Boris Johnson's endorsement of McDonald's Olympic credentials has proved to be a kiss of death, cementing the fast food giant at the bottom of a brand reputation tracker monitoring Twitter sentiment toward the 25 official sponsors of the London Games.

The mayor of London told reporters on Thursday that criticism of McDonald's was "all just bourgeois snobbery".

"It's classic liberal hysteria about very nutritious, delicious, food – extremely good for you I'm told – not that I eat a lot of it myself," he said. "Apparently this stuff is absolutely bursting with nutrients."

The comments attracted significant negative sentiment on social media, which were amplified when comedian Frankie Boyle, who has more than 800,000 followers, weighed in on the subject.

"Don't know how much sponsorship McDonalds paid for the Olympic mayor to be a fucking clown," he said on his official account @frankieboyle.

As a result the McDonald's brand took a hammering a day before the opening ceremony, in a daily Olympic Twitter tracker of the buzz around the 25 official sponsors.

The tracker – which measures factors including volume of tweets, sentiment, potential reach of the tweeter and if tweets get responses – plummeted to a record low on Thursday.

McDonald's has been languishing at the foot of the table for the last three weeks – with daily scores of between minus 70,000 to 100,000 – however Johnson's comments triggered a surge in negative sentiment to almost negative 1m.

"Johnson's comments were amplified by Frankie's Boyle's negative response," said Rory Maxwell, associate director of MediaCom Sport. "Because he is a celebrity with a big following it had a massive impact on McDonald's Olympic Twitter score. The score is a reflection of the level of negative opinion of the brand."

To put McDonald's score into perspective the next lowest rating was for Dow, on just more than 200,000, while the sponsor leading the tracker on Thursday was Coca-Cola.

Coke shot to the top due to positive comments being tweeted about boyband The Wanted making surprise visits to some torchbearers as part of the soft drink giant's support of the Olympic torch relay.

Earlier this week health campaigners published a report, called Obesity Games, which heavily criticised the International Olympic Committee for allowing junk food brands to be sponsors.

Last month Lord Sebastian Coe, the chairman of the London 2012 organising committee, staunchly defended the sponsorship of the London Olympics by fast food and soft drinks companies.

He argued that the £750m investment by brands such as Coca-Cola and McDonald's is essential to making the event a success.

Earlier this month he sparked a sponsorship row when he told BBC Radio 4's Today programme that ticket-holders might be turned away if they wore a T-shirt with non-official sponsor branding, such as Pepsi, but that people would "probably get in with Nike trainers".

London Olympics officials later claimed he misheard the question and was talking about the clothing rules for staff.