| With the continuous development of China’s economy,people have higher and higher requirements for food health as well as high quality diet.Selenium has always been an indispensable micronutrient in human body,but since selenium basically exists in inorganic form in nature with high toxicity and difficult absorption characteristics,it may lead to a series of disease problems caused by the lack of selenium content in human body.At present,organic form of selenium or nano-selenium is more easily absorbed and utilized by plants,animals and human body compared with inorganic selenium,so as to effectively supplement the selenium content required by human body.The organic form selenium and nanoselenium are mainly synthesized by physical,chemical and microbial transformation methods,among which the microbial transformation method is more favorable for organic form selenium and nanoselenium to occur and have higher stability.Lactic acid bacteria as probiotics can be used in microbial transformation method to enrich selenium efficiently and convert it into organic form selenium which is more easily absorbed by human body.Therefore,in this study,three different types of biochar,namely apple branch,rice straw and bamboo branch,were prepared by acid modification,alkali modification and oxidation modification,and different biochar additions of 0g,1g,1.5g,2g,2.5g and 3g were set to adsorb Lactobacillus plantarum,Streptococcus thermophilus and Lactobacillus bulgaricus,and the best combinations of biochar and different probiotic bacteria were screened for interloading.The three types of lactic acid bacteria and their corresponding biochar interloading combinations were screened for selenium tolerance and the effect of growth at high concentrations of sodium selenite to select the optimal biochar lactic acid bacteria interloading combination.The best biochar lactobacilli interload combinations were reduced in 25μmol/L(X25),50μmol/L(X50)and100μmol/L(X100)sodium selenite solution and the reduced solutions RX25,RX50 and RX100 were collected and sprayed with sodium selenite solution in broccoli sprouts.The growth characteristics and nutritional quality of selenium-enriched broccoli sprouts were investigated.The main results of this study were as follows:(1)The effects of different types of biochar on the adsorption of lactic acid bacteria were as follows:Lactobacillus plantarum,Streptococcus thermophilus and Lactobacillus bulgaricus all had corresponding combinations of different types of biochar co-loading capacity,and different lactic acid bacteria could improve their growth activity and increase the number of colonies under different amounts of biochar added compared with the control.Among them,the optimal biochar lactic acid bacteria co-loading combination was screened by the Tongping dish counting method,namely:1g of apple Na OH modified and Lactobacillus plantarum were co-loaded,which increased the CFU number of Lactobacillus plantarum colonies by 0.5×10~8CFU/ml;The coloading of 3g of rice unmodified biochar with Streptococcus thermophilus increased the number of CFU colonies by 4.5×10~8 CFU/ml.The co-loading of 1.5g of apple unmodified biochar with Lactobacillus bulgaricus increased the CFU number of Lactobacillus bulgaricus colonies by 4.5×10~8 CFU/ml.(2)The effect of biochar-lactic acid bacteria complex on reducing the characteristics of sodium selenite was as follows:the interloaded combination of three types of biochar lactic acid bacteria was inoculated in MRS liquid medium containing a mass concentration of10μg/m L sodium selenite,and the interloaded combination of 1.5g apple unmodified biochar and Lactobacillus bulgaricus was determined to have high selenium resistance and selenium conversion ability by comparing the turbidity degree in the bacterial liquid and the OD value of the bound seed liquid.In addition,when the mass concentration of sodium selenite of Lactobacillus bulgaricis added to biochar was 90μg/m L,the number of CFU colonies of Lactobacillus bulgaricus adsorbed by biochar reached peak of(5.79±0.30)×10~4 CFU/ml,the red turbid liquid could be clearly seen in selenium-containing medium,indicating that the biochar lactic acid bacteria coload combination still had certain biological activity under high concentrations of sodium selenite solution and could convert sodium selenite into nanoselenium or organic selenium.Finally,by comparing the selenium richness rate of Lactobacillus bulgaricus without biochar and biochar,it can be concluded that when the mass concentration of sodium selenite is 120μg/ml,the conversion rate of Lactobacillus bulgaricus without biochar to selenium is 43.33%±2.36%,while the selenium-rich rate of Lactobacillus bulgaricus added to biochar is 85.00%±2.36%.Selenium richness doubled.(3)The effects of spraying of reduced selenium solution of different concentrations on the growth characteristics and nutritional quality of broccoli sprouts were as follows:the treatment of sodium selenite solution reduced by biochar lactic acid bacteria significantly improved the selenium content and nutritional quality of broccoli sprouts compared with the application of sodium selenite solution of corresponding concentration.When biochar lactic acid bacteria were subjected to 25μmol/L sodium selenite solution,the total selenium content and organic selenium content in broccoli sprouts reached peak content,which were7.17±0.49μg/g FW and 3.53±0.64μg/g FW,respectively,which were significantly increased by 3.3 times and 4.5 times(P<0.05)compared with the control.At this concentration,the soluble protein content and total phenolic content in broccoli sprouts reached a peak of9.11±0.29mg/g FW and 0.41±0.03mg/g FW,respectively.The results showed that sodium selenite solution reduced by applying biochar lactic acid bacteria co-load combination could significantly improve the nutritional quality and antioxidant capacity of broccoli sprouts. |
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