Fruit fermentation microbiology

Table 10.1 gives a summary of the main by-products of fermentation by yeasts and other microbiological activities which can be identified in distilled spirits from different raw materials, like fruits, wine, grain, sugar cane, or other carbohydrate-containing plants. Since the sensory relevance of a flavour compound is related to its odour thresholds and odour quality. Table 10.1 presents also odour qualities and a review of threshold values of the fermentation by-products in ethanol solutions [9-10] and/or water [11-14] (Christoph and Bauer-Christoph 2006, unpublished results). 

Since around 1800, the mechanism of fermentation has been studied in a scientific way. It started when German scientist Erxleben discovered that yeast induces fermentation. Louis Pasteur, a French scientist, made many contributions to microbiology. He explained that bacteria produce lactic acid, which then conserves the food. Pasteur also noticed that unwanted fermentation can be stopped by heat treatment of the substrate (pasteurization). This technique is still widely applied today to treat milk or fruit juices. Actually, the production of neat lactic acid was also the first nonfood industrial application of fermentation. 

Amino acid production by fermentation started around 1960 in Japan. Initially glutamic acid was the main product. It was sold as sodium salt, monosodium glutamate (MSG), a flavor enhancer on oriental cuisine. Other amino acids soon followed. They are used in food and feed to increase the efficiency of low protein substrates. Microbiologically produced enzymes were introduced around 1970. They are used in grain processing, sugar production, fruit juice clarification, and as detergent additives (Table 9.1). 

Microorganisms Plant/animai cellular materials Retention of microbiological solids in activated sludge processing concn of viral/bacterial cell cultures separation of fermentation products from broth retention of cell debris in fruit juices, etc. retention of cellular matter in brewery/distillery wastes Polyphenol ics Synthetic water-soluble polymers Concn/purification of lignosulphonates Concn of PVA/CMC desize wastes... 

Hsin-Yu, C. and Chou, C.-C. 2001. Acid adaptation and temperature effect on the survival of E. coli 0157 H7 in acidic fruit juice and lactic fermented milk product. International Journal of Food Microbiology 70 189-195. 

Tanganurat, W., Quinquis, B., Leelawatcharamas, V., Bolotin, A. (2009). Genotypic and phenotypic characterization of Lactobacillus plantarum strains isolated from Thai fermented fruits and vegetables. Journal of Basic Microbiology, 49, 377-385. 

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