Effect of ultrasound pretreatment combined with enzymatic hydrolysis of non-conventional starch on sugar yields to bioethanol conversion

Bioethanol from cornstarch is the largest renewable liquid biofuel currently in use. However, corn is the basis of the population’s diet in many countries so other feedstock must be considered. This article proposes non-conventional starch from Ramon tree (Brosimum alicastrum), a specie native to the Mesoamerican region and widely distributed in the Yucatan Peninsula, Mexico. Ultrasound has appeared as a promising green technique used to make physical, chemical, and biological processes, including enzymatic reactions, more efficient. Ultrasonic pretreatments (UL) alone and combined with commercial enzymes and enzymatic extracts of native fungi (Trametes hirsuta Bm-2) with a power of 70 W at 42 kHz, for 30 min at 45 °C, 60 °C, and 70 °C, were used. The results indicate that the pretreatment conditions do not inhibit the enzymatic activity; on the contrary, they decrease the operational temperature, giving the best results at 45 °C. All the treatments presented significantly higher dextrose equivalent values than the control without sonication. In the fermentation process, 91% efficiency was reached using the native strain Candida tropicalis PL-1, which infers yields of 314 and 235 L/ton of Ramon seed flour (RF) for samples pretreated by UL combined with α-amylase and raw enzymatic extract respectively. Based on the above, the ultrasonic treatment combined with enzymes applied to RF is outlined as an option of non-conventional starch pretreatment for the bioethanol production to avoid the use of basic food in the quest of clean energy.