The intestinal tract, the largest digestive, excretory and immune organ of the human body, is also known as the second brain of the human body, also called the intestinal brain. The human intestinal tract contains a huge neural network and a large number of neurotransmitter substances, constantly exchanging information with the brain; at the same time, the intestinal tract also hosts 10 trillion bacteria, affecting the body’s body weight and digestive capacity, resistance to infections and autoimmune diseases such as the risk of disease, etc., so the intestinal flora in accordance with a certain proportion of the combination of constraints on each other and dependence on each other, and in terms of the number of the host constitutes a kind of symbiotic and win-win Ecological balance.

Human microecosystem, including the oral cavity, skin, urinary, gastrointestinal tract 4 ecosystems, to the intestinal microecosystem is the most important and complex, mainly by the intestinal normal flora and the environment in which they live together, the microbial amount of the total microbial amount of the human body accounted for 78%; not only is the digestive system is an important part of the digestive system, but also one of the key factors of the immune function, so that the human body’s 70% of the immune system is located in the intestinal tract The human gut microbiome consists of 1014 microorganisms.

The human gut microbiome consists of 1014 resident microorganisms associated with the human gut, mostly Actinobacteria, Anaplasma, Thick-walled Bacteria, and Ascomycetes; mainly located in the distal part of the digestive tract, with a biomass of more than 1011 cells per gram of content. Intestinal flora can be divided into three categories, probiotics represented by Bifidobacteria, Lactobacillus, etc., harmful bacteria represented by Enterobacter cloacae, and neutral bacteria that are harmless to humans and animals.

Intestinal flora and health

Intestinal flora plays a crucial role in the formation, development and maturation of the immune system. Impaired immune development in germ-free animals is manifested by immature gut-associated lymphoid tissues, reduced numbers of intestinal lymphocytes, and decreased levels of antimicrobial peptides and immunoglobulin IgA, and these alterations are reversed after colonization by commensal bacteria.

Meanwhile, intestinal flora were able to modulate the immune system and immune cell responses, including T cells, B cells, dendritic cells, and macrophages, by producing molecules with immunomodulatory and anti-inflammatory functions, such as short-chain fatty acids, indoles and their derivatives, and secondary bile acids. It is evident that gut flora is crucial for the formation and maintenance of the immune system.

In a healthy state, a mutually beneficial balance is maintained between the body and microorganisms. However, once the host is affected by its own and external environmental changes, such as the host’s own genotype, diet, age, disease state and foreign bacterial invasion, etc., the equilibrium between the host and the flora will be broken, resulting in an imbalance of the intestinal micro-ecosystem, disorders of the body’s functions, the emergence of pathogenic bacteria heterobacteria, the rapid reduction of probiotics, which will lead to the occurrence of disease.

In recent years, more and more researches have found that the imbalance of intestinal flora has a close relationship with the occurrence of many diseases, and the pathogenesis is not only limited to the intestinal tract, but also spreads to the whole body, such as the nervous system, the endocrine system, the cardiovascular system, tumors and so on, and may even affect the mental health.

Functional food components that regulate intestinal flora

1. Probiotics

Probiotics are live bacterial agents and their metabolites that improve the microecological balance of the host and play a beneficial role in improving the host’s health level and state of health; they mainly include two major groups of lactic acid bacteria, one group of bifidobacteria, such as Bifidobacterium infantis, Bifidobacterium longum, Bifidobacterium shortum, Bifidobacterium adolescentis, etc., and the other group of lactobacilli, such as Lactobacillus acidophilus, Lactobacillus casei, Lactobacillus rhamnosus, Lactobacillus plantarum, and Lactobacillus Royceae. Lactobacillus acidophilus, Lactobacillus casei, Lactobacillus rhamnosus, Lactobacillus plantarum and Lactobacillus rohita, etc. Probiotics used in human body include Bifidobacterium bifidum, Lactobacillus lactis, Enterococcus faecium, Escherichia coli, Bacillus subtilis, Bacillus cereus, Bacillus licheniformis, Clostridium butyricum and yeast.

From a safety point of view, currently industrial probiotics are mainly derived from healthy humans and animals, as well as traditional fermented foods such as fermented dairy products, kimchi and natto.

In 2001, the World Food Organization (FAO) and the World Health Organization (WHO) defined probiotics as follows: probiotics are live microorganisms that, when ingested in sufficient quantities, produce health benefits for their hosts; in 2014, the International Association for Prebiotics and Probiotics Science endorsed the definitions of the FAO and the WHO in its published consensus, and emphasized the identification of probiotic strains and the evaluation of their safety importance.

The Probiotics Branch of the Chinese Society of Food Science and Technology and other organizations have also jointly released the “Probiotics Scientific Consensus (2020 Edition)”, in which it is also clearly pointed out that probiotics need to have the 3 core characteristics of sufficient quantity, live bacteria status, and beneficial health functions.

