Soottawat Benjakul

Properties and antioxidant activity of fish skin gelatin film incorporated with citrus essential oils

Properties of protein-based film from fish skin gelatin incorporated with different citrus essential oils, including bergamot, kaffir lime, lemon and lime (50% based on protein) in the presence of 20% and 30% glycerol were investigated. Films containing 20% glycerol had higher tensile strength (TS) but lower elongation at break (EAB), compared with those prepared with 30% glycerol, regardless of essential oils incorporated (p<0.05). Films incorporated with essential oils, especially from lime, at both glycerol levels showed the lower TS but higher EAB than the control films (without incorporated essential oil) (p<0.05). Water vapour permeability (WVP) of films containing essential oils was lower than that of control films for both glycerol levels (p<0.05). Films with essential oils had varying ΔE(*) (total colour difference), where the highest value was observed in that added with bergamot essential oil (p<0.05). Higher glycerol content increased EAB and WVP but decreased TS of films. Fourier transforms infrared (FTIR) spectra indicated that films added with essential oils exhibited higher hydrophobicity with higher amplitude at wavenumber of 2874-2926 cm(-1) and 1731-1742 cm(-1) than control film. Film incorporated with essential oils exhibited slightly lower thermal degradation resistance, compared to the control film. Varying effect of essential oil on thermal degradation temperature and weight loss was noticeable, but all films prepared using 20% glycerol had higher thermal degradation temperature with lower weight loss, compared with those containing 30% glycerol. Films added with all types of essential oils had rough cross-section, compared with control films, irrespective of glycerol levels. However, smooth surface was observed in all film samples. Film incorporated with lemon essential oil showed the highest ABTS radical scavenging activity and ferric reducing antioxidant power (FRAP) (p<0.05), while the other films had lower activity. Thus, the incorporation of different essential oils and glycerol levels directly affected the properties of gelatin-based film from fish skin.

Biochemical and physicochemical changes in catfish (Silurus glanis Linne) muscle as influenced by different freeze–thaw cycles

Freeze–thaw cycles affected the biochemical and physicochemical properties of catfish fillets. When the number of freeze–thaw cycles increased, the activities of α-glucosidase and β-N-acetyl-glucosaminidase increased (P 0.05); however the heme iron content decreased (P 0.05) were found as affected by freeze–thaw cycles. After 3 days of chilled storage (2–4°C), a small non-significant increase in non-heme iron content was observed with a concomitant decrease in heme iron. Thiobarbituric acid-release substance increased significantly (P<0.05), especially for the fillets subjected to five freeze–thaw cycles. Components with spectral characteristics similar to hydrogen peroxide-activated hemoproteins were detected with a concomitant decrease in metmyoglobin content in five-cycle freeze–thawed samples after 3 days of storage. The freeze–thaw process therefore has a detrimental effect on the quality of catfish fillets, particularly after chilled storage.

Comparative study on the proteases from fish pyloric caeca and the use for production of gelatin hydrolysate with antioxidative activity.

Proteases from pyloric caeca extract of three fish species including brownstripe red snapper (Lutjanus vitta), bigeye snapper (Priacanthus tayenus) and threadfin bream (Nemipterus marginatus) were comparatively studied. The extracts from bigeye snapper and threadfin bream exhibited the highest hydrolytic activities toward casein, alpha-N-benzoyl-DL-arginine-p-nitroanilide and alpha-N-rho-tosyl-L-arginine methyl ester at pH 8.0 and 60 degrees C and pH 8.5 and 55 degrees C, respectively. The extract of brownstripe red snapper showed the optimal pH and temperature of 8.0 and 60 degrees C with all substrates used except the optimal temperature was 65 degrees C when casein was used. All proteases were strongly inhibited by soybean trypsin inhibitor (SBTI) and N-rho-tosyl-L-lysine chloromethylketone (TLCK) and partially inhibited by N-tosyl-L-phenylalanine chloromethylketone for all substrates tested, suggesting that trypsin-like proteases were the major enzymes. Substrate-gel activity staining of 40-60% ammonium sulfate (AS) fraction revealed that major activity bands were observed with molecular mass of 24, 22 and 20 kDa for brownstripe red snapper, bigeye snapper and threadfin bream, respectively. Those activity bands were partially inhibited by SBTI and TLCK. AS fraction was further used to produce gelatin hydrolysate from the skin of brownstripe red snapper with different degrees of hydrolysis (DH). Hydrolysate with DH of 15% exhibited the highest DPPH and ABTS radical scavenging activities and ferric reducing antioxidant power (p<0.05). Therefore, the extract from pyloric caeca could be used to produce the gelatin hydrolysates possessing antioxidative activities.

