Pretreatment of maize straw with Pleurotus ostreatus and Lentinus squarrosulus for bioethanol production using Saccharomyces cerevisiae

Maize straw (MS) is a lignocellulosic substrate that constitutes huge wastes in the environment. This work aimed to pretreat MS with mushroom alone as a biological agent, and with NaOH prior to mushroom treatment (combined chemical and biological), and subsequently converting the released reducing sugars (RS) to ethanol using Saccharomyces cerevisiae. MS was degraded by Pleurotus ostreatus (PO) and Lentinus squarrosulus singly and in combination for 35 d. Samples were collected every 7 d from the treated straw to determine the RS content. Moreover, MS samples were pretreated with NaOH prior to degradation by the selected mushroom (combined pretreatment), and then their sugar profiles were determined using High-performance liquid chromatography (HPLC). The RS recovered from the degraded MS samples were fermented using 2 molecularly-identified S. cerevisiae strains. The highest RS contents (16.79 mg/ g) were recorded when MS was pre-degraded by PO for 21 d compared to Lentinus squarrosulus (16.55 mg/ g), and with the consortium of the two fungal cultures (16.36 mg/ g). However, MS pretreated with NaOH and Pleurotus ostreatus gave better yield of RS (17.38 mg/ g), than treatment with Pleurotus ostreatus (16.79 mg/ g) alone. The sugar profiles of the NaOH-PO-pretreated MS (mg/ 100 g) included; glucose (850.60); xylose (837.04), fructose (754.29), arabinose (502.76), ribose (2.066×10-4 ) and rhamnose (3.552×10-5 ). The fermenting yeasts were molecularly identified by sequencing of ITS region as S. cerevisiae SA01 and S. cerevisiae SA02, and assigned Accession no. of MK038975 and MN491900, respectively. Equal concentration of bioethanol (1.58 g/ l) was recorded in PO and in NaOH-PO-pretreated MS, which were fermented by S. cerevisiae SA01. Accordingly, MS can be utilized as a substrate for fermentation and then bioethanol production.