Plant oil-based biodiesel processes are commercial­ized (Figure 20.7). Biodiesel productions use mostly extracted plant or vegetable oils, isolated animal fats (from meat or dairy productions), or to less extent recycled cooking oils, and transesterify the triglycerides with short-chain primary alcohols (e. g. methanol or (bio)ethanol) to make fatty acid esters (diesels). The oil extraction from plants (solid—liquid extraction) may allow coextraction of numerous phytochemicals as coproducts. The main coproduct from the transester­ification is glycerol, which can be used directly as solvent, or as feedstock for microbial fermentation production of other biochemicals, such as propane­diol, dihydroxyacetone, succinic acid, polyglycerols or polyhydroxyalkanoate, or for hydrothermal-chemical conversion to H2 (Khanna et al., 2012; Kosmider et al., 2011; Kannan et al., 2012). Grown on glycerol,
astaxanthin production by bacterium Phaffia rhodozyma (X. dendrorhous) or Sporobolomyces ruberrimus (Valduga et al., 2009), b-carotene by B. trispora (Mantzouridou et al., 2008), prodigiosin or other carotenoids by R. glutinis (da Silva et al., 2009), various carotenoids by Rhodosporidium paludigenum (Yimyoo et al., 2011), as well as b-carotene by microalgae Clamidomonas acid — ophila (Langner et al., 2009), astaxanthin by Schizochy- trium sp., and various carotenoids by Thraustochytrium have been demonstrated.