Background: Oil palm trunk (OPT) is a valuable bioresource for the biorefinery industry producing biofuels and
biochemicals. It has the distinct feature of containing a large amount of starch, which, unlike cellulose, can be easily
solubilized by water when heated and hydrolyzed to glucose by amylolytic enzymes without pretreatment for
breaking down the biomass recalcitrance. Therefore, it is suggested as beneficial to extract most of the starch from
OPT through autoclaving and subsequent amylolytic hydrolysis prior to pretreatment. However, this treatment
requires high capital and operational costs, and there could be a high probability of microbial contamination
during starch processing. In terms of biochemical conversion of OPT, this study aimed to develop a simple and
efficient ethanol conversion process without any chemical use such as acids and bases or detoxification.
Results: For comparison with the proposed efficient ethanol conversion process, OPT was subjected to hydrothermal
treatment at 180 °C for 30 min. After enzymatic hydrolysis of PWS, 43.5 g of glucose per 100 g dry biomass was
obtained, which corresponds to 81.3 % of the theoretical glucose yield. Through subsequent alcohol fermentation,
81.4 % ethanol yield of the theoretical ethanol yield was achieved. To conduct the proposed new process, starch in
OPT was converted to ethanol through enzymatic hydrolysis and subsequent fermentation prior to hydrothermal
treatment, and the resulting slurry was subjected to identical processes that were applied to control. Consequently,
a high-glucose yield of 96.3 % was achieved, and the resulting ethanol yield was 93.5 %.
Conclusions: The proposed new process was a simple method for minimizing the loss of starch during biochemical
conversion and maximizing ethanol production as well as fermentable sugars from OPT. In addition, this methodology
offers the advantage of reducing operational and capital costs due to minimizing the process for ethanol production
by excluding expensive processes related to detoxification prior to enzymatic hydrolysis and fermentation such as
washing/conditioning and solid–liquid separation of pretreated slurry. The potential future use of xylose-digestible
microorganisms could further increase the ethanol yield from the proposed process, thereby increasing its effectiveness
for the conversion of OPT into biofuels and biochemicals.