• NZ students find almost no vitamin C in drink • GlaxoSmithKline could face up to £1.1m fine

Two New Zealand schoolgirls humbled one of the world's biggest food and drugs companies after their school science experiment found that their ready-to-drink Ribena contained almost no trace of vitamin C.

Students Anna Devathasan and Jenny Suo tested the blackcurrant cordial against rival brands to test their hypothesis that cheaper brands were less healthy.

Instead, their tests found that the Ribena contained a tiny amount of vitamin C, while another brand's orange juice drink contained almost four times more.

"We thought we were doing it wrong. We thought we must have made a mistake," Anna told New Zealand's Weekend Herald. The girls were both 14 and students at Pakuranga College in Auckland when they did the experiment in 2004.

Given Ribena's advertising claims that "the blackcurrants in Ribena have four times the vitamin C of oranges", they were astonished and wrote to the manufacturers, GlaxoSmithKline (GSK). When they got no response, they phoned the company, but were given short shrift. "They didn't even really answer our questions. They just said it's the blackcurrants that have it, then they hung up," Jenny said.

But then the girls' claims were picked up by a TV consumer affairs programme, Fair Go, which suggested they take their findings to the commerce commission, a government watchdog.

GSK said the girls had tested the wrong product, and it was concentrated syrup which had four times the vitamin C of oranges. But when the commerce commission investigated, it found that although blackcurrants have more vitamin C than oranges, the same was not true of Ribena. It also said ready-to-drink Ribena contained no detectable level of vitamin C.

GSK is in court in Auckland today facing 15 charges relating to misleading advertising, risking fines of up to NZ$3m (£1.1m).

In Australia, GSK has admitted that its claims about Ribena may have misled consumers. The Australian competition and consumer commission said last week that claims on the nutrition information panel of Ribena's ready-to-drink cartons implied that the product had four times the vitamin C of orange juice drinks, when this was not correct. The girls have since visited GSK to be thanked "for bringing it to our attention".

GSK said in a statement yesterday that concerns about vitamin C only affected some products in Australia and New Zealand."GSK has conducted thorough laboratory testing of vitamin C levels in Ribena in all other markets. This testing has confirmed that Ribena drinks in all other markets, including the UK, contain the stated levels of vitamin C, as described on product labels."