Vitamin is a series of brief musical stings mostly used to accompany the "Eye Catch" title cards used to mark the end of Part 1 and beginning of Part 2 of several episodes of Cowboy Bebop. Note that many episodes may use a sound effect, silence, or, where the scene preceding or following the break uses an ongoing song cue, a fade or hard cut into or out of that cue.
Three tracks from the Vitamin series appear on OST2 - No Disc. These are Vitamin A,used in Session 7: Heavy Metal Queen; Vitamin B (Session 4: Gateway Shuffle), and Vitamin C (which is not used anywhere in the series itself). There are, however, five other short riffs that stylistically could be classed as being part of the Vitamin series which do appear in the show.
If we continue the alphabetic naming convention as used for the three variants that are included on No Disc, then Vitamin "D" is the heavily processed saxophone riff with a percussion backing, which appears in Session 3: Honky Tonk Woman (and therefore is actually the first use of this specific series of tracks in the show) and in Session 15: My Funny Valentine.
Vitamin "E" is a laid-back guitar and percussion riff, and is the Vitamin track used most frequently, appearing as an Eye Catch in Sessions 12 and 13: Jupiter Jazz Part 1 and Part 2, and again in Session 19: Wild Horses. It is particularly notable as it is the only Vitamin track also used as a Session Preview, where a looped version is used at the end of Session 25: The Real Folk Blues (Part 1).
Vitamin "G" is a laid back saxophone riff also used in Session 17: Mushroom Samba.
Finally Vitamin "H" is another laid-back jazzy solo saxophone riff and is first used—with a very wet room reverb applied—in Session 18: Speak Like a Child, and subsequently in Session 21: Boogie Woogie Feng Shui, but this appearance has a markedly reduced reverb.