Effects of yeast inoculation and fermentation on the odor of Hypophthalmichthy nobilis

Studying the effect of yeast fermentation on the odor of Hypophthalmichthy nobilis can provide a certain theoretical basis for the processing of the fish. H. nobilis thin thorns and more meat and a strong earthy smell, which is less popular with consumers. Some of them are processed into frozen fish fillets, fish meal products and fish balls. The market is mainly for live sales, the utilization rate is not high, and a lot of waste is generated, which pollutes the environment and wastes resources. In recent years, the improvement of the organoleptic properties of fish and meat products through fermentation has received considerable attention. Traditional fermented fish is fermented under natural conditions by using microorganisms carried by the environment or by itself. The fermentation process is difficult to control and it is difficult to ensure that the number and types of microorganisms are the same, and the quality of fermented products varies greatly; furthermore, the product fermentation cycle is longer, resulting in fish meat the excessive oxidation of fatty acids reduces the nutritional quality of processed products. In addition, traditional fermented fish methods are diverse, processing environments vary greatly, product quality is unstable, and fermented flavors vary greatly. Raw materials, microbial activities, environment and other factors will affect the quality of fermented fish. The core technology is the breeding of microbial starters. Microbes play an important role in the physical, chemical, nutritional and sensory properties of fermented products. Therefore, research and development of related microbial starters to improve the quality of fermented fish products has practical significance. Appropriate processes are sought to improve the flavor quality characteristics of the products. At present, lactic acid bacteria are the most used in fish fermentation, because they produce acid during the fermentation process to reduce the pH value to inhibit the growth of other spoilage bacteria, and through acid-induced protein denaturation to enhance texture characteristics and improve taste. However, yeast, as another typical food industry probiotic, can produce more pleasant fruit aromas, but it has not been used in industrial fish products. This research uses silver carp as the research object, Saccharomyces cerevisiae as the fermenting agent, and combines headspace-solid phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) with electronic nose (E-nose) to study the odor changes during 3 and 5 days of fermentation. Results showed that after yeast fermentation, there were 12 kinds of esters, including nonanal, decanal, ethyl caproate, ethyl caproate, ethyl oleate and methyl formate, which gave the fish a ‘fruity aroma’ and ‘almond aroma’, so that the flavor substances were more abundant. After fermentation, the content of 1-octen-3-ol decreased by 16.04% and 18.09% after 3 and 5 days, which greatly improved the odor of H. nobilis. The E-nose and principal component analyses found that the different groups could be discriminated easily, indicating that the smell of the fish after the S. cerevisiae fermentation has changed greatly. The analysis of odor substance activity showed that there were 8 main odor substances after 3 days of fermentation, which was 3 more than that the group without adding S. cerevisiae, indicating that add S. cerevisiae can increase the main odor substances of silver carp. Ketones and hydrocarbons in different treatment groups also contributed to flavor, such as 3-octanone, 2-heptanone, caryophyllene, D-limonene, naphthalene, ethyl nonanoate, ethyl caproate, 2-octenol, etc.