Reduction of cardiovascular disease, reduction of LDL-C
Prebiotics were first defined as non-digestible food ingredients which selectively stimulate the growth of a restricted type of bacteria in the large intestine, benefiting the host [9]. Currently, prebiotic is defined as “a substrate that is selectively utilized by host microorganisms conferring health benefits” [10]. According to these experts, non-digestible carbohydrates (oligosaccharides and polysaccharides), some peptides and proteins, phenolic compounds, and certain lipids (esters) can also be considered prebiotic ingredients according to the new definition. Thus, when prebiotics are selectively fermented by the resident microbiota the fermentation results in compounds responsible to enhance the physiological properties of the host, such as mineral absorption, intestinal function, decreased risk of colon cancer, and regulation of glucose and lipid metabolism [4, 10]. In addition, they are associated with the prevention of diet-related diseases, such as hypercholesterolemia, diabetes, gastrointestinal infections and intestinal inflammation [11]. The prebiotics consumption also encourages the development of beneficial bacteria and difficult harmful bacteria establishment in the body, which cooperate for the prevention of infections and allergies [12, 13]. The prebiotic market is growing from 2016 to 2024 at an 8% CAGR (Compound Annual Growth Rate), prospecting 989.4 kilotons in 2021 [14].
In the same direction, the market for synbiotic products has also been increasing considerably. When a prebiotic and probiotic are used simultaneously in a product, the combination is called synbiotic. The updated definition of a synbiotic is “a mixture containing living microorganisms and substrate(s) used selectively by host microorganisms that confer a benefit to the host’s health” [15]. The requirement that the components should meet for evidence of its beneficial action and prove the dose established for prebiotics and probiotics individually, could represent a difficult scenario [15]. Thus, there are two different categories of synbiotics, the complementary and the synergistic synbiotic [15]. In a complementary synbiotic, the prebiotic and probiotic works independently in order to provide at least one health benefit, while a synergistic synbiotic is the mixture of the selectively utilized substrate (prebiotic) and a live microorganism (probiotic), which works together to achieve one or more health benefits [15]. With these new and defined terms and their confusion cleared up, it became much easier for the industry and researchers to explore and create new synbiotics.
In this sense, recently, it was observed an increased quantity of scientific studies using prebiotics or synbiotics ingredients with prospective health claims in dairy products. This chapter will present the main updates on prebiotic and synbiotic dairy products and their health benefits.
2.2 Prebiotics
In 2017, the term prebiotic was redefined as “a substrate that is selectively used by host microorganisms that confer a health benefit” [10]. Prebiotics are often associated with carbohydrates of low molecular weight which are not digested in the human gastrointestinal tract and could positively improve the activity and composition of the microbiota of the intestine. However, the more recently definition of prebiotics opens opportunities to other compounds, such as polyunsaturated fatty acid, phytochemicals, linoleic acid, and phenolic compounds. Furthermore, it allows the utilization of prebiotics in many parts of the body besides the gastrointestinal tract and also other products, such as feed for poultry, aquaculture, and livestock [10]. In 2018, a group of scientists met again to analyse the advances in the prebiotics field, focusing on topics that affect research methodology, functionality, and geographical impacts [16]. Prebiotics are commonly highlighted in the studies, but the mechanisms of action and the health benefits need further evaluations [17].
Non-digestible carbohydrates, such as oligosaccharides, such as galactooligosaccharides (GOS), fructooligosaccharides (FOS), isomaltooligosaccharides (IMO), xylooligosaccharides (XOS), raffinose oligosaccharides (RFOs), mannan oligosaccharides (MOS), arabinoxylan oligosaccharides (AXOS), inulin, lactulose, and others, and polysaccharides (pectin, resistant starch, and dextrin) are considered food components with prebiotic properties (Table 2.2) [12].
The prebiotics with established health effects are separated into three groups: I) oligosaccharides (GOS, inulin, FOS, IMO, XOS, isomaltulose, RFOS, among others), II) polyols (xylitol, lactulose, lactitol, mannitol), and III) fibers (dextrins, cellulose, β-glucans, pectins) [18]. They have a diversity of chemical compositions, and the differences in the units (monosaccharides) and the type of glycosidic bonds in the non-digestible carbohydrates enable the prebiotics to be classified in many classes of oli-gossacharides [19].
The intestinal microbiota ferments the prebiotic compounds and can produce short-chain fatty acids (SCFA), such as acetate, propionate, and butyrate. These compounds can enhance many physiological effects, such as the function of the intestine, the absorption of minerals, the regulation of the metabolism of glucose and lipids, and also could reduce the risk of colon cancer [10]. Some health effects of orally administered combinations of a prebiotic substrate are reported in Figure 2.1 [10]. The consumption of prebiotics can favor the increase in the counts of beneficial bacteria and hinder the establishment of pathogenic bacteria, reducing the risk allergies and infections [18]. There are convincing and reproducible results in the literature of studies on animals that have consumed prebiotics demonstrating effectiveness in the reduction of risk or treatment of many diseases, e.g., irritable bowel syndrome, colon cancer, obesity, cardiovascular diseases and type 2 diabetes [16].
Table 2.2 Prebiotic substances, their source, and structure. Adapted from Sako and Tanaka [20].
| Designation | Source | Structure |
| Lactulose | Lactose |
|
| Galactooligosaccharides | Lactose |
|
