Mutation Breeding Of Bacillus Natto And Technology Of Flavored Natto

Natto is a traditional fermented food with high nutritive value in Japan, which is rich in protein, multivitamins and active enzymes and has the functions of disease prevention and health care. It enjoys great popularity among countries such as Japan, the United States and Korea, etc. as a functional food. Although natto has very good health care function, the unique flavor produced by fermentation can hardly be accepted by the majority of Chinese consumers, which hinders its promotion and development in the Chinese market. Therefore, it is especially important to enhance the edibility of natto and improve its functionality in China. In this paper, bacillus natto isolated from commercially available natto was used as original strain. A bacillus natto strain(temporarily named as P-1) resistant to high sugar & high salt environment and with strong ability of producing nattokinase, was obtained through preliminary screening of the original strain with plates containing high sugar & high salt and casein plates, and then through secondary screening with agarose-fibrin plates, using ultraviolet mutagenesis method. The obtained strain not only showed significantly higher enzyme production capacity than the original strain, but also with better genetic stability. On the basis of the obtained strain resistant to high sugar & high salt environment, and with strong ability of producing nattokinase, the effects of adding suitable amount of auxiliary materials(sugar, vinegar, salt, soybean sauce, monosodium glutamate, aniseed, thirteen spice, pepper and Chinese prickly ash, etc.) at different stages throughout the fermentation process of bacillus natto on the quality indicators of natto such as ropiness, smell, taste, color, glutinousness and nattokinase activity, etc. were studied in order to adjust the flavor of traditional Japanese natto and make it suitable for Chinese consumers’ taste on the basis of not destroying its original components. Final, the following results were obtained through the test: ①Recipe for natto with salty flavor: add 3 % salt when soaking beans, and add 0.4 % monosodium glutamate before sterilization; ②Recipe for natto with sweet flavor: add 3 % salt when soaking beans, and add 24 % sugar before sterilization; ③Recipe for natto with spicy flavor: add 3 % salt when soaking beans, and add 2 % pepper before sterilization; ④Recipe for natto with sweet & sour flavor: add 3 % salt when soaking beans, and add 24 % sugar and 3 % vinegar before sterilization; ⑤Recipe for natto with comprehensive flavor: add 3 % salt when soaking beans, add 24 % sugar and 3 % Chinese prickly ash before sterilization, and add 2 % pepper during after-ripening. And then, the viable bacteria counts of flavored nattos based on the above 5 recipes were determined, and the results showed that the addition of auxiliary materials had different level of effects on the viable bacteria count of natto bacillus. The nattos based on the above 5 recipes not only can cover up the ammonia-flavor of traditionally-fermented natto and perfect the taste to make it better accepted by Chinese consumers, but also can greatly improve the enzymatic activity of nattokinase over traditionally-fermented natto.At last, the activity of nattokinase(hereinafter abbreviated to as NK), amylase(Amy), cellulose(Cel), protease(Pro) and lipase(Lip) and the level of vitamin E(VE) and vitamin B2(VB2) in the flavored natto based on the above five recipes were determined and compared with commercially available natto respectively. The results indicated that the activity of nattokinase, amylase, cellulose and the content of vitamin E and vitamin B2 in the flavored natto based on the above five recipes were significantly higher than those of commercially available natto; Thereinto, recipe 3 was with the highest nattokinase activity(reaching 1401 U/mL), which was 38.05 % higher than commercially available natto; recipe 4 was with the highest amylase activity(reaching 127.440 U/mL), which was 123.78 % higher than commercially available natto; recipe 5 was with the highest cellulose activity(reaching 266.090 U/mL), which was 149.09 % higher than commercially available natto; recipe 1 was not only with the highest vitamin E content(reaching 1.278 mg/100g), but also with the highest vitamin B2 content(reaching 1.142 mg/100g), which was 80 % and 84.19 % higher than commercially available natto respectively. While, the activity of protease and lipase in the flavored natto based on the above five recipes were significantly lower than that of commercially available natto; Thereinto, recipe 2 was with the lowest lipase activity(reaching 1.667 U/mL), which was 91.67 % lower than commercially available natto; only recipe 1 was with the protease activity higher than commercially available natto, and the other four are all lower than commercially available natto. Changes of these active components during shelf life(14d under refrigerated conditions) were tracked and determined, and the results indicated that the active components in the flavored natto based on different recipes showed different changes. Through the comprehensive evaluation, it was considered that flavored natto within the first 7 days of the shelf life may maintain a high level of active components.