Optimization of gelatine extraction from grass carp (Catenopharyngodon idella) fish skin by response surface methodology
Introduction
Gelatine represents a major source of good quality protein biopolymer with many applications in the food, pharmaceutical, photographic and cosmetics industries. Collagen found in the skin and bone of animals and fish, yields high quality gelatine when it undergoes thermal denaturing (Choi and Regenstein, 2000, Cole and Roberts, 1996, Fernandez-Diaz et al., 2003, Muyonga et al., 2004). Most commercial gelatines are derived from by-products of mammalian sources and fish from deep cold water and are well characterized. Animal sources are preferred to fish sources because their gelatine has superior functional properties (Choi and Regenstein, 2000, Cho et al., 2005). However, with regard to the occurrence of bovine spongiform encephalopathy (BSE) and the fact that Muslims and Jews advocate abstinence from pork, recently the use of fish skin and bone to process gelatine is gaining interest. It is estimated that nearly 30% of fish by-products comprises skins and bones after removal of the edible parts (Shahidi, 1994).
Fish by-products from freshwater are seldom used as a source of raw materials for gelatine extraction. They are mainly used for animal feed supplements due to their small size (Gildberg, 2002). However, some studies have ascertained freshwater fish to have vast amounts of waste after removal of useful edible parts and high gelatine yield being expected from them; Tilapia (Jamilah and Harvinder, 2002, Grossman and Bergman, 1992) and Nile perch (Muyonga et al., 2004). Additionally, most findings suggest that gelatine from these species has an advantage over those extracted from cold water species, providing better rheological properties nearly similar to mammalian gelatines (Cho et al., 2005, Gilsenan and Ross-Murphy, 2000).
Rheological properties (gel strength, gelling and melting points and viscosity) are associated with the contents of hydroxyproline and proline in collagens of different species (Ilona et al., 2004). The gel formation involves the partial denaturation and aggregation of individual denatured gelatine molecules. Hydroxyproline and proline play great role in aggregation of gelatine subunits (Johnston-Banks, 1990, Kinsella et al., 1994). This is mainly because the imino acid rich regions of the polypeptide chains adopt helical conformation on cooling, giving rise to junction zones capable of immobilising water by hydrogen bonding to form a gel (Christopher, 1993). These imino acids are present in higher amounts in warm blooded animals and fish residing in warm waters than cold water fishes (Ilona et al., 2004).
The prosperity of aquaculture and economic reform movement in China has resulted in rapid increase in carp fish species catches. Grass carp which contributes 9.5% of Chinese catches, occurs naturally and grows well in large rivers of eastern China and the former Soviet Union at temperatures between 10 and 26 °C (Bureau of Fisheries Management and Fishing Port Superintendent, Beijing, 2002). Vast waste obtained from them after filleting are either discarded or utilized for low value products. In this context, therefore, interest in grass carp skin utilizations to produce gelatine is not only to ensure efficient exploitation of by-products but also potential value-added product in market, meanwhile, providing an alternative means of solving an old problem of waste disposal. Moreover, a need to replace mammalian gelatine which is at risk of contamination from bovine spongiform encephalopathy (BSE) cannot be ignored, as customers are still uneasy about purchasing the same for food, pharmaceutical and cosmetic applications. Additionally, in some religious societies where the cow is considered deity, such as in the vast Indian sub-continent, fish gelatine provides an attractive alternative.
Yield and quality of gelatine depend on extraction method by which collagen is treated (Montero et al., 1999). Basically acid processing is mainly used with fish skin in which the collagen is acidified at given period of time and then heated to denature and solubilize the collagen. The severity and duration of both acid and extraction temperature requires a monitoring process to yield gelatine with better quality. Response surface methodology (RSM) has been an effective tool to control food processes. It is an important experimental design and a critical technology in process optimization (Cho et al., 2004, Zhou and Regenstein, 2004).
This study was aimed at optimizing the extraction of gelatine. It was also desired to investigate the functional properties of the gelatine extracted from grass carp fish skin residing in fresh warm water. The gel strength and yield were determined as the responses. Additionally, the functional properties of the extracted gelatine were studied.
Section snippets
Raw materials
Grass carp (Catenopharyngodon idella) fish skins were purchased from Wuxi City fish market, Jiangsu, P.R. China. Before skinning and deboning, fish weight and lengths were measured and recorded. The weight range was from 1.2 to 9.3 kg with length range from 39 to 73 cm. The raw materials were transported to the laboratory under ice. Bovine gelatine (230 blooms) was from Defeng Tiasheng Pharmaceutical and Chemical Manufacture Co. Ltd., Jiangsu, P.R. China; and porcine gelatine, G2500 (300 blooms)
Optimization of gelatine extraction
In order to establish the optimized extraction of gelatine from grass carp fish, RSM was used in this study. The estimated model coefficients of β of Eq. (1) were calculated by regression analysis on experimental responses YD and GS, and values (P > 0.1) were left out in the final regression equations. Y1 = − 10.9716 + 3.5365A + 0.626C + 0.9972D − 1.357A2 − 0.0048C2 − 0.0534D2 − 0.0072AC + 0.1266AD − 0.007 and Y2 = 135.3088 + 14.4733B + 5.233C + 71.2828D − 11.6607A2 − 0.3227B2 − 0.066C2 − 3.3483D2 − 0.8889BD. The results revealed the
Conclusion
The gelatine from grass carp fish skin showed high yield and gel strength and, can be used in food applications to replace mammalian gelatine which is not only at risk of contamination with bovine spongiform encephalopathy (BSE), but also got some resistance from koshers and halal. RSM provided a powerful tool to optimize the extraction parameters and the results may be adapted for industrial extraction of gelatine from grass carp fish skins.
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