Flavor Improvement Of Antarctic Krill Enzymatic Hydrolysate By Maillard Reaction

Antarctic krill?Euphausia superba?,which has rich resource and much a little fat,protein and abundant nutrition,is one of the important protein resources in 21 st century.Its inclusion which is nutritious has bright prospects for being used to product natural seafood seasoning.However,there are some defects such as high fluorine content,single flavor,poor aroma and weak mallow taste in Antarctic krill enzymatic hydrolysate,which limit its further processing and utilized at present.In this thesis,the optimum conditions for Antarctic krill enzymatic hydrolysate by enzyme technology using Antarctic krill endogenous enzyme and exogenous enzyme,fluoride reduction technology and flavor improvement by Maillard reaction were studied,and the volatile and non-volatile flavor composition of Antarctic krill flavor base material before and after Maillard reaction got by former two technologies were analyzed and compared with chemical analysis and instrument analysis,expecting to provide theory foundation for the development of high-grade seafood seasoning using Antarctic Krill.Main contents and results are as follows.1.The preparation process of enzymatic hydrolysate with low fluoride level from Antarctic krill was optimized by response surface methodology to maximize the removal of fluorine and provide theoretical basis for its industrialized production.Based on single-factor experiment,using fluoride removal rate as response value,calcium acetate addition,initial pH,reaction temperature and reaction time were selected as independent variables.According to principal of Box-Behnken experimental design,the significance and interaction of these 4 factors were analyzed by response surface methodology with 4 factors and 3 levels.The results showed that calcium acetate addition and initial pH had extremely significant effects on fluoride removal rate,as well as the interaction between calcium acetate addition and reaction temperature.The optimal process conditions were as follow: calcium acetate addition of 21.5 mg/mL,initial pH of 10.2,reaction time of 120 min and reaction temperature of 30.24?.Under the above optimum conditions,the fluoride removal rate was 84.15%±1.37%?P>0.05?,which was close to predictive value of model?85.37%?.After reaction,the total nitrogen?TN?and the degree of hydrolysis?DH?did not reduce significantly,which proved that nutrition constituents in Antarctic krill enzymatic hydrolysate was changed little.The optimized preparation process of enzymatic hydrolysate with low fluoride level is simple to operate,efficient and does not have significant effects on flavor or nutrient composition of the enzymatic hydrolysate,which is workable.The established model can be used to predict in actual production.2.Fuzzy mathematic evaluation model was introduced to optimize the Maillard reaction technology of Antarctic krill enzymatic hydrolysate.As four key factors,colour,texture,taste and odor of Maillard reaction products were on weight analysis based on sensory evaluation,and the integrated assessment system was established.The technology of Maillard reaction products was optimized by single factor and orthogonal tests,combining with sensory evaluation method of fuzzy mathematic.The effects of addition of D-xylose,initial pH,reaction time,reaction temperature on sensory evaluation for Maillard Reaction were investigated.The results showed that the optimum stewed conditions were as follows: D-xylose addition of 40 g/L,initial pH of 8.5,reaction time of 90 min,reaction temperature of 105?,salt addition of 20 g/L and amino acid addition of 30 g/L.Under this optimal condition,the sensory evaluation level of Maillard reaction products was excellent with the peak of 0.462.3.The flavor Profiles of Antarctic krill enzymatic hydrolysate before and after Maillard reaction were analyzed by Sensory evaluation and electronic nose fingerprint.The results showed that difference of flavor in Antarctic krill enzymatic hydrolysate before and after Maillard reaction existed,and it preserved shrimp flavor combined in harmony with a high quality touch of baking flavor and meat flavor,therefore the volatile flavor of Antarctic krill enzymatic hydrolysate was improved by Maillard reaction.The fingerprints of Antarctic krill enzymatic hydrolysate before and after Maillard reaction were acquired by electronic nose technology.The response signals were analyzed by principal component analysis,discrimination function analysis,soft independent modeling of class analogy and odor radar chart.The result of electronic nose coincided with sensory evaluation,which showed that its overall flavor was changed greatly.Qualitative and quantitative analysis of the volatiles in Antarctic krill enzymatic hydrolysate before and after Maillard reaction were conducted by GC-MC technique and the odor active value?OAV?of each volatile was calculated,the results showed that the components in Antarctic krill enzymatic hydrolysate before and after Maillard reaction were complex,including hydrocarbons,alcohols,nitrogen compounds,acids,aldehydes,ketones,esters,phenols,furans,pyrazines and so on.And pyrazine,acids and lipids were main components in Antarctic krill enzymatic hydrolysate after Maillard reaction.The types of volatiles in Antarctic krill enzymatic hydrolysate before and after Maillard reaction were increased from 64 to 119,the content of volatiles was increased from 45.16 ?g/100 mL to 167.28 ?g/100 mL,and the types of odor active compounds were increased from 16 to 20.According to the flavor characteristics,the odor active compounds could be classified under “toasted ”,“shrimp meaty ”,“sweet,fruity ”,“caramel ” aroma and other organoleptic perception.These results coincided with the results of sensory evaluation.4.The taste profiles of Antarctic krill enzymatic hydrolysate before and after Maillard reaction were analyzed by flavor profile test and electronic tongue fingerprint.The results showed that the umami taste of Antarctic krill enzymatic hydrolysate before Maillard reaction was very strong;after Maillard reaction,the mellow taste and after taste were improved obviously,the umami taste was decreased slightly,so the overall taste was improved.The fingerprints of Antarctic krill enzymatic hydrolysate before and after Maillard reaction were acquired by electronic tongue technology.The response signals were analyzed by principal component analysis,discrimination function analysis and taste radar chart.The results showed that the flavor characteristics of Antarctic krill enzymatic hydrolysate before and after Maillard reaction shared similarity.The response signals did not coincide,which revealed the tastes before and after Maillard reaction were different.The result coincided with the results of flavor profiles.The non-volatile taste active compounds,including free amino acids,nucleotide related compounds,betaine,glycogen,organic acid and mineral salts in Antarctic krill enzymatic hydrolysate before and after Maillard reaction,were analyzed and compared by chemical and instrumental analysis.The results showed that after Maillard reaction,the role of the taste active compounds in the taste of Maillard reaction products was changed in different levels with their changes in content.The content of free amino acids in Antarctic krill enzymatic hydrolysate was reduced by 32.73%.The content of basic amino acid?Arginine,histidine and lysine?was reduced significantly and the content of delicious amino acid?aspartic acid and glutamic acid?was changed little.The content of sugar and betaine was changed little?P>0.05?while the content of short peptide was decreased by 9.8%.The content of mineral salts(Na⁺,K⁺,Mg²⁺,Ca²⁺,Cl^-,PO₄^3-)in aquatic products was analyzed systematically.Na+ and Cl-had the highest amount of mineral salts,increased by 87.2% and 60.1%.The other mineral salts were changed very little.Four kinds of nucleotide related compounds were detected before and after Maillard reaction.The content of AMP,HxR and Hx before reaction were 472.68 mg/L,355.04 mg/L and 39.02 mg/L.Maillard reaction reduced IMP content and enhanced HxR content little.Organic acids were the main components of aquatic products flavor,which were considered to be the flavor enhancer.Malic acid,lactic acid and succinic acid were detected with the content of lactate acid being the highest?2508.0 mg/L and increased by 3.7% after reaction?.It is proved that the amplitude difference of Organic acid had little effect on the quality of total flavor.