Processing technology and flavor characteristics of Shanghai smoked fish (Micropterus salmoides)

Shanghai smoked fish is a traditional Chinese dish with crispy crust, delicious taste and rich nutrition, belonging to Shanghai cuisine. Traditional Shanghai smoked fish uses Mylopharyngodon piceus or Ctenopharyngodon idella as raw materials. In recent years, the amount of M. piceus farmed has declined, C. idella is a typical herbivorous fish with a strong earthy smell, and both M. piceus and C. idella have intermuscular spines, which is not convenient for the elderly and children to eat. Micropterus salmoides with abundantly nutritional values is an omnivorous freshwater bass with meat as the main food. The earthy smell of M. salmoides is lighter than that of M. piceus and C. idella. The meat of M. salmoides is tender and has no intermuscular spines, also its mouthfeel and flavor are better than C. idella, which is popular among the public. In this experiment, on the basis of the original technology, better raw materials were selected to develop new processed products for M. salmoides. In order to overcome the shortcomings of processing Shanghai smoked fish by M. piceus and C. idella, M. salmoides was used to replace C. idella in processing Shanghai smoked fish. Single factor experimental design and orthogonal experimental design were used to improve the processing technology of Shanghai smoked fish. Headspace solid phase micro-extraction gas chromatography-mass spectrometry (SPME-GC-MS) was to analyze the changes of volatile flavor active substances in deep-fried Shanghai smoked fish, Shanghai smoked fish with no spices in the fried soaking liquor and Shanghai smoked fish (final product). Key volatile compounds were detected by qualitative and quantitative analysis of gas chromatography-mass spectrometry and high-performance liquid chromatography (HPLC) was used to determine flavor nucleotides. The result showed that, better processing method is to fry M. salmoides for 6 min and then to soak it in the soaking liquor of soy sauce / white sugar=4 ∶ 3. The volatile compounds in three samples are 37, 47 and 55 kinds. Aldehydes, ketones, alcohols, hydrocarbons, aromatics and nitrogen, sulfur-containing substances are the main flavor compounds of Shanghai smoked fish. IMP is the main umami nucleotide. In conclusion, first soaking, deep-frying, and soaking after frying were the key processes for removing and concealing the earthy smell of freshwater fish. At the same time, the Maillard Reaction in the process of frying can increase the aroma of the fish and make cooked dishes with excellent aroma and rich nutrition. The Maillard Reaction, thermal degradation and fatty acid oxidation that happened in the deep-frying process help to reduce fishy smell and form the characteristic flavor of Shanghai smoked fish. Soaking and deep-frying are excellent processing methods to improve the quality of fish products.