Typical doping agents include nitrocellulose, cellulose acetate and cellulose acetate butyrate. Diets yielding butyrate and acetate from bacterial fermentation show increased T expression. Examples include ethanol, acetate, lactate, and butyrate. Butyric acid is used in the preparation of various butyrate esters. The VFAs, including acetate, lactate, propionate and butyrate, provide carbon and energy for bacterial metabolism. The ester formed from 1-pentanol and butyric acid is pentyl butyrate, which smells like apricot. Low-molecular-weight esters of butyric acid, such as methyl butyrate, have mostly pleasant aromas or tastes. Acetate, propionate, and butyrate are the three most common SCFAs. Many laboratories also perform a butyrate esterase test and a beta-lactamase test. A variety of butyrate esters are known. Several species form acetone and "n"-butanol in an alternative pathway, which starts as butyrate fermentation. One example is sodium butyrate, a colorless, water-soluble salt. Higher levels of intestinal bacteria that produce butyrate may be protective. In nature, the cation associated with butyrate is unknown or unimportant to the metabolizing enzymes. In addition that butyrate production affects serotonin level.