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- Herausgeber: Bentham Science Publishers
- Kategorie: Fachliteratur
- Sprache: Englisch
Postbiotics: Science, Technology, and Applications explains fundamental and applied knowledge about postbiotics. Chapters cover the definition and classification of postbiotics, principal methods for preparing them, information about the main postbiotic constituents and their biological activities and their clinical health benefits. The authors also familiarize the reader with potential applications of postbiotics in the food industry, pharmaceutical chemistry, medicine, and veterinary practice. The text is supported by informative illustrations, tables, and references for further reading. This comprehensive reference, with its emphasis on both basic and applied knowledge, is useful for researchers, academics, veterinarians, and students in the field of microbiology, immunology, pharmacology, biotechnology, food science, and agriculture.
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Seitenzahl: 865
Veröffentlichungsjahr: 2021
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PREFACE
Probiotics, prebiotics, and postbiotics are the main ingredients of functional foods that have recently become popular with researchers. Live probiotic cells and their derived postbiotics are frequently applying in commercial pharmaceutical and food-based products. The results of studies demonstrated that these bioactive elements could be linked with the host’s cellular processes and metabolic pathways and possess a vital role in preserving and reestablishing host health. Despite the appropriate outcomes from the use of live probiotics, scientists have presented the postbiotic theory to find its precise mechanisms of action or optimize beneficial effects as well as to meet the requirements of customers to offer a safe product with a health claim. Currently, the scientific literature confirms that a large part of the molecular mechanism of probiotics is related to their derived postbiotics. These biomolecules, due to their unique pharmacokinetic properties, could be used, in their pure form and with high performance in veterinary, medical, and food practice to improve animal growth rate and health status, prevent and/or treat some acute/chronic diseases, and develop functional foods.
On the other hand, postbiotics with their unique features in terms of clinical, technological, and economic aspects can be applying as a promising approach (as potential alternative agents for probiotics and common antibiotics) in the food and drug industry for rising food safety and health effects as well as therapeutic targets. The fermentation process is the most natural production method of postbiotics, which enriches the fermented food matrices with these biomolecules. Nevertheless, postbiotics can be generated in a purer form and with high performance through several laboratory manners, which have the potential to be applied to an extensive range of food matrices to develop their nutritional values, storage stability, and health-promotion aims in customers. In the industry, manufacturers cannot easily add ingredients into the food matrix to produce functional food products that contain postbiotic compounds and, at the same time, have the desired quality and safety properties. Therefore it is indispensable that recognize the inherent characteristics of postbiotic compounds and select appropriate nanostructure carriers to design the best delivery system for the targeted delivery of postbiotics.
CONSENT FOR PUBLICATION
Not applicable.
CONFLICT OF INTEREST
The author declares no conflict of interest, financial or otherwise.
ACKNOWLEDGEMENTS
The authors would like to especially thank Dr. Hamideh Fathi Zavoshti for her helpful comments on the work.
ABOUT THE AUTHORS
Amin Abbasi was born in 1994 and is a Master of Science in Food Safety and Hygiene with significant contribution in science by publishing valuable articles in the well-known and top journals of food science and nutrition, and currently is working on probiotics and postbiotics in Food Science and Technology Department of Tabriz University of Medical Sciences.
Elham Sheykhsaran was born in 1989 and is a Ph.D. student of medical bacteriology with more than 25 publications in well-known journals of microbiology and currently is working on postbiotics in the Microbiology Department of Tabriz University of Medical Sciences.
Dr. Kafil was born in 1983 and is an assistant professor of medical microbiology with more than 250 published papers and an h-index of 24. He finished his Ph.D. in medical microbiology, and his main topics of researches are clinical microbiology, immunology, and biotechnology. He has five patents on diagnosis methods. He currently works as the head of microbiology research in the Drug Applied Research Center and Imam Reza Hospital. Hossein is well-known for his antimicrobial approach and diagnostic innovations.
