WO2001007563A1

WO2001007563A1 - Device for surface culture fermentation

Info

Publication number: WO2001007563A1
Application number: PCT/US2000/021994
Authority: WO
Inventors: James Drysdale
Original assignee: Alltech, Inc.
Priority date: 1999-07-28
Filing date: 2000-07-28
Publication date: 2001-02-01
Also published as: GB0203335D0; AU7825700A; GB2368347B; GB2368347A

Abstract

A fermentation device (10) is described whereby a single fermentation vessel (1) is used to conduct deep bed solid state fermentation of microorganisms to generate useful products. The device incorporates an assembly for agitation (9) of the fermentation substrate which allows injection of fluids into the substrate bed to maintain homogenous culture conditions throughout the substrate regardless of the depth of the substrate bed.

Description

DEVICE FOR SURFACE CULTURE FERMENTATION

FIELD OF THE INVENTION

The present invention relates to a vessel or device utilized to conduct surface culture fermentation, also referred to as solid-state fermentation and method of use thereof.

BACKGROUND OF THE INVENTION

Submerged liquid fermentation (SmF) is traditionally used in the United States for fermentation processes such as, for example, the production of microbially-derived molecules such as enzymes and antibiotics. Solid state fermentation (SSF) refers to the growth of microorganisms on solid (or substantially solid) materials, e.g., without the presence of free flowing liquid. Solid-state fermentation technology has advanced in some countries, notably Japan. In Japan SSF has advanced to a point such that automated fermentation plants with significant economic advantages over conventional SmF processes have been established, however, the details of these processes remain proprietary and are, therefore, confidential information. Examples of existing uses of SSF include fermented oriental foods, mold-ripened cheese, and compost.

SSF (also known as Surface Culture Fermentation) presents advantages over SmF. Among the advantages are: decreased requirement for absolutely sterile fermentation conditions, high productivity per unit volume of the reactor, use of lower-cost raw materials such as unrefined agricultural residues as substrates, reduced energy requirement, low wastewater output, and low capital investment. "Semi-sterile" fermentation conditions are possible with SSF in part because of the restricted availability of free water to contaminating organisms such as yeasts and bacteria. The reduced energy requirement in SSF derives partially from greater ease of aeration of solid or semi-solid substrates. Submerged culture fermentation requires sparging of oxygen through the media, which is often difficult due to low solubility of oxygen in water. Commonly used substrates include wheat bran, wheat straw, cereal grains, rice hull, and sugar beet pulp.

The industrial acceptance of SSF worldwide has been hindered by the lack of fermentation equipment and materials handling systems, the dearth of knowledge of physiology and growth mechanisms of microbes on solid media, and the inadequacy of control schemes for regulating heat and moisture levels in the reactors. In particular, the lack of a suitably efficient bioreactor for high-volume (i.e. production scale) SSF has hindered the development of SSF technology.

The most common devices currently in use for SSF are systems based on shallow trays. These tray systems have numerous disadvantages, including requirements for large amounts of warehousing space, significant requirements in terms of manual labor for conducting fermentations, difficulty in maintaining aseptic and/or anaerobic conditions when required, and difficulty in maintaining homogenous fermentation conditions within and between individual fermentation trays. Consequently, a means for conducting SSF which allows use of a deeper bed of fermentation substrate than is possible for existing tray systems is required. Use of a deep bed of fermentation substrate, however, raises additional issues. In particular, it is critical to maintain homogeneous culture conditions, i.e., optimal temperature, humidity, partial pressure of oxygen within a fermentation bioreactor but more critically within the deep bed of fermentation substrate itself.

Thus, an improved device for conducting solid-state fermentation would represent a significant benefit to innumerable industries whose products are based on fermentation technology. A device allowing efficient SSF on a deep bed of fermentation substrate would be of particular benefit. In order to allow such "deep-bed" SSF, such a device would require a means for maintaining homogeneous culture conditions throughout the entire fermentation substrate bed.

SUMMARY OF THE INVENTION

The device of the invention comprises a multipurpose fermentation tank in which the growth of various microorganisms may be conducted upon solid (or substantially solid substrates), and in which the conditions and environment necessary for their growth may be strictly controlled in an enclosed, sanitary system. The device is arranged so that it may serve as a feπnentation tank, extraction vessel, and drier, invalidating the need for separate vessels for each function, reducing the need for handling and risk of contamination, and reducing the labor needed to conduct solid-state fermentations.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a cut away schematic view of one embodiment of the Solid State Fermenter of the present invention showing the interior of the fermentation tank and a movable means for agitation of the fermentation substrate (the agitation assembly).

