[Paper Review] Electro-stimulation of Saccharomyces cerevisiae wine yeasts by Pulsed Electric Field and its effect on fermentation performance

Jessy Mattar, Mohammad Turk+4 more|arXiv (Cornell University)|Apr 21, 2013

Microbial Inactivation Methods40 references4 citations

TL;DR

This study investigates pulsed electric field (PEF) pre-treatment of *Saccharomyces cerevisiae* wine yeast (Actiflore F33) to enhance fermentation performance. PEF at 100 and 6000 V/cm significantly accelerated sugar consumption during the lag phase, with fructose consumption 3.98 times higher at 6000 V/cm after 40 hours, and reduced mass loss by 30% by 120 hours—achieving in 120 hours what control samples took 140 hours to reach.

ABSTRACT

The batch fermentation process, inoculated by pulsed electric field (PEF) treated wine yeasts (S. cerevisiae Actiflore F33), was studied. PEF treatment was applied to the aqueous yeast suspensions (0.12 % wt.) at the electric field strengths of E=100 and 6000 V/cm using the same pulse protocol (number of pulses of n=1000, pulse duration of ti=100 mks, and pulse repetition time of dt=100 ms). Electro-stimulation was confirmed by the observed growth of electrical conductivity of suspensions. The fermentation was running at 30°C for 150 hours in an incubator with synchronic agitation. The obtained results clearly evidence the positive impact of PEF treatment on the batch fermentation process. Electro-stimulation resulted in improvement of such process characteristics as mass losses, consumption of soluble matter content (°Brix) and synthesis of proteins. It also resulted in a noticeable acceleration of consumption of sugars at the initial stage of fermentation in the lag phase. At the end of the lag phase (t=40 hours), consumption of fructose in samples with electrically activated inocula exceeded fructose consumption in samples with control inocula by 2.33 times when it was activated at E=100 V/cm and by 3.98 times after treatment at E=6000 V/cm. At the end of the log phase (120 hours of fermentation), 30% mass reduction was reached in samples with PEF-treated inocula (E=6000 V/cm), whereas the same mass reduction of the control sample required approximately, 20 hours of extra fermentation. The possible mechanisms of electro-stimulation are also discussed in details.

Motivation & Objective

• To evaluate the impact of pulsed electric field (PEF) pre-treatment on *Saccharomyces cerevisiae* fermentation performance in wine production.
• To determine if electro-stimulation via PEF enhances metabolic activity during the lag and log phases of fermentation.
• To quantify improvements in fermentation kinetics, including sugar consumption, mass loss, and protein synthesis.
• To identify optimal PEF parameters (1000 pulses, 100 µs pulse width, 100 ms repetition) for maximizing fermentation efficiency.
• To explore the underlying mechanisms of electro-stimulation in yeast cells at the cellular and metabolic level.

Proposed method

• Pre-treatment of *S. cerevisiae* suspensions (0.12% wt.) with PEF at electric field strengths of 100 V/cm and 6000 V/cm.
• Application of identical pulse protocol: 1000 pulses, 100 µs pulse duration, 100 ms pulse repetition time.
• Monitoring of electrical conductivity to confirm electro-stimulation effects in yeast suspensions.
• Conducting batch fermentation at 30°C with continuous agitation for 150 hours to assess fermentation dynamics.
• Measuring key fermentation parameters: mass loss, °Brix reduction, fructose consumption, and protein synthesis over time.
• Comparing PEF-treated inocula with untreated control samples to evaluate performance differences.

Experimental results

Research questions

• RQ1 Does PEF pre-treatment of *S. cerevisiae* significantly accelerate sugar consumption during the initial lag phase of wine fermentation?
• RQ2 To what extent does PEF treatment enhance mass loss and reduction of soluble solids (°Brix) during fermentation compared to controls?
• RQ3 How does PEF treatment affect protein synthesis and metabolic activity in *S. cerevisiae* during batch fermentation?
• RQ4 What is the relationship between PEF electric field strength (100 V/cm vs. 6000 V/cm) and fermentation performance improvement?
• RQ5 What are the potential cellular mechanisms underlying the observed electro-stimulation effects in yeast cells?

Key findings

• PEF pre-treatment at 6000 V/cm increased fructose consumption by 3.98 times compared to control after 40 hours of fermentation.
• At 40 hours, fructose consumption in PEF-treated samples (6000 V/cm) was 2.33 times higher than in controls at 100 V/cm.
• By 120 hours, samples with PEF-treated inocula (6000 V/cm) achieved 30% mass reduction, a result that required an additional 20 hours in the control sample.
• Electro-stimulation was confirmed by measurable increases in electrical conductivity of yeast suspensions post-PEF treatment.
• PEF treatment enhanced overall fermentation performance, including faster consumption of soluble matter and improved protein synthesis.
• The study suggests that PEF pre-treatment significantly accelerates the initial fermentation phase, particularly during the lag phase, without altering the core fermentation protocol.