Ecology of the Human Gastrointestinal Tract
Amin Abbasi,Elham Sheykhsaran,Yalda Rahbar Saadat,Hossein Samadi KafilAbstract
The digestive system has an explicit role in decomposing nutrients into energy and other necessary substances required by the body. The gastrointestinal tract contains a complex set of different microorganisms. It is considered the most dynamic and active organ in the body from a biological perspective. The environmental condition and daily diet are principal parameters that significantly influence the composition of gut microbiota. From birth to middle age, it undergoes significant changes. Several factors, such as maternal microbiota, birth status (natural, cesarean section), postpartum nutrition practices, microbial infections, overuse of antibiotics, diet (highly processed, low fiber), chronic diarrhea, and stress in life, have a significant effect on the gut microbiome. All of these factors lead to impaired bowel function and health. One of the most important strategies for overcoming dysbiosis conditions and establishing eubiosis conditions is the employment of foods containing probiotic, prebiotic, and postbiotic ingredients. Hence, this chapter provides a review of the concept and health-promoting issues regarding probiotics and prebiotics, with a focus on their biological role in the establishment of health.
Introduction
The digestive system has an explicit role in decomposing nutrients into energy and other necessary substances required by the body. In a person with a natural life span, about 60 tons of foodstuffs pass through the digestive tract. The gastrointestinal environment is a complex set of different microorganisms, which, from a biological perspective, are considered the most dynamic and active organs in the body [1, 2]. In addition to the central role of the gastrointestinal tract in the digestion and absorption of consumed nutrients, the complex metabolic activities in this episode have a well-known effect on human health. It is supposed that there are 1014 living microbes in the various part of the human body, even more than the number of cells in the human body, that is, approximately 1013 [3]. More than 400 different microbial species have been recognized in the samples of feces of a healthy individual, which in terms of microbial population is estimated to be about 1013 CFU/g. This number in the small intestine reaches 104-108 CFU/g, and in the stomach, only 101-102 CFU/g (Fig. 1) [4].
Fig. (1)) Distribution of microbial species in different parts of the gastrointestinal tract.The environmental condition and daily diet are principal parameters that significantly influence the composition of gut microbiota. From birth to middle age, it undergoes significant changes. During childbirth, the fetal gastrointestinal tract is free of any bacteria and sterile, but immediately after birth, replacement of the bacteria begins from the mother's genital tract in this episode [5]. Some factors such as sanitary conditions, type of delivery (normal-cesarean section), maternal microbial flora, nutrition, and other environmental factors potentially influence the composition of the gut microbial species [6]. During the first few days, the species Coliform, Enterococcus, Clostridium, Lactobacillus, and Bifidobacterium appear and form the dominant gut microbiota until the end of the first week. Therefore, in infants fed with breast milk, the bacterial population reaches 1010 CFU/gr of stool. It is a general rule that the type of feeding (breast or formula) significantly affects the composition of the microbial population in the baby's digestive tract [7, 8]. In the gastrointestinal tract of breast-fed infants, the levels of Bifidobacterium species are higher than those fed with formula, which in turn reduces the population of facultative anaerobic bacteria in this ecosystem. On the other hand, breast milk has less buffering power than formula and plays a significant role in intestinal acidification. This acidity act as a growth-inhibitor and inhibits the growth and development of Clostridia and Bacteroides sp, which in turn provides a specific platform for the growth of bifidobacteria (Table 1) [9].
