# Mechanistic elucidation of Rhizopus stolonifer-fermented orange peel in enhancing Saccharomyces cerevisiae growth and multi-stress tolerance: process optimization, metabolomics, and pathway analysis

## TL;DR

This study shows that fermenting orange peel with Rhizopus stolonifer boosts yeast growth and stress tolerance, helping improve biofuel production.

## Contribution

The study provides a novel method for valorizing citrus waste through optimized fermentation to enhance yeast performance under industrial stress conditions.

## Key findings

- Fermented orange peel significantly improved yeast viability under ethanol, low pH, and heat stress.
- Optimized fermentation increased flavonoid content, which enhanced yeast physiological functions.
- FOP supplementation boosted sugar consumption and alcohol production in a 15-l fermenter.

## Abstract

Saccharomyces cerevisiae, a pivotal organism in ethanol fermentation, frequently encounters challenges in high-stress industrial settings due to ethanol toxicity, acidic conditions, and thermal stress. This study aimed to optimize the fermentation of orange peel to enhance bioactive compounds and evaluate its impact on the stress tolerance of S. cerevisiae. The optimized conditions led to an increase in the total flavonoid content of the fermented orange peel (FOP). Supplementation with FOP significantly enhanced yeast tolerance; viability exceeded that of the control under 20% ethanol, improved at pH 2.8, and cell counts increased after 24 h at 40 °C. Experiments conducted in a 15-l fermenter demonstrated that FOP significantly promotes sugar consumption and alcohol production. Further mechanistic analysis revealed that hesperidin and rutin in FOP both exhibit potential to enhance yeast tolerance. This approach not only offers a cost-effective method for valorizing orange waste but also enhances yeast productivity and biofuel yield.

•Optimized fermentation of orange peel enhances its bioactive components.•Fermented orange peel promotes the growth of Saccharomyces cerevisiae.•Fermented orange peel enhanced S. cerevisiae tolerance to ethanol, low pH, and heat stress significantly.•Metabolomics shows that bioactive components in FOP enhance the physiological functions of yeast.•Provides an innovative solution for the valorization of citrus waste and cost-effective biofuel production.

Optimized fermentation of orange peel enhances its bioactive components.

Fermented orange peel promotes the growth of Saccharomyces cerevisiae.

Fermented orange peel enhanced S. cerevisiae tolerance to ethanol, low pH, and heat stress significantly.

Metabolomics shows that bioactive components in FOP enhance the physiological functions of yeast.

Provides an innovative solution for the valorization of citrus waste and cost-effective biofuel production.