Determination and comparison of vitamin C, calcium and potassium in four selected conventionally and organically grown fruits and vegetables

It is evident that the growing interest in organically grown produce has correspondingly necessitated the debate on the nutritional supremacy between organically and conventionally grown produce. A study was carried out to determine and compare vitamin C, calcium and potassium in organically and conventionally grown cabbage, carrots, Cos lettuce and Valencia oranges. Samples were purchased from local supermarkets within Central Coast, New South Wales in Australia from late March to early April 2007. Vitamin C content was determined by 2,6-dichloroindophenol titrimetric method while calcium and potassium were determined by atomic absorption spectroscopy. Results from the study showed inconsistent pattern with respect to vitamin C, calcium and potassium contents in the conventionally and organically grown samples. No significant differences were observed in vitamin C content in conventionally and organically grown cabbage, carrots and Cos lettuce while significant differences were observed in Valencia oranges which showed higher vitamin C content in organic Valencia oranges as compared to conventional ones (51.8 to 43.4 mg/100 g fresh weight). Results on calcium and potassium contents showed significant differences in all the samples with the trend of higher values for organically grown cabbage, carrots and Cos lettuce as opposed to their conventionally grown counterparts. However, for Valencia oranges, results showed that the calcium and potassium contents were significantly higher in conventional Valencia oranges compared to the organic Valencia orange (54.5 and 192.0 mg to 51.8 and 189.5 mg/100 g, respectively).