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Factors affecting the nitrate content of foods Bodhiphala, Tewee


The nitrate content of some foods was determined. Canned food, baby food, frozen food, and fresh vegetables were analyzed. Among them spinach and beet were found to have the highest nitrate-nitrogen content and frozen food had higher nitrate-nitrogen content than other food products analyzed. Nitrate-nitrogen of food is partially transferred to the liquid portion whenever the food consists of any liquid. The amount of nitrate in the liquid portion seemed, to be higher than in the solid portion except in bean which has a protective surface layer as a factor of lowering the nitrate found in the liquid portion. The rate of nitrate transferring from solid portion to liquid portion was not the same for all foods and was not the same even from different parts of the same plant. Nitrate-nitrogen was not destroyed by cooking. Even after pouring off cooking water, some nitrate-nitrogen still remained in the solid portion. The distribution of nitrate among different plant parts was not uniform: bean leaves, beet root and spinach petioles were found to have higher nitrate than other parts. Nitrogen fertilization readily increased nitrate-nitrogen content in spinach. The sodium salicylate method was found to be the most reliable method for nitrate determination among different methods used in this study. The determination might be affected by many factors occuring during the procedure of analysis such as procedure of extraction and the spectrophotometer blanks used. Oxidising agents, arid reducing agents do not seem to affect the analysis but pH variation and sucrose which might occur in food probably are factors affecting apparent nitrate content. Cooking did quickly destroy spinach nitrate reductase enzyme activity. This means that nitrite will not be found after cooking unless the enzyme is regenerated, or unless there is microbial activity.

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