Are your ready prepared fruit & veg as healthy as you think? Tests show far lower levels of vitamin C than unprepared produce

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Sainsbury's ready trimmed broccoli should contain 79mg of vitamin C but actually contains 36.7mg

Walk into any super-market and it’s impossible to miss them — pack after pack of pre-washed bags of salad, ready- to-cook vegetables and ready-to-eat fruit.

From tiny peas plucked from their pods to minutely diced onions, from fingers of glistening pineapple to crescents of carefully cut apple, they’ll all be there.

And, make no mistake, it is no coincidence that these shelves of perfect-looking, plastic-wrapped produce are lined up to greet shoppers just as they arrive. The message they give is clear: here, we sell food that is healthy and convenient.

Unsurprisingly, for time-poor Britons these groceries have an irresistible lure. Last year, the fruit and vegetable market was worth £16 billion. Of that, sales of so-called ‘value-added’ pre-prepared fruit and vegetables are estimated to account for as much as £1 billion.

According to a Mintel survey, every week one in five adults purchases ready-to-eat fruit portions. A similar number buy ready-to-cook vegetables, such as sliced carrots, chopped onions and pre-prepared stir-fry packs. That number doubles when it comes to bagged or prepared salads.

Their popularity is highest among the under-45s. Be they singletons with busy lives or rushed-off-their-feet parents, all are desperate to save time while still eating healthily.

And the supermarkets know this. So it is that the pack of peas at Waitrose is labelled ‘fresh and tender’, while the Marks & Spencer washed wild rocket is described as ‘deliciously healthy’.

But are these products as virtuous as billed? And do consumers really know what’s happened to them from field to fork? Sure, the packets generally state where the items originated — anyone can see the peas are from 4,000 miles away in Kenya, the rocket from Italy and the beans from Tanzania.

Use-by dates are also there, plain to see — some extending a full six days beyond when they first appear on the shelves. How long it took them to get to the supermarket one can only speculate, but it will have been additional days, not hours.

Because first they will have been picked, then transported to a processing hub, where they will have been washed, prepared, packed and chilled. From there, the next stop would be the nearest airport to be air-freighted to Britain.

But beyond the environmental effects of all those air miles, what impact does the way in which this produce is processed, packed and stored have on the nutritional value of these supposedly ‘fresh’ and ‘healthy’ foods?

Marks and Spencer pre-packed carrot batons should contain 2mg/100g of vitamin C but in reality they actually contains then than 50 per cent or 1mg/100g

To find out, the Daily Mail purchased 20 items of ready-to-eat fruit, ready-to-cook vegetables and bagged salads, and then had them tested at an independent laboratory to precisely measure their levels of vitamin C.

They came from Waitrose, Marks & Spencer, Sainsbury’s and Tesco, and all were tested within their ‘best before’ or ‘use by’ date. The laboratory results were then compared against the ‘textbook’ amount typically found in raw fruit and vegetables sold in the UK. While vitamin C is just one of many vitamins and nutrients these items contain, it is a key one and gives an indication of freshness.

Our tests showed that levels in the prepared packs of fruit and vegetables were, mostly, far lower than what might be found in fresh, unprepared produce.

For example, that ‘mild, succulent’ pack of baby spinach from Waitrose had just 2.8mg of vitamin C per 100g — less than 10 per cent of the amount recorded as standard for baby spinach in the latest edition of McCance and Widdowson’s The Composition Of Foods, the authoritative record of nutrient data for the most commonly consumed foods in the UK.

A bag of M&S rocket had 84 per cent less vitamin C than the textbook level, while a pack of the store’s runner beans was similarly depleted.

As for the amount of vitamin C in sliced apple snack packs, those from both Tesco and Sainsbury’s came in at less than 1mg — too low to accurately measure — and way down on the textbook levels of 6mg.

So why is this? As soon as they are harvested, levels of nutrients in fruit and vegetables will begin to decrease. However, this will be accentuated by further processing — particularly cutting or peeling.

Suppliers have the added problem of having to wash produce so it can be eaten straight from the pack, then ensuring it can survive for days without going soft or discolouring.

In her new book, Swallow This: Serving Up The Food Industry’s Darkest Secrets, investigative journalist Joanna Blythman lifts the lid on the myriad processes at the industry’s disposal to achieve ‘fresh-like’ food — food that is more than a week old, but which still looks fresh.

Sainsbury's mango pieces from Brazil should contain 37mg of vitamin C but actually has 26.3mg (71 per cent)

Blythman describes how salads are pre-washed in tanks of water that are not changed for eight hours at a time and which contain chlorine or fruit acids. These act as a disinfectant, but at the same time can reduce levels of vitamins A, C and E, essential for a healthy immune system, as well as folates, which play a role in preventing birth defects.

Meanwhile, cutting or dicing vegetables — as with carrots or broccoli florets — creates what scientists refer to as ‘wounded tissues’, which deteriorate more rapidly than intact fruit and veg. To counter this, producers may treat cut fruit and veg with enzymes or fruit acids, which will firm them up and preserve their shape during processing.

Interestingly, some of the products tested actually had more vitamin C than might be expected. The Tesco pineapple fingers, for example, had four times the textbook amount.

This may well be accounted for by the fact that, prior to packaging, the retailer revealed to the Mail, it was washed in Citrox, a disinfectant derived from citrus fruits used to decontaminate ready-to-eat foods.

(The Tesco spokesman also revealed the apple slices had been treated with a product called NatureSeal. The makers of this product, a blend of vitamins and minerals, boast that it can extend the shelf-life of fruit for a staggering 21 days).

Another weapon at producers’ disposal is modified atmosphere packaging (MAP). This involves altering the composition of air in plastic packs, so it contains significantly less, or no, oxygen. This further slows the ageing process. (Whenever used, packs will generally bear the words ‘packaged in a protective atmosphere’).

While the industry claims this has no impact on the nutritional qualities of anything within, Blythman says it all goes towards creating a situation whereby the wool is being pulled over consumers’ eyes.

She says we have even come to associate the endless refrigeration process as a positive, equating coldness with freshness. ‘The perception is that you’re getting something very fresh to start with,’ she says.

‘But what it really has is a hidden history we know nothing about, which probably stretches back five to seven days before we have even picked up the pack. What that is doing is really manipulating the very idea of freshness. It is not about being genuinely fresh; it’s about creating this “fresh-like” quality.’

The test was carried out by Daily Mail to find out what levels of vitamin C were in pre-packed fruit and veg

She adds: ‘My friend, a greengrocer, talks about “greengrocer’s freshness” — essentially something that is picked that day, which goes in a box to a warehouse, is picked up by the greengrocer, who sells it the next day without refrigeration, and, by the next day, it is regarded as old. That is true freshness.

‘The minute that you involve refrigeration, use MAP, or do things that involve cutting and breaking down cell structures, you are playing around with that idea of freshness.’

But what about the argument that the way in which these fruit and vegetables have been prepared is irrelevant, so long as they retain some of their goodness? Or that because they are ‘easy’ to use, this will encourage people to eat them?

‘I don’t agree with that,’ says Blythman. ‘It makes eating vegetables enormously expensive — the minute you chop up anything, you can double the price and more.

‘It nominally ticks the box of health, but how does it encourage people if someone spends £2 on a bag of lettuce and it tastes rubbish?’

And the mark-ups are substantial. Compared with loose produce, some of the items purchased by the Mail were not just double, but four, five or even more times as expensive. Which, given the reduced nutrition they may offer, is a mighty big premium.