Based on the efficacy of probiotics in regulating intestinal flora. The relationship between intestinal flora is complex and close, some are mutualistic, some are antagonistic, they take the food ingested by the host and the various components secreted in the digestive tract as nutrients for growth, and constantly proliferate and be discharged; not only and the intestinal mucosa together constitute a protective barrier to prevent the invasion of harmful bacteria, viruses, and food antigens, etc., but also to stimulate the immune organs of the intestinal tract to exert stronger immune functions.

Probiotics, as the dominant flora, can form the biological barrier of the intestinal tract with the intestinal mucosa, and inhibit the overgrowth of conditionally pathogenic bacteria and the invasion of foreign pathogenic bacteria through the occupancy effect, nutrient competition, and its secretion of a variety of metabolites and bacteriocins, etc., which plays an important role in the maintenance of intestinal micro-ecological balance.

2.Dietary fiber

Dietary fiber, naturally occurring in plants, extracted from plants or directly synthesized polymerization degree ≥ 3, edible, can not be digested and absorbed by the human small intestine, the human body has a health significance of carbohydrate polymers; can be divided into water-soluble dietary fiber and non-water-soluble dietary fiber. Insoluble dietary fiber can increase the amount of stool, enhance absorption, improve immunity, etc.; soluble dietary fiber can prevent constipation, improve oral and dental function, conducive to weight loss.

In 1991, nutrition experts of the World Health Organization separated dietary fiber from the carbohydrate family and listed it as the “seventh major nutrient element” following carbohydrates, proteins, fats, water, minerals and vitamins.

Based on the efficacy of dietary fiber in regulating intestinal flora. Dietary fiber can affect the body’s intestinal flora, through the increase of probiotics to protect the intestinal barrier, inhibit the proliferation of endotoxin-producing gram-negative bacteria induced in the intestinal tract, reduce intestinal permeability, reduce the chances of disease.

3.Functional oligosaccharide

Oligosaccharides, commonly known as oligosaccharides, are straight-chain or branched low-degree polymerized sugars combined by 2-10 monosaccharide molecules of the same or different species through interactions between glycosidic bonds; they are mainly divided into special oligosaccharides that have functionality and ordinary oligosaccharides that do not have functionality.

Functional oligosaccharides are non-digestible oligosaccharides, consisting of 2 to 10 monosaccharide molecules that are dehydrated and connected by α and β glycosidic bonds to form straight-chain and branched low-grade polymerized sugars with sweetness, viscosity, and other sugar characteristics, which can not be absorbed by the human body but can proliferate beneficial bacteria and inhibit harmful bacteria after entering the large intestine and have the efficacy of low calorie, lowing cholesterol, improving immunity and preventing tumors; Mainly includes oligofructose (Fructo oligosaccharide), oligogalactose (Galactooligosaccharides,), oligoisomaltose (Isomal maltose oligomeric), oligo-xylose (Xylooligosaccharides), oligo-gentiooligsaccharide (Gentiooligosaccharides), and so on. Gentiooligsaccharide), etc. Therefore, functional oligosaccharides have become important raw materials or food additives for the development of functional foods.

Based on the efficacy of functional oligosaccharides in regulating intestinal flora. Since enzymes that can break down functional oligosaccharides do not exist in human saliva and gastrointestinal tract, functional oligosaccharides can directly enter the large intestine without being digested and absorbed. In the large intestine, it is preferentially utilized by Bifidobacterium, which has a significant effect on adjusting the intestinal flora, maintaining the balance of the intestinal environment, regulating the physiological function of the intestinal tract, and improving human health.

4. Polyphenols

Dietary polyphenols, the most widely used phytochemicals in food, are mainly found in a variety of fruits, vegetables, tea, cereals, herbs, with antioxidant, anti-tumor, liver protection and anti-obesity and other biological activities, such as tea polyphenols, bioflavonoids, phenolic acids and astragalus.

Based on the efficacy of dietary polyphenols in regulating intestinal flora. Intestinal flora can influence the stability of dietary polyphenols through multiple enzymatic reactions, including deglycosylation, sulfation, glucuronidation, C-ring cleavage of the benzo-γ-pyrone system, dehydroxylation, decarboxylation, and hydrogenation, which allow polyphenols to be converted into low molecular weight biologically active metabolites that can be absorbed by the body.

At the same time, polyphenols can inhibit the growth and reproduction of harmful flora in the intestinal tract, promote the growth of beneficial bacteria such as Lactobacillus, Bifidobacterium, etc., and reduce the ratio of the thick-walled bacillus phylum to the anaplastic bacillus phylum, which can in turn alleviate obesity and other metabolic syndromes, etc., caused by a high-fat diet.

With the increasing concern for health, more and more consumers are paying attention to gut health. Functional food for intestinal health can not only help improve the function of the digestive system and maintain intestinal micro-ecological balance, but also enhance the body’s immunity, and is therefore favored by the majority of consumers. Therefore, the development and innovation of intestinal flora regulation functional food is not only the immediate need of contemporary health needs, but also the development direction and trend of functional food, which has a broad development prospect.