics of Polyphenoloxidase from Pacific White Shrimp (Litopenaeus vannamei).

Distribution of polyphenoloxidase (PPO) from different anatomical parts of Pacific white shrimp was examined. Among all parts, cephalothorax possessed the maximal PPO activity (P < 0.05), followed by pereopods, telson, pleopods, carapace, cuticle, and muscle, respectively. The higher PPO activity in cephalothorax was in line with the greater melanosis in this part during chilled storage. According to activity-staining toward 3,4-dihydroxy-ʟ-phenylalanine (ʟ-DOPA), PPO exhibited an activity band with a molecular weight (MW) of 210 kDa. When cephalothorax PPO was purified using ammonium sulfate precipitation and a series of chromatographic techniques, involving DEAE-Sepharose anion exchange and Sephadex G-75 gel filtration columns, homogeneity was obtained. Based on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and native-PAGE, the Sephadex G-75 fraction showed a single band. The MW band on SDS-PAGE and gel filtration was estimated as 210 kDa, suggesting a monomeric molecule. For the inhibitor study, cysteine and 4-hexylresorcinol showed competitive inhibition toward PPO, while epigallocatechin gallate and kojic acid demonstrated mixed-type inhibition toward PPO. PRACTICAL APPLICATION: Melanosis (black spot formation) triggered by polyphenoloxidase (PPO) drastically reduces the shelf-life of shrimp. PPO was localized in several anatomical parts of Pacific white shrimp with varying activities. Certain compounds, including cysteine, 4-hexylresorcinol, epigallocatechin gallate, and kojic acid, showed PPO inhibitory activity with different modes of inhibition. The obtained information provided a promising method for manufacturers to keep the prime eating quality of Pacific white shrimp throughout postmortem transportation and storage using selected PPO inhibitors.

Effect of Chamuang (Garcinia cowaRoxb.) leaf extract on inhibition of melanosis and quality changes of Pacific white shrimp during refrigerated storage.

Inhibition of Pacific white shrimp polyphenoloxidase (PPO) with Chamuang leaf extract (CLE) was studied. CLE was rich in polyphenolic glycosides, in which chrysoeriol 6-C-glucoside-8-C-arabinopyranoside and 2-feruloyl-l-sinapoylgentiobiose were dominant. It also contained organic acids including hydroxycitric acid and oxalosuccinic acid. CLE with copper chelation activity could inhibit PPO in a dose dependent manner. Shrimp treated with 1% CLE had the lower melanosis score than 1.25% sodium metabisulfite (SMS) treated shrimp and the control throughout the refrigerated storage of 12 days at 4 °C (P < 0.05). Lower total volatile base (TVB) and thiobarbituric acid reactive substances (TBARS) were detected in shrimp treated with 1% CLE, compared to others (P < 0.05). Lower counts of mesophile, psychrophile, Pseudomonas, Enterobacteriaceae and H2S-producing bacteria were obtained with 1% CLE treatment than the control and SMS treated sample during entire storage. Thus, soaking of shrimps in 1% CLE solution effectively reduced melanosis and quality deterioration.

Lipase from liver of seabass (Lates calcarifer): Characteristics and the use for defatting of fish skin.

Lipase from liver of seabass (Lates calcarifer), with a molecular weight of 60kDa, was purified to homogeneity using ammonium sulfate precipitation and a series of chromatographies, including diethylaminoethyl sepharose (DEAE) and Sephadex G-75 size exclusion columns. The optimal pH and temperature were 8.0 and 50°C, respectively. Purified lipase had Michaelis-Menten constant (Km) and catalytic constant (kcat) of 0.30mM and 2.16s-1, respectively, when p-nitrophenyl palmitate (p-NPP) was used as the substrate. When seabass skin was treated with crude lipase from seabass liver at various levels (0.15 and 0.30units/g dry skin) for 1-3h at 30°C, the skin treated with lipase at 0.30 units/g dry skin for 3h had the highest lipid removal (84.57%) with lower lipid distribution in skin. Efficacy in defatting was higher than when isopropanol was used. Thus, lipase from liver of seabass could be used to remove fat in fish skin.

Effect of catechin and its derivatives on inhibition of polyphenoloxidase and melanosis of Pacific white shrimp.

This study aimed to investigate the effect of tea catechin (C) and 4 of its derivatives on the Pacific white shrimp PPO inhibition and melanosis during refrigerated storage. Epigallocatechin gallate (EGCG) exhibited the highest inhibition towards PPO, followed by C. Inhibitory activity of all compounds tested was in a dose dependent manner (0.1-2.0 mM). Based on activity staining, EGCG most effectively inhibited PPO. For inhibition kinetic studies, C and epicatechin (EC) showed uncompetitive type, whereas epicatechin gallate (ECG), epigallocatechin (EGC) and EGCG exhibited mixed type inhibition. When whole shrimps were treated with EGCG solution at various concentrations (0.25-0.75%), those treated with 0.5 or 0.75% EGCG had lower melanosis scores throughout storage for 10 days at 4 °C, compared with the control and the 1.25% sodium metabisulfite treated samples (P < 0.05). Therefore, EGCG could be used as a potential inhibitor for melanosis in raw Pacific white shrimp during refrigerated storage.

Antioxidant activities and selected characteristics of gelatin hydrolysates from seabass (Lates calcarifer) skin as affected by production processes.

Antioxidant activities and selected characteristics of gelatin hydrolysates from seabass skin as affected by production processes were investigated. Hydrolysates were prepared using different processes, including hydrolysis during and after gelatin extraction. Samples hydrolysed during gelatin extraction showed a higher degree of hydrolysis (DH) and yield compared with those hydrolysed after gelatin extraction (p < 0.05). All hydrolysates had a creamy yellowish colour. A lower abundance of volatile compounds was found in the hydrolysates produced during gelatin extraction, in comparison with those obtained after gelatin extraction. Hydrolysates prepared during gelatin extraction had higher 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity, ferric reducing antioxidative power (FRAP) and ferrous ion chelating activity (p < 0.05). Following a simulated in vitro gastrointestinal digestion, the DPPH radical scavenging activity and FRAP of the hydrolysates was retained, whilst ferrous ion chelating activity increased. The most appropriate conditions for the generation of antioxidant hydrolysates from seabass skin were identified.

Changes in lipids and fishy odour development in skin from Nile tilapia (Oreochromis niloticus) stored in ice.

Changes in lipids, lipoxygenase activity and fishy odour development in the skin of Nile tilapia (Oreochromis niloticus) during iced storage of 18 days were monitored. Triacylglycerol content of skin decreased with coincidental increases in free fatty acid, monoacylglycerol, diacylglycerol and phospholipid contents during storage (p<0.05). During iced storage, peroxide value increased at day 9 and subsequently decreased up to 18 days (p<0.05). Thiobarbituric acid reactive substances values and lipoxygenase activity increased throughout 18 days of iced storage (p<0.05). With increasing storage time, a progressive formation of hydroperoxide was found as evidenced by the increase in amplitude of peak at 3600-3200 cm(-1) in Fourier transform infrared spectra. Those changes indicated that lipid oxidation took place during iced storage. The increase in fishy odour of skin was observed as the storage time increased. The development of fishy odour in Nile tilapia skin during iced storage was mostly governed by lipid oxidation via autoxidation or induced by lipoxygenase. Thus, the extended storage time of whole fish resulted in the pronounced changes in lipids and the increased fishy odour in the skin.