Changes in composition and functional properties of proteins and their contributions to Nham characteristics

Changes in composition and functional properties of proteins during fermentation of Nham, a Thai-fermented sausage, were studied. An alkaline-soluble fraction constituted a major protein component of Nham. The amount of each protein fraction in Nham varied, depending on the fermentation time. As fermentation proceeded, the progressive decrease in sarcoplasmic and myofibrillar protein fractions was accompanied by an increase in the alkaline-soluble fraction and non-protein constituents (P<0.05). Slow pH lowering to pH 4.6 during fermentation as a result of bacterial growth and accumulation of lactic acid affected the molecular conformation of the muscle proteins and resulted in changes in protein functional properties. The acid produced resulted in changes in solubility, water-binding capacity, textural properties, and color characteristics. Proteolysis of Nham proteins occurred during fermentation, resulting in increases in TCA-soluble peptides and free α-amino acids, which may contribute to the taste and aroma of Nham.

Changes in physico-chemical properties and gel-forming ability of lizardfish (Saurida tumbil) during post-mortem storage in ice

Changes in physico-chemical properties and gel-forming ability of lizardfish muscle (Saurida tumbil), stored in ice, were investigated up to 15 days. Heading and eviscerating, prior to iced storage, retarded myosin heavy chain degradation and formaldehyde formation. Additionally, denaturation of myosin and troponin was slightly impeded as monitored by the lower decrease in Ca2+-ATPase and lower increase in Mg2+–EGTA-ATPase, respectively. Gel-forming ability of surimi, prepared under different setting and/or heating conditions, decreased as storage time increased (P<0.05). However, superior breaking force and deformation of surimi gel, from headed/eviscerated fish, to that from whole fish was observed throughout the storage. Whiteness of surimi gel from headed/eviscerated fish was much higher than that from whole fish, especially when the storage time increased. Therefore, storage time and pretreatment were found to be crucial factors, determining the changes in physico-chemical properties and gel-forming ability of lizardfish during iced storage.

Characteristics of acid soluble collagen and pepsin soluble collagen from scale of spotted golden goatfish (Parupeneus heptacanthus)

Acid soluble collagen (ASC) and pepsin soluble collagen (PSC) were extracted from scale of spotted golden goatfish (Parupeneus heptacanthus) with the yields of 0.46% and 1.20% (based on dry weight basis), respectively. Both ASC and PSC were characterised as type I collagen, containing α1 and α2 chains. β and γ components were also found in both collagens. Based on FTIR spectra, the limited digestion by pepsin did not disrupt the triple helical structure of collagen. ASC and PSC contained glycine (336-340 residues/1000 residues) as the major amino acid and had imino acids of 186-189 residues/1000 residues. Maximal transition temperatures (Tmax) were 41.58 and 41.01°C for ASC and PSC, respectively. From zeta potential analysis, net charge of zero was found at pH 4.96 and 5.39 for ASC and PSC, respectively. Both collagens exhibited high solubility in acidic pH (2-4) and were soluble in the presence of NaCl at concentration up to 20 and 30g/l for ASC and PSC, respectively.

Separation and quality of fish oil from precooked and non-precooked tuna heads

Abstract Separation of crude oil from precooked and non-precooked skipjack tuna heads by a wet reduction method was carried out. Both heating temperature and time affected the separation and oil quality. Optimum conditions for separation of crude oil involved heating samples at 85°C for 30 min, followed by pressing at 140 tons/m 2 using a hydraulic press. Yields of crude oil prepared from precooked and non-precooked samples were 2.8 and 4.8%, respectively. Crude oil obtained from non-precooked samples showed markedly higher quality than that from precooked samples. Crude oil from precooked samples had a higher peroxide value and much darker colour than that from non-precooked samples. However, crude oil from precooked samples had higher DHA (25.5%) than that from non-precooked samples (18.8%).

