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Abstract (English):
The article studies composition and some physicochemical properties of gelatin prepared from the scales of seabream ( Sparus latus Houttuyn). The yield of extracted gelatin was 15.1%. Gelatin sample contained high protein content (91.7%), a low ash content (1.15%), carbohydrates (0.04 ± 0.01%), the moisture percentage of 7.11%, fat was absent. The physicochemical properties of gelatin were investigated: gel strength of 232 g, melting point at 29°C, gelling temperature at 12°C and melting temperature at 25°C. The values of foaming capacity and stability were 240% and 50%, respectively. The carried out comparison revealed higher protein content and lower ash and moisture content in in the gelatin obtained from seabream scales compared to commercial gelatin extracted from hogskin, which makes it possible to use in food industry as a potential substitution of commercial analogues.

seabream, scale, gelatin, physicochemical properties
Introduction Vietnam, with a coastline of over 3.260 kilometers and more than 3.000 islands and islets scattered offshore, plus up to 2.860 rivers and estuaries, has been geographically endowed with ideal conditions for the thriving fishery sector which currently exists. The great potential of fishery sector in Vietnam is embedded in water bodies of 1.700.000 ha in which 811.700 ha freshwater, 635.400 ha brackish waters and 125.700 ha coves and 300.000-400.000 ha wetland areas might be exploited for aquaculture development. The fishery sector plays an important role in the Vietnamese economy. Production in the fishery sector grew dramatically from 1991 to 2010, reaching 5.2 million tons (406% increase compared to 1990) earning more than 5.0 billion USD from export revenue (24 556% relative to 1990). Much of the growth is due to a rapid expansion in aquaculture, which increased from a 30% share in 1990 to 52% in 2010 of the sector. Although there is a growing domestic market as Vietnamese people’s incomes improve and local demand is increasing, but most of the fishery products are exported. A large number of by-products would be produced during the fish processing procedure. These sub-materials have a high content of collagen, which could be used as potential sources for gelatin production but are not still utilized in Vietnam [1]. Gelatin, derived from partial hydrolysis of fibrous protein collagen that has been widely used in the food and pharmaceutical industries due to its unique functional properties. Commercial gelatins are produced mainly from skin and bone of porcine and bovine by alkaline or acidic extraction. However, both Judaism and Islam forbid the consumption of any pork-related products, while Hindus do not consume cow-related products, besides, the bovine gelatin has a high risk for bovine spongiform encephalopathy [2]. In addition, the need of reusing the fishing industry waste has increased the interest in the study of fish gelatin as an alternative to mammals [3]. Fish gelatin has been studied since the 1950s. In recent years, many works on extraction and characterization of gelatins from fish collagen-containing materials have been reported [4, 5]. Most of the studies have been carried out on gelatin extracted from fish skin and bones [5, 6]. In Center for Drug Research and Development (Institute of Marine Biochemistry, Vietnam Academy of Science and Technology), the fish gelatin was successfully extracted from seabream (Sparus latus Houttuyn) scales by the chemical method. The main purpose of this work was to investigate the proximate composition and some physicochemical properties such as pH, gel strength, melting point and melting temperature, foaming ability and stability of gelatin from the scales of seabream in comparison with commercial gelatin from pig skin. Material and Methods Material and Chemicals The scales of seabream (Sparus latus Houttuyn) were collected at VietTruong Seafood Processing and Import-Export Co., Ltd (Haiphong, Vietnam) in 2016 summer. The diameters of the fish scales were from 0.5 to 1.0 cm. The scales were washed by tap water to remove the impurities adhering to the surface, placed in polyethylene bags and then stored at -18°C until analysis (the storage time was 6 months). Collagenase (Type I, 0.25-1.0 FALGPA units/mg solid, ≥ 125 CDU/mg solid) was purchased from Sigma-Aldrich Chemical Co. (St. Louis, MO, USA). All other chemicals and reagents used were of analytical grade (GA). Preparation of gelatin from seabream scales The chosen method used to obtain gelatin based on collecting collagen from the scales by removing non-collagenous protein, degradation a part of protein using enzyme Collagenase from Clostridium histolyticum in 6 hrs at 40°C with a concentration of enzyme was 0.5% (w/w). In the