Rheological and functional properties of gelatin from the skin of Bigeye snapper (Priacanthus hamrur) fish: Influence of gelatin on the gel-forming ability of fish mince
Introduction
Gelatin is a polypeptide derived by hydrolytic degradation of collagen, the principle component of animal connective tissue. Gelatin is considered a highly digestible dietary food ideal as a complement in certain types of diet. Gelatin has found application in food, photographic, cosmetic and pharmaceutical industries over the years. Recently, its use is expanding to new applications such as colloid stabilizer, foaming agent and emulsifier (McClements, 2005; Surh, Decker, & McClements, 2006)
The source and type of collagen will influence the properties of the resulting gelatins. The main raw material for gelatin production is skin and bones from bovine and porcine source. With the outbreak of bovine spongiform encephalopathy (BSE) in bovine animals, there has been an interest in the gelatin production from non-bovine source (Badii & Howell, 2006). Fish-processing waste can form an ideal raw material for gelatin preparation as fish skin and bone is a major by-product of the fish-processing industry (Haug, Draget, & Smidsrod, 2004). The utilization of fish skin for the production of gelatin could add value to the processing waste. (Kristinsson & Rasco, 2000; Sato, Katayama, Sawabe, & Saeki, 2003).
The quality of food-grade gelatin depends largely on its thermal and rheological properties (Gimenez, Gomez-Guillen, & Montero, 2005). The gel strength, viscosity, setting behavior and melting point of gelatin depends on their molecular weight distribution and the amino acid composition (Johnston-Banks, 1990). Appropriate rheological properties are required for many applications and are related to their chemical characteristics. Competitive gelling agents like starch, alginate, pectin, agar, carrageenan, etc. are all carbohydrates from vegetable sources, but their gels lack the melt in the mouth and elastic properties of gelatin gels.
A number of studies have been devoted to the processing and functional properties of fish gelatin. The gelatins were prepared either from skin, bone or cartilage and mantle of squid. The species of fish that were used for gelatin production were: lumpfish (Osborne, Voight, & Hall, 1990), tilapia (Grossman & Bergman, 1992; Jamilah & Harvinder, 2002), conger eel and arrow squid (mollusk) (Kim & Cho, 1996), shark (Yoshimura et al., 2000), megrim (Montero &Gomez-Guillen, 2000), cod (Gomez-Guillen et al., 2002), nile perch (Muyonga, Cole, & Duodu, 2004), shark cartilage (Cho et al., 2004), pollock (Zhou & Regenstein, 2004), yellow fin tuna (Cho, Gu, & Kim, 2005), skate (Cho, Jahncke, Chin, & Eun, 2006), catfish (Yang et al., 2007), sin croaker and shortfin scad (Cheow, Norizah, Kyaw, & Howell, 2007). The available literature suggests that rheological properties of gelatins from fish skin have not been fully evaluated with reference to flow behavior. It is well recognized that rheological properties play a vital role in process design, evaluation and modeling. These properties are sometimes measured as an indicator of product quality. Rheological data are required for calculation in any process involving fluid flow and play an important role in the analysis of flow conditions in different food processing operations. The use of gelatin from fish skin in different product formulation calls for deeper understanding of various rheological properties with reference to concentration and temperature.
The application of non-meat proteins as functional ingredients to improve the gelling ability of myofibrillar proteins have been assessed (Alvarez, Smith, Morgan, & Booren, 1990; Atughonu, Zayas, Herald, & Harbers ,1998; Chin, Keeton, Miller, Longnecker, & Lamkey, 2000; Ensor, Mandigo, Calkins, & Quint, 1987; Hsu & Lung-Yueh Sun, 2006; Slavin, 1991). Many carbohydrate hydrocolloids are widely used in a variety of comminuted meat products for their ability to enhance gelling character and retain water and to provide a desirable texture (Barbut & Mittal, 1996; Gomez-Guillen, Solas, Borderías, & Montero, 1996; Montero, Hurtado, & Pérez-Mateos, 2000). However, very limited research has been undertaken on protein biopolymer-like gelatin obtained from fish and their behavior in fish-gelled products.
In the present investigation, gelatin from the skin of bigeye snapper (Priacanthus hamrur) fish was prepared and its properties were assessed. The skin of the bigeye snapper is relatively thick and can form an ideal raw material for gelatin production. The objectives of the present study were to prepare gelatin from the skin of bigeye snapper and characterize for physico-chemical and rheological properties. Further, gelatin at various concentrations was incorporated to mince from threadfin bream (Nemipterus japonicus) fish and gelling characteristics were assessed by small deformation test.
Section snippets
Gelatin preparation
Skin of fresh bigeye snapper (P. hamrur) was used for gelatin preparation according to the method as described by Badii and Howell (2006). The fish was caught by trawl net during the month of October along the coast of Mangalore, West coast of India. The habitat temperature where the fish was harvested ranged from 26 to 27 °C.
Proximate composition
The moisture, ash and fat content of fresh fish skin and extracted gelatin was determined according to the method as described by AOAC (2006). The crude protein content was
Results and discussion
The proximate composition of fresh fish skin indicated a protein content of 25.19% and moisture content of 52.79%. The fat content of fish skin was less than 2% (Table 1(A)).
The yield of gelatin from the whole skin was 4% (Table 1(B)). The gelatin yields obtained for tilapia and hake was in the range of 5–8% (Gomez-Guillen et al., 2002; Jamilah & Harvinder, 2002). Leaching of collagen in the skin and degradation of gelatin during extraction are the probable reasons for lower yield (Jamilah &
Conclusion
The physicochemical and rheological properties of gelatin from skin of bigeye snapper have been evaluated. Bloom strength value of the gelatin was found to be 108 g and solidification of gelatin (as given by setting index) was found to be concentration dependant. The gelling and melting temperatures of gelatin were found to be 10 and 16.8 °C, respectively as revealed by dynamic rheological testing. Flow profile of gelatin solution as a function of temperature and concentration exhibited
Acknowledgement
The authors gratefully acknowledge the funding received from European Commission, Brussels, under contract no. ICA4-CT-2001-10032 for carrying out this work.
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