Drying and smoking of capelin (Mallotus villosus) and sardine (Sardinella gibbosa) – the influence on physicochemical properties and consumers acceptance

Abstract

Drying and smoking are affordable fish preservation methods that are commonly used in most developing countries where poorly developed logistics limit marketing of fresh fish. In Eastern Africa dried and smoked fish are important sources of low cost stable dietary protein. Small fish, mainly sardine, is commonly blanched in brine prior to drying on the ground. The dried fish is often of low quality, restricting the sales of dried fish to low income groups shopping in open-air markets. At the same time there is an increasing demand among middle class consumers for dried and smoked small fish of high quality sold in supermarkets. Increased demand for dried and smoked small fish could be met by imports or improved processing methods. The aim of this study was to improve the quality and safety of dried and smoked small fish, and study acceptability of new products such as dried capelin caught in Icelandic waters in markets accustomed to dried small fish. The effects of blanching, drying and smoking methods on fish quality were evaluated. The influence of lipid content and packaging methods on lipid degradation, sensory properties and microbial quality during storage of dried and smoked fish was assessed, as well as the marketing potential of sardine dried under more hygienic conditions and imported dried capelin. Blanching prior to drying of sardine and capelin resulted in low quality and sensory properties, and protein denaturation/aggregation. Fat content of capelin depends on the time of year and when capelin of 9-10% lipid content rather than 7-7.5% was used, drying rate was reduced and moisture content in the end product increased, while the fat protected proteins during blanching, drying and smoking. Drying under controlled conditions improved quality demonstrating the need for developing a commercial drier for processing of small fish. Industrially dried and smoked capelin and sardine were found to be rich in essential polyunsaturated fatty acids. Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) constituted approximately 13% and 20% of the total fatty acids of these fish respectively. Lipid content and microbial stability as well dehydration were higher in hot smoked than cold smoked capelin and sardine but hot smoking reduced the yield. Lipid content influenced hydrolysis and oxidation as well as sensory properties during storage of smoked and dried capelin. Lipid hydrolysis was higher in lower lipid capelin while lipid oxidation was higher in fatty capelin. When atmospheric oxygen was removed by vacuum packaging, dried and smoked fatty capelin became more stable during storage with less lipid degradation, less rancid odour and lower counts of microbes. Vacuum packaging had no influence on lipid hydrolysis. Vacuum packaged hot smoked fish was stable during four weeks of chill storage. Dried capelin had moisture content <25% and water activity <0.70 and was stable and safe, during five months storage at room temperature. Improved dried sardine and capelin received high acceptability ratings, indicating consumers of traditional dried small fish might accept new dried fish products. The results from this study show that well processed and packaged dried and smoked small fish can be highly nutritious and could contribute to the reduction of malnutrition prevailing in many developing countries.