BIOACTIVE CARBOHYDRATES: AN OVERVIEW

Prebiotics, especially dietary fibers are the main types of biologically active carbohydrates that can be incorporated into food products. Prebiotics are non-absorbable food components that confer significant positive effects on human health by selectively stimulating the growth of health-promoting gut microorganisms, i.e., Bifidobacteria and Lactobacillus species (Bigliardi and Galati, 2013). They are mainly carbohydrate components such as dietary fibers, which can promote the number and activity of the normal intestinal microbiota and finally render some health benefits to the host (Sarao and Arora, 2017). Prebiotics are also certain dietaiy substances, which are not absorbed in the small intestine and can pass the upper part of the gastrointestinal tract without any degradation in colon conditions and then become fermentable substances for the gut microbiota and stimulate the growth of health-promoting bacteria, Bifidobacteria, and Lactobacilli species and simultaneously they can suppress the growth of food-borne pathogens such as Salmonella and Escherichia coli (Figure 3.1) (Al-Sheraji et al., 2013). Among the carbohydrates having potential prebiotic activity for the gut bacteria, only galactooligosaccharides (GOS) and fructans, i.e., inulin, and fructooligosaccharides (FOS) can accomplish all the criteria required to be deliberated as prebiotic components (Nobre et al., 2015). Nevertheless, the prebiotic activity of lactulose and p-glucan has also been reported in some dairy products. In addition, there are some miscellaneous bioactive carbohydrates available with their positive applications in food products. Therefore, the prebiotics inulin, FOS, GOS, lactulose, and p-glucan, as well as some of the novel Iranian hydrocolloids (basil seed gum and Persian gum), their sources, and production methods will be discussed in more detail in this chapter.

Potential applications of prebiotics

FIGURE 3.1 Potential applications of prebiotics.

INULIN

Inulin is a polydisperse oligomer containing fructose units joined by p-(2-l) linkages, and terminated by one glucose moiety. The degree of polymerization (DP) of inulin usually ranges from 2-60 (Figure 3.2 A) (Arcia et al., 2011; Glibowski and Bukowska, 2011; Kalyani Nair et al., 2010). Inulin can be found in onions (Allium сера), Jerusalem artichoke (Helianthus tuberosus), asparagus (Asparagus qfficianalis), leeks {Allium ampeloprasum), wheat, and chicoiy (Cichoriumintybus) root (Figure 3.3) (Mutanda et al., 2014). It is a dietaiy fiber and has well-known prebiotic activity and some important technological features (used as sugar and fat replacers in low-calorie foods, thickening, emulsifying, and gelling agents) (Lopes et al., 2015). The

General chemical structure of inulin. A) fructooligosaccharides (FOS), B) 1-kestose [n = 2], C) Nystose [n = 3], and D) Fructofuranosylnystose [n = 4]

FIGURE 3.2 General chemical structure of inulin. A) fructooligosaccharides (FOS), B) 1-kestose [n = 2], C) Nystose [n = 3], and D) Fructofuranosylnystose [n = 4].

Source: Reprinted with permission from Bali et al. (2015). © Taylor & Francis.

Distribution of inulin in various plant sources. Source

FIGURE 3.3 Distribution of inulin in various plant sources. Source: Figure modified from Mutanda et al. (2014).

standard chicory inulin (DP=12) has a neutral taste, 10% sweetness than that of sucrose, 120 g L_1 water solubility at 25°C, and 1.6 rnPa.s viscosity in the water at 10°C (5% solution) (Kalyani Nair et al., 2010).

Inulin has a low glycemic index and caloric value of 46 and 1.5 kcal g~‘, respectively (Mcdevitt-Pugh and Meyer, 2005). Inulin does not digest by enzymes of the mammalian small intestine like sucrase, a-amylase, and maltase, but is preferentially utilized by Bifidobacteria and Lactobacilli in the colon. As, inulin can be hydrolyzed by the action of p-fructosidase produced from Bifidobacteria and subsequently can be utilized by the host (Schaller-Povolny and Smith, 1999). It is a prebiotic carbohydrate, which affects human physiology and possesses many positive health effects (Glibowski, 2010). Some documented physiological activities of inulin were attributed to its numerous effects such as antibacterial effects against pathogenic bacteria, anticancer effects, lowering blood serum lipids, blood urea, and uric acid levels, increasing the absorption of calcium, magnesium, copper, iron, and zinc (anti-osteoporosis), decreasing the risk of cardiovascular diseases, and atherosclerosis and so forth (Karimi et al., 2015). Inulin is mainly produced from chicory at industrial scales (Glibowski and Bukowska, 2011) through three steps, as illustrated in Figure

3.4 (De Leenheer, 1996; Mensink et al., 2015).

Enzymatic production by inulosucrase type fructosyltransferase is also another production method used to synthesize inulin from sucrose through both transglycosylation and hydrolysis routs (Ozirnek et al., 2006). The enzyme can be obtained from different microorganisms such as Bacillus species, Escherichia coli, Streptococcus mutans, Lactobacillus strains, Leuconostoccitreum CW 28, Aspergillus oryzae KB, and plant sources like Helianthus tuberosus, which produce inulins with different molecular weights (Karimi et al., 2015).

Inulin production steps (De Leenheer, 1996; Mensink et al., 2015)

FIGURE 3.4 Inulin production steps (De Leenheer, 1996; Mensink et al., 2015).

Long-chain inulins are used as a fat substitute and form a particulate gel in the presence of water which in turn modifies the texture and also gives a fatlike mouthfeel to the product. However, the short-chain ones are used as partially sucrose replacers and they can improve the sweetness and flavor of related products (Arcia et al., 2011). In addition, inulins with DP of 22-25 have low solubility and form high viscous aqueous solutions, which enhance the viscosity, creaminess, and consistency of dairy-based products (Lopes et al., 2015). Inulin and oligofructose have an average daily consumption of 1-4 g in the USA and 3-11 g in Europe (Giri et al., 2014).

 
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