【作者】 曹峰；

【导师】 陆晓滨；

【作者基本信息】 山东轻工业学院 ， 食品科学， 2008， 硕士

【摘要】 纳豆是日本的一种传统食品,由纳豆菌(Bacillus natto)或枯草杆菌(Bacillus subtilis)发酵蒸煮大豆而制成。研究表明,纳豆不仅营养丰富,其周围的黏性物质中还含有一些生理活性物质如纳豆激酶、纳豆菌、血管紧张肽转化酶抑制剂、维生素k2、吡啶二羧酸等,具有溶血栓、降血压、防止骨质疏松等多种保健功能。利用筛选出的一株纳豆菌发酵大豆制成纳豆后不经后熟,直接用无菌生理盐水将纳豆周围的黏性物质洗脱,然后对洗脱液进行冷冻干燥,并对干燥过程中保护剂对纳豆激酶的酶活保持率和纳豆菌存活率的影响进行研究,通过单因素试验和正交试验,从脱脂乳粉、蔗糖、麦芽糊精、抗坏血酸、麦芽糖、乳糖、海藻糖和山梨醇中筛选出了最佳保护剂组合:脱脂乳粉10%、麦芽糊精3%、蔗糖5%、抗坏血酸0.5%,在此条件下纳豆激酶的酶活保持率和纳豆菌存活率与对照组相比分别提高了69.8%和76.7%。利用电阻法测定了添加保护剂后纳豆洗脱液的共晶点和共熔点。在此基础上对冷冻干燥过程中影响干燥速率、纳豆激酶酶活保持率及纳豆菌存活率的其它因素进行了研究和优化,确定了最佳冷休克处理条件及最优冷冻干燥工艺条件。适当的冷休克处理可以提高纳豆菌的抗冻能力,但对纳豆激酶的影响并不显著,纳豆菌经8℃、5 h的冷休克处理,冻干后的存活率与未处理的相比提高了3.1%。最优工艺条件为:纳豆洗脱液的pH值为7.0～7.5,预冻结温度为–30℃,冻结速率为1.5℃/min,冻结时间120min,冷阱温度为–40℃,冻结物料厚度为10 mm,干燥室真空度为30Pa,升华温度为30℃,解析温度为40℃。在优化的工艺条件下,纳豆活性成分洗脱液的干燥速率为0.83 mm/h,总干燥时间为12 h,冻干后纳豆激酶酶活保持率为81.8%,纳豆菌的存活率为90.9%,冻干粉的含水量为2.93%。利用加速储存试验对冻干粉中纳豆激酶和纳豆菌的储存稳定性进行了研究,并估算出了纳豆激酶和纳豆菌在25℃和4℃下的储存寿命。25℃下纳豆激酶酶活损失10%和50%所需时间为19.8d和130.3d(0.36年),纳豆菌菌体死亡10%和50%所需时间为31.7d和208.1d(0.57年);4℃下纳豆激酶酶活损失10%和50%所需时间为325.3d(0.89年)和2138.9d(5.86年),纳豆菌菌体死亡10%和50%所需时间为421.6d(1.15年)和2772d(7.59年)。对4℃条件下的加速储存试验结果进行了验证,结果显示由加速储存试验推算出的结果和验证试验得出的结果较接近,证明可以利用加速储存试验估算纳豆活性物质冻干粉中纳豆激酶和纳豆菌的储存寿命。更多还原

【Abstract】 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.更多还原