| Natto is a healthy fermented soybean product,rich in nutrients,contains various active substances such as nattokinase,and has a high market value.However,most people do not accept its special smell and taste,and fermentation microorganisms limit its biological activity,which seriously hinders the development and promotion of natto as a functional health food.Today,with the development of modern fermented food processing technology,people have more diverse dietary requirements,and dietary therapy to intervene in the physical health status has become extremely attractive.Therefore,this study developed a popular healthy natto product by adjusting the natto starter formula to improve the sensory quality of the product,increase the content of nattokinase and other biological activities,which has a great role in preventing and alleviating cardiovascular and cerebrovascular diseases.(1)In this study,bacillus subtilis GUTU09 was used as the main strain to ferment natto with Mucor,Lactobacillus or Bifidobacterium,and the effects of different fermentation combinations on natto were investigated.The combination of the two strains showed the best fermentation performance among all samples.The NK and protease activity and FAN content in double-strain fermentation increased by10.33 FU/g,88.78 U/g,and 2.34 g/kg,respectively,compared with those in single-strain fermentation.This method also reduced the contents of various biogenic amines in natto compared with single-strain fermentation.Tyramine,cadaverine,spermine,and spermidine were significantly reduced,whereas histamine was slightly increased.The total biogenic amines decreased from 390.76 mg/kg to a minimum of16.16 mg/kg.Some Mucor strains also reduced the contents of various biogenic amines.In addition,co-fermentation was better than staged fermentation in the combination of GUTU09 and Mucor.Therefore,this subject preliminarily studied the composition of natto starter.(2)For further study on fermentation parameters on the influence of the mixed bacteria fermentation natto,and improve the fermentation performance,this study used GUTU09 and Bifidobacterium BZ25 as the fermentation combination to investigate the seven factors of NaCl addition,sucrose addition,strain proportion,inoculation amount,fermentation time,fermentation temperature and ripening time.The results showed that fermentation time,fermentation temperature,Na Cl addition,sucrose addition and inoculation amount had significant effects.Besides,response surface methodology was used to optimize the fermentation process to obtain better natto products(3)After fermentation,the contents of furans,aldehydes and amines in soybean decreased significantly,while the volatile components of ketones,esters,pyrazines and acids increased significantly.Among them,fermentation strain BZ25 played a great role,including producing a large number of ester aroma components,reducing amine nitrogenous substances,to reduce the"ammonia smell"of natto and improve the flavor of natto.During the fermentation process,spermine content increased significantly,tyramine also showed an increasing trend,putrescine,cadaverine,and spermidine changed little,but no biogenic amines such as histamine,tryptamine and2-phenylethylamine were detected,which indicated that the strain had good biological safety.The free amino acid analysis showed that cooking and BZ25 fermentation had little influence,but under the action of GUTU09 and mixed bacteria,the total amino acid content increased to 5.63 and 4.242 times of the raw material,respectively,and the proportion of essential amino acid increased from 10.82%to 56.41%.Therefore,mixed bacteria fermentation improved the nutritional value of natto.These results provided theoretical support for further exploring the fermentation characteristics of the strain and exploring the mechanism of the quality change of natto during fermentation.(4)With the development of natto fermentation,the thrombolytic area and nattokinase activity showed a significant positive correlation,with the highest values being 302.73±10.3 mm~2 and 161±1.96 FU/g respectively,and the diluted natto extract showed excellent anticoagulant activity.In vitro antioxidant activity test showed that:after fermentation,the total flavonoids content increased from 1.18±0.04 mg RE/g to the highest 2.4±0.06 mg RE/g,the total phenol content from 1.92±0.04 mg GAE/g to the highest 5.09±0.14 mg GAE/g,DPPH radical scavenging activity,ABTS radical scavenging activity and FRAP reducing activity were increased significantly,and has a significant correlation between them.These studies show that the mixed fermentation can improve the quality of natto and provide a reference for its potential industrial large-scale application. |
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