The ability to replace fat is higher in long-chain and inulin with high molecular weight. The high DP results in a lower solubility of inulin, increasing its ability to form microcrystals when added to milk. The addition of long-chain inulin (5%) in a fresh Kashar cheese (70% fat reduction) resulted in softer product (lower hardness), which was attributed to the alterations in the chemical composition (higher moisture) and to the higher cheese volume, with a consequent decrease in the protein content [66]. When inulin was used at 10% concentration, a cheese with creamy texture and chemical characteristics similar to the full-fat cheese was obtained [63]. When compared to other fibers, inulin had better results on fat substitution in mozzarella cheese than methoxypectin, polydextrose, and resistant starch [67]. Long-chain inulin was used as fat substitute (2, 3, and 7%) in fresh goat milk cheese, and the inulin-added product showed a less compact structure compared to the conventional cheese, which was associated with the lower fat distribution in the matrix. Inulin was incorporated in the casein network, interrupting the casein network, and resulting in a softer gel structure [68].
Galactooligosaccharides can be easily added to dairy products, such as yogurt, ice cream, dehydrated buttermilk, and dairy beverages due to their excellent solubility. In ice cream, galactooligosaccharides have a positive effect on optical, physical-chemical, and sensory characteristics. The products with inulin showed higher firmness and lower melting rate, resulting in a product with greater stability. Furthermore, they presented better flavor and sensory attributes [69]. In yogurt, galactooligosaccharides can be added before or after fermentation, and the structure of the yogurt becomes smoother and more creamy. In addition, the bacteria used to make yogurt do not use galactooligosaccharides as a carbon source, which prevents it from being metabolized until it reaches the large intestine [70]. It is also possible to produce powdered buttermilk containing galactooligosaccharides in its formulation. This product can be easily used, for example, in the preparation of fermented dairy products [71].
Xylooligosaccharides are used in the formulation of prebiotic dairy products. The physicochemical and sensory aspects of yogurt enriched with xylooligosaccharides were compared to those with yogurts containing gelatin. The pH, acidity, and total solids were significantly affected by the addition of xylooligosaccharides. The taste and overall acceptability were not impacted by xylooligosaccharides addition (< 3.5%), but an increased residual flavor was observed [72]. In addition, yogurt enriched with xylooligosaccharides showed significant improvement in mineral absorption and reduced glucose content in rats [73]. Thus, xylooligosaccharides can be used as a functional compound in the formulation of dairy products with health benefits. Cream cheese with xylooligosaccharides showed a more compact and denser structure, with higher apparent viscosity, firmness, and elasticity. Furthermore, it improved the physicochemical properties (decreased particle size and viscosity and increased melting rate), rheological characteristics, and sensory characteristics (improved acidic flavor and salty taste, and better homogeneity, and less bitter taste) [74].
2.4 Synbiotics
The concept of synbiotic was described at first time about 25 years ago, and it involved the combination of probiotics and non-digestible ingredients that could be selectively fermented (prebiotics). Thus, synbiotics were reported as mixtures of “probiotics and prebiotics that beneficially affect the host” [9]. The term was composed by the Greek prefix “syn”, which means “together” and the suffix “biotic”, which means “belonging to life”. However, confusion about synbiotic products remained, in part, because the original definition “mixtures of probiotics and prebi-otics that beneficially affect the host, improving survival and implantation in the gastrointestinal tract, selectively stimulating the growth and/or activation of the metabolism of one or a limited number of health-promoting bacteria, and thus improving the host’s well-being” lacked precision. Furthermore, the inclusion of other agents in the ‘–biotics’ category, including post-biotic [75] and pharmabiotics [76], may further contribute to the confusion. In May 2019, a panel updated the definition of synbiotic to “a mixture containing living microorganisms and substrate(s) used selectively by host microorganisms that confer a benefit to the host’s health”. The panel reported that defining synbiotics simply as a mixture of probiotics and prebiotics could preclude the innovation of synbiot-ics that are produced to work cooperatively. Therefore, the requirement that each component must meet for evidence of its action and the dose established for probiotics and prebiotics individually could represent an obstacle. A complementary synbiotic could not be designed for its parts to work cooperatively and, therefore, must be composed of a probiotic plus a prebiotic (Figure 2.2). Thus, in a complementary synbiotic, the prebiotic and probiotic works independently to achieve at least one health effect [15]. On the other hand, a synergistic synbiotic is where the substrate is designed to be used selectively by the probiotic microorganisms administered together (Figure 2.3). The mixture of the selectively utilized substrate (prebiotic) and a live microorganism (probiotic) works together to achieve at least one health effect [15].
Consumption of a combination of prebiotics and probiotics appropriately selected can improve the beneficial effects of the compounds when used individually. Fructooligosaccharides and inulin can stimulate the growth of bifidobacterial in the intestine (bifidogenic effect) and suppress the activity of undesirable bacteria (Enterococcus faecalis, Escherichia coli, and Proteus genus). Consequently, there is a reduction in the pH values because the beneficial microorganisms produce acids, and an antagonist effect against harmful or pathogenic bacteria may be observed, with decreases in the concentration of toxic metabolites [77].
Figure 2.2 Mechanism of action of a complementary synbiotic.
Figure 2.3 Mechanism of action of a synergistic synbiotic.
The synergistic activity between prebiotics probiotics and was considered efficient because they could improve the implantation and survival of probiotics in the gastrointestinal tract. Some health effects of orally administered combinations of live microorganisms and a prebiotic substrate are reported in Figure 2.4 [15]. Randomized controlled trials have been reported including adults with overweight, metabolic diseases, obesity, non-alcoholic fatty liver disease, and type 2 diabetes mellitus [15]. In addition, the investigation of other outcomes also was conducted, such as surgical infections, irritable bowel syndrome, atopic dermatitis, chronic kidney disease, eradication of Helicobacter pylori infection, and management of gestational diabetes mellitus [15]. However, it is important to note that for a formulation to be called synbiotic, there needs to be evidence to prove the selective use by the host microbiota (complementary synbiotic) or by the live microorganism that is co-administered (synergistic synbiotic) [15].
Synbiotics have as the main benefit the increase in the permanence of probiotics in the gastrointestinal environment. Synbiotics can control infections, which is associated with the formation of compounds during the fermentation process in the large intestine by probiotic cultures [78]. They can improve the functionality of epithelial barriers and modify the ecosystem of bacteria [79]. Prebiotics