Salvestrols are found in many fruits, they are a defence mechanism against mould. The problem is since WWII we've been spraying fruits with anti-fungals. So, when there's no mould the plant never mounts a response, so, no salvestrols. This is why you really only want to eat organic fruit, so that you get all the nutrients you pay for. Additionally, salvestrols are bitter, and by breeding the bitterness out of fruit we've been shooting ourselves in the foot, choosing sugar (bad) over salvestrols (good) - this is why growing heirloom fruits is a better choice than modern varieties.