The Nutritional Components, Physicochemical Properties, Flavor Characteristics And Microflora Composition Of Smelly Mandarin Fish

Mandarin fish is a kind of high-quality freshwater fish with high protein and low fat. After salting or fermentation, the nutrition and flavor of mandarin fish were significantly changed under the action of its own enzymes and microorganisms, and it would produce a special flavor, not like smell, but like fragrance. As a traditional salted fish product, smelly mandarin fish was favored and enjoyed by a large amount of consumers, due to the the unique flavor and delicious taste. However, there is little research on the smelly mandarin fish. Based on the above reasons, we used the traditional smelly mandarin fish as raw material in this study, and its nutritional quality was compared with the fresh mandarin fish. Besides, the flavor compounds in the fresh mandarin fish, smelly mandarin fish and cooked smelly mandarin fish were investigated, to identify the substances which endowed the mandarin fish with delicious taste and unique flavor. In addition, the physical and chemical properties of the mandarin fish in the whole process of fermentation were researched, and finally the dominate bacteria were further identified using molecular technique. These results could provided an important theoretical basis for improving the stability and safety of the smelly mandarin fish products and its commercial production.Firstly, the nutritional components of the fresh mandarin fish and smelly mandarin fish were compared and the changes of the nutritional components in the smelly mandarin fish were analyzed. It was found that the content of moisture was reduced after salting, which caused the crude protein, crude fat and ash content to be increased relatively in smelly mandarin fish. The contents of umami amino acid and free amino acids were increased, from 5.90% to 6.12%, and from 33.33mg·100g’1 to 468.08mg.100g-1, respectively. The content of saturated fatty smell perch (SFA) was increased, but unsaturated fatty acid (USFA) was decreased in smelly mandarin fish. With regard to minerals, the contents of zinc and calcium were increased in the smelly mandarin fish.Secondly, the changes of physical and chemical properties from smelly mandarin fish in the whole process of fermentation were researched. The results indicated that the texture characteristics of smelly mandarin fish in the process of curing were significantly changed. Hardness, adhesion, chewiness and cohesiveness were increased, and flexibility and recovery was reduced. The mouthfeel of smelly mandarin fish was better than that of fresh mandarin fish, which was correlated with the gradual increase of sodium chloride in the smelly mandarin fish meat. And the contents of trimethylamine and TVBN were also increased. At the same time, the levels of protein hydrolysis was further elevated, which caused the TCA soluble peptide, non protein peptide and amino nitrogen content to be increased, among which the amino nitrogen endowed smelly mandarin fish with delicious taste. Safety indexes such as biogenic amines and nitrite content were also increased, among which the content of histamine, one of the most toxic biogenic amine, was 268.82 mg/kg. The total analysis results indicated that though the freshness and safety of smelly mandarin fish were decreased, it was still safe and could be used for food. And umami substances and special flavor were gradually increased in the whole process of fermentation.Moreover, the distinctive flavor of smelly mandarin was studied by using headspace solid-phase microextraction and gas chromatography/mass spectrometry.72 compounds were detected in the fresh mandarin fish,83 compounds in the smelly mandarin fish and 78 compounds in the cooked smelly mandarin fish. Compared with the fresh mandarin fish, the content of aldehydes, ketones, alkanes and alkenes gradually reduced in the smelly mandarin fish, showing differences between them. The content of esters, ethers, phenols, carboxylic acids, sulphur-containing compounds, aromatic and cyclic hydrocarbons gradually increased, while alcohols and nitrogenous compounds remarkably increased. However, after the smelly mandarin fish was cooked, the content of alcohols, nitrogenous compounds significantly decreased, sulphur compounds increased markedly, but with no obvious changes in esters, ethers, phenols, carboxylic acids, aromatic and cyclic hydrocarbons, aldehydes, ketones, alkanes and alkenes. Through the calculation of odor activity value (OAV),17 kinds of key aroma-active compounds were identified, including trimethylamine, Linalool,3-methyl-l-butanol, hexyl alcohol, 1-octene-3-alcohol, butyl aldehyde, hexanal, heptanal, caprylic aldehyde, nonyl aldehyde,2-nonene aldehyde, decanal,2,3-symplectic diketone, limonene, carbon disulfide, dimethyl sulfide and butyric acid.Finally, the changes of microflora compositions from smelly mandarin fish were investigated in the process of curing, and the dominate bacteria were also investigated. The dominant position of Lactobacillus were found. Four main microorganisms were identified: Lactobacillus buchneri, Serratia plymuthica, Enterococcus faecalis, Bacillus subtilis, and the proportions were 51.10%,39.85%,51.10% and 39.85%, respectively.