Sittichoke Sinthusamran

Characteristics and gel properties of gelatin from skin of seabass (Lates calcarifer) as influenced by extraction conditions

Characteristics and gel properties of gelatin from seabass skin, as influenced by extraction conditions, were studied. Yields of gelatin extracted at 45 and 55 °C for various times were 51.6-57.3% and 62.0-66.4% (dry weight basis), respectively. All gelatins contained β-chain and α-chains as the predominant components and showed a high imino acid content (198-202 residues/1000 residues). Generally, the gel strength of gelatins decreased as the extraction temperature and time increased. Gelatin extracted at 45 °C for 3h exhibited the highest gel strength (369 g). Gelling and melting temperatures for seabass skin gelatin were 19.5-20.0 and 26.3-27.0 °C, respectively. All gelatins could be set at 25 °C within 30 min, however gelatins extracted at 45 °C had a shorter setting time than those extracted at 55 °C (P<0.05). Gelatin from seabass skin showed a higher gel strength than bovine gelatin and could be used as a potential replacement for land animal gelatins.

Comparative study on molecular characteristics of acid soluble collagens from skin and swim bladder of seabass (Lates calcarifer)

Acid soluble collagens (ASCs) from skin and swim bladder of seabass (Lates calcarifer) were isolated and comparatively characterised. Higher yield (28.5%) was obtained for ASC from swim bladder, compared with that from skin (15.8%). ASCs from both skin and swim bladder had the similar protein patterns and were identified to be type I. Both α- and β-chains constituted as major components. Fourier transform infrared (FTIR) spectra revealed that both ASCs were triple helix in structure. ASC from both sources contained glycine as the major amino acid with imino acids (proline and hydroxyproline) of 194-195 residues/1000 residues). Peptide maps of both ASCs digested by chymotrypsin and trypsin showed slight differences, suggesting some differences in their primary structure. The thermal transition temperature of swim bladder ASC (35.02°C) was slightly higher than its skin counterpart (33.33°C). Based on zeta potential analysis, ASCs from skin and swim bladder had a net charge of zero at pH 6.46 and 6.64, respectively. Therefore, both the skin and swim bladder of seabass could be used potentially for collagen extraction.

Molecular characteristics and properties of gelatin from skin of seabass with different sizes.

Gelatin was extracted from the skin of seabass (Lates calcarifer) with different average sizes (2, 4 and 6 kg/fish), termed G2, G4 and G6, respectively and their characteristics and functional properties were determined. Yields of G2, G4 and G6 were 38.22, 40.50 and 43.48% (based on dry weight), respectively. G2 contained α-chains as dominant component, whilst G4 and G6 comprised α-, β- and γ-chains with a larger content of high MW cross-links. All gelatins had the similar imino acid (hydroxyproline and proline) content. Net charge of G2, G4 and G6 became zero at pH of 6.73, 6.41 and 7.12, respectively. Amongst all gelatin samples, G6 exhibited the highest gel strength (321.5 g) (p<0.05), but had the lowest turbidity (p<0.05). Gels of G6 sample had the lower L*-value but higher a*-, b*- and ΔE*-value, compared with others. Gelling and melting temperatures of all gelatins were 17.09-19.01 and 26.92-28.85 °C, respectively. Furthermore, all gelatins were able to set at room temperature, regardless of size of seabass used. G6 had the shorter setting time at room temperature than others. Therefore, size of seabass, in which skin was used for gelatin extraction, had the impact on yield, composition and properties of resulting gelatin.

Characteristics of collagen from rohu (Labeo rohita) skin

ABSTRACT Acid soluble collagen (ASC) and pepsin soluble collagen (PSC) were isolated from rohu skin with the yield of 64.2 and 6.8% (dry weight basis), respectively. Both collagens had glycine as the major amino acid with imino acid content of 196–202 residues/1,000 residues and were characterized as type I collagen with molecular composition of (α1)2α2-heterotrimer. Fourier transform infrared spectra of both collagens were similar, with no shift in wavenumber of all amide bands. The Tmax value of ASC and PSC was 36.40 and 35.48°C, respectively. The zero surface net charge of ASC and PSC was found at pH 5.9 and 5.3, respectively.

PHYSICAL AND SENSORY PROPERTIES OF GELATIN FROM SEABASS (LATES CALCARIFER) AS AFFECTED BY AGAR AND Κ-CARRAGEENAN

Physical and sensory properties of gelatin from skin and swim bladder of seabass (SK and SW, respectively) as affected by agar or κ-carrageenan at 10 and 20% substitution were investigated. Hardness of both SK and SW gels containing agar increased with increasing level of agar. However, the addition of κ-carrageenan lowered hardness of mixed gels. Springiness and cohesiveness of either SK or SW gels decreased as the level of both agar or κ-carrageenan increased. Gelling and melting temperatures generally increased when the level of hydrocolloids was increased. The highest gelling (∼36C) and melting temperatures (∼43C) were obtained for SK added with 20% agar and 20% κ-carrageenan, respectively. However, the addition of both hydrocolloids at 10% affected gel microstructure differently. Furthermore, the addition of agar at 10% could increase the likeness score of sensory properties of gelatin gel. Therefore, the addition of hydrocolloids with appropriate level could improve the texture and sensory properties of gelatin from seabass. PRACTICAL APPLICATIONS Due to the poor gelling property of fish gelatin, compared to its mammalian counterpart, improvement of this property using the selected hydrocolloids can be a promising means. In this work, it was found that agar or κ-carrageenan can be incorporated to fish gelatin to improve gelling, textural and sensory properties of gelatin from skin of seabass (Lates calcarifer). Both agar and κ-carrageenan could increase gelling and melting temperatures of seabass gelatin. The incorporation of hydrocolloids (agar and κ-carrageenan) could also improve the quality of fish gelatin gel, which in turn can widen the applications of fish gelatin in the food and other industries.

Effect of drying and frying conditions on physical and chemical characteristics of fish maw from swim bladder of seabass (Lates calcarifer)

BACKGROUND Swim bladder is generated as a by-product during evisceration. It has been used for the production of fish maw, in which several processing parameters determine the characteristics or quality of the resulting fish maw. The present study aimed to investigate the characteristics of fish maws from seabass swim bladder as influenced by drying and frying conditions. RESULTS The expansion ratio and oil uptake content of fish maw increased as the moisture content of swim bladder increased (P < 0.05). Nevertheless, the expansion ratio of fish maw decreased when the moisture content was higher than 150 g kg(-1) . The L*-value decreased, whilst the a*- and b*-values of fish maw increased with increasing moisture content. When pre-frying and frying temperatures increased, the expansion ratio of fish maw increased (P < 0.05). However, the expansion ratio decreased when the frying was performed at a temperature higher than 200 °C. The oil uptake contents of fish maw with frying temperatures of 180 and 200 °C were in the range of 451.06-578.06 g kg(-1) , whereas the lower contents (378.60-417.17 g kg(-1) ) were found in those having frying temperatures of 220-240 °C. Hardness of fish maw decreased but no changes in fracturability were observed with increasing pre-frying temperature when subsequent frying was carried out 200 °C. CONCLUSION Drying temperatures, moisture content, pre-frying and frying temperatures were the factors influencing the characteristics and properties of fish maws from seabass swim bladder. Fish maw could be prepared by pre-frying swim bladder, dried at 60 °C to obtain 150 g kg(-1) moisture content, at 110 °C for 5 min, followed by frying at 200 °C for 20 s.