Studies On Vacuum Freeze-Drying Technology And The Storage Stability Of Natto's Active Components

Natto is a kind of traditional fermented food of Japan which is produced by Bac-illus natto or Bacillus subtilis thrugh fermenting soybeans.Natto contains not only rich variety of nutrients,but also a number of physiologically active substances such as:nattokinase;Bacillus natto;ACE Inhibitor;vitamin K2 and pyridine carboxylic acid etc,which can dissolve blood thrombus,lower the blood pressure,help digestion and pre- vent osteoporosis.After fermenting,use the saline to dissolve the effective components of natto directly without ripening.The effects of cryoprotectants on the retention rate of the nattokinase activity and the survival rate of Bacillus natto were researched in this paper.Through single factor design and orthogonal design,the optimum cryoprotect- ants that were screened from skimmed milk powder,sucrose,maltodextrin,Vc,maltose, lactose,sorbitol and trehalose.The best cryoprotectant as follows:skimmed milk powder 10%,maltodextrin 3%,sucrose 5%,Vc0.5%.Under the above factor,the retention rate of the nattokinase activity increased 69.8% and the survival rate of Bacillus natto increased 76.7%.In this paper,the co-crystal and co-melting temperatures of the solution which contains the effective compenents,(after adding cryoprotectants) are determined by me- asuring the change of resistance.The effects on the freeze-drying velocity,the retention rate of the nattokinase activity and the survival rate of the Bacillus natto were re- searched in this paper,and the optimum conditions of freeze-drying were determined. It was sured that suitable cold shock treatment can improve the survival rate of Bacillus natto,but it could not improve the retention rate of the nattokinase activity, the survival rate of the Bacillus natto increased 3.1% under the best cold shock treat- ment: 8℃5h.The optimum conditions of freeze-drying are as follows: pH of the solution was 7.0～7.5, temperature of prefreezing was -30℃,velocity of prefreezing was 1.5℃/ min,time of prefreezing was 120min,temperature of cold trap was -40℃, thickness of material was10mm,vacuum degree was 30Pa,temperature of sublimation was 30℃, temperature of resolution was 45℃.Under the above conditions,the freeze-drying velocity was 0.83 mm/h,the total freeze-drying time was 12h,the retention rate of the nattokinase activity was 81.8% and the survival rate of Bacillus natto was 90.9%,the moisture of freeze- drying powder was 2.93%.The accelearated storage test was carried out to test the stability of Nattokinase and Bacillus natto,and the shelf life of Nattokinase and Bacillus natto at 25℃and 4℃were estimated too.The results of accelearated storage test showed that the activity of nattokinase decreased by 10% after 19.8days, 325.3days (0.89year) and decreased by 50% after 130.3 days(0.36year), 2138.9 days (5.86years) when it was kept at 25℃and 4℃. The death rate of Bacillus natto decreased by 10% after 31.7days, 421.6 days (1.15years) and decreased by 50% after 208.1days (0.57year), 2772days (7.59years) when it was kept at 25℃and 4℃. The accelearated storage test was tested at 4℃,it was sured that the results estimated by the accelearated storage test were similar with the results of verifiation test, therefor,the accelearated storage test can be used to estimate the shelf life of Nattokinase and Bacillus natto.