https://www.nature.com/articles/nature12362
In the Celery Juice book, the Medical Medium makes the surprising (at least to me) statement that the vitamin C in celery is different from other fruits, in that it's small vitamin C content is "methylated" and does not have to be processed by the liver. (I am on kindle and will update THE LIST with the exact wording.) The liver book states flatly that all nutrients are first processed by the liver, which was news to me, and this book now implies that vitamin C is "methylated" by the liver (but that the form in celery juice is already converted.).
Here is a definition of methylation
In the chemical sciences, methylation denotes the addition of a methyl group on a substrate, or the substitution of an atom (or group) by a methyl group. Methylation is a form of alkylation, with a methyl group, rather than a larger carbon chain, replacing a hydrogen atom. These terms are commonly used in chemistry, biochemistry, soil science, and the biological sciences.
In biological systems, methylation is catalyzed by enzymes; such methylation can be involved in modification of heavy metals, regulation of gene expression, regulation of protein function, and RNA processing. In vitro methylation of tissue samples is also one method for reducing certain histological staining artifacts. The counterpart of methylation is called demethylation.
https://en.wikipedia.org/wiki/Methylation