Tuesday, July 13, 2010

Sodium in food

Most people like to have salt on their food. In mediaeval England, salt was expensive and only the nobility could afford it, as it was made by evaporating salt water over a fire. The salt was placed in the middle of the high table; the commoners sat at lower trestle tables and did not have access to the salt. Thus they were "below the salt" and this came to be an indication of rank.

Around 1650, rock salt was mined in Cheshire and salt became more readily available. The connotation of the value of salt remains, however, in expressions like "He's worthy of his salt".

These days, we probably have too much salt in our diets. In New Zealand, for instance, we consume around 150% of the recommended upper intake level. Much of this intake is involuntary - manufacturers add it to foods including bread, sausages and pies. The recent television series "Master Chef" had the judges saying repeatedly "Don't forget the seasonings", meaning not just herbs and spices, but also salt.

So, should we just ban salt in food and let individuals add salt to taste?

The answer may surprise some readers. Salt (sodium chloride) contributes to the safety of food and is essential for developing texture and flavour in processed meats. It helps to bind proteins, improving texture; it increases water binding capacity of proteins, also contributing to texture and assists in stabilising meat batters by improving fat binding. It also decreases fluid loss in vacuum-packed, thermally processed products.

Not only that - salt improves safety and shelf life by inhibiting the growth of bacteria, though relatively high levels are required if salt is used alone. It helps to reduce the water activity* of the food, making it more difficult for bacteria to grow. That's why salted beef and pork were carried on long sea voyages - the meat was preserved.

Stringer and Pin (Institute of Food Research, Norwich, UK) have noted that "There is scope to reduce salt in foods. However, as salt influences bacterial growth, survival and recovery after adverse treatments, reducing salt in foods will have consequences for food safety that must be considered". These researchers used predictive models to show that reducing sodium content from 1.5g/100g to 0.76g/100g food allowed a much greater growth rate of certain foodborne pathogens. This could be acceptable, but other preservative mechanisms would need to be put in place. For example, other preservatives might be added at low levels and refrigeration might be necessary. Above all, reducing salt content would require even stricter adherence to good manufacturing practices, particularly with respect to plant and operator hygiene.

I'll write more on sodium in food in a follow-up posting.

* See the end of "Free Choice or Safety of the Population" in this blog for an explanation of water activity.

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