Research On The Effect Of Storage Conditions On Nitrate, Nitrite And Quality Of Spinach

Vegetables are rich in vitamin, minerals and fiber, and they are necessities of human life. Vegetables could easily be decayed and accumulated nitrate this kind of harmful substance during storage time, so it was very necessary to strengthen the research of vegetables preservation. In this paper, spinach was used as a representative vegetable material to study the influence of different storage temperature, CO2, O2and closed conditions to spinach post-harvest nitrate, nitrite and quality. The main results were as follows:1. Spinach post-harvest quality and nitrate metabolism could be greatly effected by gas condition, under cold (4℃)and sealed environment, spinach soluble solids, Vc and chlorophyll content decrease were significantly slowed and maintained higher level nitrate reductase(NR) and antioxidant enzymes (SOD, POD, CAT) activities, meanwhile the production of malondialdehyde was inhibited, and the content of nitrate and nitrite was reduced too. When stored for eighth days, nitrate and nitrite of sealed spinach achieved1318.44mg/kg and0.42mg/kg, declineded31.96%and26.19%respectively compared with the control. Sealed environment in low temperature could effectively reduce the content of spinach nitrate and nitrite and maintains good storage quality.2. Temperature, oxygen and carbon dioxide single factor test result showed that: temperature, oxygen and carbon dioxide effected the content of spinach nitrate and nitrite, but they could be effectively controlled under1-8℃, oxygen8-12%, carbon dioxide6-10%storage conditions. According to the results of single factor experiments, multi-factor orthogonal experiments was further setted, and the results showed that the temperature was the prerequisite factor which affected nitrate and nitrite, then was the CO2and O2in turn.1℃temperature,12%oxygen and8%carbon dioxide were the best storage conditions for spinach to control the nitrate and nitrite accumulation.3. According to multi-factor orthogonal experiments screening and low temperature modified atmosphere optimal trial, spinach ambient temperature, low temperature experiments were arranged to compare and analysis the nitrate, nitrite accumulation mechanism further more. The results showed that under low temperature and modified atmosphere, spinach respiration intensity were minimum, malondialdehyde content was lowest, nitrate reductase(NR) and anti-enzymes (SOD, CAT, POD) activity kept at a higher level, soluble solids, Vc and chlorophyll of spinach maintained at a higher level too, consequentially nitrate and nitrite content kept the lowest. The change of nitrate content showed the trend of increase-reduce-increase-reduce, while the nitrite showed rise-fall-rise. During earlier storage time, the changes trend of SOD and POD enzyme activity were basically same the trend of the two kinds of nitrates, but CAT activity had reciprocal relationship with nitrate and nitrite; NR activity continued to decline, two kinds of nitrate reductase accumulation change rule was not consistent, the reason might be that in addition to nitrate and nitrite content also was effectted by nitrite reductase (NiR), otherwise it related to nitrite reductase which could convert nitrite to NH4+and denitrification bacteria.