Chemistry: molecular biology and microbiology – Micro-organism – tissue cell culture or enzyme using process... – Preparing oxygen-containing organic compound
Reexamination Certificate
2000-03-30
2002-07-16
Tate, Christopher R. (Department: 1651)
Chemistry: molecular biology and microbiology
Micro-organism, tissue cell culture or enzyme using process...
Preparing oxygen-containing organic compound
C435S161000, C435S177000, C435S243000, C426S062000
Reexamination Certificate
active
06420146
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an improved process for the preparation of stable yeast crystals and a process for the enhanced production of ethanol using the said stable yeast crystals. This invention, particularly, relates to a process for the preparation of stable yeast crystals and production of ethanol using these crystals, which has wide industrial application as solvent, food, medicine and intermediate for synthesis of variety of organic compounds.
BACKGROUND OF INVENTION
The demand for ethanol is ever increasing mainly due to the rapid industrialization and fast population growth, which resulted in renewed interest in the development of suitable fermentation processes for ethanol production. Even today, ethanol production is carried out by conventional batch fermentation techniques using
Sachhromyces cereviceae
cultures. This method of ethanol fermentation with yeast cultures requires maintenance of yeast cultures and pitching of yeast for every batch. Hitherto several attempts have been made to enhance the ethanol production with free and immobilized yeast cells. The ethanol fermentations are generally carried out using
Sacchromyces cereviceae
in diluted molasses solutions in a batch reactor for a period of 24-48 hours [S. V. Ramakrishna, V. P. Sreedharan and P. Prema. In
Bioreactor Immobilized Enzymes and Cells: Fundamentals and Applications
(Ed MoodYoung), Elsevier
Appl. Sci.,
Amsterdam, 1988, 251-260]. The major disadvantages of the batch process are its low productivity, extremely slow and inefficient, higher operating as well as capital investment [D. Das. R. G. Nandkishor, K. Murali and P. S. Gupta
J. Ferment.Bioengg.
1993, 75, 132-137: D. Weuster-Botz
Appl. Microbiol. Biotechnol,
1993, 39, 679-684]. Many alternative fermentation strategies such as high cell densities in the fermentor, larger throughput by continuous mode of operation using cell recycle [C. W. Lee and H. N. Chang
Biotehcnol. Bioengg,
1987, 29, 1105-1112], extractive fermentation [M. Minier and G. Goma Biotehcnol. Bioengg. 1982, 24, 1565-1579] and whole cell immobilization by various techniques [S. V. Ramakrishna and R. S. Prakasham
Current Science,
1999, 77, 87-100] have been attempted to enhance volumetric productivity of the system. But these methodologies suffer from the drawback that the yeast cells has to be added in every batch. Continuous fermentation with cell recycles [T. K. Ghosh and R. D. Tyagi
Biotechnol. Bioengg,
1979, 21; 1387; G. H. Gil, W. J. Jones and T. G. Tomabene
Enzyme Microb. Technol.,
1991, 13; 390] and vacuume fermentation [G. R. Cysewski and C. R. Wilke
Biotechnol, Bioengg,
1977, 19; 1125] have resulted in considerable increase in the productivity. However, the cell recycling system involves considerable cost input for separation of yeast cells from the fermented broth. One of the attractive alternate method received wide attention is the high cell density fermentations. In this regard the reuse of immobilized yeast cells, instead of free cells, has been attempted by several researchers [R. Jamuna and S. V. Ramakrishna
Biomass Bioenergy,
1992, 3; 117-119]. Many methods of cell immobilization such as absorption on solid matrices, cross-linking covalent bonding and entrapment have been tried [S. V. Ramakrishna and R. S. Prakasham
Curr. Sci.,
1999, 77; 87-100] using natural polymers such as agar, agarose, alginates & carageenan and synthetic polymers like polyacrylamide, poly vinyl alcohol have been used for entrapment [S. V. Ramakrishna and R. S. Prakasham
Curr. Sci.,
