Fermentation processes

#The present invention relates to processes for producing fermentation products from starch-containing material, including processes for producing ethanol.

#Fermentation processes are used for making a vast number of commercial products, including alcohols (e.g. ethanol, methanol, butanol, 1,3-propanediol); organic acids (e.g., citric acid, acetic acid, itaconic acid, gluconic acid, gluconate, lactic acid, succinic acid, 2,5-diketo-D-gluconic acid; ketones (e.g., acetone); amino acids (e.g. glutamic acid); gases (e.g., H2 and CO2), and more complex compounds, including, for example, antibiotics (e.g., penicillin and tetracycline); enzymes; vitamins (e.g., riboflavin, B12, beta-carotene); hormones, and other compounds which are difficult to produce synthetically. Fermentation processes are also commonly used in dairy (e.g., in the production of yogurt and cheese), leather, and tobacco industries.

#Fermentation products are produced industrially in large fermentation tanks capable of holding upwards of 10 cubic meters fermentation medium. In order to build up a suitable fermenting organism population and concentration in the fermentation tank a fermentation process usually requires a process time of between 48 and 120 hours or more. Because of the large-sized tanks and long fermentation times it is difficult to maintain the fermentation system free of contamination. Unwanted contaminant bacteria are often gram-positive bacteria from the genus Lactobacillus that converts glucose into lactic acid and acetic acid. Also gram-negative bacteria are known to contaminate fermentation processes. Unfortunately the fermentation conditions are usually conducive for bacterial growth. If bacterial contamination occurs the entire fermentation tank must be emptied, cleaned and sterilized and the fermentation medium is useless. This is of course time-consuming and costly. Further, many bacteria compete with the fermenting organism for the sugar. This results in a reduced fermentation yield.

#FIG. 1 shows the growth of mixture of four Lactobacillus strains over 24 hours at different concentrations of antibacterial Peptide A.

#FIG. 2 shows the growth of mixture of four Lactobacillus strains over 24 hours at different concentrations of antibacterial Peptide B.

#FIG. 3 shows the total count of Lactobacilli after 0, 24, 48, and 72 hours of SSF.

#The object of the present invention is to provide fermentation processes or processes including a fermentation step wherein unwanted bacteria are killed and/or unwanted bacteria growth is inhibited. Unwanted bacteria themselves and their metabolic end-products, such as lactic acid and/or acetic acid, lead to reduced fermentation yields which lead to considerable economical loss to the producer (see Thomas et al., 2001, J. Applied Microbiology, 90: 819-828). The unwanted bacteria compete with the fermenting organism (e.g., yeast) for sugar (carbon source) in the fermentation medium. The lactic acid and/or acetic acid produced by the unwanted bacteria may also have a negative impact on yeast growth.

#The present inventors have found that antibacterial agents may advantageously be used to kill and/or inhibit growth of unwanted bacteria which are known to contaminate fermentation processes. A process of the invention may be used as an alternative to, e.g., adding antibiotics, such as especially penicillin, to fermentation processes, which may be undesired for one reason or another. A process of the invention may result in a fermentation yield that is increased compared to the yield obtained in a corresponding process where no antibacterial agent is added.

#According to the invention especially bacterial contamination by lactic acid and/or acetic acid producing bacteria may be prevented and/or reduced. Lactic acid and/or acetic acid producing bacteria of especially the genus Lactobacillus are known to contaminate fermentation processes. Examples of species of Lactobacillus that has been found to contaminate fermentation processes include strains of Lactobacillus collinoides. Lactobacillus brevis, Lactobacillus fermentum, Lactobacillus paracasei, Lactobacillus plantarum, and/or Lactobacillus rhamnosus, or a mixture thereof.