Mmeltdowns is a popular candy with "fruity taste".
Advertisements of Mmeltdowns were visible on the street throughout New York. After the advent of the Alien Monster, this ad has been replaced by that of Sunbursts candies. This change mirrors the shadow of nuclear war over the people while it lasted, and afterwards the renewed interest about space and an imminent alien attack.
It's made obvious that Mmeltdowns/Sunbursts are a product of Veidt Enterprises, who used this change deliberately in order to manipulate this change of interests of the buying market (the way he altered Nostalgia to Millennium).
Similiary, it's made obvious that Veidt used the brand and marketing of Nostalgia as a manner to make people long about an idyllic past and be uncertain about a shadowy future. More certainly, the contrast between Nostalgia and the later Millennium, would make the buying market conform more effectively to his new utopia after the threat of the nuclear war.