| Antarctic krill has abound resources and high nutritional value.It is characterized as high protein,low fat and rich mineral elements.It is a "protein resource warehouse for the future of mankind" and listed as an important high-seas resource by all countries in the world.Antarctic krill contain abundant flavor components,such as amino acids,nucleotides,organic acids and so on.It is an ideal raw material for preparing seasonings.The preparation method of aquatic product seasoning mainly includes enzymatic hydrolysis and fermentation.The enzymatic hydrolyzed aquatic product seasoning has high protein utilization rate,mild condition,thick taste,but lacking of aroma;the fermented aquatic product seasoning has rich aroma,delicious taste and abound nutrition,but the fermentation time is long.This study combines the advantages of these two methods,using Antarctic krill as raw material,selecting Lactobacillus plantarum,Saccharomyces rouxii and Staphylococcus xylosus as starter cultures for semi-solid mixed fermentation and using flavor enzymes for enzymatic hydrolysis to improve the utilization of protein,shorten fermentation time and improve flavor.Then Antarctic krill flavor base material with excellent flavor is prepared.Finally,sensory evaluation and chemical analysis were used to analyze the flavor components of the flavor base material,which provided theoretical basis and technical support for the development of high-grade seafood seasonings for Antarctic krill.The main research contents and results are as follows:1.Taking sensory score and amino nitrogen content as indexes,the single factor experiment was carried out on the proportion of bacteria,fermentation temperature,fermentation time and inoculation quantity of compound starter.Based on the results of single factor experiments,the experiment design of 3 factors and 3 levels was carried out according to the Box-Behnken center combination method,and the response surface analysis was carried out.The results show that the optimum conditions for the fermentation of Antarctic krill: The ratio of Lactobacillus plantarum to Saccharomyces rouxii and Staphylococcus xylosus was 1:2:3,fermentation temperature 31℃,fermentation time 22 h,inoculum size 4 %.Under this condition,the total score of sensory evaluation of fermented Antarctic krill broth was 4.39.The fermented broth is rich in nutrition,full of flavor,unique and harmonious in taste.2.The volatile flavor components of Antarctic krill flavor base materials wereanalyzed by sensory evaluation and electronic nose.The results showed that,the fishy smell of Antarctic krill decreased obviously,and the roast,sweet flower and fruit aroma,shrimp meat aroma and unique fermented flavor were added after fermentation and enzymatic hydrolysis.The fermented flavor increased obviously.According to the analysis of electronic nose odor fingerprints by odor radar,principal component analysis and discriminant factor analysis,it was found that there is part of the radar signal overlap,and the analysis shows that Antarctic krill and its flavor base materials have different odor.The difference between them could be detected by electronic nose,indicating that the flavor base materials remained the basic shrimp flavor and many characteristic flavors were added,which was consistent with the sensory evaluation results.Qualitative and quantitative analysis of volatile compounds of Antarctic krill flavor base materials were conducted by GC-MS.The results showed that,the kinds and contents of odor components increased from 70,146.27 μg/100 mL to 105,1458.91μg/100 mL,and the kinds and contents of alcohols,aldehydes and esters increased significantly after fermentation and enzymatic hydrolysis.The contents of benzaldehyde,phenylacetaldehyde,heptaldehyde,nonanal and 2-octenaldehyde in aldehydes increased to 11.63 μg/100 mL,23.53 μg/100 mL,6.99 μg/100 mL,14.68 μg/100 mL,0.54 μg/100 mL respectively,and their odor activity values were all higher than 1,which contributed greatly to the fragrance and nutty aroma of flavoring base.The 2-heptanone(5.35μg/100mL),2,3-butanedione(4.50 μg/100mL)and acetophenone(2.42 μg/100mL)in the flavor base materials have blueberry,cream and sweet fruit aroma respectively,and they contribute to the odor of the flavor base materials.The ethyl acetate(68.21 μg/100mL),hexyl formate(5.31μg/100mL)and ethyl phenylacetate(0.55 μg/100mL)in the flavor base materials give the product a sweet pineapple,fruit and strong honey aroma respectively.The flavor base materials was filled with fruit and cream aroma and promoted the formation of characteristic flavor.The newly added nitrogen compounds such as trimethylpyrazine(14.24 μg/100mL),3-ethyl-2,5-dimethylpyrazine(62.19μg/100mL),2-ethyl-3,5,6-threemethylpyrazine(3.26 μg/100mL),2,3-dimethyl-5-propyl-pyrazine(9.04 μg/100mL)contributed to the barbecue aroma.Acids,alcohols and sulfur compounds also increased.They make the shrimp aromas,sweet flowers and fruits,grass and roasted aromas in the characteristic flavors of Antarctic krill stronger than before,while forming a unique fermented flavor.It can be seen that after microbial mixed fermentation and enzymatic hydrolysis,the smell of Antarctic krill has been improved obviously,becoming more abundant,and the aroma is pleasant and lasting.3.The changes of taste profile of Antarctic krill flavor base materials were analyzed by flavor profile and electronic tongue.The results showed that,compared with the Antarctic krill,taste of flavor base materials was enhanced significantly,the sweetness and sour taste increased slightly,the umami and bitterness did not change significantly and the overall taste and mellowness were enhanced after fermentation and enzymatic hydrolysis.The data collected from electronic tongue were analyzed by principal component analysis and discriminant factor analysis.It was found that,the taste of Antarctic krill and its flavor base materials had obvious differences.The contents of free amino acids,nucleotides,organic acids and inorganic ions in Antarctic krill and flavor base materials were determined by chemical analysis and instrumental analysis.The taste active compounds and their contribution were evaluated by taste activity value(TAV).The results showed that the contents of free amino acids,nucleotides and organic acids in the flavor base materials increased significantly after the fermentation and enzymatic hydrolysis.The total content of amino acids increased 5times to 22.6 g/100 g,and TAV exceeded 1.The TAV of glutamic(0.68 g/100g),aspartic(1.08 g/100g),glycine(1.79 g/100g),alanine(2.01 g/100g)were 22.7,10.8,13.8,33.5respectively;IMP was 384.33 mg/L,TAV was 1.5;TAV of lactic acid(3273.46 mg/L)and succinic(3446.46 mg/L)were 2.6,32.5;the contents of betaine and inorganic ions were not much different.The increase of these flavoring substances makes the flavor base materials of Antarctic krill are more delicious and higher nutritional value. |
