Revitalizing the ethanologenic bacterium Zymomonas mobilis for sugar reduction in high-sugar-content fruits and commercial products

Mimi Hu,Mian Li,Shihui Yang,Jun Du,Xiangyu Chen,Ju Huang

doi:10.1186/s40643-021-00467-2

Abstract

The excessive consumption of sugars can cause health issues. Different strategies have been developed to reduce sugars in the diets. However, sugars in fruits and commercial products may be difficult to reduce, limiting their usage among certain populations of people. Zymomonas mobilis is a generally recognized as safe (GRAS) probiotic bacterium with the capability to produce levan-type prebiotics, and thrives in high-sugar environments with unique characteristics to be developed for lignocellulosic biofuel and biochemical production. In this study, the sugar reduction capabilities of Z. mobilis ZM4 were examined using two fruits of pear and persimmon and three high-sugar-content commercial products of two pear pastes (PPs) and one Chinese traditional wine (CTW). Our results demonstrated that Z. mobilis ZM4 can utilize sugars in fruits with about 20 g/L ethanol and less than 5 g/L sorbitol produced within 22 h using pears, and about 45 g/L ethanol and 30 g/L sorbitol produced within 34 h using persimmons. When PPs made from pears were used, Z. mobilis can utilize nearly all glucose (ca. 60 g/L) and most fructose (110 g/L) within 100 h with 40 ~ 60 g/L ethanol and more than 20 g/L sorbitol produced resulting in a final sorbitol concentration above 80 g/L. In the high-sugar-content alcoholic Chinese traditional wine, which contains mostly glucose and ethanol, Z. mobilis can reduce nearly all sugars with about 30 g/L ethanol produced, resulting in a final ethanol above 90 g/L. The ethanol yield and percentage yield of Z. mobilis in 50 ~ 60% CTW were 0.44 ~ 0.50 g/g and 86 ~ 97%, respectively, which are close to its theoretical yields—especially in 60% CTW. Although the ethanol yield and percentage yield in PPs were lower than those in CTW, they were similar to those in fruits of pears and persimmons with an ethanol yield around 0.30 ~ 0.37 g/g and ethanol percentage yield around 60 ~ 72%, which could be due to the formation of sorbitol and/or levan in the presence of both glucose and fructose. Our study also compared the fermentation performance of the classical ethanologenic yeast Saccharomyces cerevisiae BY4743 to Z. mobilis, with results suggesting that Z. mobilis ZM4 had better performance than that of yeast S. cerevisiae BY4743 given a higher sugar conversion rate and ethanol yield for sugar reduction. This work thus laid a foundation for utilizing the advantages of Z. mobilis in the food industry to reduce sugar concentrations or potentially produce alcoholic prebiotic beverages.Graphical

Highlights

Consumption of high-sugar content drinks and products affect the absorption of nutrients such as protein and vitamins, and increase the risk of kidney stones, obesity, diabetes, cardiovascular disease, oral diseases, and even cancers (Bantle et al 2009; Delli Bovi et al 2017; Febbraio et al 2021; Johnson et al 2018; Kohn et al 2017; Taylor et al 2021)
Our results demonstrated that glucose is the preferable sugar compared to fructose for Z. mobilis, and sorbitol cannot be produced by Z. mobilis in monosaccharide medium of glucose or fructose (Fig. 1)
Sorbitol formation in Z. mobilis fermentations is a result of glucose-fructose oxidoreductase (Gfo), which is involved in the complete catalytic cycle of oxidation of glucose to gluconate with concomitant reduction of fructose to sorbitol (Additional file 1: Fig. S1)

Summary

Introduction

Consumption of high-sugar content drinks and products affect the absorption of nutrients such as protein and vitamins, and increase the risk of kidney stones, obesity, diabetes, cardiovascular disease, oral diseases, and even cancers (Bantle et al 2009; Delli Bovi et al 2017; Febbraio et al 2021; Johnson et al 2018; Kohn et al 2017; Taylor et al 2021). Besides controlling the diet and pharmacotherapy treatment (Apovian and Gokce 2012), different strategies have been developing to address the dilemma associated with the popularity of consuming high-sugar-content products and the pursuit of a healthy lifestyle with the usage of sugar substitutes such as sugar alcohols and artificial sweeteners. S. cerevisiae SY was used to ferment Dangshan pear with 14.10 ± 0.27% (v/v) ethanol produced from an initial 240 g/L total sugar within 15 days (Yang et al 2019). S. cerevisiae and Acetobacter aceti were used to ferment waste pineapple residues for the production of fruit wine and vinegar in two consecutive steps for approximately 40 days with a final 7% (v/v) ethanol and 5% (v/v) acetic acid obtained (Roda et al 2017)

Methods

Results

Conclusion