J.H. Cunningham, G. Milligan and L. Trevisan
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Abstract
Potassium, sodium, calcium, magnesium, iron and zinc levels in 44 types of Australian fruits and vegetables were measured in samples purchased in Melbourne, Australia in 2000 or 2001 and compared with the results of analyses conducted between 1981 and 1985 for the same items of produce purchased in Sydney, Australia. A comparison of values at the two time periods does not indicate that there have been significant or consistent changes in the content of these minerals over this time. Overall mean potassium content of these items in 2000/01 and 1981-85 respectively was 230 and 220 mg/100 g, sodium was 9 and 8 mg/100g, magnesium 15 and 11 mg/100 g, calcium 18 and 16 mg/100 g, iron 0.3 and 0.5 mg/100 g and zinc 0.2 and 0.3 mg/100 g. Comparisons of mineral levels measured at these two times must be made with caution as samples were collected in different locations, sometimes at different times of the year, possibly at different stages of ripeness and in many cases were different varieties. In addition, the older analyses were conducted using a less sensitive analytical technique than the method used in 2000-01. Any minor changes from year to year in mineral levels in these foods would be very unlikely to be of dietary significance.
Introduction
Australian media reports in 2001 (e.g. Patty 2001, Moynihan 2001) raised questions about whether or not nutrient levels in Australian horticultural produce are declining due to changing soil conditions and horticultural practices. These reports were triggered by a British article (Mayer 1997) that compared the mineral content of 20 types of produce reported in the 1980s UK food composition tables, with the same types of produce reported in the 1960s UK tables. The paper claimed a significant reduction in the levels of calcium, magnesium, copper and sodium in vegetables and of magnesium, iron, copper and potassium in fruits. Moisture content in fruits increased over this time. There was no analysis in this paper of whether the varieties (for example of 'eating apples') analysed had changed over the time period of interest. Mayer suggested that a nutritional problem (the nature of which was unspecified) associated with the quality of food has developed over this time. One of the key issues raised in the Australian media reports of Mayer's paper was the age of the published Australian nutrient data for fruits and vegetables; these data were generated in the early 1980s.
Food Standards Australia New Zealand (FSANZ) maintains a database of nutrients in Australian foods and uses this database to prepare food composition publications such as AUSNUT(Australia New Zealand Food Authority 1999). In order to assess the need to up-date nutrient data for fruits and vegetables, a small analytical program was instituted in 2002 to measure the levels of six minerals in 44 types of now common fruits and vegetables. These mineral levels were then compared to those measured between 1981 and 1985 in analytical programs conducted by researchers at the University of New South Wales (UNSW).