and can be produced using chitin from shrimp and crabs, which are subjected to a partial acid hydrolysis [34] or by using bacterial chitinase [35]. The consumption of chitin oligosaccharides is associated with improvements on the intestinal microbiota, and antimicrobial and immunomodulatory activities [36].
Maltooligosaccharides and isomaltooligosaccharides, palatinose oligomers, α-glycosyl saccharose, lactosaccharose, nigerooligosaccharides, gentiooligosaccharides, and chitosanoligosaccharides are other commercially available oligosaccharides. Although these compounds have not necessarily been used as prebiotics, they may have bifidogenic activity. Furthermore, prebiotic agents are possible fractions of oligosaccharides obtained from a partial hydrolysis of non-starch polysaccharides, such as acacia gum, guar gum, and wheat bran [20].
Recently, new sources are being explored in order to discover or isolate new prebiotic compounds [37]. For example, the consumption of a water extract of Hirsutella sinensis (medicinal mushroom) by mice fed a high-fat diet (HFD) was able to reduce inflammation, obesity, and insulin resistance. Furthermore, the consumption of a fraction of the high molecular weight polysaccharide (> 300 kDa) obtained from the water extract was able to reduce the body weight (50%), the metabolic endotoxemia, intestinal permeability, insulin resistance, and inflammation. At the same time, P. goldsteinii counts were increased, which suggest that the health effects may be associated to the mediation of the intestinal microbiota and the increase in the probiotic P. goldsteinii [37]. The effects were dependent on the sensitivity of the bacteria to neomycin [38]. Therefore, polysaccharides from the H. sinensis mushroom can therefore be used as a prebiotic in the reduction of risk of obesity and its complications [38].
Several studies are still being carried out to identify new sources of compounds with prebiotic properties. Cereal grains can be used as sources of prebiotic compounds, such as wheat, corn, oats, and barley [17]. Fructose and fructooligosaccharides can be obtained using reusable bioreactors and biocatalysts with immobilized inulinase [39]. Aloevera, due to its antibiotic activity, can be a source of prebiotic compounds. Its fructans can increase the populations of microorganisms in a higher rate compared to inulin [40]. Algae such as brown algae (Osmundea pinnatifida, Ecklonia radiate) and red algae (Gelidium sesquipedale) can have laminarin as prebiotic compounds, resulting in increases in the number of beneficial microorganisms in the intestinal communities [41]. Dark roasted coffee beans and ground coffee have oligosaccharides that can have prebiotic properties [42]. Stevia rebaudiana can be a source of fructooligosaccharides and inulin, mainly due to the high concentration of steviol glycosides in the leaves [17]. The continuous use of cashew powder (Anacardium occidentale L.) was associated with increases in the counts of Lactobacillus species, suggesting prebiotic properties [43].
In addition to naturally occurring sources, prebiotic compounds may also be synthesized by microorganisms, and many industries aim to design or synthesize value-added biocomposites in a sustainable manner [44]. In this sense, the technology of microbiological processes that deal with mixtures of different substrates is valuable, such as agro-industrial residues and corn flour in solid-state fermentation systems [12]. Furthermore, Penicillium oxalicum may is being used for producing inulinase, which may be used for obtaining inulin. Agave salmiana spp. is composed of agave-fructans, which can increase the counts of Lacticaseibacillus paracasei and Lacticaseibacillus casei [17]. These are some examples of research involving new prebiotic substance sources; however, next-generation prebiotic substances are in high profile today and are continually being updated.
2.3 Prebiotic Dairy Functional Foods
Prebiotics can change the quality characteristics of dairy products, mainly because they can interact with the components of the matrix. Inulin and oligofructose are the main prebiotics used in dairy products, and the effect of their addition is dependent on their DP [25]. Therefore, inulin-type fructans can be added as ingredients in functional products and can improve the nutritional, technological, and functional properties of the products. Inulin has a higher DP, therefore, its sweetness is low (< 10% compared to sucrose) and is moderately soluble in water (10% at ambient temperature) [45]. It is used as a fat replacer in dairy products, due to the ability to promote in the mouth a sensation similar to that of fat. It can form microcrystals when mixed with water or milk, which are not perceived in the mouth, but interact and result in a finely creamy texture [25]. On the other hand, oligofructoses have properties similar to those glucose syrups and sugar, as they have a greater number of free sugars. Sweetness in its pure form is 30 to 35% when compared to sucrose, and it has a low caloric value (1 to 2 kcal/g) [46]. Thus, they are used to prepare functional dairy products low concentrations of sugar. For these reasons, inulin and oligofructose are widely applied in the dairy industry [45]. The application of prebiotics has been described as showing promising results in yogurts and fermented milks. Table 2.3 describes applications of prebiotic agents in fermented milk and dairy beverages.
The utilization of inulin and fructooligosaccharides as fat replacer in sheep milk ice cream resulted in products with similar rheological properties (viscoelasticity, hardness, and consistency) compared to the full-fat product. Furthermore, the prebiotic formulations were perceived to be creamier and shinier than the control sample. In addition, most prebiotic ice creams were mentioned as being sweeter, which suggests that the prebiotics can replace conventional sweeteners [59]. Therefore, inulin and fructooligosaccharides can improve the functional, physiological, and nutritional properties of ice cream, reducing the caloric value and increasing the functionality of the products [60]. In addition, inulin can help to control the crystallization and recrystallization of frozen dairy products [61].
Inulin has also been widely used in cheese as a fat substitute [45]. Non-fat cheeses may have rheological, texture, sensory and functional defects, such as a rubber texture characteristic, flavor alterations, increased bitterness, unpleasant taste, altered melting capacity, and non-typical color [62]. Thus, it is a technological challenge to use fat substitutes that maintain the same sensory and functional properties as cheese without reducing their fat content [63]. In this sense, inulin seems to be suitable for replacing fat in cheeses with low-fat content, as it improves the feeling of softness in the mouth [64]. This feeling of creaminess is generated through the encapsulation of a large amount of water and complexation with protein aggregates [52, 65].
Table 2.3 Some examples of the application of prebiotic agents in fermented milk and dairy beverages. Adapted from Dantas et al. [47].
| Dairy product | Prebiotic | Reference |
| Fermented milk | Inulin | [48] |
| Soursop dairy beverage | Inulin | [49] |
| Sheep milk yogurt | Inulin | [50] |
| Low-fat yogurt | Inulin and agave fructans | [51] |
| Low-fat yogurt | Inulins with varied DPs | [52] |
| Low-fat yogurt | Inulin | [53] |
| Low-fat yogurt | Inulin | [54] |
| Low-fat yogurt | Inulins with varied DPs | [55] |
| Yogurt |