Besides, breast milk contains natural oligosaccharides, which are a stimulant for the growth of beneficial bacteria. So, it can be stated that breast milk contains thousands of bioactive compounds that boost the pediatric immune system and significantly affects the digestive tract ecosystem. When mothers decide to start the weaning process, i.e., “mother-led weaning,” the population and composition of gut microbes undergo noticeable changes. In this condition, the residents of Bifidobacteria spp. decrease, and the species of Bacteroides form the dominant intestinal flora [10]. The population and composition of adult gut microbiota are almost constant. Still, it can alter with increasing age so that significant changes in this composition (diminution in the quantity of bifidobacteria sp and an increase in pathogenic bacteria such as Clostridium perfringens) cause diarrhea in elderly individuals [11, 12]. In addition to age, other factors that can disrupt this microbial balance may include genetics, geographic location, weather, economic conditions, lifestyle, stress, chronic diseases, the overdose of medication, microbial corruption, and diet. Interestingly, any change in this microbial balance will allow for the dominance of pathogenic germs, which in turn may cause a variety of diseases (Fig. 2).
Several factors such as maternal microbiota, birth status (natural, cesarean section), postpartum nutrition practices, microbial infections, overuse of antibiotics, diet (highly processed, low fiber), chronic diarrhea, and stress in life, have a significant effect on the gut microbiome that all of these factors lead to impaired bowel function and health [13]. One of the main side-effects is dysbiosis, a state in which microbial balance is disturbed, and pathogenic germs are created the dominant population in the gut environment. The use of antibiotics for a long time to treat chronic diseases such as diabetes, cystic fibrosis, tuberculosis, arthritis, cancer, etc., is one of the most important causes of dysbiosis [14, 15]. “Eubiosis” is also a condition against dysbiosis, which refers to establishing a microbial balance in the gut ecosystem. In these conditions, Bifidobacterium and Lactobacillus species are predominant and possess health-promoting effects [16, 17]. One of the most important strategies for overcoming dysbiosis conditions and the establishment of eubiosis conditions is the use of foods containing probiotic, prebiotic, and postbiotic ingredients [18]. The application of probiotics and synbiotics in the food industry, with gut homeostasis promoting goal, have been blooming during the past decade. With the advances of science, the role of probiotics and symbiotic is more evident in the treatment of diseases. However, in some cases, probiotics or synbiotics do not exhibit the appropriate efficiency. In this regard, scientists investigate the activity and characteristics of soluble factors (postbiotics) derived from probiotics. So, discussing the definition of some terms, history, and their applications in the food industry seems to be necessary. We have heard this sentence repeatedly: there is a strong relationship between drinking milk and longevity. Metchnikoff's works and intentions were considering as the new phrase as probiotics. Probiotics are beneficial microbes to promote health. Nowadays, it is elucidated that, in the intestine, some beneficial microorganisms protect them against diseases. It is well explicates that gut microbiota has deficiencies to deal with pathogens. Hence, it is a necessity to get probiotics through the diet. Supplements containing probiotics repair these shortages.
Probiotics
Probiotic (probios, exact mean is life) are characterized as non-pathogenic microorganisms that exert beneficial effects on the host when consumed in sufficient quantities. FAO-WHO (Food and Agriculture Organization of the United Nations –World Health Organization) expert group consensus statement in 2001 confirms this definition of probiotics [19]. The fermentation process was first described by Louis Pasteur in the 1900s. Also, Metchnikoff (1907) explained the secret of longevity in the Bulgarian rural population in regular dairy product consumption. He considered the Lactobacilli as probiotics with positive effects on human health in particular gut regularity functions [20]. At the end of the First World War, major groups of children suffered from intestinal complications. Following the work of Metchnikoff, another researcher Isaac Carasso created in 1919 Danone in Barcelona where the production of yogurt from the Pasteur Institute took place utilizing ferments. Later, Rettger and Cheplin in 1921 demonstrated that Lactobacillus acidophilus implantation in the human gut could help fight diarrhea, constipation, and other intestinal complications. Meanwhile, in 1917 an Escherichia coli strain was isolated by Nissle (1918) which successfully treated acute cases of infectious gut complications like salmonellosis and shigellosis. This strain is a typical example of a non-lactic acid bacteria probiotic available in the market and sold as Mutaflor® (Ardeypharm GmbH, Germany). Nevertheless, probiotics history returns to 10000 years ago. In the Indian ancient culture, the consumption of milk was considered the main diet. Approximately 3200 BC, produced fermented milk by the Egyptians and also dairy products during the pharaonic period has referred to the usage of probiotics in ancient times.