Physicochemical and enzymatic changes of cod muscle proteins subjected to different freeze-thaw cycles

The effects of freeze–thaw cycles on the physicochemical and enzymatic changes of cod muscle proteins were investigated. The activities of α-glucosidase and β-N-acetyl-glucosaminidase increased as the the number of freeze–thaw cycles increased. A loss of Ca2+-ATPase and Mg2+-Ca2+-ATPase activities was observed, while Mg2+-EGTA-ATPase activity increased, especially after one cycle of freezing–thawing, with a concomitant decrease in Ca2+ sensitivity. The surface sulphhydryl group content decreased with increasing freeze–thaw cycles, while no changes in total sulphhydryl group content were found. The surface hydrophobicity of actomyosin did not change significantly with the number of freeze–thaw cycles. The loss of protein solubility increased with increasing freeze–thaw cycles. However, no cross-linked proteins induced by formaldehyde were found. The results revealed that freeze–thaw cycles directly affected the physicochemical and enzymatic properties of cod muscle proteins. © 2000 Society of Chemical Industry

Melanosis and quality changes of Pacific white shrimp (Litopenaeus vannamei) treated with catechin during iced storage.

Melanosis, microbiological, chemical, and physical changes of Pacific white shrimp (Litopenaeus vannamei) treated with catechin were monitored during iced storage of 10 days. Whole shrimp treated with catechin solution (0.05 or 0.1%) had retarded growth of psychrophilic bacteria and spoilage microorganisms including H(2)S-producing bacteria and enterobacteriaceae throughout storage in comparison with the control and those treated with 1.25% sodium metabisilfite (SMS) (P < 0.05). The lower increases in pH and total volatile base (TVB) content were obtained in the shrimp treated with catechin solution at both levels, compared with those of other samples (P < 0.05). Lipid oxidation, loss in freshness and melanosis were lowered by catechin treatment. In general, the efficacy of catechin in lowering melanosis and quality losses increased with increasing levels used. Additionally, catechin (0.01, 0.05, and 0.1% (w/v)) showed inhibitory activity toward polyphenoloxidase (PPO) of Pacific white shrimp in a dose-dependent manner. Therefore, catechin can be used as a promising melanosis inhibitor as well as an antimicrobial and an antioxidant in ice-stored shrimp.

Amino Acid Composition and Antioxidative Peptides from Protein Hydrolysates of Yellow Stripe Trevally (Selaroides leptolepis)

Hydrolysates from yellow stripe trevally meat with 15% degree of hydrolysis (DH) obtained using Alcalase (HA) and Flavourzyme (HF) following pH-stat method were characterized. Both hydrolysates, HA and HF, contained glutamic acid and glutamine as the major amino acids, while glycine was the dominant amino acid in fish flesh. Hydrolysates were also rich in aspartic acid, asparagine, alanine, lysine, and leucine. Essential amino acid/nonessential amino acid ratios were 0.55, 0.63, and 0.62 for flesh, HA, and HF, respectively. After separation on a Sephadex G-50 column, antioxidative activity of hydrolysate fractions was determined as Trolox equivalent antioxidant capacity. The fraction of HF with molecular weight (MW) of 1.77 kDa exhibited the strongest antioxidative activity, compared with other fractions. Among all fractions of HA, the one having a MW of 2.44 kDa showed the highest antioxidative activity. Thereafter, the selected Sephadex G-50 fractions from both HA and HF were further chromatographed using a Sephadex C-25 column, followed by HPLC. MW of antioxidative peptides from HA and HF determined by Maldi TOF/TOF was 656 and 617 Da, respectively. However, peptides isolated from both HA and HF possessed a lower antioxidative activity than Trolox at the same concentration (P < 0.05). HA and HF prevented DNA oxidative damage in Fenton reaction system tested by in vitro plasmid DNA relaxation assay. These results indicate that hydrolysates from yellow stripe trevally can be used as an important source of amino acids and serve as alternative natural antioxidants.