Fresh isn’t always best

THERE’S a common fallacy which suggests that fresh foods, especially fresh fruit and vegetables, are nutritionally superior to their frozen counterparts.

This belief probably has as much to do with the recent backlash against any kind of food processing or preservation, as it does with nutritional science.

Processed versus fresh

While it’s true that many types of processing can deplete the nutrient content of food, there are some exceptions. For example, fresh tomatoes are rich in a powerful antioxidant called lycopene, a potent antidote to the free radicals which can damage our tissues causing ageing and disease.

You’d be forgiven for thinking the fresher your tomatoes, the better the antioxidant effect you’d get from this lycopene. But you’d be wrong. In reality, while the lycopene contents of fresh, pulped, puréed, tinned and fried tomatoes are all pretty similar, the bioavailability of their lycopene, and therefore the beneficial effect of this nutrient in the body, is significantly greater in the processed and cooked varieties. (Also see page 15)

In a similar way, there are many foods whose protein content is used more efficiently after cooking.

Indeed, the enhanced bioavailability of proteins from cooked meat was a key factor in facilitating larger brain development in early humans, a critical evolutionary milestone which ultimately allowed the species to flourish.

In addition, there is now a growing range of fortified foods such as breakfast cereals, milks, spreads and breads that are enriched with important vitamins and minerals, and have superior nutritional value to their unfortified equivalents. So while the nutrient content of fresh food is often better than processed or cooked varieties, this clearly isn’t always the case.

Frozen versus fresh

One of the major problems in categorising frozen foods like fruit and vegetables alongside other ‘processed’ or ‘preserved’ foods, is you’re not really comparing like with like.

For example, processed food that’s created by grinding its raw ingredients together in a factory, adding salt and various stabilisers and emulsifiers, cooking at high temperature and storing before and after packaging will incur significant nutrient loss at each of these steps.

Frozen fruit and vegetables however, are simply harvested on the farm and taken shortly afterwards for blast freezing. The rationale for doing so is that microbial spoilage (or rotting caused by fungi or bacteria) is minimised, giving the producer a greater crop yield in terms of what they can sell to their wholesaler.

The wonderful side-effect of this freezing process, however, is that it also rapidly arrests the loss of many micronutrients, especially delicate antioxidants like vitamins A and C which would be depleted at higher temperatures. In fact, the only nutrient which really suffers as a result of the freezing process is vitamin E, although even in this case, it could be argued that the losses incurred by freezing are less than those which would have occurred naturally as the food sat at room temperature waiting to be prepared and cooked.

‘But what about fresh fruits and vegetables?’ I hear you ask. ‘Surely their nutrient content is best of all?’.

Often, this is not the case. The length of time between when these foods are harvested and when they are eaten can be anything up to two weeks, during which time the more fragile nutrients will be markedly depleted.

By avoiding this long, nutrient-sapping period between harvest and consumption, your frozen broccoli, blueberries and carrots will often trump their ‘fresh’ alternatives in terms of nutrients.

¦ Dr Daniel McCartney, Lecturer in Human Nutrition & Dietetics at DIT

HOT OFF THE PRESS

Fortified foods

A recent US study, which examined the nutritional adequacy of children’s diets, has found that fortified foods, such as breads, milks, breakfast cereals and juices, significantly contributed to vitamin and mineral intakes. These provided children with more than half of their total vitamin D and folate, and between 20 to 47% of their overall vitamin A, vitamin B12, vitamin C and iron. These nutrients are critical to optimal growth and development in infancy, childhood and adolescence. However, several of these vitamins and minerals are consumed in low amounts by Irish children.

A QUICK FIX

Pea, mint and coriander dip

Blend 300g of defrosted peas, a handful of coriander, a half a handful of mint, 50mls of lemon juice, two cloves of garlic, and a finely chopped red chilli together with 100g of low-fat natural yoghurt and a teaspoon of ground cumin.

Serve as a dip directly out of the fridge, with toasted pitta bread or carrot or celery sticks for a delicious, nutritious treat.