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Novel potato peel processing method may prove profitable to Penn chip makers

With more than two dozen potato chip makers in Pennsylvania, US, it is no wonder that researchers in Penn State's College of Agricultural Sciences have developed a novel approach to more efficiently convert potato waste into ethanol. The process could reduce biofuel production costs, add value and reduce waste for chip makers.

Developed by Penn State University researchers, the novel simultaneous saccharification process uses potato mash made from peelings and residuals from potato processing to produce ethanol.

Using potato mash made from the peelings and potato residuals from a Pennsylvania food-processor, researchers at the Department of Agricultural and Biological Engineering, Penn State University triggered simultaneous saccharification — the process of breaking down the complex carbohydrate starch into simple sugars — and fermentation — the process in which sugars are converted to ethanol by yeasts or other microorganisms in bioreactors.

The results of the research have been published in a paper entitled “Simultaneous saccharification and fermentation of ethanol from potato waste by co-cultures of Aspergillus niger and Saccharomyces cerevisiae in biofilm reactors” in the journal Fuel.

Novel simultaneous process

The simultaneous nature of the process was innovative, according to researcher Ali Demirci, Professor of Agricultural and Biological Engineering. The addition to the bioreactor of mold and yeast — Aspergillus niger and Saccharomyces cerevisiae, respectively — catalyzed the conversion of potato waste to ethanol.

The bioreactor had plastic composite supports to encourage and enhance biofilm formation and to increase the microbial population. Biofilms are a natural way of immobilizing microbial cells on a solid support material.

Penn State researchers evaluated biofilm formation on the plastic composite supports in the bioreactor. They discovered that when mold and yeast are allowed to form a biofilm, hyphae of the mold provide surface area for the yeasts’ attachment, improving ethanol production (image courtesy Dimerci Lab).

Penn State researchers evaluated biofilm formation on the plastic composite supports in the bioreactor. They discovered that when mold and yeast are allowed to form a biofilm, hyphae of the mold provide surface area for the yeasts’ attachment, improving ethanol production (image courtesy Dimerci Lab).

High-temperature tolerant yeast

In a biofilm environment, microbial cells are abundant and more resistant to environmental stress causing higher productivities. In this application, these benefits were especially important because mold enzyme activity required higher temperature and the yeast had to tolerate this.

Researchers evaluated the effects of temperature, pH and aeration rates in biofilm reactors, and the optimal conditions were found to be 95 degrees Fahrenheit and a pH of 5.8 with no aeration. After 72 hours, the researchers achieved the maximum ethanol concentration of 37.93 grams per liter. The yield was 0.41 grams or ethanol per gram of starch.

These results are promising because the co-culture biofilm reactor provided similar ethanol production — 37.93 grams per leader — compared to the conventional ethanol production — 37.05 grams per liter — which required pre-treatment with added commercial enzymes at a higher temperature. Therefore, eliminating the externally added enzyme and energy costs will certainly reduce the cost of bioethanol production, Demirci explained.

Researchers also evaluated biofilm formation of co-culture on the plastic composite supports using a scanning electron microscope.

Scanning electron microscope images revealed that when mold and yeast are allowed to form a biofilm, hyphae (filaments) of the mold provide surface area for the yeasts’ attachment. That’s a good thing, said researcher Gulten Izmirlioglu, a doctoral student in agricultural and biological engineering on a scholarship from the Turkish Ministry of Education when the study was conducted.

Results significant for industry

The research findings demonstrated that plastic composite supports can be used for simultaneous saccharification and fermentation processes in biofilm reactors with co-cultures when producing ethanol and Izmirlioglu believes the results are significant for the industry.

Overall, bioethanol production from starchy industrial wastes can be improved with the application of biofilm reactors, while the production cost is reduced with integrations of the simultaneous saccharification and fermentation process and co-culturing, she said.

Researcher Ali Demirci adjusts a bioreactor in which potato waste is being used to produce bioethanol with a novel process that simultaneously employs mold and yeast to convert starch to sugar and sugar to ethanol (photo courtesy Dimerci Lab).

Researcher Ali Demirci adjusts a bioreactor in which potato waste is being used to produce bioethanol with a novel process that simultaneously employs mold and yeast to convert starch to sugar and sugar to ethanol (photo courtesy Dimerci Lab).

More efficient bioethanol production is needed to meet the demand for renewable energy and reduce the negative environmental impacts of petroleum fuel, Demirci noted. To make ethanol production cost-competitive, inexpensive, and easily available, feedstocks such as potato mash are needed, as well as improved processing technologies with higher productivities.

This research is of great interest to Keystone Potato Products in Hegins, Pennsylvania, a subsidiary of Sterman Masser Inc. The company is paying attention to this project, hoping this novel approach may help it add more value to its waste potato mash. Industrial food wastes are potentially a great substrate in the production of value-added products to reduce the cost while managing the waste economically and environmentally, said Demirci.

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