NITRATE, NITRITE AND UREA LEVELS IN SOME FRESH, COOKED AND REFRIGERATOR STORED VEGETABLES: CHEMICAL AND MICROBIOLOGICAL STUDIES | ||||
| Journal of Food and Dairy Sciences | ||||
| Article 2, Volume 27, Issue 11, November 2002, Page 7513-7527 PDF (18.32 MB) | ||||
| Document Type: Original Article | ||||
| DOI: 10.21608/jfds.2002.257128 | ||||
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| Authors | ||||
| A. M. EI-Okazy,; S. I. Saleh; M. M. Shabayek; S. M. Daoud | ||||
| Central Lab. for Food and Feed, Agricultural Research Center, Alexandria. | ||||
| Abstract | ||||
| Nitrate, nitrite and urea were determined in 11 fresh vegetables (eggplant, white potatoes, squash, okra, spinach, green French bean, Jew's mallow, yellow carrot, onion, gariic and tomato) collected from five Alexandrian markets. The highest nitrate level was recorded in spinach and squash, and the lowest was that of tomato. The highest nitrite content was recorded in Jew's mallow and okra while the lowest nitrite value was recorded in tomato. Gariic was found to contain the highest urea level while spinach showed the lowest. Cooking significantly reduced nitrate levels in the studied vegetables. The overall mean nitrate content showed a n.66 % deCrease on cooking. The mean nitrite content of the studied items showed increases on cooking of eggplant, white potatoes and squash. While okra, spinach and Jew's mallow nitrite levels decreased with cooking. The mean urea level of six of the studied vegetables showed increases after cooking. The highest rise in urea took place in eggplant (250.5%) while the lowest increase was recorded in squash (12.8%). Jew's mallow showed 16.3% reduction in the mean urea level after cooking. Nitrate level Significantly increased after two days of storage. Then a significant drop off occurred after 4 and 6 days of storage. Nitrite concentration increased in cooked vegetables on cold storage. It was also recognized that there was a significant variation in the effect of refrigerator storage on different vegetables under investigation. Cooked Jew's Mallow and white potatoes showed the highest Increases in concentrations of nitrite (622 % and 556 %) after six days of refrigerator storage. On the other hand, cooked squash showed the least rise in nitrite contents (129.6%) after the same period of storage under the same conditions. Urea level decreased through storage period. This reduction in urea level was directly proportional to the storage time. The total bacterial counts of the studied items showed a highly significant increase with storage under refrigerator temperature. Cooked white potato and Jew's Mallow were highly susceptible to contain higher microbial counts during storage at refrigerator temperature than other kinds of cooked vegetables. A highly significant decrease was recorded in spore counts of the studied items with storage under refrigerator temperature. Coliform bacteria counts increased significantly with the storage duration in Coliform- positive samples, okra, spinach and jew' s mallow. The other studied types were negative for Coliform. All cooked items were positive for Staphyfococcus aureuos and Citrobacrer sp < /em>. and negative for. Salmonella sp < /em>. along the storage period. Shigella sp < /em>. was detected in cooked eggplant, French bean and vegetable soup, while others were negative for it. Enterobacter sp < /em>. was detected in eggplant and vegetable soup. A signifteant negative correlation between nitrite and urea levels and a highly significant positive correlation between nitrite and bacterial total counts were found in cooked vegetables throughout the experiment. Nitrite also showed a highly Significant positive correlation with Coliform count. Urea levels showed inSignificant positive correlations with nitrate and nitrite and insignificant negative ones with bacterial, spores and Coliform counts during the storage period of the studied cooked vegetables. These findings indicated that storage of cooked vegetables in the refrigerator did not sufficiently inhibit bacterial growth in the studied foods. Certain species of food-born bacteria assimilate proteins and nitrate of the cooked stuffs for the ultimate synthesis of their own proteins resulting in increasing nitrite level. Such Increase may represent a health hazard for the consumer. | ||||
| Keywords | ||||
| Vegetables; Nitrate; Nitrite; Urea; Cooking; Storage; Contamination; and Microbiology | ||||
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