Supermarkets are putting appearance ahead of taste when it comes to their fruit and vegetables, according to a new report.
Which? questioned the pricing of pre-prepared fruit and vegetables
Consumer magazine Which? said some supermarkets treated taste as an optional, more expensive extra.
Its report also warned that some pre-prepared produce contained far less vitamin C than in whole form.
Supermarkets have denied taste is being sidelined and questioned the depth of the Which? investigation.
Which? editor Malcolm Coles said: "Supermarket fruit and veg looks perfect, but it isn't.
The magazine's investigation found Asda sliced runner beans had 11% of the textbook level of vitamin C, and Marks & Spencer's fresh mango just 42%.
Mike Day, from the National Institute of Agricultural Botany, which tests new vegetable varieties, told the report supermarkets focused on what consumers could see.
"Supermarkets often place more emphasis on appearance than taste or nutritional content as it's easier to measure physical characteristics," he said.
Which? commented: "It is understandable that supermarkets want to stock fruit and veg that appeals to
shoppers - but you'd imagine a major factor would be what the food tastes like."
"Most supermarkets do have test panels, but there's definitely scope for improvement."
But Marks & Spencer questioned the depth of the study and insisted it valued the taste of its products.
In a statement it said: "Firstly, it is important to highlight that the results are based on only one sample of each product.
"The level of vitamin C in fruit and vegetables varies considerably with each
piece and also throughout its season.
"Secondly, in response to the Which? report, Marks & Spencer would like to
make it clear that 'taste' is a very important quality of any product it sells."
The magazine also claimed that pre-packaged fruit and vegetables were sometimes sold at "inflated prices".
It pointed to bags of broccoli florets selling for 98p in an Asda - at 35p per 100g working out to more than three times the price of the loose broccoli, at £1.19 per kilogram.
The per gram price was displayed on a small shelf label, the magazine said.
The reverse situation could also occur, the report added.
Which? found loose cherry tomatoes at Tesco cost £3.99 per kilogram, while those in a punnet cost 68p per pack - or £2.72 per kilogram.
Which? found some pre-prepared vegetables had less vitamin C
"Supermarkets should give shoppers more information about where their food comes from, how it's been prepared and how nutritious it is," Mr Coles said.
"But a good start would be to tell them how much it costs in a clear and consistent way."
In response to the report Tesco said it had stopped selling loose tomatoes.
A spokesman said: "The reason they were more expensive was because they were packed in green
trays and cardboard boxes which had to be done by hand but the ones in punnets are packed by machinery.
"We recognise they didn't offer good value for money and stopped selling them loose about two months ago."