Methods for fermenting carbohydrate-rich crops

Abstract

A method for fermenting carbohydrate-rich crops is provided. Sugar beet, sugar cane, sweet sorghum, tropical maize hybrids and fruits are rich in simple sugars; potato, sweet potato, cassava and yam are rich in starch; and Jerusalem artichoke is rich in inulin. This method uses vacuum infusion to infuse yeast into the intercellular space (apoplast) of the parenchyma tissue. The simple sugars diffuse into the apoplast, come into contact with the yeast and produce ethanol. Ethanol can be extracted from the crop by vacuum stripping or crushing or can be left inside the starchy crop to preserve it. In some variants, pectinase enzymes degrade the parenchyma cell walls to speed up diffusion of simple sugars to the yeast, speed up diffusion of amylase to starch granules or speed up diffusion of inulinase to insoluble inulin.

Description

PRIORITY DATA[0001]This patent application is a non-provisional application with priority to U.S. Provisional Patent App. No. 62 / 127,637, filed Mar. 3, 2015, and to U.S. Provisional Patent App. No. 62 / 139,881, filed Mar. 30, 2015, each of which is hereby incorporated by reference herein.FIELD OF THE INVENTION[0002]The present invention generally relates to methods for fermenting carbohydrate-rich crops.BACKGROUND OF THE INVENTION[0003]Many fermentation organisms convert carbohydrates to ethanol. The most widely used fermentation organisms, brewer's yeast and baker's yeast, are strains of Saccharomyces cerevisiae. Ethanol has significant economic value as beverages, transportation fuels and precursors for other organic compounds.[0004]Fermentation organisms can directly convert glucose, fructose, maltose (glucose dimer) and sucrose (glucose-fructose dimer) to ethanol. Herein, monomers and dimers of glucose and fructose will be referred to as simple sugars and fermentation organisms t...

AI Technical Summary

Benefits of technology

[0040](b) exposing the carbohydrate-rich plant parenchyma tissue to a gas-phase preparation pressure for a preparation time, the gas-phase preparation pressure being less than atmospheric pressure;

[0041](c) exposing the carbohydrate-rich plant parenchyma tissue to an aqueous reagent solution at a reagent temperature and a gas-phase infusion pressure, the aqueous reagent solution containing a fermentation organism and the gas-phase infusion pressure being less than atmospheric pressure, and

[0042](d) maintaining a gas-phase fermentation pressure for a fermentation time to produce the fermentation products within the carbohydrate-rich plant parenchyma tissue, wherein the gas-phase fermentation pressure is greater than two times the gas-phase infusion pressure and wherein at least 25% of the mass of the fermentation products is ethanol.

Problems solved by technology

This means that fermenting an 18% sugar solution will result in a temperature rise of 34° C., which means that cooling of the fermentation medium is required.

All of these techniques are quite capital-intensive.

The parenchyma cells are packed tightly together, but there are small gaps between them because the packing is imperfect.

This causes the contents of the vacuoles to leak out of the parenchyma cells and causes enzymes to more easily diffuse into the vacuoles.

Pectate lyase and polygalacturanase, when they degrade pectin, also produce methanol which is often an undesirable product when producing ethanol.

One significant problem with current techniques for fermenting sugars to ethanol is bacterial contamination, in particular contamination by Lactobacillus.

Without wishing to be bound by any particular theory, it is believed that turbulent mixing propagates bacteria throughout the fermentation medium, and since the contaminating bacteria can out-compete yeast, there is significant contamination.

Because the parenchyma cells are so small, it takes a lot of energy to crush them or to extract the sugar from them with hot water.

Almost 35% of the capital and operating costs of producing sugar from stalks is due to the cost of crushing.

Similarly, much of the cost of producing sugar from sugar beets is due to the cost of hot water extraction.

Since transportation costs are primarily a function of volume (and not weight), and since crops are often harvested significant distances from where they're processed, it is quite expensive to transport sugars at such low densities since only 5% to 10% of the volume of a truck is taken up by sugar.

Since the outer layer of the sugar beets are often abraded and damaged by harvesting, microorganisms can more easily penetrate the outer layers of the sugar beet, leading to sugar losses due to fermentation to lactic acid and acetic acid.

Similarly, sugar cane, sweet sorghum and tropical maize hybrid are more susceptible to microorganisms penetrating the pith because the cane has been cut open into billets during harvesting.

Much of the capital cost and operating cost of producing ethanol from carbohydrate-rich crops is the cost of heating the feedstock.

Another significant capital cost and operating cost of producing ethanol from carbohydrate-rich crops is the cost of cooling the fermentation reactor.

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