Fermentation, intestinal bacteria

Lactose is hydrolyzed to glucose and galactose in the intestine by the enzyme lactase. People who are lactose-intolerant lack this enzyme. In these people, lactose advances in the digestive tract to the large intestine, where it is fermented by intestinal bacteria to produce large amounts of carbon dioxide and organic acids. Today, people with lactose intolerance can purchase milk in which the lactose has already been hydrolyzed, or can buy lactase supplements. 

Some intestinal bacteria (e.g. Escherichia coli, sal-monellae, and especially gram-negative pathogens) are also equipped with a fermentation capacity and produce small amounts of alcohol. No alcohol is detectable in... 

Undigested amylose passes into the large intestine (colon) where it is fermented by bacteria that produce short-chain fatty acids, hydrogen and methane. These compounds cause intestinal discomfort and intestinal bloating and their production explains the well-known association between flatulence and the consumption of baked... 

Salazar, N., Gueimonde, M., Hemandez-Barranco, A. M., Ruas-Madiedo, P., Clara, G. (2008). Exopolysaccharides produced by intestinal Bifidobacterium strains act as fermentable substrates for human intestinal bacteria. Applied and Environmental Microbiology, 74(15), 4737-4745. 

Crittenden, R., Karppinen, S., Ojanen, S., Tenkanen, M., Fagerstrom, R., Mattb, J., et al. (2002). In vitro fermentation of cereal dietary fibre carbohydrates by probiotic and intestinal bacteria. Journal of the Science of Food and Agriculture, 82, 781-789. 

In order to be considered as prebiotics, carbohydrates must fulfill three criteria, namely (1) resistance to gastric acidity, hydrolysis by mammalian enzymes and gastrointestinal absorption (2) fermentation by intestinal microflora and (3) selective stimulation of the growth and/or activity of those intestinal bacteria that contribute to health and well-being. ... 

Oligosaccharides consist of three or four monosaccharide units (trisaccharides and tetrasaccharides), and occasionally more, linked by glycoside bonds. Nutritionally, they are not particularly important, and indeed they are generally not digested, although they may be fermented by intestinal bacteria and make a significant contribution to the production of intestinal gas. 

There are a number of other polysaccharides in foods. Collectively they are known as non-starch polysaccharides, the major components of dietary fibre (section 7.3.3.2). Non-starch polysaccharides are not digested by human enzymes, although all can be fermented to some extent by intestinal bacteria, and the products of bacterial fermentation may be absorbed and metabolized as metabolic fuels. The major nonstarch polysaccharides (shown in Figure 4.8) are ... 

Non-starch polysaccharides A group of polysaccharides other than starch which occur in plant foods. They are not digested by human enzymes, although they may be fermented by intestinal bacteria. They provide the major part of dietary fibre. The main non-starch polysaccharides are cellulose, hemicellulose (insoluble non-starch polysaccharides) and pectin and the plant gums and mucilages (soluble non-starch polysaccharides). 

Van Laere, K. M. J., Hartemink, R., Bosveld, M., Schols, H. A. Voragen, A. G. J. (2000). Fermentation of plant cell wall derived polysaccharides and their corresponding oligosaccharides by intestinal bacteria. Journal of Agriculture and Food Chemistry, 48, 1644-1652. 

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