next step, recovered scales were extracted. Extraction was carried out 2 times with electrochemically activated water with pH 2 at 60°C for 3 hrs with a ratio of water/scales of 2/1. The filtrate was dried in plastic trays at room temperature upon using air conditioning at 18°C for 24 hrs. The dried thin films were ground by using a coffee grinder. The yield of gelatin from the seabream scales was calculated on the dry weight basic and expressed as a percentage. The commercial gelatin was purchased at supermarket "Big C" in Hanoi, Vietnam [1]. Physicochemical analyses Determination of proximate composition. The proximate composition of fish scales and the extracted gelatin were determined according to the method of AOAC. To determine protein content, AOAC method 955.04 in which Kjeldahl method was used. AOAC method 900.02 was used to obtain the ash content which the muffle furnace was used in ash determination. According to AOAC method 920.39, lipid content was determined by Soxhlet extraction method. The moisture content (oven-drying procedure) was evaluated by using AOAC method 934.01. A conversion factor of 5.55 was used for calculating protein content in final product [7]. Determination of gel strength. Gel strength was determined by using a Texture analyzer according to Wangtueai [8]. The dried gelatin was dissolved in distilled water at 45°C to obtain the final concentration of 6.67% (w/v). The gelatin solution was placed in a 25 ml glass beaker, and then cooled in a refrigerator at 10°C and matured for 18 hrs. The gel strength was determined on a texture analyzer with a cell load of 100 N, a cross-head speed of 1 mm/s, equipped with a 1.27 cm-diameter flat-faced cylindrical Teflon. The dimensions of the gel samples were approximately 33 mm in diameter and 22 mm in height. Gel strength was expressed as maximum force (in g) when the plunger had penetrated 4 mm into the gelatin gel; each sample was tested in three times. Determination of melting point. The determination of melting point was done according to the method described by Choi and Regenstein (2000): gelatin solutions 6.67% (w/w) were prepared with distilled water, and a 5 ml aliquot of each sample was transferred to a small glass tube (12 × 75 mm). The samples were degassed in desiccators for 5 min. The tubes were covered with Parafilm®M and heated in a water bath (LOIP LB-140, Loip, Russia) at 60°C for 15 min, then cooled in ice chilled water and matured at 10°C for 17 hrs. Five drops of a mixture of 75% chloroform and 25% red dye were placed on the surface of the gel. The gel samples were put in a water bath (LOIP LB-217, Loip, Russia) at 10°C and the bath was heated at the rate of 0.2 °C/min. The temperature at which the dye drops began to move freely down the gel was taken as the melting point. Determination of gelling temperature and melting temperature. The gelatin extracts (20 ml) were transferred into a tube reaction and held in a cold box cooled with crushed ice tubes until the gelatin gelled, transferred it into a glass beaker and soaked in a water bath at 40°C. The melting temperature was measured when the gelatin gel was melting. Determination of foaming properties. Foaming properties included foaming capacity and foaming stability. 100 ml of 6.67% (w/v) gelatin solution were whipped for 2 min in a dispersion machine. Foaming solution was poured into a 500 ml cylinder. The total sample volume was recorded at 0 min for foaming ability and at 10 min for foaming stability. Foaming ability (%) = (foam volume after whipping/solution volume before whipping) × 100. Foaming stability (%) = (foam volume after standing/foam volume after whipping) × 100. Statistical analyses All experiments were performed in triplicate, and the data were expressed as means ± standard deviation. The analysis was performed using SPSS software (SPSS 11.5 for Windows). Results and Discussions Gelatin yield The yield of the gelatin obtained from seabream scales was 15.1%. It was lower than that from bighead carp (19.15%) [9], sea bass (18.49%) [10]. Gelatin yield depends on the process of obtainment applied (temperature, time, pH, a ratio of fish/liquid) and the protein content in the raw material, which may range among different species [11]. The proximate composition of air-dried scale and gelatin One of the most important characteristics of the edible gelatin is nutritional value, including protein content. The proximate composition of scale and gelatin extracted from it is shown in Table 1. The air-dried scale of seabream contained 0.1% fat, 11.22% moisture, 36.95% ash, 0.81% carbohydrate, and 50.92% protein. After the extraction, the scale gelatin contained 7.11% moisture, 1.15% ash, 0.04% carbohydrate, 91.7% protein, and no fat. Table 1 Proximate composition* of seabream scale, gelatin from it and