The term ‘-biotics’ is associated with the dietetic approaches, which can be applied to the gut microbiota direction towards a more beneficial state to host health. The ‘biotic’ term has a Greek root biotik-ós, meaning ‘about life’ and refers to the biological ecosystem including living organisms in a mutualistic relationship with their physical environment [21, 22]. Lactobacillus, Bifidobac-terium, and Streptococcus genera have immunomodulatory ability and display positive functions. In children, probiotics play an essential role in treating some complications such as allergy, irritable bowel syndrome, and respiratory infections [23-25]. However, in immunocompromised cases, probiotics must be taken cautiously [18].
The principal part of the probiotic products includes a well-known and limited list of bacterial taxa that include mostly lactic acid bacteria (LAB) like the Bifidobacterium spp., and Lactobacillus spp. That has the potency to be generally regarded as safe (GRAS) [26]. The diversity of probiotics has always been increasing, i.e., modern investigations lead to the recognition of the new races and species that include useful traits for humans. Also, probiotics have been divide into two scopes including general and provisional types in terms of efficiency. Lactobacillus acidophilus and Bifidobacterium are considered probiotics under any conditions. Other genera such as Bacillus and Escherichia in specific circumstances are placed in the probiotics category, for instance, in animals. Nevertheless, the selection criteria for probiotics are as follow;
Be GRAS (Generally recognized as safe) and not toxic or pathogenicPreferably be a member of normal flora with human originResistance to pH, bile saltsThe ability of desirable attachment to epithelial cellsHigh potential for proliferation and colonizationResistance to antibiotics, bacteriophages, and detrimental bacteria such as Helicobacter pylori, Listeria monocytogenes, etc. [27].In addition to the above cases, cost-effectiveness is almost of importance in this regard. It has been evident that the gut microbiota can be affected by probiotics through the prohibition of pathogens by preventing their adhesion and colonization in the gut. Moreover, probiotics probably exert a critical role in the development of the immune system, synthesis of important nutrient components like vitamins, and improvement of the intestinal barrier integrity through the up-regulation of involved genes in tight junction signaling [28-30].
Beneficial Properties of Probiotics
Beneficial Properties of Probiotics Several investigations have been performed regarding the valuable benefits of probiotics on human health through animal studies or trials. Some of the properties are as follows:
Anticancer activity [31].Prevention of allergic responses [32].Decreasing serum cholesterol [33].Stimulation of the immune system [34].Improvement of lactose malabsorption [35].Positive effects on gut microbiota [36].Improvement of the gut functions [37].Prevention of detrimental bacteria growth [38].Probiotic and Gut Microbiota
For decades, the potential health benefits of probiotics have been an area of growing scientific interest. The positive benefits of probiotic supplements have been investigating in various diseases, including gastrointestinal and metabolic disorders where the outcomes of the studies have supported the potential application of probiotics as therapeutic agents [39-41].
Probiotics exert their health-promoting impact on the host by several possible mechanisms that entail: amelioration of intestinal barrier function by influencing the epithelium and mucus lining; manipulating intestinal microbial communities; producing antimicrobial elements; competitive relation with pathogenic germs; balancing luminal acidity, immune-modulation; and stimulating proliferation and differentiation of epithelial cells [42, 43].
Researches have attributed the beneficial effects of probiotic consumption to several health outcomes. A growing series of studies have highlighted the significant effects of probiotic consumption in particular health pathologies; moreover, there is still substantial evidence that supports the health-promoting effects of probiotics in healthy individuals [44]. Hou et al. found that Firmicutes, Bacteroidetes, Proteobacteria, Actinobacteria, and Tenericutes were the predominant phyla in the fecal microbiota of all healthy participants [43]. The prevalent indicator of the gut microbiota composition is the F/B ratio. The gut microbiota composition in healthy grown-ups and the discrepancies in their responses to the same probiotic intervention are considered principal factors in defining their roles in human health and wellbeing.
