| Skipjack tuna has high nutritional and economical values.It is usually processed into canned food and sashimi.With the increasing domestic market demand,a wide variety of skipjack tuna products have been developed to meet consumers.In recent years,aquatic raw materials,such as fish and shrimp,have been processed into natural flavouring which is riched in peptides,amino acid,sugar and nucleotides,and have gained favour in markets.In this paper,a new bonito flavoring product has been developed with skipjack tuna and smoked bonito powder as main raw materials,and the effects of different storage conditions on product quality were also studied.The main results were as follows:(1)Enzymatic hydrolysis effect of bonito fish protein by papain,trypsin and neutral protease were studied,and hydrolysis conditions including enzyme concentration,substrate concentration and hydrolysis time were optimized.The results of dual enzymatic hydrolysis of optimization indicated that the degree of hydrolysis of three kinds of hydrolysates grew gently after 4 h and trypsin > neutral protease > papain.Sensory evaluation was discovered the best score at the same time,the score showed by the order of trypsin > papain > neutral protease.The total contents of free amino acid by trypsin,neutral protease and papain increased from 186 mg/100 mL to 1716 mg/100 mL,1432 mg/100 mL and 1099 mg/100 mL respectively.The amino acids which made significant contribution to taste were Glu,Met,Phe,His and Lys by TAV analysis.For these we chose trypsin and papain to the dual enzymatic hydrolysis of skipjack tuna.(2)Conditions of dual enzymatic hydrolysis of skipjack tuna by trypsin and papain were investigated,and the hydrolysates properties were studied.To further optimize the hydrolysis conditions,response surface methodology was used,on the basis of the single factor experiment.The results showed that the optimal conditions for skipjack tuna hydrolysis were: enzyme-to-substrate ratio 3000U/g,papain to trypsin ratio 1:3,substrate concentration 25%.Under this condition,the total free amino acids content of the hydrolysate kept increasing during the hydrolysis.The content of bitter taste free amino acid decreased while that of umami taste free amino acids had an increase after hydrolysis.According to TAV analysis,Glu,Met,Ile and His played important roles in the contribution of hydrolysate flavor.Distribution of small molecular weight peptides in the hydrolysate increased gradually during the hydrolysis,indicated that macromolecular protein was effectively degraded gradually.The contents of IMP and GMP kept increasing during the hydrolysis.(3)Conditions of dual enzymatic hydrolysis of smoked skipjack tuna was optimized.The results showed that the enzyme concentrations were 2000 U/g for trypsin and 1000 U/g for flavourzyme respectively.Under this condition,the degree of hydrolysis(DH)and FAA contents kept increasing constantly during 30 h of hydrolysis.Sensory evaluation showed that the hydrolyzate has a favorable sensory score in 10 h.Nitrogen solubility index and total volatile base nitrogen content in smoked skipjack tuna hydrolysate increased continuously with hydrolysis time.Phenols,aldehydes,alcohols were detected in the hydrolysis by GC-MS,and among,phenols gave the greatest contribution to smoked flavor of hydrolysate,but the content of phenols decreased over hydrolysis time.Considering from the volatile flavor and sensory quality of smoked skipjack tuna hydrolysate,hydrolysis time should be controlled within 10 h.(4)The sensory quality of skipjack tuna flavouring were valuated by fuzzy mathematics comprehensively,and the ingredient ratio of the product was accodingly optimized.The results showed that the oprimal drying time and temeperature were 40 min and 45?,respectively.The study also found that 1% of silicon dioxide has good anti-caking effect on the product.Thermal stability analysis of the volatile flavor of the product in the drying process showed that the main substance contributing to the flavor of the product was phenol in 45? dry conditions and in 70? dry conditions.However,the volatile flavour compounds of of the product dried at 70? were much less than that at 45?,therefore,to retain the smoked flavor in the product to a greater degree,the drying temperature should be controlled at about 45?.(5)The influence of packaging and storage temperatures on the color,TVB-N value,total plate count,fat oxidation of the product during storage were studied,and also,the variation of the product quality during the storage were analyzed.Results showed that lower temperature was more effective in maintaining the product color,reducing the rate of fat oxidation and inhibiting the growth of microorganisms,and also,dark storage and deoxygenated packaging were more conducive to the product storage stability. |
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