After prebiotics are eaten, they go directly to the large intestine, where they are fermented by coliform bacteria for energy utilization, and produce short-chain fatty acids SCFA, mainly acetic acid, propionic acid and butyric acid, as well as lactic acid and gas. [6]
(1) Acid production
The organic acids generated by the intestinal flora metabolize food, on the one hand, can provide the energy needed by the human body, on the other hand, it can reduce the pH value of the intestinal tract and form an environment that is not conducive to the survival of pathogenic bacteria, thereby effectively inhibiting intestinal corruption and improving. The absorption rate of mineral elements, promote intestinal peristalsis and facilitate defecation. Generally, Lactobacillus only produces lactic acid, while Bifidobacterium mainly produces acetic acid and a small amount of lactic acid. After prebiotics are metabolized by intestinal flora, a large amount of organic acids will also be generated, which will lower the intestinal pH [7]. Among them, galacto-oligosaccharide and lactulose had the largest acid production, and inulin had the smallest acid production. The production of various organic acids after prebiotics are metabolized are: acetic acid LACT, GOS, SOS>FOS, IMO, XOS>Inulin; lactic acid GOS, SOS>XOS, IMO, LACT>FOS, Inulin; propionic acid LACT, Inulin , XOS, FOS>SOS, COS>IMO. [6]
(2) Gas production
In addition to bifidobacteria and lactobacilli in the human intestinal tract, almost all other flora can produce gas, causing the human body to experience different degrees of flatulence and farting. After prebiotics are metabolized by intestinal flora, a certain amount of gases such as CO2, H2, and CH4 can be produced. Wait. Due to the difference in glycosidic bond and composition, various prebiotics will be utilized by different types of gas-producing bacteria, and the gas produced will be different. Rycroft et al. compared the total gas production of different prebiotics through in vitro experiments, and found that isomaltooligosaccharides and galactooligosaccharides are the prebiotics with the least total gas production, while inulin is the one with the largest total gas production (see image 3). In addition, Oku et al. [conducted clinical verification on the hydrogen production of three prebiotics, oligofructose, oligofructose, and isomaltooligosaccharide. No matter the dietary dose of 10g/d or 20g/d, all oligomeric Fructose produced the largest amount of hydrogen gas, while isomaltooligosaccharides produced the least amount of hydrogen gas.