In recent centuries, the composition of the host gut microbiota has received much consideration as a significant risk factor for disease progression that has the potential to be manipulated through probiotic consumption. The findings of several studies indicated the relationship between some gut microbiota and metabolic diseases such as obesity, diabetes, and gastrointestinal diseases [44-46]. Besides, other gut microbiotas are necessarily involved in functional processes such as digestion of indigestible nutrients, and the production of vitamins and micronutrients [47]. Taken all together, the gut microbiota population and any alternations in its composition, are closely attributed to human health. Hence, the health-effects of probiotic consumption on gut microbiota could be exploited as a tool for the maintenance and promotion of host health.
Modulation of the Intestinal Microbiota by the Application of Probiotics
The concept of probiotics to the scientific community was introduced by Nobel laureate Elie Metchnikoff. He reported that the longevity of Bulgarians was related to the consumption of viable Lactobacilli contained fermented milk products [48]. The observation suggested that ingestion of certain microbes may exert a beneficial role in human health. Since then, probiotics as dietary supplements or functional foods had been widely exploited. The gut microbiome supports the function and integrity of the gastrointestinal tract, maintenance of immune homeostasis, and host energy metabolism [49]. Intestinal dysbiosis, an imbalance in microbial communities, leads to disrupted interactions between microbes and their host. The alternations of the microbiome composition and function may underlie susceptibility to various diseases [50]. Several lines of evidence have revealed the link between gut dysbiosis and chronic low-grade inflammation and metabolic disorders, which consequently lead to metabolic syndrome (e.g. obesity and diabetes), infections in the gastrointestinal tract, inflammatory bowel disease (IBD), and irritable bowel syndrome (IBS) [49, 51, 52].
Maintaining the richness and diversity balance of the intestinal microbiome is being achieved by treatment methods. Probiotics can represent positive functions in the gastrointestinal tract or increase the functionality of resident microbial communities. This characteristic of probiotics arises from competition for nutrients, secretion of growth substrates or inhibitors, and modulation of intestinal immunity. The findings of randomized controlled clinical trials supporting the positive effects of probiotics during the treatment of gastrointestinal diseases [42, 53-55].
Antimicrobial agents/metabolic compounds secreted by probiotics result in growth suppression of other microorganisms or competing for receptors and binding sites on the intestinal mucosa [56, 57]. It has been showing that Lactobacillus strains improve the integrity of the intestinal barrier, which subsequently can result in preservation of immune tolerance, reduction of bacterial translocation across the intestinal mucosa, and disease phenotypes such as gastrointestinal infections, IBS, and IBD [58]. Furthermore, probiotics can regulate gut immunity and the intestinal epithelial' responsiveness and immune cells to microorganisms in the intestinal lumen [59].
Several tools and methods have been applied to study the effects of probiotics on the composition, diversity, and function of the gut microbiota. The result of a clinical study indicates the diminished pain and flatulence in patients with IBS after receiving a 4-week rose-hip drink containing 5×107 CFU/ml of L. plantarum DSM 9843 daily [60]. The amelioration of the clinical symptoms was attributed to the attendance of L. plantarum and reduced amounts of enterococci in fecal specimens of patients. A more recent study regarding patients with diarrhea-dominant IBS (IBS-D) demonstrated symptomatic relief after administration of a probiotic mixture of L. acidophilus, L. plantarum, L. rhamnosus, Bifidobacterium breve, B. lactis, B. longum, and Streptococcus thermophilus. Remarkably, fecal microbiota analysis of the patients applying denaturing gradient gel electrophoresis (DGGE) revealed that in probiotics-treated patients the microbial composition was more stable than those of the placebo group [61]. Recent advancements in DNA sequencing and bioinformatics have opened new horizons in the field of the human microbiome and how various treatment methods can alter the composition and function of the microbial populations. Recently, using a high-throughput, culture-independent method, research conducted to analyze the fecal microbiota of 6-month old infants treated with supplements of L. rhamnosus (LGG) per day. Their findings illustrated the abundance of LGG and an increased evenness index in the fecal microbiota of these infants, which in turn suggests ecological stability [62]. In another study, the ability of probiotics in the alternation of gut microbiota was investigated using 16S rRNA metagenomic sequencing in L. reuteri-treated neonatal mouse model. Their results demonstrated a transitory augmentation in community evenness and diversity of the distal intestinal microbiome in L. reuteri-treated animals in comparison to the vehicle-treated animals [63]. The microbial population diversity is related to the increased ecological stability. So, probiotics can modify intestinal microbiota and stabilize microbial communities [64].
