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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	Oligofructose	[56]
Yogurt	Asparagus fiber	[57]
Yogurt	Inulin and potential prebiotics from commercial apple, wheat, and bamboo fibers	[58]

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].