According to the test methods in the existing literature, most of the indicators used to evaluate the effect of prebiotics are: the proliferation effect of beneficial bacteria (such as Bifidobacterium and lactic acid bacteria); Inhibition of harmful bacteria (such as Fusobacterium) and non-proliferation of potential pathogenic bacteria (such as Escherichia coli, Enterococcus, Bacteroides, etc.). ); Acid production and gas production after metabolism of intestinal flora. Comparison of prebiotics of different functional oligosaccharides (isomaltooligosaccharides (IMO): fructooligosaccharides (FOS), galactooligosaccharides (GOS), xylooligosaccharides (XOS), lactulose oligosaccharides (SOS), inulin, etc. ) as follows:

Proliferation of Bifidobacterium 1

Generally speaking, there are 8 kinds of intestinal bifidobacteria, among which Bifidobacterium bifidum, Bifidobacterium infantis, Bifidobacterium adolescentis, Bifidobacterium longum and Bifidobacterium brevis have the largest number. The composition and proportion of intestinal bifidobacteria are different in different age groups. For example, in children, Bifidobacterium infantis, Bifidobacterium bifidum and Bifidobacterium longum are the main types, while in young adults and the elderly, Bifidobacterium adolescentis and Bifidobacterium longum are the main types. With the increase of age, or the influence of bad eating habits and diseases, the number and proportion of intestinal bifidobacteria are likely to drop sharply, which is not conducive to the maintenance of human health.

Many studies have confirmed that isomaltooligosaccharides, fructooligosaccharides, galactooligosaccharides and xylooligosaccharides have obvious effects on the proliferation of Bifidobacterium. Ryerofi et al.' s in vitro fermentation study showed that these seven oligosaccharides had obvious proliferation effects on Bifidobacterium, but the proliferation degree was slightly different (see figure 1). Specifically, the availability and utilization rate of different oligosaccharides by five kinds of bifidobacteria in the intestine are also different (see table 1).

Table 1 Utilization ratio of probiotics to five kinds of bifidobacteria

Figure 1 Effects of different prebiotics on the proliferation of intestinal Bifidobacterium

Claire's research shows that galactooligosaccharides and isomaltooligosaccharides are prebiotics that can be well utilized by various bifidobacteria with high proliferation rate, but the latter is more utilized by Bifidobacterium longum and Bifidobacterium adolescentis. Xylo-oligosaccharides can be used by Bifidobacterium adolescentis and Bifidobacterium longum, but the availability of other Bifidobacterium is poor. Therefore, galactooligosaccharides and isomaltooligosaccharides are prebiotics suitable for people of all ages.

2 Proliferation of lactic acid bacteria

Found isomaltooligosaccharides, galactooligosaccharides, fructooligosaccharides, xylooligosaccharides, soybean oligosaccharides and so on. All of them have obvious proliferation effect on human intestinal lactobacillus (see table 2). Among them, galactooligosaccharides have the greatest and most comprehensive effect on the proliferation of lactic acid bacteria [5].

Table 2 Effects of different prebiotics on the proliferation of intestinal Lactobacillus

Table 3 Utilization ratio of prebiotics by four lactic acid bacteria

3 Inhibition of harmful bacteria

The harmful bacteria in human intestine mainly refer to Clostridium. In addition, some facultative bacteria can also be transformed into harmful bacteria that are not conducive to human health, such as Escherichia coli and Bacteroides. Successful prebiotics should not only proliferate beneficial bacteria, but also inhibit the proliferation of harmful bacteria.

In vitro experiments and human clinical studies have confirmed that isomaltooligosaccharide has obvious inhibitory effect on harmful bacteria Clostridium, but has no proliferative effect on potential pathogenic bacteria (such as Enterobacter and Enterococcus) (see Table 4). Like isomaltooligosaccharides, galactooligosaccharides, fructooligosaccharides and xylooligosaccharides also have good inhibitory effects on harmful bacteria and facultative bacteria (Figure 2).

Table 4 Inhibitory effect of isomaltooligosaccharide IMO on harmful bacteria

Fig. 2 Inhibitory effects of different prebiotics on Clostridium.

4 intestinal flora metabolism

Prebiotics directly enter the large intestine after eating, where they are fermented by Escherichia coli and used as energy, and produce short-chain fatty acids SCFA, mainly acetic acid, propionic acid and butyric acid, lactic acid and gas.

(1) acid production

On the one hand, the organic acids produced by food metabolized by intestinal flora can provide the energy needed by human body, on the other hand, it can reduce the pH value of intestinal tract and form an environment that is not conducive to the survival of pathogenic bacteria, thus effectively inhibiting intestinal corruption, improving the absorption rate of mineral elements, promoting intestinal peristalsis and facilitating defecation. Generally, lactic acid bacteria only produce lactic acid, while Bifidobacterium mainly produces acetic acid and a small amount of lactic acid. After prebiotics are metabolized by intestinal flora, they will also produce a large number of organic acids, which will reduce the pH value of the intestine. Among them, galactooligosaccharides and lactulose have the largest acid production, while inulin has the smallest acid production. The output of various organic acids after prebiotic metabolism is: LACT acetate, GOS, SOS >；; FOS、IMO、XOS & gt； Inulin; Goss lactate, SOS & gtXOS, IMO, LACT & gt；; Fructooligosaccharides, inulin; LACT propionate, inulin, XOS, fructooligosaccharides & gtSOS, COS> IMO.

(2) Natural gas production

Except for Bifidobacterium and Lactobacillus, almost all other flora in human intestine can produce gas, causing flatulence and farting to varying degrees. After prebiotics are metabolized by intestinal flora, they can produce a certain amount of gases, such as CO2, H2 and CH4. Wait a minute. Because of the different glycosidic bonds and compositions, various prebiotics will be utilized by different types of gas-producing bacteria, and the gases 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 were the least among many prebiotics, while inulin was the largest (see Figure 3). In addition, Oku et al. [clinically verified the hydrogen production of three prebiotics, namely fructooligosaccharide, lactulose oligosaccharide and isomaltooligosaccharide. Whether the food dosage is 10g/d or 20g/d, the hydrogen production of fructooligosaccharides is the largest, while that of isomaltooligosaccharides is the least (see Figures 5 and 6).

Fig. 3 Comparison of gas production of different prebiotics.

Fig. 4 Hydrogen production of FOS/GS/IMO (10g/d)

Fig. 5 Hydrogen production of FOS/GS/IMO (20g/d