Exploring Natural Fermented Foods as a Source for New Efficient Thermotolerant Yeasts for the Production of Second-Generation Bioethanol

Abstract

Considering the cost-effectiveness of bioethanol production at high temperatures, there is an enduring need to find new thermotolerant ethanologenic yeasts. In this study, a total of eighteen thermotolerant yeasts were isolated from various natural fermented products in Morocco. Ethanol production using 50 g/L glucose or 50 g/L xylose as the sole carbon source revealed potential yeasts with high productivities and volumetric ethanol productivities at high temperatures. Based on molecular identification, the selected thermotolerant fermentative isolates were affiliated with Pichia kudriavzevii, Kluyveromyces marxianus, and Kluyveromyces sp. During the simultaneous saccharification and fermentation of lignocellulosic biomass at a high temperature (42 °C), the designated yeast P. kudriavzevii YSR7 produced an ethanol concentration of 22.36 g/L, 18.2 g/L and 6.34 g/L from 100 g/L barley straw (BS), chickpea straw (CS), and olive tree pruning (OTP), respectively. It also exhibited multi-stress tolerance, such as ethanol, acetic acid, and osmotic tolerance. Therefore, the yeast P. kudriavzevii YSR7 showed promising attributes for biorefinery-scale ethanol production in the future.

Isolation, screening and identification of ethanol producing yeasts from Ethiopian fermented beverages

“…Morphologically distinct isolates from a given fermented beverage were considered different yeast species and/or strains and were designated differently (data not shown). This is in agreement with several reports that states traditional fermented beverages are an important niche for yeasts in general and ethanol producing yeasts in particular [ 47 , 68 , 69 ].…”

“…However, none of them ferment and assimilate arabinose, mannitol, lactose, xylose and starch ( Sd Table 5 and 6 ) . This is in line with the reports of [ 41 , 42 , 47 ], investigated that most yeast isolates ferment and assimilate glucose, sucrose, maltose, fructose and galactose. In addition, [89] investigated that among 90 Saccharomyces species tested, the majority of strains showed a very poor metabolic index for arabinose and xylose.…”

“…A protocol developed by [47] was used to examine the pH tolerance and requirement of isolates in terms of their glucose fermentation and growth at YPD broth adjusted to different pH values (3, 3.5, 4, 4.5, 5, 5.5, 6 and 6.5). A 1 mL of each yeast isolate (10 8 CFU/mL, adjusted by 0.5 McFarland standard) was inoculated separately into 40 mL YEPD broth medium in bottles and test tubes and incubated at 30 °C.…”

“…Growth response was evaluated via variation in their dry biomass, and fermentation response was estimated by measuring the formation of gas (in terms of the amount of liquid replaced by gas) in the Durham tube. The formation of gas was evaluated every 12 hrs [47] .…”

A Thermotolerant Yeast Cyberlindnera rhodanensis DK Isolated from Laphet-so Capable of Extracellular Thermostable β-Glucosidase Production

“…The focus of our investigation was on identifying thermotolerant yeasts from various samples across different regions, crucial for their potential in industrial applications. Notably, yeasts capable of thriving at 40 • C were considered thermotolerant in our study [40]. To situate our findings, several studies have identified the significance of natural fermented foods, soil and plants as promising sources for isolating thermotolerant yeasts.…”