High-temperature ethanol fermentation from pineapple waste hydrolysate and gene expression analysis of thermotolerant yeast Saccharomyces cerevisiae

Abstract

High-temperature ethanol fermentation by thermotolerant yeast is considered a promising technology for ethanol production, especially in tropical and subtropical regions. In this study, optimization conditions for high-temperature ethanol fermentation of pineapple waste hydrolysate (PWH) using a newly isolated thermotolerant yeast, Saccharomyces cerevisiae HG1.1, and the expression of genes during ethanol fermentation at 40 °C were carried out. Three independent variables, including cell concentration, pH, and yeast extract, positively affected ethanol production from PWH at 40 °C. The optimum levels of these significant factors evaluated using response surface methodology (RSM) based on central composite design (CCD) were a cell concentration of 8.0 × 107 cells/mL, a pH of 5.5, and a yeast extract concentration of 4.95 g/L, yielding a maximum ethanol concentration of 36.85 g/L and productivity of 3.07 g/L. Gene expression analysis during high-temperature ethanol fermentation using RT–qPCR revealed that the acquisition of thermotolerance ability and ethanol fermentation efficiency of S. cerevisiae HG1.1 are associated with genes responsible for growth and ethanol stress, oxidative stress, acetic acid stress, DNA repair, the pyruvate-to-tricarboxylic acid (TCA) pathway, and the pyruvate-to-ethanol pathway.

The potential of multistress tolerant yeast, Saccharomycodes ludwigii, for second-generation bioethanol production

“…Other sugars in pineapple fruit, such as sucrose, were not detected in the PWH. This finding may be explained by the fact that sucrose is converted into glucose and fructose during dilute acid pretreatment, which was similar to that reported by Phong et al 32 .…”

“…No 5-HMF or phenolic compounds were detected in the hydrolysate. The acetic acid and furfural concentrations in the PWH were 131 mM and 3.95 mM, respectively, which were comparable to those reported by Phong et al 32 . When PWH was directly used as a feedstock for ethanol production at 37 °C using S. ludwigii APRE2, a maximum ethanol concentration of 38.02 g/L, the productivity of 1.58 g/L.h, and an ethanol yield of 82.35% were achieved (Fig.…”

“…The ethanol production efficiency of S. ludwigii APRE2 was compared with other ethanologenic yeasts using different feedstocks, and the results are summarized in Table 6 . The ethanol concentration produced by S. ludwigii APRE2 was comparable to that produced by S. cerevisiae using pomelo peel waste 85 , S. cerevisiae TISTR 5048 using pineapple peel waste 86 , P. kudriavzevii RZ8-1 using sugarcane bagasse 29 , and S. cerevisiae HG1.1 using pineapple waste 32 as feedstock. In contrast, the ethanol concentration and productivity achieved from S. ludwigii APRE2 were approximately 4.1- to 4.7-fold higher than those from P. kudriavzevii RGB3.2 and K. marxianus RGB4.5, respectively, using rice straw hydrolysate as feedstock 31 .…”

“…Among these, pineapple peel and core are promising raw materials for second-generation bioethanol production since they are highly biodegradable and rich in proteins and carbohydrates 84 . These pineapple wastes contain a high amount of cellulose (16.57%) and hemicellulose (28.81%) with a low level of lignin (3.04% of the total dry matter) 32 . This study assessed ethanol production from acid-pretreated PWH by the selected yeast S. ludwigii APRE2.…”

“…The yeast strain produced a maximum ethanol concentration of 9.1 g/L from rice straw hydrolysate using a simultaneous saccharification and fermentation (SSF) process at 45 °C. Phong et al 32 recently reported another multistress-tolerant yeast species, Saccharomyces cerevisiae HG1.1, isolated from soil samples in Vietnam. It exhibited significant tolerance toward acetic acid at 4 g/L and ethanol at 14% (v/v) and produced a maximum ethanol concentration of 36.85 g/L with a productivity of 3.07 g/L.h at 40 °C using pineapple waste hydrolysate (PWH) as feedstock.…”