DESCRIPTION OF THE INVENTION

A presently preferred embodiment of the current invention is provided in Figure 1. In general, Figure 1 describes a solid state fermentation device 10 comprised of a tank 1 which contains the fermentation substrate. In a presently preferred embodiment of the current invention, tank 1 is a stainless steel, cylindrical tank. However, it may be appreciated that a tank of any suitable shape and any suitable material may be incorporated into the design of the present invention. Tank 1 is provided with a selectively porous false bottom 3 such that heated and/or humidified air (conditioned air) or another fluid (liquid or other gas) can be injected into tank 1 via an intake port 5. A presently preferred embodiment of the current invention provides that the porous false bottom 3 is a slotted, stainless steel flat bottom. However, it may be appreciated that any design of selectively porous false bottom known in the art, such as a slotted bottom whereby said slots may be opened or closed, a perforated or mesh screen bottom of metal or any other suitable material currently used in the art, or a permeable or semi-permeable bio-membrane, is envisioned in the design of the current invention. Fluid passing through intake port 5 may be passed through a desired fermentation substrate within the body of cylindrical tank 1. The forced air or liquid normally exits the cylindrical tank 1 via an exhaust port 7. Alternatively, however, the fluid flow can be reversed such that fluid can be reverse-circulated through the substrate within tank 1 via entry through exhaust port 7 and exit via intake port 5. Thus, a desirable fluid can enter the tank 1 and pass through the substrate either from the bottom or from the top of the substrate column within tank 1.

It can be appreciated that the fluid (e.g., conditioned air or liquid) which is utilized may also be re-circulated within the tank, for the purposes of maintaining homogenous fermentation conditions or for drying the fermentation substrate. Suitable homogenous fermentation conditions for culture of various microorganisms, e.g., temperature, humidity, C0₂, and concentration of oxygen, are known in the art, but may vary in accordance with the particular microorganism to be cultured. Accordingly, it should be appreciated that the design of the present invention allows the condition of the fluid entering or exiting tank 1 via intake port 5 or exhaust port 7 to be monitored and suitably altered for controlling, e.g., temperature, C0₂ content, pH and the like of the fermentation substrate and/or the interior of the fermentation vessel or tank. Figure 1 also depicts an agitation assembly 9 comprised of a variable speed motor drive (not shown), located external of the body of the fermentation vessel or tank 1, which drives hollow shaft 11 and the attached knives or paddles 13. The hollow shaft 11 may be driven or rotated in either a clockwise or counter-clockwise direction, depending on the desired function.

The hollow shaft 11 is also equipped with a means (not shown) for moving the shaft vertically (raising and lowering the shaft) which is located adjacent the variable speed motor drive and external to the body of fermentation tank 1, such that application of the moving means allows hollow shaft 11 to be raised or lowered along the vertical axis of hollow shaft 11 within the fermentation vessel to position paddles 13 at a desired level. Paddles 13 may be positioned at a desired depth within the body of tank 1 and likewise to a desired level within a substrate located within the tank l. Thus, uniform agitation of the substrate can occur at a desired speed, depth and direction of rotation of paddles 13 within tank 1.

Paddles 13 are attached to hollow shaft 11 by a plurality of horizontal arms 15, the number of which is dependent on the diameter of the vessel and the desired number of paddles 13. A plurality of paddles 13 may extend outward and vertically from said horizontal arms 15. In one embodiment, the plurality of paddles 13 descend vertically from arms 15 in a manner such that they may enter any fermentation substrate contained within the vessel. As set forth in greater detail below, the paddles (via means of a pivotal attachment to horizontal arms 15) may serve multiple functions, e.g., as a paddle for agitation, as a knife for smoothing out lumpy or uneven substrate or to evacuate substrate from tank 1 via discharge port 21.

The vertically descending (knives) or paddles 13 may, in turn, be fitted with smaller side (knives) or blades 17 which extend horizontally at a desired angle such that, when the horizontal arms 15 are rotated the substrate bed receives adequate but gentle movement during fermentation. In a presently preferred embodiment, vertical paddles 13 are of the type similar to those described in U.S. Patent No. 4,333,393. It can be appreciated by the skilled artisan that other paddle configurations are possible and even desirable depending upon the choice of substrate, the viscosity of the substrate (amount of moisture and the like) and the desired end fermentation product.

