Flow Injection Assessment of Nitrate Contents in Fresh and Cooked Fruits and Vegetables Grown in Fiji

Abstract

Nitrates form part of the essential chemistry of soils and plants. Thus, plant roots are able to absorb nitrate directly from the soil. It has been discovered that human nitrate intake is mainly from vegetables. Vegetables play an important role in human nutrition since they are an outstanding source for vitamins, minerals, and biologically active compounds. In risk assessment of nitrate contents, this study reports the nitrate levels of 8 commonly consumed fruits and vegetables grown in Fiji, tomato (Lycopersicon esculentum), eggplant (Solanum melongena), capsicum (Capsicum annuum var. grossum), breadfruit (Artocarpus altilis), long bean (Vigna sesquipedalis), jackfruit (A. heterophyllus), pumpkin (Cucurbita pepo), and cucumber (Cucumis sativus). The effects of different types of cooking methods, baking, boiling, and frying, have also been studied. The validated flow injection analysis technique has been used to quantify the nitrate-N levels in the chosen products following nitrate extraction using the activated carbon technique. The mean values of nitrate levels in fresh products ranged from 25.83 to 281.02 mg NO(3) (-) kg(-1) . The study shows that boiling reduced nitrate contents by 65.37% to 25.25%. The frying in soy bean oil elevated nitrate contents from 354.79% to 86.69%, but after baking, nitrate contents remained almost constant with slight increasing trend in the case of tomato (19.97%). The nitrate levels published in the literature for the same types of fruits and vegetables studied have also been reviewed and compared. The average nitrate-N values were comparable or lower than overseas data, but did not present unpredictably high values, that is, they were below the risk level.

Development of a reference database for assessing dietary nitrate in vegetables

“…Processing factors also have an effect on the nitrate concentration of vegetables. Nitrates are water soluble therefore washing and cooking has been shown to decrease the nitrate content of the vegetable . Boiling vegetables can reduce the nitrate content up to 75% ; however, information regarding the effect of other cooking methods (microwaving, steaming, frying, etc.)…”

Nitrates/Nitrites in Food—Risk for Nitrosative Stress and Benefits

“…Studies have assessed that processing methods such as heat treatments and storage conditions cause the loss of nitrates. The effect of increased storage temperature on decreasing the nitrite content of vegetables has been indicated due to increased bacterial facilitated reduction of nitrates to nitrites [11]. Research carried out by Ding et al [6] on the evaluation of nitrate and nitrite contents in pickled fruit and vegetable products indicated that nitrate content in pickled products (among others pickled beets, cauliflowers, carrots, Brussels sprouts) was generally lower compared to fresh fruits and vegetables.…”

African nightshades (Solanum nigrum complex): The potential contribution to human nutrition and livelihoods in sub‐Saharan Africa

“…Besides, the consumption of more than 600 to 700 g of ANS per day is beyond the RDA of nitrate and can cause health effects. The application of heat treatments, high‐temperature storage conditions, and fermentation reduced nitrate content in vegetables (Ding et al., 2018; Prasad & Chetty, 2011), similarly to ANS leaves.…”