The chemical mechanism by which beta-carotene neutralizes free radicals via its polyene chain's conjugated double bonds and electron delocalization is a fundamental textbook principle of organic chemistry and biochemistry, requiring no specific citation.
The claim describes a well-established biochemical mechanism involving the conjugated polyene chain of beta-carotene and electron delocalization (often framed through conjugated double bond structures as noted in papers like [2]). Because it represents foundational chemical knowledge taught as a baseline principle rather than a contested empirical finding, it is classified as common knowledge.