Glucose vs. Starch Pellets Fermentation by Yeast

INTRODUCTION By the process of fermentation, yeast

perform internal oxidation and reduction reactions to convert carbohydrates, such as glucose and starch pellets, to energy, also creating by-products of CO2 and ethanol. For this experiment, Optical Density, Index of Refraction, Specific Gravity and % Alcohol and Sugar were measured.

(Mainly OD was used to determine difference in Biomass)

Materials 2 500 mL Erlenmeyer Flasks 2 Stir Plates 2 Sets Tubing 2 250 mL Beakers 2 Stoppers Hydrometer Refractometer Graduated Cylinder (Future-Use

Pipette) Spec 20

Methods In each Erlenmeyer Flask, 500 mL of

water was added. In Flask 1: 5.0029 g Glucose, 1.2501 g Yeast Extract, 0.1525 g K2HPO4, and 0.5011 g Baker’s Yeast was added to achieve a concentration of 10 g/L glucose. The first three ingredients are used as substrate/nutrients or yeast, the fourth ingredient is the living yeast.

In Flask 2, 5.0011 g Starch Pellets, 1.2703 g Yeast Extract, 0.1155 g K2HPO4, and 0.5150 g living Yeast added to achieve a concentration of 10 g/L starch pellets.

Methods2 Each Flash was then placed on a stir

plate and topped with rubber stoppers to prevent oxygen from entering. There parameters ensure a suspended culture in an anaerobic, batch environment.

Data Summary

Glucose (10 g/L)

Day OD ⁰ Brix S.G.% Sugars

Alcohol by Volume (%)

00.71

1 1.01.00

0 1 0

10.89

5 1.01.01

0 1 0

21.21

2 1.21.08

0 0.5 1

31.09

0 1.01.06

0 0.4 1

40.98

5 0.91.04

0 0.2 1.1

50.88

9 0.81.01

0 0 1.1

60.87

5 0.81.00

0 0 1.2

Starch (10 g/L)

Day OD ⁰ Brix S.G.% Sugars

Alcohol by Volume (%)

0 0.561 11.06

0 1.2 0

1 0.677 11.06

0 1.1 0.2

2 0.792 0.81.04

0 1 0.2

3 0.578 0.51.02

0 0.8 0.5

4 0.436 0.21.01

0 0.2 0.8

5 0.416 01.00

0 0 1

6 0.440 01.00

0 0 1

Questions How do I know if my OD reading is from

substrate of biomass. At time zero, you can assume it’s mostly substrate but as S is utilized how can you tell what %OD is from biomass vs. substrate? COD?

Problems

Cant have OD reading over 1, and after diluting (1:10) still used readings from (0-1).

Don’t know the exact volumes in reactors as time went on, need info to exact %sugars since use per 100g soln to equate.

Hard time figuring biomass yield and substrate utilization. Directly related. Thought could get latter through %sugar, but not 100% of the substrate is sugar. How to fix?

After converting mu from day to 1/hr, it changed rxb from 56 to 2. so when decay rate was figured, it didn’t make sense bc it basically equalled biomass formation rate.

Which mu to use, monod model or graphs. If model, then would mu be the same since substrate concentrations and innoculum were the same?

I used OD reading at end of exponedtial phase on graph to calculate biomass formation. Is this correct?

Never had a starch calibration curve.