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Utilization of Catfish Skins as a Gelatin Source


The main goal of this multi-disciplinary (engineering, fishery, food science, and pharmacy) and multi-university (Auburn University and Cornell University) project renewal is to use the skin of catfish, a by-product of catfish processing, as a raw material for producing high-value fish gelatin that can then be used as an ingredient in further-processed foods and pharmaceutical products. Over a three year period we have agreed to: <OL> <LI>optimizing a method to manufacture gelatin from catfish skins that is acceptable functionally, sensorially and still economically feasible (year 1); <LI>measure the chemical, physical, and sensory properties of the gelatins obtained by different processing methods to determine the most acceptable gelatin for functional and sensory traits (year 2); and <LI>explore applications of catfish gelatin in food and pharmaceutical products (year 3).</ol> Based on the achievement of optimizing multi-step extraction of catfish gelatin (year 1), we plan to do the following to accomplish the objectives for this year (year 2): a) investigate the relationship between the nano-scale structure and functional properties of gelatin; b) investigate the effects of electrolyzed acid water and alkaline water on the gelatin extraction; and c) measure the chemical, physical, and sensory properties of the catfish gelatins obtained by different processing methods.

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NON-TECHNICAL SUMMARY: Gelatin is a soluble polypeptide derived from the insoluble parent protein collagen. It is the only food material that gels and melts reversibly below human body temperature (37 C). Because of its unique and outstanding functional properties, along with its reasonable cost, gelatin is the most widely used food and pharmaceutical ingredient by weight. Most commercial gelatin is made from mammals, mainly from pork skin, bovine hide, and bovine bone. Less than 1% of the gelatin in the world market is obtained from fish and other species. In recent years, due to food-safety concerns, economic issues, and the preferences of specific religious groups, research on the production of gelatin from fish processing by-products has attracted extensive attention from various industry and research groups. The United States was ranked among the top ten countries in aquaculture production in 2002 with 497.3 thousand metric tons of product. The amount of farm-raised catfish processed by the major processors in the United States reached 273 thousand tons in 2005. It appears that commercial fish production may be able to supply an alternate source of gelatin for food and pharmaceutical uses for American consumers, and possibly for export. Clearly, alternate forms of gelatin are needed for food and pharmaceutical products for some of these markets. It appears that gelatin derived from fish byproducts is a possible alternative source of the raw material. However, research is needed to help determine how best to use by-products from fish processing plants to extract gelatin.<P>APPROACH:<BR> 1.Investigate the relationship between the nano-scale structure and functional properties The functional properties of gelatin (such as viscosity, melting point, and gel strength) are very important to its application in the food and pharmaceutical industries. These properties are determined by the sources of the raw materials, and the conditions of pretreatment and extraction. Different sources of raw materials and different processing conditions result in different structures of the gelatin extracted, consequently, result in different functional properties. Nanotechnology enables researchers to have a better insight into the relationship between these functional properties and molecular structure, degree of order, and interaction of molecules in natural materials and man-made materials. Thus, we plan to use an Atomic Force Microscopy (AFM) to investigate the nano-scale structures of fish skin gelatins obtained from different pretreatments and extraction methods as well as gelatins extracted from mammalian sources (pork skin and beef hide). Also, we plan to study changes of gelatin nano-scale structure during extraction and processing, and the relationships between molecular structures and functional properties. <P>2. Investigate the effects of electrolyzed water on the gelatin extraction Normally, before extracting gelatin from fish skin, the skin should be cleaned with tap water and then soaked with alkaline (NaOH) or acid (acetic acid) solution for certain periods of time. This process is known as skin pretreatment. We plan to use electrolyzed acid water and alkaline water to replace traditional alkaline (NaOH) or acid (acetic acid) solution in pretreatment. This work will test whether electrolyzed water, either acid or alkaline, can improve the functional properties of gelatin. <p>3. Measure the physical, chemical, and sensory properties The properties of gelatins obtained by different extraction methods are very important factors with which to evaluate the quality of the gelatins obtained and also as a basis to select the optimism process. In this research, gel strength, viscosity, melting point, yield, hydroxyproline content, and flavor/odor characteristics will be determined.<P>PROGRESS: 2006/10 TO 2007/09<BR>
October 24, 2007: Presentations and smoked catfish products demonstration to catfish grower and processors during a workshop in west Alabama. <BR>February 23, 2007: Demonstration of smoked catfish product during the annual E-Day (Engineering Day). (Auburn University, AL). <BR>October 21, 2006: Demonstration of smoked catfish product in the annual Ag Round-up, (Auburn University, AL). <BR>September 27, 2006: Demonstration of smoked catfish product to CEO of Poseidon Enterprises, Inc. at the Auburn University Hotel. <P>IMPACT: 2006/10 TO 2007/09<BR>
We accomplished following activities according to the research timeline: <BR><ol type="a"> <LI> Recipes and products We developed three series of hot-smoked catfish fillet products: 1) traditional, 2) Cajun and 3) Southeast Asian. Within each series we tested plain, mild and strong flavors. We held several tasting sessions and used valuable feedback from the consumer panels to direct further development of these three products. <LI>Evaluation of textural properties of catfish fillets with the natural contour method A novel sampling technique was used to sample thickness contours on the fillets. Indentation force (g) of the "finger" method and shear force (g) of the "toot" method were measured at different contour levels of four myomere cone bands on the fillets. Shear force and indentation force of the fresh catfish fillets increased with the increasing thickness as measured by the "tooth" and "finger" methods. Both methods could be used to measure the textural properties of catfish fillet. The "finger" method was recommended because its non-destructive nature and applicability to both raw and smoked catfish samples. <LI>Effects of brine concentrations and brine times on the salt content of catfish fillets before smoking Smoked channel catfish products are being developed to explore potential market values on catfish. Certain regulations must be met before the commercialization of this product. FDA guidelines on the hot-smoked reduced oxygen packaging fish product require at least 3.5% WPS (water phase salt) in the loin muscle to inhibit the toxin formation of Clostridium botulinum which will cause consumer illness and death. An equation that summarizes the effects of brine concentration, brine times to the after-brine fillet salt content was obtained based on the regression analysis of the results. <LI> Shelf-life of hot-smoked catfish filleted vacuum- packed with films with different oxygen transmission rates and stored under different temperatures Before this product can be commercialized a shelf-life study is needed to provide information on stability of this product. Three oxygen transmission rate (OTR) levels (0, 4,000, and 10,000) and two storage temperature conditions (4 and 25 degree C) were treatment combinations. No clear pattern could be observed from the bacterial growth of the smoked catfish packed with 4,000 and 10,000 OTR film and stored under 4degree C, which produced approximately 38 (4,000 OTR) and 32 (10,000 OTR) days of shelf-life. The 0 OTR package showed slow growth period (lag-time) of about 35 days followed by a stage of exponential growth. Its shelf-life ended about 56 days after the processing and packaging. No C. botulinum was detected in any sample of the treatments. <LI>Shelf-life of vacuum-packed hot-smoked catfish brined with different salinity solutions and stored under different temperatures So if the C. botulinum can be eliminated from the products through the processing procedures a lower salt level product together with some other preservation methods (e.g. preservatives in this case) could produce a product with better taste and longer shelf-life.

Wang, Yifen
Auburn University
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