Further, probiotics may also modulate the global metabolic function of the intestinal microbiome. In gnotobiotic mice and monozygotic twins administration of fermented milk products containing several probiotic strains did not alter the composition of the intestinal bacterial population [65]. However, fecal meta-transcriptomic analysis in probiotics-treated animals revealed significant alternations in the expression of microbial enzymes (particularly enzymes of carbohydrate metabolism). Additionally, mass spectrometric analysis of urinary metabolites demonstrated abundant levels of several carbohydrate metabolites. To sum up, these observations proposed that probiotics may lead to the global metabolic function of the intestinal microbiome.
Modulation of Gut Microbiota-brain Axis by Probiotics
The gut and the brain are closely associated with 200-600 million neurons [66]. It has been evident that brain signals may affect the motor, sensory, and secretory modalities of the gastrointestinal tract, besides, the gut’s visceral messages can alter brain function, though, and there is a reciprocal interaction between the gut and the brain [67, 68]. Since expanding evidence validated the indispensable role of gut microbiota in the gut-brain axis, the concept may be reconsidered as the gut microbiota-brain axis [69-72]. Nonetheless, the interaction pathways (possibly through neural, endocrine, and immune pathways) of gut microbiota (and/or metabolites produced by microbiota) and the brain are still far from being fully elucidated [73]. A growing body of evidence demonstrated that probiotics can modulate reciprocal interaction between gut microbiota and the brain and exert favorable impacts on brain activity and behavior. The safety aspects such as surviving in the gastrointestinal tract and non-pathogenicity with the human origin must be taken into account in probiotic strains used for human consumption [74].
Although the relationship between gut microbiota and mental disorders is complex, it is possible to improve the mentioned disorders through modulation of gut microbiota by probiotics consumption. For instance, Bercik et al. showed that Bifidobacterium longum results in normalized anxiety-like behavior induced by the noninvasive parasite Trichuris muris infection [74]; Bravo et al. illustrated that Lactobacillus rhamnosus (JB-1)-treated Trichuris muris-infected mice results in reduced anxiety- and depression-related behavior. Consumption of certain probiotics may affect brain activity in humans. Two-month administration of Lactobacillus casei strain Shirota in patients with chronic fatigue syndrome caused significant augmentation of both Lactobacillus and Bifidobacterium and a substantial decrease in anxiety symptoms in patients treated with the probiotic [74]. In another study oral administration of L. helveticus R0052 and B. longum R0175 ameliorated anxiety and depressive symptoms in healthy volunteers after 2 weeks of consumption, which was measured by the Hopkins Symptom Checklist (HSCL-90), the Hospital Anxiety and Depression Scale (HADS). Similarly, four-week administration of fermented milk product with probiotics (FMPP) (comprising Bifidobacterium animalis subsp. lactis, Streptococcus thermophiles, Lactobacillus bulgaricus, and Lactococcus lactis subsp. lactis) to the healthy women, changed control central processing of emotion and sensation in the brain, including affective, viscerosensory, and somatosensory cortices [75].