The horizontal arms 15 and vertically oriented paddles 13 further have a channel therethrough which is in fluid communication with the hollow shaft 11 such that said channel serves, in conjunction with the hollow shaft 11 as a conduit for addition or removal of fluids at the base 19 of vertical paddles 13. This conduit thereby permits injection of fluids as desired into the fermentation substrate via a pumping assembly (not shown) located external to the fermentation tank 1. A desirable, if not a key feature of the agitation assembly 9 is that hollow shaft 11 is freely movable along its vertical axis by the aforementioned moving means such that the horizontal arms 15, and the vertical paddles 13 attached thereto may be raised and lowered within the body of tank 1 and into the fermentation substrate to any desired level.

In one embodiment, the vertical paddles 13 are arranged such that a partial pivoting is possible at the point at which the paddles 13 connect to the horizontal arm 15. In this manner, depending on the direction of rotation of the horizontal arms 15 effected by the motor drive arrangement, the angle of paddles 13 is altered by contact with the fermentation substrate, allowing paddles 13 to serve several functions.

In one embodiment, paddles 13 when rotated in a first direction, e.g., in a clockwise direction, can serve in a standard capacity to generally stir or agitate the solid substrate within tank 1. Alternatively, when rotated in a second, e.g., a counter-clockwise direction the paddles 13 may be so attached as to pivot and change the angle of attack of the paddle blades 13. Thus, when the hollow shaft 11 is lifted or raised along the vertical axis to a vertically retracted position and then is rotated in the second direction (counter clockwise), paddles 13 (knives) may be used, e.g., to smooth an uneven mass of substrate which can result as the tank 1 is filled with substrate. Likewise, upon completion of the solid state fermentation process, rotation of the agitation assembly 9, (paddles 13) in the second or counterclockwise direction can cause the contents of tank 1 to be emptied or forced from tank 1 through discharge port 21.

The device of the invention may also be equipped with one or more observation ports 23 and one or more sampling ports 25 for monitoring of the fermentation process. Advantages provided by the fermentation device described in the present invention include, but are not limited to:

1) Applicability to a wide range of organisms and substrates;

2) Use as multi-purpose vessel, including as a fermentation tank, an extraction vessel, a drying vessel, or for discharge of fermentation substrate;

3) Ability to lift the agitation device clear of the fermentation substrate such that flow of conditioned air or gaseous mixtures is uniform throughout the entire mass of substrate;

4) Ability to use said agitation device both to level the mass of fermentation substrate and to discharge said substrate after fermentation with reduction in moving parts and consequent ease of operation and reduction in capital costs;

5) Ability to deliver (conduct) fluids from an external source to any point on or in the fermentation substrate via the hollow shaft of the agitation device, i.e. the hollow shaft, horizontal arms, and vertical paddles coupled with said paddles vertical movability.

Accordingly, it is an object of the present invention to provide an improved vessel or device to conduct surface culture fermentation, also referred to as solid-state fermentation.

It is also an object of the invention to provide an improved method of solid state fermentation utilizing the device of the invention. The method of the invention provides steps which include monitoring and controlling (adjusting) of the fermentation conditions (e.g., temperature, pH, viscosity, humidity (or other fluid content), C0₂ levels) to desired or predetermined levels. The method also provides steps for selected agitation of the fermentation substrate to produce a desired uniform consistency of the substrate. The monitoring, adjusting and agitating steps provided by the method thereby result in a more complete utilization (exhaustion) of the available substrate and produce a higher yield of fermentation product.

Additional objects, advantages, and other novel features of the invention will be set forth in part in the description that follows, and in part will become apparent to those skilled in the art upon examination of the foregoing or may be learned with practice of the invention.

The foregoing description of the preferred embodiment of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiment was chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.

Claims

What is claimed is:

1. A device for conducting fermentations involving growth of microorganisms utilizing a substantially solid fermentation substrate comprising: a vessel having an upper surface, a lower surface and a plurality of side surfaces, said upper, lower, and side surfaces defining an interior body of said vessel; movable means for agitation of said substantially solid substrate contained within said vessel; means for introduction into and removal from said interior body of said vessel said suitable substantially solid substrate. means for introduction into and removal from said interior body of a fluid from said vessel;

2. The device of Claim 1, whereby said side surface defines a substantially cylindrical shape of said vessel.

3. The device of Claim 1, whereby said vessel is equipped with a means for rotatably moving said means for agitation of said substantially solid substrate in a first and a second direction.

4. The device of Claim 1, whereby said vessel is equipped with a means for moving said means for agitation of said substantially solid substrate vertically, allowing raising and lowering of said means for agitation of said substantially solid substrate to any desired position within said interior of said vessel.

