Fresh food is undoubtedly the best option for a healthy diet, but a lot of the food on supermarket shelves is far from fresh. Much of it has racked up a fair few air miles and it’s difficult to work out just how fresh something is.
Until we have a “Picked on…” date as well as a “Sell by…” date on packets, it’s going to be hard to judge. Even then, different fruit and veg deteriorates at different rates.
That’s because there’s more than one factor involved in the deterioration of fruit and veg. For instance, they stay alive even after they’ve been picked and that very fact contributes to their spoilage and loss of nutrients.
Fruit and vegetables continue breathe after picking and the respiration process breaks down stored organic materials such as carbohydrates, proteins and fats. This in turn leads to loss of food value, flavour and nutrients.
Produce will also lose heat and moisture from this respiration which is another way that nutrients are lost. Warm, dry air speeds up this process, which is why we keep things in the fridge.
The rate of respiration varies from one fruit or veg variety to another, so some fruit and vegetables stay fresher longer than others. Asparagus, broccoli, mushrooms, peas and sweet corn have a very high respiration rate so will lose nutrition and flavour quicker than apples, garlic or onions, all of which have low respiration rates.
The longer produce has to breathe before it’s eaten, the less likely it is to retain nutrients. Studies show that food transported long distances is not likely to be as nutritious as food grown and consumed locally.
Plants also contain enzymes which can cause nutrient and colour loss as well as flavour changes. When you cut an apple and expose it to air it turns brown. This is down to enzyme activity. The browning is a sign that the nutrient value is also dropping. It’s a prelude to decay. The way to stop this is to destroy the enzymes by blanching - cooking for a short time in boiling water, then plunging into ice water.
Another factor has to do with whether the fruit or vegetable was ripe when it was picked. Climacteric crops, like tomatoes, can be picked before they’re fully ripe but while they might get full ripened colour after picking, they won’t achieve the highest nutrient levels. Vitamin C has been shown to be higher in tomatoes that are picked when they’re ripe.