Beverages like beer, whisky, wine, and shochu come from agricultural products—malt, grapes, sweet potato, and so on—which are fermented using yeast to produce their alcohol content. The resulting alcohol is not only a luxury that makes life more comfortable and enjoyable; it can also be used as a source of fuel to make our daily life more comfortable. Our main energy sources today, petroleum and natural gas, are limited and will one day run out.
Our existing energy sources increase the amount of carbon dioxide in our atmosphere, which may be one of the key factors driving global warming (the major causes of global warming are still a matter of scientific debate). In an effort to address these issues, Suntory has been involved in a research project aimed at producing alcohol from waste trees and grass.
* We conducted this research participating in a project of the New Energy and Industrial Technology Development Organization (NEDO).
There are concerns that using large amounts of agricultural products to produce alcohol could create food shortages for people and livestock, or drive up crop prices and make these products more difficult to come by. To avoid these risks, we came up with the idea of producing ethanol from trees and grass that would otherwise be discarded as waste—a strategy that would produce fuel while mitigating one of the suspected major causes of global warming. Trees and grass absorb carbon dioxide from the air and emit oxygen in the process of photosynthesis. Using them to produce alcohol for fuel sets up a cycle whereby the carbon dioxide emitted from burning the alcohol will eventually be absorbed again by the trees and grass for their growth. This means that unlike energy from petroleum, energy from biomass materials does not result in an overall increase in the amount of carbon dioxide in the air.
The starch found in agricultural products like malt and sweet potatoes consists of long chains of glucose bonded together. Alcohol is produced by breaking down these chains using malt or Aspergillus oryzae enzymes and then letting yeasts feed on the resulting glucose. On the other hand, the major components of "biomass," trees and grass, are cellulose, hemicellulose, and lignin, which constitute a very hard structure.
Cellulose, like starch, is made of glucose—but the glucose units are bonded in a different way. These bonds cannot be broken down with the enzymes used for conventional alcohol production. The enzymes that can decompose cellulose act slowly and are costly to produce. We sought to make this decomposition process cheaper and more efficient by and reduce costs by giving the yeast itself the ability to produce the enzymes that can decompose cellulose into glucose. Hemicellulose presented an additional challenge in that is primarily composed of another type of sugar called xylose, which does not produce alcohol with yeast. Our team therefore had to come up with an ingenious strategy to give yeast the ability to efficiently consume xylose and produce alcohol.
The method we used was called “consolidated bioprocessing for simultaneous saccharification and fermentation,” or CBP for short. It gave yeast the ability to produce the enzymes needed to decompose biomass materials and produce alcohol as a byproduct. Genetic recombination was used to create yeasts that could not only decompose cellulose and hemicellulose, but also had the ability to efficiently ferment xylose. A unique marker recycling system allowed us to introduce the multiple genes needed to create yeasts with so many different characteristics.
The goal of this study was to use yeasts to produce alcohol from biomass materials. However, biomasses have the potential to generate not only alcohol, but many other substances as well—basic materials that could replace petroleum products or useful enzymes among them. We will continue to use sophisticated biotechnologies to convert waste and unused materials into valuable resources, resulting in healthy sustainable material cycles that will serve our planet for generations to come.