| Popis: |
Present research is the first complex study in Estonia about nitrate and nitrite contents, which comprises the complete vegetable production chain from raw material to final product. In accordance with data from literature, the vegetables and vegetable-based foods are the main source of nitrates for man. High doses of nitrates and nitrites are the risks for human health, especially for infants and for small children. Final aim for present work was to expose the possible exceeding of ADI values for nitrate and nitrite, especially in the case of small children who belong to the main risk group. In the present investigation, the mean values and contents of nitrates and nitrites in vegetable products were determined. For the first time in Estonia the daily intake of nitrates from vegetables or vegetable-based foods by children and the whole population was estimated. The results of the analyses of nitrate and nitrite contents demonstrated that permitted nitrate limit concentrations were exceeded only a few cases. The nitrate content is dependent on the harvesting period and on the growing conditions. Vegetables grown under cover showed higher levels of nitrate than those grown in the open field conditions. The results of this study showed that nitrate content varied highly between the species of vegetables used for the raw juice production. Lower initial contents of nitrate were detected in industrial carrot juice and in home-made carrot and cabbage raw juices. Initial microbial counts and pH-values were similar for all raw juices. The nitrate contents decreased and nitrite contents increased after 24 h and 48 h of storage. The changes in nitrate and nitrite contents were lower in industrial raw vegetable juices compared to home-made raw juices but tendencies were generally similar. All microbial counts, such as total viable counts, coliform counts, mold and yeast counts, increased. The highest increase of total viable counts was reported in home-made raw juices after 48 h of storage at ambient temperatures. The microbial growth had correlation with the decrease of pH-values. The raw juices should be consumed soon after preparation and stored only shortly at refrigerated temperatures. The decreases of nitrate contents in industrial vegetable-based infant foods were registered along the entire technological production line. At first stage the nitrate contents were analysed from vegetables before and after peeling and washing. The decrease of nitrates from 17 to 52% was reported, depending on vegetable species. The analyses of nitrate contents from different technological stages of industrial infant food production showed that from the stage of vegetable mixture, all the other technological stages until to the final product decreased the concentration of nitrate. The total average decrease of the nitrate content was 45%. Nitrates are easily soluble in water and after adding the drinking water with low nitrate content, the overall nitrate content of food mixture is decreasing. According to the results of this study the final nitrate concentration in infant foods depended mainly on the initial nitrate content of the raw-vegetable mixture and on the amounts of the food ingredients. The imported infant food cans, purchased from retail markets, contained nitrate in lower concentrations compared to commercial infant foods produced in Estonia. It was related with the fact that in Estonian infant foods the vegetable-based ingredients percentage was higher than in imported products. In this study, the levels of nitrates in the final products ranged from 72 to 145 mg kg-1, which remains below the EU maximum permitted level, 200 mg kg-1. The infant foods storage experiments were performed after 24 h and 48 h of storage of opened infant food cans at different storage temperatures. In opened infant foods the nitrate content decreased, being the highest for the foods containing several vegetable species. Our results of analyses proved that the self-life of opened infant foods at refrigerated temperatures is at least two days. Higher nitrate concentration decrease was registered in opened infant foods stored at ambient temperatures. The nitrite contents in all infant food samples stayed below detection limit |
