| Summary: | Since the amounts of unutilized by-products are high in fish industry, extraction of fish gelatin is one way to utilize it better and increase the total yield. Fish bones and skins generally have high collagen contents and are therefore suitable for gelatin extraction. Gelatin is a collagen derivative, and it has high amount of the amino acids proline and hydroxyproline, which are used for qualitative and quantitative determinations of the gelatin and gelatin hydrolysate quality. The collagen type of the raw material, the tissue type, species, and age effect what type of gelatin is obtained from the diverse fish by-products. Gelatin is, when properly processed transparent, odourless and tasteless. Gelatin also has good gelling properties and viscosity which is why it is widely used in different industries. There are many different methods to extract gelatin from fish. Commonly used methods are based on the application of different acids and/or enzymes, while alkalic treatments are not so often used for fish. The aim of this study was to extract fish gelatin from mackerel by-products by using three different methods, i.e. acid, alkali and enzyme extractions. The mackerel is a fairly novel fish species in Iceland fishing waters, and it may contain up to 30% fat, which makes it a challenging raw material. Gelatin extraction processes are divided into a pre-treatment step involving the removal of non-collagenous proteins, defatting, demineralizing and partial hydrolyse of collagen. The gelatin is then extracted from the raw material by heat. A gelatin powder is gained when most of the water has been removed. The produced gelatines were analysed by various quality methods. Results showed that the alkali method had the highest values in yield, dry matter and pH of the end product, but it had the lowest values in hydroxyproline content and gel strength. All samples had a steady water activity and the skin resulted in the best hydroxyproline content, but the gelatin from acid extracted mackerel backbones had the best ...
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