commercial gelatin Proximate composition, % Sea bream scale Gelatin samples From seabream scale Commercial Moisture 11.22 ± 0.15 7.11 ± 0.23 11.15 ± 0,50 Fat 0.10 ± 0.01 - 0.32 ± 0.03 Ash 36.95 ± 1.23 1.15 ± 0.11 1.51 ± 0.34 Carbohydrate 0.81 ± 0.02 0.04 ± 0.01 0.05 ± 0.01 Protein 50.92 ± 1.25 91.70 ± 0.35 86.97 ± 1.15 * Results are mean values of three replicates ± SD (p < 0.05). The gelatin sample from seabream scales had the higher content of protein, the lower content of ash and moisture in comparison with commercial gelatin from pig skin. In general, recommended moisture and ash content for edible gelatin is less than 15% and 2%, respectively [12]. Therefore, gelatin extracted from fish scale could be used as a potential source of protein for food application. Physicochemical characteristics of gelatins The major physicochemical properties of gelatin are gel strength, melting point, gelling and melting temperatures, which are governed mainly by the imino acid content (proline and hydroxyproline), molecular weight distribution and also the ratio of α/β chains in molecular. All parameters are shown in Table 2. Gel strength From Table 2, the gelatin extracted from seabream scales showed gel strength 232 g. This value was lower than those of commercial gelatin (249 g), of gelatins from red tilapia (384.9 g) [13], bovine (322 g) [12], grass carp fish scales (276 g) [14], lizardfish scales (268 g) [8], sea bass (305 g) [10], higher than those of gelatin from porcine (180 g), siliver carp (152 g) [15]. These differences are possibly due to differences in the composition of collagen-containing materials, the size of the protein chains, as well as complex interactions determined by the amino acids composition [6]. Table 2 Physicochemical properties* of gelatin from seabream scale Physicochemical properties Gelatin samples From seabream scale Commercial, from pigskin Gel strength, g 232 ± 9.1 249 ± 8.2 Melting point, oC 29 ± 0.7 31 ± 0.3 Gelling temperature, oC 12 ± 0.5 14 ± 0.5 Melting temperature, oC 25 ± 0.3 27 ± 0.3 * Results are mean values of three replicates ± SD (p < 0.05). Melting point Gel melting point is one of the major physical properties of gelatin gel. The melting point of the gelatin extracted from seabream scales was 29°C as shown in Table 2. This value was significantly higher than that of the gelatin extracted from black tilapia [5], hake (14°C), sole (19.4°C), megrim (18.8°C) [16], grass carp (19.5°C) [17], and cod (13.8°C) [16]. These values of melting point were much higher than those reported for cod skin which were in the range of 8-10°C [4]. This difference was explained by fish species [18]. In this study, gelatin extracted from sea bream scales presented relatively high melting point and gel strength. Gelling temperature and melting temperature of gel Gelling and melting temperatures of gelatin from seabream scales are shown in Table 2. The result showed that gelling and melting temperatures of gelatin from fish scales were lower than those of commercial gelatin (12°C for gelling and 25°C for melting temperatures, respectively). These might be caused by its low proline content. Karim and Bhat reported that the gelling and melting temperature values of fish gelatin are about 8-25°C and 11-28°C, respectively [19]. The range of gelling temperature could be contributed by the residual of chemicals after processing and the raw material. The melting temperature of gelatin prepared from the skin of warm-blooded animals and warm-water fishes is higher than that of gelatin from the skin of fishes living in cold-water [20]. Foaming properties Foaming capacity and stability of gelatin solution are showed in Fig. 1. Fig. 1. Foaming properties of gelatins Fig. 1 showed the foaming capacity of fish gelatin was superior to commercial gelatin from pig skin. These values were 240% and 230% for fish gelatin and commercial gelatin, respectively. But the foam stability of fish gelatin was similar to mammalian gelatin (approximately 50%). Foaming properties of gelatin could be influenced by protein source, intrinsic properties of protein, the composition, and conformation of the protein in solution and at the air/water interface [21]. Conclusion In this study, gelatin was extracted from seabream scales collected in Haiphong, Vietnam. The proximate composition, pH and some physicochemical characteristics of gelatin as gel strength, melting point, gelling and melting temperature, and foaming property were investigated. The gelatin had a high content of protein, low contents of ash and moisture in comparison with commercial gelatin from pig skin. The results of analysis showed the relatively high quality of gelatin from fish sources. Therefore, gelatin from seabream scales could be used as a potential replacement for bovine and porcine gelatin.

