Progress in Fishery Sciences (Apr 2023)
Effect of the Time of NaCl Addition on Nutrient Migration and Micro and Nanoparticles of Channa argus Head Soup
Abstract
Channa argus is a bottom-dwelling freshwater fish with high nutritional and economic value and, in China, is known as the "treasure of fish". C. argus meat is mainly used to produce fish fillets; however, head and bone are occasionally utilized in food production. The head of C. argus is rich in mineral elements, amino acids, and unsaturated fatty acids and is commonly used in China for fish head soup. The preparation of fish head soup is particularly time-consuming and can take several hours. Therefore, a high demand exists for the research and development of instant fish head soup products. With the development of modern food colloid research technology, the formation of micro/nanoparticles (MNPs) in soups and the biological effects of the tissue units as active ingredients have attracted increasing attention. In terms of the cooking process of fish soup, in addition to the heating method and cooking time, the seasoning added during cooking is also an important factor. In particular, salt is a key determinant of soup flavor. Although the content is the same, the addition of salt affects the dissolution and migration of nutrients from the fish head during the cooking process. However, the effect of the addition time of salt on the nutritious flavor during the preparation of fish soup has not been studied clearly. Furthermore, the stability of fish soup has not been adequately evaluated.In this work, the C. argus head was chosen as the base material for the soup and the nutrient migration and particles in the C. argus head soup were studied. Water-soluble protein, total sugar, total minerals, solids, nucleotides, free amino acid content, and colloidal particle stability were chosen as indicators to evaluate the transfer of nutrients and flavor. In addition, the morphological structure and distribution of MNPs in the soup were observed using laser scanning confocal microscopy (LSCM). The results showed that the content of water-soluble proteins first increased and then decreased with the delay in salt addition time. The migration trend of total sugars was similar to that of the proteins. Meanwhile, the ash content in the soup generally increased and then decreased. The change in the content of soluble solids could represent changes in various nutrients. The migration of solids and the content of ash peaked when the salting time was at 90 min. The boiled samples with salt added at different times showed significant differences in the migration of nucleotides. It could be concluded that salting was ideal at 60 min or 90 min, based on the changes in the total amount of nucleotides. Furthermore, the contents of total free amino acids and umami-flavored amino acids were also the highest in the samples with salt added at 60 min or 90 min. When the addition time was 60 min, the stability of the MNP system in the fish head soup could effectively be improved by inhibiting the aggregation of macromolecules, which would promote the retention of various nutrients. The particle size and polydispersity (PDI) were lowest in the samples with salt added at 60 min. In addition, the zeta potential value of the sample with salt added at 60 min was higher than that at 90 min. Therefore, the system was relatively stable at 60 min, which was conducive to nutrient retention. This is consistent with the results of the microstructure analysis.The maximum dissolution of nutrients and flavor substances occurred when salt was added after boiling for 60 min. Meanwhile, MNPs in the soup were stable, uniform, double-layer, spherical particles. The results of LSCM showed that nonpolar triglycerides self-assembled into spherical particles, which were located in the center of the particles, and protein molecules dispersed around or were bound to the surface of the particles. The fish head soup system was the most stable under the conditions of particle size, potential, and polydispersion index. Therefore, adding salt after boiling for 60 min was the optimal procedure for making fish soup with high nutritional value, delicious taste, and stable content. This study provides a baseline procedure for C. argus head soup with high and stable nutritional content.The results provide technical support for preparing a convenient and delicious fish head soup. People can enjoy delicious food shortly after a hard day´s work. In addition, the results showed that the timing of adding salt had a significant impact on the nutrition of fish head soup, which suggests that attention should be paid to the timing of adding salt when preparing fish head soup at home. C. argus head, a by-product of processing, can increase in value and provide a solution for producers to decrease waste and increase profits.
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