Ask Wendy: Preservatives - when more is less

Why do some products have more than one preservative?

Laura R of Cape Town asks: “At a time when the 'no preservatives’ claim is a drawcard for consumers choosing to follow a healthy diet, why would a manufacturer of a fruit juice, for example, add not one, but three preservatives?

A: Prof Gunnar Sigge, head of Stellenbosch University’s Food Science department, explains: “It’s a case of 'more is less' because preservatives often work synergistically, which means by adding small amounts of three preservatives, they’re actually adding less than they would if they only added one preservative.

"So, the total mass of preservatives added is much less than the mass of only adding one preservative. This is part of what is often referred to as the 'hurdle effect' - by placing many, smaller hurdles in the path of the bacteria, a better end result is obtained.  Refrigerating the fruit juice is yet another ‘hurdle'.