Several studies tried to define probiotics’ mechanisms of action that are involved in gut-brain axis signaling. Altered gut microbiota composition is related to brain anomalies. Probiotics can relatively or completely balance the dysbiosis of the microbiota induced by some brain diseases. Vagus nerve-mediated, immune response-mediated, and metabolite-mediated pathways are among different pathways involved in the modulation of the gut microbiota-brain axis. Developing novel microbial-based therapeutic approaches for brain diseases relies on a deeper understanding of gut bacteria communication and their hosts.
Dietary supplementation may probably alter the composition of the gut microbiota in infants and adults. Probiotics are considered as preventive and therapeutic measures, which may lead to the maintenance of the healthy gut microbiome composition and function. Identification of new indigenous microbial species and tools as a result of human microbiome studies can positively modify the gut microbial populations. Well-designed experiments in applicable experimental models (in vitro or in vivo) may increase understandings of the biology and potential manipulation of the microbiome in the human host. Novel probiotic strains and medicinal components produced by the microbiome may be exploited as future strategies to promote health and prevent/treat different diseases.
Prebiotics
For two recent decades, researchers Professor Roberfroid, Gibson introduced the concept of prebiotics. This term has become an interesting topic in science in different fields, in particular biomedical and nutrition. A majority group of non-digestible oligosaccharides (NDOs) is consists of 3–10 sugar moieties including glycosidic bonds in the beta-configuration, therefore, rendering the endogenous enzymes of animals including fish-resistant and hydrolysis are implemented to the alpha glycosidic linkage recognition as a typical in starch [76]. Oligosaccharides prebiotic can provide the essential energy for selecting responsible bacterial species to the product of short-chain organic acids. Indeed, metabolic cross-feeding is a process whereby metabolites from one bacterial species are the source of energy to other bacteria with the resulting short-chain fatty acids (SCFAs) production, primarily lactic, propionate, acetate, and butyrate. The functional properties of prebiotics presumably induce production of SCFA leads to blood lipid modulation, energy sources resulting in intestinal cell proliferation, GI/systemic immunomodulation, and improved intestinal barrier function improvement. Decreasing pH aids general nutritional support and absorption of minerals. The synergistic promotion of symbiotic and commensal microorganisms provides the competitive exclusion of pathogens, decreasing toxic microbial metabolites, and preventing intestinal inflammation [77]. The SCFAs have a crucial role in the growth and intestinal tissue physiology and systemic metabolism in animals and humans to produce a large proportion of colonocytes' energy requirements. Limited knowledge for the fish is available however, it has been demonstrated that enterocytes of fish can absorb SCFAs. Acetate acts as a primary fuel for the heart, brain, and skeletal muscle. Propionate stimulates the crypt cells of the absorptive epithelium in mammals. Also, it has been revealed that propionate can reduce the output of hepatic glucose and modulate biosynthesis cholesterol. Butyrate, as the most common SCFAs is produced by gut microbiota and accounts for the oxygen requirements for the intestinal microorganisms in fish. The fatty acid presumably up-regulates glutathione S-transferase and expression of catalase in the distal intestine. The latter is crucial animal enzymes that belong to the primary antioxidant enzyme system and help suppress free radical generation and oxidative stress. Also, butyrate is correlating with the osmoregulation processes of the intestine and sodium absorption [18, 78].
