BIOETHANOL PRODUCTION FROM AQUEOUS EXTRACTS

OF GRAPE SKINS

Joana A.S. Mendes1,2,*, Ana M.R.B. Xavier1, Dmitry V. Evtuguin1, Luísa P. Cruz Lopes2

a Chemistry Dept. and CICECO, University of Aveiro, 3810-193 Aveiro, Portugal b Environment Dept. and CI&DETS, Polytechnic Institute of Viseu, 3504-510 Viseu, Portugal

*Email: joanamendes@ua.pt

1. INTRODUCTION

Winemaking is an important agricultural sector in the European Union with an annual production of about 175 million hL of wine

[1]. Among by-products of winemaking, pomace, consisting of grape skins, grape seeds and grape stalks, is the most abundant

and needs to be processed according to environmental regulations [2,3]. In particular, grape skins are without advanced

applications, one method involves grape skins’ pre-extraction by water. Aqueous extracts contain essentially oligosaccharides

and monosugars, besides small amounts of tannins and volatile organic acids. Therefore, these extracts may be a promising

source for the production of second generation bioethanol. This work reports the results of bioethanol production from aqueous

extract of grape skins from white pomace produced in Central Region of Portugal.

4. CONCLUSIONS

The fermentation of aqueous extracts of grape skins showed very promising results. This subproduct of wine making,

grape skins of white grape pomace, can be valorizated, and have a high potential for bioethanol production.

ACKNOWLEDGEMENTS

The authors thank Portuguese Foundation for Science and Technology (FCT project PTDC/AGR-AAM/104911/2008) and the

Operation Program of Competitive Factors COMPETE, ref. FCOMP-01-0124-FEDER-008734) for the financial support of this work.

Authors also thank the Quinta do Serrado (Tavfer group) for the samples of grape pomace.

Parameters Fermentation 1

(with yeast extract)

Fermentation 2 (without yeast extract)

S initial (g.L-1) 43.4 44.9

S final (g.L-1) 2.24 2.60

X initial (g.L-1) 0.11 0.09

X final (g.L-1) 4.61 4.52

Ethanol (g.L-1) 22.0 19.2

µ máx (h-1) 0.28 0.39

rs (g.L-1h-1) 1.12 1.15

rp (g.L-1h-1) 1.34 1.22

YX/S (g X/g S) 0.05 0.06

Yp/S (g P/g S) 0.51 0.42

2. EXPERIMENTAL

3. RESULTS AND DISCUSSIONS

REFERENCES

[1] European Comission, What is the Current Situation of the European Union's Wine Sector?,

http://ec.europa.eu/agriculture/markets/wine/index_en.htm, acessed at 11 of February (2011).

[2] Ping, L., Brosseb, N., Sannigrahi, P., Ragauskas, A., Evaluation of Grape Stalks as a Bioresource, Industrial Crops &

Products, 33 (2011) 200.

[3] Prozil, S.O., Evtuguin, D.V., Cruz Lopes, L.P. Chemical Composition of Grape Stalks of Vitis vinifera L. from Red Grape

Pomaces, Industrial Crops & Products (2011), doi:10.1016/j.indcrop.2011.06.035.

Aqueous extract of grape

skins

• Pre-hydrolysis with H2SO4

• Treatment with NH4OH.

Monosaccharides (S) and ethanol (P)

concentration analysed by HPLC.

Biomass concentration (X) determined by

optical density.

Batch

tests

Fermented

average

Figure 1. Kinetic monitoring of biomass growth, consumption

of monosaccharides and ethanol production during: fermentation 1

(with yeast extract ) and fermentation 2 (without yeast extract).

Table 1. Fermentation parameters.

PH analysis. Saccharomyces cerevisiae

(28ºC, 180 rpm)

Calibration curve: optical density vs biomass

concentration.

Supplementary medium:

1) With or without yeast

extract

2) (NH4)2HPO4

3) (NH4)2SO4

4) MgSO4.7H2O

Aqueous extracts of grape skins were successfully fermented by

S. cerevisae.

Suplementation with yeast extract did not show great

advantages in fermentations.

The conversion of hexoses to ethanol without yeast extract

was high and 19.2 g.L-1 of ethanol and a yield of 0.42 g

ethanol/g sugar were obtained.

There is no need to add the yeast extract, because aqueous

extract of grape skins certainly has already enough

nutrients and enzymatic factors for the conversion of sugars

into ethanol.