If you're precious about the salt and sugar content in your tomato sauce, you might want to examine the difference between the tinned and bottled versions of the iconic Wattie's variety.

Differences have been discovered in the nutritional values of the canned versus the plastic-bottle version of the popular brand.

The tinned tomato sauce contained 475mg of salt and 20g of sugar, per 100g.

The ingredients may be largely the same, but the proportions don't match up.

However, the plastic-contained version carried nearly twice as much salt and 10g more sugar than its canned counterpart, coming in at 950mg and 30g respectively.

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The quantity of the principal ingredient differed, too, with the tinned recipe containing 11 per cent more tomatoes than the bottled version.

Branding was identical between the two styles of the sauces.

Food Innovation Network spokesperson Angus Brown said the difference in ingredients between the two products came down the sterilisation processes each packaging style had to go through.

The canning process involves subjecting the goods to high pressurised water normally above 85 degrees inside an autoclave which preserved and sterilised the food, Brown said.

However, if the same method were used for food packaged in bottles, the plastic wouldn't be able to withstand the high temperatures and warping of the packaging would occur, rending the product unusable, he said.

So by adding more salt to plastic bottle recipe, the manufacturer was able to process the sauce at lower temperatures and achieve a similar shelf life to the canned version, he said.

Additional sugar was also added to balance out the flavour of the increased salt content, he said.

A number of consumers have taken to Wattie's Facebook to express their concern about the different recipes.