Beneficial Properties of Prebiotics
The main health-promoting effects of prebiotics on human health include; a) reducing cancer risk, b) balancing cholesterol levels, c) increasing minerals' absorption, d) promoting hormonal balance, e) regulating lipid metabolism, f) lowering the risk of cardiovascular disease, g) decreasing acute gastroenteritis, h) and lowering autoimmune reactions. Recently, a growing interest in prebiotics has been conducted, which selectively enhances useful components of the intestine microbiota. Their use is directing towards favoring beneficial compounds within the gut microbial milieu like the lactobacilli and bifidobacteria. They are distinct from most dietary fibers such as cellulose, xylan, and pectin. These components are not selectively metabolized by intestine microbiota. Contrary to probiotics, prebiotics can be added to different foods such as baked or cooked since they lack the survivability issues related to probiotics [79]. The fructan such as oligofructose, inulin, and no sugar are present market leaders to prebiotics across the globe. The majority of fructan is either synthesized from sucrose or commercially prepared inulin-rich plant sources like the chicory root (Cichorium intybus). Nevertheless, several alternative sources of inulin, including burdock (Arctium lappa) Jerusalem artichoke (JA) (Helianthus tuberosusand) are currently being commercialized, and there is increasing scientific supportive literature of their equivalence to chicory-derived inulin. These prebiotics as emerging candidates probably finds their way into the world market. Nevertheless, there is a need to approve their efficiency utilizing reliable methodologies in various trials and formulations.
The Consumption of Functional Foods and the Establishment of Gastrointestinal Health
The results of studies in recent decades have highlighted the positive role of food in the hosts' health and quality of life. In this respect, the primary function of diet, as a source of energy, has changed to its biological role in preventing various types of diseases and creating a variety of health-promoting effects on the host (human and/or animal). Antimicrobial, antioxidant, immunomodulation, and anti-cancer activities are well-known examples of their biological roles. It is noteworthy that such activities are closely related to the presence of various compounds with bioactive properties in the matrix of various (dairy and non-dairy) foods. Therefore, many efforts have been made to develop functional foods, a specific type of foods that in addition to their basic nutritional value and primary role in energy supplying have particular health effects on the host [80]. In general, these foods may promote general body circumstances ( e.g. probiotics), diminish the risk of certain diseases ( e.g. cholesterol-lowering products), and potentially be implicated in the prevention and treatment of various diseases. Through the years, these foods have started as foods enriched with vitamins and/or minerals (Food, Vitamin C, Vitamin E, Folic Acid, Zinc, Iron, and Calcium) and have grown into foods that promote healthy nutrition and prevent various diseases, containing micronutrients such as omega-3 fatty acids, phytosterols and soluble fibers [81].
Today, along with increasing awareness and acceptance of consumers, the consumption of functional foods in the world, especially Europe, America, and Japan, has spread dramatically. The results of clinical studies indicate a significant relationship between lifestyle (especially diet), a variety of diseases, and consumer health status. In this regard in 1990, functional foods were first marketed in Japan to prevent chronic diseases such as diabetes, hypertension, cancer as well as reducing health care costs [82]. In recent years, along with increasing awareness and reporting of beneficial effects of functional foods on health status, scientific communities, manufacturers, and consumers have shown great interest in these groups of foods. So that the production and consumption of functional foods in developed countries such as Europe, America, and Japan have significant progress. However, some countries lack it for several scientific and economic reasons. Japan is one of the countries with a piece of good knowledge about functional foods, and it is usually considering one of the leading countries in the formulation, production, consumption, and setting of relevant standards in this field [83]. Various factors such as high costs of treatments, un-favorable side effects of some treatment (in chronic diseases like cancer), the importance of prevention before treatment, consumer desire to consume a variety of foods with health-promoting benefits and ultimately improve the quality of life are the important reasons for the growing demand for functional foods [84]. In Europe, probiotics and prebiotic foods account for 60 percent of the market for functional foods, while in the US this is slightly lower. In Japan, 270 types of probiotic and prebiotic functional food products are formulated and manufactured, of which more than 46 are relating to protein and peptide compounds [85]. On the other hand, investigations on postbiotic compounds demonstrated higher stability of these compounds during the production process, storage (with a shelf-life of more than five years in foods and beverages), and the digestive tract conditions [86]. Consequently, due to the favorable characteristics of postbiotics in terms of safety, stability, pharmacokinetics, standardization, and transportation, they can utilize in a wide range of functional foods (fermented and/ or non-fermented) to enhance their nutritional value, shelf-life, and health-promotion goals for consumers [87].
