Crop description. Madhuca indica—commonly known as madhuka, yappa, mahuda, mahua, mauwa, mohwa, hippe, butter tree, mahwa, mahula, or elupa—belongs to the family Sapotaceae and grows up to 21 m high. This deciduous tree is distributed mainly in India (see Fig. 4.9). The kernels are 70% of seed by weight. Seeds content includes 35% oil and 16% protein. Main fatty acids are palmitic acid (16-28.2%), stearic acid (20-25.1%), arachidic acid (3.3%), oleic acid (41-51%), and linoleic acid (8.9-13.7%) [106].

Main uses. Traditionally, it has been used as a source of natural hard fat in soap manufacture. The seed oil is used as an ointment in rheuma­tism and to prevent dry, cracked skin in winter. It is used in foods, cos­metics, and lighting. The cake presents toxic and bitter saponins that preclude its use as animal feed. However, mahua cake can be used as organic manure [106]. Several approaches to produce biodiesel can be found. Ghadge and Raheman have proposed a two-step pretreatment to reduce high FFA levels. Transesterification was carried out adding 0.25 v/v methanol and 0.7% KOH. Fuel properties were found comparable to those of diesel fuel [107]. Some authors have proposed different successful

alternatives to produce biodiesel: ethanol and sulfuric acid, and methanol and NaOH [108-110]. Puhan et al. have found better diesel engine performance for methyl esters compared to ethyl and butyl esters, while ethyl esters show lower NOx emissions compared to the rest [111]. Systematic studies on the lubrication properties of biodiesel have shown that the preferred range of blending with diesel fuel is 5-20% [51].