1. Cao Thi Hue, Nguyen Thi Minh Hang, Le Nguyen Thanh, Nguyen Van Hung, Razumovskaya R.G. Research on the extraction of gelatin from fish scale Saurida tumbil Bloch by chemical method. Proceeding of The conference about Marine Biology and Development. Vietnam, Publishing House "Science and Technology", 2014, 352-357.

2. Nagarajan M., Benjakul S., Prodpran T., Songtipya P., Kishimura H. Characteristics and functional properties of gelatin from splendid squid (Loligo formosana) skin as affected by extraction temperatures. Food Hydrocolloids, 2012, 29(2), 389-397.

3. Gómez-Guillén M. C., Gimonez B., Lúpez-Caballero M., Montero M. P. Functional and bioactive properties of collagen and gelatin from alternative sources: a review. Food Hydrocolloids, 2011, 25(8), 1813-1827.

4. Gudmundsson M., Hafsteinsson H. Gelatin from cod skins as affected by chemical treatments. Journal of Food Science, 1997, 62(1), 37-39.

5. Jamilah B., Havinder K. Properties of gelatins from skins of fish black tilapia (Oreochromis mossambicus) and red tilapia (Oreochromis nilotica). Food Chemistry, 2002, 77(1), 81-84.

6. Muyonga J., Cole C., Duodu K. Extraction and physicochemical characterisation of Nile perch (Lates niloticus) skin and bone gelatin. Food Hydrocollolids, 2004, 18(4), 581-592.

7. A.O.A.C. Official method of analysis of Association of Official Analytical Chemists. Published by the A.O.A.C. International, 18th Ed. Washington, D.C. 2003.

8. Wangtueai S., Noomhorm A. Processing optimization and characterization of gelatin from lizard fish (Saurida spp) scales. LWT-Food Science and Technology, 2009, 42(4), 825-834.

9. Tu Z. C., Huang T., Wang H., Sha X. M., Shi Y., Huang X. Q., Man Z. Z., Li D. J. Physicochemical properties of gelatin from bighead carp (Hypophthalmichthys nobilis) scales by ultrasound-assisted extraction. Journal of Food Science and Technology, 2015, 52, 2166-2174.

10. DinÇer M., Ağçay Ö., Sargin H., Bayram H. Functional properties of gelatin recovered from scales of farmed sea bass (Dicentrarchus labrax). Turkish Journal of Veterinary & Animal Sciences, 2015, 39, 102-109.

11. Koli J. M., Basu S., Nayak B. B., Patange S. B., Pagarkar A. U., Venkateshwarlu G. Functional characteristics of gelatin extracted from sin and bone of Tiger toothed croaker (Otolithesruber) and Pink perch (Nemipterus japonicas). Food and Bioproducts Processing, 2012, 90(3), 555-562.

12. GME. Standard methods for the testing of edible gelatine. Gelatine Monograph. Gelatin Manufacturers of Europe, 2005.

13. Jamilah B., Tan K., Hartina U. M., Azizah A. Gelatins from three cultured freshwater fish skins obtained by liming process. Food Hydrocolloids, 2011, 25(5), 1256-1260.

14. Zhang F., Xu S., Zang Z. Pre-treatment optimization and properties of gelatin from freshwater fish scales. Journal of Food Bioproduct Processing, 2011, 89(3), 185-193.

15. Wang Y., Regenstein J. M. Effect of EDTA, HCl, and citric acid on Ca salt removal from Asian (silver) carp scales prior to gelatin extraction. Journal of Food Science, 2009, 74 (6), 426-431.

16. Gómez-Guillén M. C., Turnay J., Fernandez-Diáz M., Ulmo N., Lizarbe M., Montero P. Structural and physical properties of gelatin extracted from different marine species: a comparative study. Food Hydrocolloids, 2002, 16(1), 25-34.

17. Kasankala L. M., Xue Y., Weilong Y., Hong S. D., He Q. Optimization of gelatin extraction from grass carp (Catenopharyngodon idella) fish skin by response surface methodology. Bioresource Technology, 2007, 98(17), 3338-3343.

18. Yudi P., Djagal W., Hafni R. Characteristics of gelatins extracted from fresh and sun dried sea water fish skins in Indonesia. International Food Research Journal, 2011, 18, 59-65.

19. Pranoto Y., Chong M. L., Hyun J. P. Characterizations of fish gelatin films added with gellan and k-carrageenan. LWT - Food Science and Technology, 2007, 40, 766-774.

20. Gilsenan P. M., Ross-Murphy S. B. Rheological characterization of gelatins from mammalian and marine sources. Food Hydrocolloids, 2000, 14, 191-196.

21. Zayas J. F. Solubility of proteins. In: Functionality of Proteins in Food, 1997, Berlin, Springer-Verlag, 6-22.

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