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Controlled coculture fermentation for the production of new beverages
Bader, J., Mast-Gerlach, E., Stahl, U.

Special strains of Gluconobacter, Lactobacillus and Kluyveromyces have been selected for the production of a new beverage on the basis of wort. This beverage contains the health benefiting substances gluconic acid, lactic acid and an ethanol concentration below 0.5 % (v/v). Fermentation was adapted for growth behaviour and to maximise production - the strategy developed concurrently produces (a) gluconic acid by using the strictly aerobic Gluconobacter strain and (b) lactic acid by using the anaerobic strain of Lactobacillus. The concentrations of the simultaneously produced organic acids are controlled by the level of oxygen in the fermentation medium. The following mixed fermentation of Lactobacillus, Gluconobacter and Kluyveromyces using the chosen yeast strain resulted in producing a pleasant flavour. Many microorganisms have long been used for the production of different foods. Traditionally, microbiological fermentation has been used in the production of yoghurt, beer, salami, cheese, sauerkraut and wine. Flavour, agreeableness and storage life can also be increased by using microorganisms. Many foods are produced by cocultivation of different microorganisms. Some examples are sauerkraut, Belgian Lambic beer1, wine [2], cacao beans3, cheese4 and coffee beans [5]. During the fermentation process, growth and product formation of the different microorganisms continually change throughout the different phases of fermentation. The sequence of the microorganisms involved is regulated by conditions such as metabolites, pH, temperature, oxygen availability and substrate concentrations as well as the complex interaction between different microorganisms. The controlled fermentation of mixed cultures requires a complex fermentation strategy. The influence of changing substrate and product concentrations on the various microorganisms and the parameters already mentioned need to be taken into account6.Bacteria of the genus Gluconobacter are Gram-negative catalase positive rods which belong to the family Acetobacteraceae [7]. These strictly aerobic microorganisms are found in fruit and flowers in nature. They are characterized by the incomplete oxidation of carbohydrates, alcohols and related compounds. Glucose is metabolized via the pentose phosphate pathway. Glycolysis is blocked due to a missing phosphofructokinase.The oxidation of glucose to gluconic acid, which is beneficial for human health, is crucial for the development of the beverage. The oral intake of gluconic acid effects the formation of butyrate in the colon8 which inhibits cancer formation and may activate apoptosis in cancer cells.Lactobacillaceae are Gram-positive facultative anaerobic bacteria. Lactobacillus L0610, the strain used, is an obligate homofermentative bacterium. This means that more than 90% of the glucose is metabolized to lactic acid. Lactic acid has a positive influence on colon function and enhances digestibility [9].Lactic acid bacteria (LAB) are used in the food industry for the production of yoghurt, cheese and sourdough. As L(+)-lactic acid is beneficial to health; strains which form this conformation of lactic acid are preferred. Probiotic strains can be used to increase health benefits in the production of food. These strains are resistant to bile acid, positively influence intestinal flora and improve the immune system [10]. The treatment of colitis11 and the prevention of cancer [12,13] is discussed with different strains of LAB.The yeast of the genus Kluyveromyces belongs to the family of the Saccharomycetaceae and is a Crabtree negative yeast, no ethanol is produced under aerobic conditions, even when glucose concentration is high. Kluyveromyces strains are used in the food industry for the production of kefir. Some strains are able to produce flavour compounds such as 2‑phenylethanol14. Due to high secretory capacity, strains of this yeast are also used for recombinant production of proteins e.g. human serum albumine [15] or human lysozyme16,4.Mixed fermentation In the field of industrial biotechnology, only one strain is normally selected and cultivated for the manufacture of a particular product under sterile conditions. The presence of other microorganisms has to be avoided. The only exception is waste water treatment and, in some cases, the fermentation of food where mixed cultivations may be utilized.Most biotransformations in nature take place by the combination of metabolisms from different microorganisms e.g. in large intestine of mammals and in soil. The interaction between the different microorganisms may be advantageous for the strains involved. In other cases there may be competition for substrates and habitat. Therefore, microorganisms have developed different strategies to protect substrates and defend their habitat against competitors.

Descriptors: beverage, Gluconobacter, Kluyveromyces, Lactobacillus, cocultivation

BrewingScience - Monatsschrift fr Brauwissenschaft, 60 (September/October 2007), pp. 128-134