Nitrate And Nitrite Contents In Sweet Sorghum And Its Reduction Technology

Nitrite is converted from nitrates in plants during storage and processing.It is a poisonous substance harmful to animals and humans.Excessive intake of nitrite will threaten the health of the body.In this study,sweet sorghum（Sorghum bicolor）was selected as the test material,and the nitrate and nitrite contents in the production,processing and preservation were investigated,and the effects of lactic acid bacteria inoculation on nitrate and nitrate contents during ensiling were studied,in order to obtain better and safe sweet sorghum for animals.The main findings are as follows:（1）Three fertilization levels of 100,200 and 300 kg/hm² were set.The fertilizer was a15:15:15 compound fertilizer with urea at a 3:1 ratio.As the fertilization amount increased,the thickness of the stem,crude protein yield and dry matter yield of sorghum increased significantly（P<0.05）.The ranges of crude protein yield and dry matter yield were1.43-2.54 t/hm² and 22.85-32.27 t/hm^2,respectively.The highest plant height was obtained at fertilization of 200 kg/hm².However,the highest dry matter yield,crude protein yield,and relative feed value were obtained at 300 kg/hm² and the nutritional value was higher.The contents of crude fat,crude protein and soluble sugar were significantly higher in treatment of 300 kg/hm² than those in the other two treatments.（P<0.05）.Although the contents of nitrate and nitrite at fertilization of 300 kg/hm² were the highest,they were still within safe values.That is,fertilizer application at 300 kg/hm² could obtain better quality forage sorghum.（2）Through the screening test for 13 high-quality lactic acid bacteria strains in the laboratory,it was found that these lactic acid bacteria could effectively remove nitrite from the culture medium.All lactic acid bacteria were capable of removing nitrite up to near100%in 60 h of culture.The degradation rates of nitrite in the medium by Lactobacillus reuteri and Leuconostoc mesenteroides were 100%in 24 h.That is,L.reuteri and Leu.mesenteroides were selected out due to high removal rate of nitrite from 13 strains of lactic acid bacteria.（3）Using the above two strains of Lactobacillus（L.reuteri,Leu.mesenteroides）as an additive and adding them to the harvested sorghum for the silage test,the results showed that the pH value significantly decreased to 4.0 or less on the 3 d before silage（P<0.05）,the content of ammonia nitrogen increased with the increase of silage time,and the number of microorganisms decreased with time after reaching the maximum value on the 3rd day.The content of lactic acid and acetic acid increased with the increase of silage time,and the propionic acid content reached the maximum value at the 14th day of silage.The occurrence of nitrous acid peaks advances with increasing fertilization.Addition of strains can obtain lower pH value,ammonia nitrogen content and nitrite content,higher lactic acid content,and higher silage effect and safety.（4）After the silage was opened,two different storage methods of open storage and sealed storage were conducted.The test results showed that the pH value of the storage material stored in the open mouth increased significantly with the opening time（P<0.05）.There was no significant difference in the pH value of the sealed storage（P>0.05）.The nitrite content was kept at a low level under the sealed condition.The nitrite content in the open mouth increased significantly at 96 h（P<0.05）,and even at 192 h,the nitrite content was higher than the safe value（10mg/kg）.There were two peaks of nitrates exposed to the open air,which were 48 and 144 h respectively,and the maximum nitrate content was reached at 96 h.As a result,proper sealed storage,silage stability,and nitrite uptake can be better controlled.