1999, 77; 87-100]. Due to toxicity problems, the synthetic polymers have been found to have limited use. One of the major limitation with entrapped cells in natural polymers is its low mechanical strength and its density due to which the entrapped particles tends to float, causing serious engineering problems both in packed and fluidized bed reactor. Recently, T. E. Abraham et all (1990) have developed high density gel beads by incorporating dense inert compounds [T. E. Abraham, J. Rajagopalan, S. V. Ramakrishna and A. D. Damadaran, Indian Patent, 761/DEL/90]. However, the resultant gel beads with improved density were found to have lower mechanical strength due to weak ionic bonds of the polymeric network. There is not report available production of stable immobilized yeast beads. Various types of reactor configurations have been attempted to produce ethanol with entrapped cells [F. Godia, C. Casad, and C. Sola
Process Biochem,
1987, 43-48]. One of the major limitation with entrapped cells is that the gas generated during fermentation get entrapped in the gel particles which in turn lowers the density disintegrates the beads [S. V. Ramakrishna, V. P. Sreedharan and P. Prema. In:
Bioreactor Immobilized Enzymes and Cells: Fundamentals and Applications
(Ed MoodYoung), Elsevier
Appl. Sci.,
Amsterdam, 1988, 251-260].
OBJECTIVES OF THE INVENTION
The first objective of the present invention is to provide an improved process for the preparation of stable yeast crystals.
The second objective of the present invention is the use of the stable yeast crystals prepared by the process of present invention for enhanced production of ethanol.
The third objective of the present invention is to store the stable yeast crystals at room temperature without loosing its activity.
The fourth objective of the present invention is to provide an easy transportation of stable yeast crystals.
The fifth objective of the present invention is to provide stable yeast crystals for repeated use.
The sixth objective of this invention is to provide cost effective improved alcohol fermentation.
The seventh objective of the present invention is to reduce the product inhibition during ethanol fermentation.
The eighth objective of the present invention is to provide an easy process of ethanol production.
The ninth objective of the present invention is to enhance the rate of ethanol fermentation.
SUMMARY OF THE INVENTION
The novelty lies in the present invention is the preparation of novel stable yeast crystals which are mechanically strong and biologically active, they can be employed either in stirred tank reactors or in fluidized beds in batch or continuous fermentations, for enhanced ethanol production. The gas generation during fermentation does not lower its density nor weaken the integrity of the matrix.
DETAILED DESCRIPTION OF THE INVENTION
Accordingly, the present invention provides an improved process for the preparation of stable yeast crystals for enhanced production of ethanol which comprises culturing of yeast (
Sacchromyces cereviceae
) in a conventional growth medium, separating the yeast, immobilization of yeast using aqueous natural polymer solution by known methods to obtain immobilized yeast beads, separation of the said immobilized yeast beads and dehydration at the temperature in the range of 24-36° C. for a period of 2-20 hours to obtain stable yeast crystals having the moisture content in the range between 5-30%, adding novel stable yeast crystals to 5-8% molasses solution and incubating the said crystals for a period ranging between 6-48 hours at a temperature ranging between 24-32° C. to obtain activated stable yeast crystals, separating activated stable yeast crystals by conventional methods followed by incubating novel activated stable yeast crystals in the range of 0.2 to 5% of the volume of the fermentation broth containing molasses having a total reducing sugar concentration in the range of 10-30% and recovering the ethanol from the fermentation broth by known methods.
In an embodiment of the present invention, the growth media used comprises (g/1) malt extract, 1.0-5.0; yeast extract, 1.0-5.0; Peptone, 3.0-10.0 and Molasses, 30.0-50.0.
In an other embodiment of the present invention the yeast used is commercially available Sacchromyces species.
In another embodiment of the present invention, the yeast is cultured by incubating at the tempe
Komaraiah Palle
Prakasham Reddy Shetty
Ramakrishna Sonti Venkata
Council of Scientific & Industrial Research
Lackenbach Siegel
Nissen J. Harold
Tate Christopher R.
Winston Randall
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