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Change in Sodium Content of Potato, Pasta and Rice with Different Cooking Methods

Institutions
LGC, Ltd
Start date
2006
End date
2006
Objective
A review of the literature revealed that there was limited information available regarding the amount of salt that is taken up by food during boiling in salted water. The degree to which differences in salt concentration of boiling water affect the sodium concentration in the food is of particular interest to the Food Standards Agency as they aim to reduce salt intake in the population to 6g per day by 2010 (FSA Strategic plan, 2005-10). This is potentially of importance when considering staple carbohydrates such as potatoes, pasta and rice.

The purpose of this research project therefore was to determine the effect of adding salt to cooking water on the uptake of sodium into potatoes, pasta and rice. A number of varieties of food type were chosen to represent those commonly purchased by public sector institutions: potatoes (old floury, old waxy and new), pasta (white spaghetti, white penne, wholewheat spaghetti, rice based) and rice (white long grain, brown wholegrain).

More information
In order to replicate current cooking practices a variety of schools and public sector institutions within Scotland were consulted to establish the amounts of salt added when boiling each of potatoes, pasta and rice. As a result of this the following amounts of salt were added whilst cooking: Potatoes 4g /kg raw potatoes, Pasta, 4g and 40g/kg raw pasta and Rice 4g and 24g/kg raw rice. For each food type and variety raw composites were formed from 10 different samples on an equal weight basis. Each composite was cooked in duplicate with and without salt at the above levels.

As expected, a strong correlation was found between the amount of added salt during cooking and the final sodium concentration of each of the food types.

Potatoes were found to take up significantly different quantities of sodium, depending on the variety of potato studied. This effect was most striking when comparing new and old potatoes cooked with 4g salt / kg raw potato. New potatoes took up approximately one third of the sodium (16mg Na/100g) when compared with old potatoes (54mg Na/100g). These differences can be explained by the fact that the new potatoes were unpeeled (old potatoes were peeled and pared) which will have provided a barrier to the absorption of sodium. The waxy nature of the potatoes may also have contributed to their reduced sodium absorption.

In uncooked pasta, the concentration of sodium was higher in the rice based pasta products (24 mg/100g) compared with the wheat-based pasta (2.3 mg/100g). The sodium content in pasta cooked with different levels of salt increased approximately linearly with the amount of salt added to the cooking water. Pasta cooked in 4g salt/100g raw took up on average 28 mg Na/100g whereas when cooked in 40g/100g raw this increased approximately 10 fold to 230 mg Na/100g.

Similarly, the amount of sodium taken up by rice cooked with different levels of salt increased approximately linearly in proportion to the amount of salt added to the cooking water. Rice cooked in 4 g salt took up on average 31 mg Na/100g, this increased to 162 mg Na/100g when cooked in 24 g salt /kg raw.

These results have been compared with the 6th edition of McCance and Widdowson’s The Composition of Foods (2) and on the whole compare well with one exception. The sodium concentration of uncooked wholewheat pasta was found to be lower than previously published values (3 mg Na/100g raw pasta compared with the published value of 130 mg Na/100g) but did compare well with the levels indicated by packaging labelling.

The results of this study provide valuable additional data to that already available in McCance and Widdowson’s The Composition of Foods (1) and also provide further evidence regarding uptake of sodium during cooking. This information will be helpful in setting guidance for caterers involved in food provision to schools and public sector institutions. In conclusion, the uptake of salt into staple carbohydrates (potatoes, pasta and rice) on cooking at the levels currently added by caterers in the public sector are reassuringly low and in line with the Agency’s “a little” guidance on salt intake.

Find more about this project and other FSA food safety-related projects at the Food Standards Agency Research webpage.

Funding Source
Food Standards Agency
Project number
S14018
Categories
Food Preparation and Handling
Packaging Residues
Commodities
Produce