5. The device of Claim 1, whereby said vessel is equipped with a selectively porous false bottom defining a space between said false bottom and said lower surface of said vessel, and which provides support for said substantially solid substrate.

6. The device of Claim 5, whereby said vessel is equipped with at least one port in fluid communication with the space between said selectively porous false bottom of said vessel and said lower surface of said vessel or tank, allowing introduction into and withdrawal of fluids from said vessel into contact with said selectively porous false bottom and thereby selectively into contact with the lower surface of said substantially solid fermentation substrate.

7. The device of Claim 1, whereby said vessel is equipped with at least one port in fluid communication with the interior of said vessel between said selectively porous false bottom and said upper surface of said vessel, allowing introduction into and withdrawal of fluids from said vessel.

8. The device of Claim 1, whereby said vessel is equipped with a plurality of ports allowing communication therethrough with said interior of said vessel.

9. The device of Claim 8, whereby said vessel is equipped with at least one port suitable for removal of a portion or the entirety of said substantially solid fermentation substrate.

10. The device of Claim 1, whereby said movable means for agitation of said substantially solid substrate contained within said vessel comprises: at least one hollow shaft depending vertically from said upper surface of said vessel; a plurality of arms extending horizontally from said hollow shaft, said arms containing channels therethrough in fluid communication with said hollow shaft; at least one paddle depending vertically from each of said arms, said paddles containing channels therethrough in fluid communication with said horizontal arms, and therethrough in fluid communication with said hollow shaft.

11. The device of Claim 10, whereby said movable means for agitation of said substantially solid substrate may be rotatably moved in a first and a second direction.

12. The device of Claim 10, whereby said movable means for agitation of said substantially solid substrate may be moved vertically, allowing raising or lowering of said agitation assembly to any desired level within said vessel and thereby to any desired level within said substantially solid fermentation substrate.

13. The device of Claim 10, whereby said paddles depending vertically from said horizontal arms are hingedly connected to said horizontal arms such that, when said movable means for agitation of said substantially solid substrate is rotatably moved in a first direction, said paddles serve as stirring devices to stir or agitate said substantially solid substrate.

14. The device of Claim 10, whereby said paddles depending vertically from said horizontal arms are hingedly connected to said horizontal arms such that, when said movable means for agitation of said substantially solid substrate raised to a desired level within said substrate and is rotatably moved in a second direction, said paddles serve to smooth uneven substrate mass, or to empty or discharge said substrate from said vessel.

15. A movable means for agitation of a substantially solid substrate contained within a fermentation vessel comprising: at least one hollow shaft depending vertically from an upper surface of said vessel; a plurality of arms extending horizontally from said hollow shaft, said arms containing channels therethrough in fluid communication with said hollow shaft; at least one paddle depending vertically from each of said arms, said paddles containing channels therethrough in fluid communication with said horizontal arms, and therethrough in fluid communication with said hollow shaft. 15

16. The device of Claim 15, whereby said movable means for agitation of said substantially solid substrate may be rotatably moved in a first and a second direction.

17. The device of Claim 15, whereby said movable means for agitation of said substantially solid substrate may be moved in a vertical direction, allowing raising or lowering of said agitation assembly to any desired level within said vessel and thereby to any desired level within said substantially solid fermentation substrate.

18. The device of Claim 15, whereby said paddles depending vertically from said horizontal arms are hingedly connected to said horizontal arms such that, when said movable means for agitation of said substantially solid substrate is raised or lowered to a desired level within said substrate and is rotatably moved in a first direction, said paddles serve as stirring devices to stir or agitate said substantially solid substrate.

19. The device of Claim 15, whereby said paddles depending vertically from said horizontal arms are hingedly connected to said horizontal arms such that, when said movable means for agitation of said substantially solid substrate is raised or lowered to a desired level within said substrate and is rotatably moved in a second direction, said paddles serve to smooth uneven substrate mass, or to empty or discharge a portion or the entirety of said substrate from said vessel.

20. The device of Claim 15, whereby a fluid may be introduced into said means for agitation of said substantially solid substrate via said hollow shaft, and therefrom via said channels through said horizontal arms and said vertical paddles into said substantially solid substrate, said means for agitation of said substantially solid substrate being raised or lowered to a desired level in order to maintain homogeneous fermentation culture conditions throughout said substantially solid substrate.

21. The device of Claim 20, whereby said fluid is conditioned air.

22. The device of Claim 20, whereby said fluid is a desired nutrient solution.

23. The device of Claim 20, whereby said fluid is water.