| Antarctic krill is rich in protein and is known as "the largest protein pool of mankind".Its protein content is believed to be between 60-65% of its dry weight.The protein in krill contains all nine essential amino acids required by human beings.In addition to protein,it is also a potential source of long-chain polyunsaturated fatty acids,including eicosapentaenoic acid(EPA)and docosahexaenoic acid(DHA),known as brain gold,with the advantages of easy absorption.Antioxidants such as astaxanthin and astaxanthin also have considerable commercial value.It can be said that the whole body is treasure.Because of the huge development potential of Antarctic krill,the utilization and development of its resources has become an important part of the development of pelagic fisheries.The development of Antarctic krill food has attracted much attention.Sufficient research has shown that Antarctic krill has the possibility of developing highly delicious and characteristic food.Shrimp sauce is a traditional fermented aquatic product in China.The formation of its delicious and rich flavor is not only related to the composition of raw materials and production and processing,but also related to the biochemical action of microorganisms and the degradation characteristics of enzymes.A large number of bacteria release a variety of hydrolytic enzymes,proteins,fats and carbohydrates in the fermentation liquid during the fermentation process,and decompose them into polypeptides,fatty acids and carbohydrates in the raw materials,thus forming a "flavor precursor pool".During the mature stage of shrimp sauce,a series of complex processes such as fermentation,oxidation-reduction reaction,esterification,amino acid degradation,Maillard reaction and so on will produce corresponding metabolites,Make the food have new and unique flavor and nutritional value.In this paper,Antarctic krill is used as raw material to make shrimp paste,and the thawing mode of Antarctic krill,the degradation of Antarctic krill protein during fermentation,and the composition of bacteria and volatile flavor components during fermentation are identified and analyzed,and the relationship between microbial community composition and flavor substances during fermentation is explored,and the dominant bacteria in shrimp paste samples and the bacteria that are mainly related to flavor formation are determined,The main results of this paper are as follows:(1)The Antarctic krill was thawed using five thawing methods: natural,low temperature,still water,running water,and microwave.The sensory scores,degree of spoilage,lipid oxidation,protein denaturation,microbial indicators,and fluorine migration were observed under different thawing methods.Different thawing methods have great differences in the appearance,physical and chemical properties of Antarctic krill.The flowing water thawing generally shows the best quality.(2)In this study,Antarctic krill was used as raw material to make shrimp paste,and the changes of p H,Aw,degree of protein hydrolysis(NPN content change,TCA-soluble peptide,amino acid nitrogen as reference index)in shrimp paste protein content,amino acid composition and other indicators during Antarctic krill fermentation were investigated to deepen the understanding of protein degradation process during Antarctic krill fermentation.The results showed that in the fermentation process,according to the protein hydrolysis index,the protein was initially hydrolyzed into nonprotein nitrogen species,including the generation of peptides,amino acids,etc.Peptides are further decomposed to produce smaller peptides and free amino acids.(3)The composition of bacterial community in shrimp paste was analyzed by highthroughput sequencing method.The results showed that there were four dominant phyla in the fermentation process of Antarctic krill,namely,Firmicutes,Actinobacteriota,Proteobacteria and Bacteroidota.There are 22 species of bacteria with relative abundance more than 1%.TetragenococcusăAlkalibacteriumăAtopostipes is the top three,which exists in the whole fermentation process and accounts for 95.73% of mature shrimp paste,indicating that these three genera play an important role in the fermentation process of shrimp paste.The flavor volatile substances of shrimp paste from four different raw materials were detected by SPME-GC-MS,and alcohols,aldehydes,ketones,esters,acids,sulfur compounds,pyrazine,pyridine,hydrocarbons,amines,aromatic compounds and other components were detected.Aldehydes,acids,pyrazine and other substances accounted for a relatively high proportion in shrimp paste.(4)Using O2PLS model to analyze the correlation between volatile components and bacterial composition,it can be found that the formation of flavor compounds in fermented food is closely related to microbial activities.Among them,Tetragenococcus,Alkalibacterium and Atopostipes are the top three bacteria in shrimp paste,which exist in the whole fermentation system and contribute greatly to the formation of volatile flavor compounds,indicating that these three bacteria play an important role in the changes of volatile components in each stage of shrimp paste fermentation,and are important bacteria that affect the quality of shrimp paste. |
