Vitamin C and nitrates contents in fruit and vegetables from farmers' markets and supermarkets

Monika Sabolová,Lenka Kouřimská

doi:10.5219/1347

Abstract

Fruits and vegetables are the best food sources of vitamin C. However, fruits and vegetables can be also sources of potentially harmful substances to the human body, nitrates being one of these. The aim of this study was to compare vitamin C and nitrates contents in selected fruits and vegetables from supermarkets and local farmers' markets. Samples of plums, strawberries, apples, spinach, red peppers and tomatoes were chosen for analysis. Content of vitamin C and nitrates was analyzed by HPLC/DAD. The hypothesis was that local market fruits and vegetables contain more vitamin C and fewer nitrates than samples bought in supermarkets. Laboratory analyses showed that there were differences in vitamin C in the case of strawberries, tomatoes and red peppers. The highest level of ascorbic acid was in red pepper samples (141 mg.100g-1). In the case of fruit, the highest content was in strawberries (70 mg.100g-1). As far as nitrates content is concerned, in three cases out of six, the fruit and vegetables we tested from farmers' markets contained lower concentrations of nitrates than those purchased at supermarkets and the hypothesis was accepted in these cases. There was no significant difference between the nitrate content of the local market and supermarket strawberries and red peppers. Tomatoes had significantly higher nitrate content when purchased at farmers' markets than at supermarkets. Leafy vegetables are considered to be the major source of nitrates, and this was confirmed by this study. The highest content of nitrates was in the spinach sample (2969 mg.kg-1). Among all fruit samples, strawberries had the highest nitrates levels (maximum 131 mg.kg-1). The results of this work showed that the content of ascorbic acid and nitrates differs significantly depending on the type of fruit or vegetables.

Highlights

Fruit and vegetables are an important part of human nutrition and their adequate daily consumption can help prevent serious diseases (WHO, 2003)
As far as nitrates content is concerned, in three cases out of six, the fruit and vegetables we tested from farmers' markets contained lower concentrations of nitrates than those purchased at supermarkets and the hypothesis was accepted in these cases
There was no significant difference between the nitrate content of the local market and supermarket strawberries and red peppers

Summary

Introduction

Fruit and vegetables are an important part of human nutrition and their adequate daily consumption can help prevent serious diseases (WHO, 2003). The WHO (2004) recommended at least 400 g of fruit and vegetables daily to prevent chronic diseases such as heart and cancer, type 2 diabetes mellitus and obesity, as well as to prevent and reduce micronutrient deficiencies, in less developed countries (WHO, 2003). Vitamin C is the most important vitamin in fruits and vegetables. More than 90% of vitamin C in the human diet comes from fruit and vegetables. The highest amounts of this vitamin occur in blackcurrants, citrus fruits, spinach, tomatoes, red peppers (Lewin, 1976; Lee and Kader, 2000; Saxholt et al, 2008; Rekha et al, 2012)

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