text: The most stable lactones are the 5-membered γ-lactones and 6-membered δ-lactones because, as in most organic cycles, 5 and 6 membered rings minimize the strain of bond angles. β-lactones appear in a number of natural products, but are only stable in artificial conditions (i.e. a test tube).  αLactones can be detected as transient species in mass spectrometry experiments. The reactions of lactones are similar to those of esters.
  Many naturally-occurring lactones are γ- and δ-lactones, both  saturated and unsaturated. They contribute to the aroma of fruits, butter, cheese, and other foods.
  Macrocyclic lactones are also important natural products. Cyclopentadecanolide is responsible for the musklike odor of angelica root oil. Of the naturally occurring bicyclic lactones, phthalides are responsible for the odors of celery and lovage oils, and coumarin for woodruff. Lactones are present in oak wood, and they contribute to the flavour profile of barrel-aged beers.
  Lactone rings occur widely as building blocks in nature, such as in ascorbic acid, kavain, nepetalactone, gluconolactone, hormones (spironolactone, mevalonolactone), enzymes (lactonase), neurotransmitters (butyrolactone, avermectins), antibiotics (macrolides like erythromycin; amphotericin B), anticancer drugs (vernolepin, epothilones), phytoestrogens (resorcylic acid lactones, cardiac glycosides).