# Bacterial Diversity and Dominant Spoilage Microorganisms in Fresh-Cut Broccoli
## 4 Discussion
Moreover, they produced petolytic enzymes to hydrolyze the cell walls of fruits and vegetables, resulting in rot and deterioration of fruits and vegetables, such as petolytic enzymes produced in _Pseudomonas viridifluxa_ and _Pseudomonas chlororaphis_, which caused organoleptic properties to decline as well as spoilage in fresh-cut vegetables [33]. The color of vegetables is considered to be an extremely crucial factor for consumer acceptance, especially the unique green color in vegetables, and the dominant reason for de-greening of broccoli was chlorophyll deterioration. Compared with the control group, the chlorophyll of broccoli infected by bacteria decreased in varying degrees, especially the group inoculated with _Pseudomonas_ sp. BRO-C11, _Pseudomonas_ sp. BRO-G12 and _Comamonas_ sp. BRO-C5, which also indicated that the infected group was more prone to yellowing in the experiment, explaining that bacterial infection promoted the yellowing of broccoli and destroyed the appearance of broccoli. This result may explain the yellowing of fresh-cut broccoli after longer storage periods. In order to maintain the pleasant appearance of broccoli, measures to avoid broccoli being polluted by bacteria, _Pseudomonas_ spp. particularly, should be taken. Agricultural standards clearly stipulate the limit standards of nitrate and nitrite in vegetables. Our research investigated potential correlations between bacterial infection and the formation or depletion of nitrite during storage, and microorganisms in fresh-cut fruits and vegetables were the main cause of nitrite accumulation. With storage, the concentration of nitrite reached a maximum, the nitrite peak, and then began to decrease. Among the microorganisms, _Pseudomonas_ sp. BRO-C11 had the most important effects on the content of nitrite in broccoli. In the harvest period, _Pseudomonas_ sp. BRO-C11 with nitrate reductase proliferated in large numbers, resulting in the nitrate in fresh-cut broccoli to be reduced to nitrite. However, the growth of aerobic _Pseudomonas_ sp. BRO-C11 was inhibited when the oxygen was consumed, resulting in the activity of nitrate reductase to be inhibited, promoting large amounts of nitrite to be decomposed. In general, controlling the content of nitrite and nitrate in vegetables was the key to scientific production and edible vegetables. In the follow-up study, the spoilage bacteria that had important impacts on nitrite content should be strictly controlled. Malondialdehydedehyde (MDA), as the main product of membrane lipid peroxidation, indicates the integrity of cell membranes. The content of malondialdehydedehyde in plant is positively correlated with the degree of cell membrane damage. In our study, the content of MDA in all samples exhibited approximately the same first increased then decreased trend, and the group inoculated with _Pseudomonas_ sp. BRO-C11 and _Pseudomonas_ sp. BRO-G12 increased at a higher rate than the control group at 48 h of storage. The results showed that after being infected by bacteria, the permeability of the cell membrane increased, which might be due to the damage by bacteria to plant cells by secreting hydrolases and toxins, resulting in the loss of contained logistics in plant cells. The substance in cells, which was conducive for the growth and reproduction of microorganisms, flowed out due to the rupture of the cell membrane, and further aggravated the damage to the cell membrane, leading to the increase of MDA content. Overall, the content of MDA increased, and the senescence process of broccoli was enhanced after being infected. Soluble sugar has the function to maintain the turgidity of cells, and it is able to protect the membranes of cells from damage caused by the abiotic stress. In this study, under infection, the soluble sugar content of broccoli inoculated with _Pseudomonas_ sp. BRO-C11, _Pseudomonas_ sp. BRO-G12 and _Comamonas_ sp. BRO-C5 increased at 48 h, which meant that the broccoli could adapt to bacterial infection in the short term.