Properties and Functionality of Cereal Non-Starch Polysaccharides in Breadmaking

Abstract

Non-starch polysaccharides (NSPs) are biopolymers included in the fiber of cereal grains and seeds. Among NSPs, arabinoxylans and β-glucans are considered to play the most important role in breadmaking. In the literature to date, there is a lack of studies that summarize the current information on the properties and role of NSPs in this process. This review summarizes the up-to-date knowledge concerning the properties and functionality of the most common cereal NSPs in bread baking. In studies conducted to date, it has been shown that the addition of both arabinoxylans and β-glucans in amounts up to about 6% causes an increase in the water absorption of flour, and as a consequence, it forces the use of a larger addition of water to achieve the desired consistency of the dough. Even a small addition of NSPs can have a positive effect on the dough yield; making more bread from the same amount of flour and such bread is less caloric since neither NSPs nor water contributes to additional calories. Moreover, it has been shown that even a small addition of arabinoxylans or β-glucans has a positive effect on bread volume, moisture, and texture of the bread crumb as well as the preservation of bread freshness. The knowledge concerning cereal NSPs, especially modified ones and of defined structure, is incomplete and further research is needed to characterize their functionality in breadmaking.

1. Introduction

Non-starch polysaccharides (NSPs) are found abundantly in the cell walls of seeds (including cereal grains) as well as fungi and are one of the main components of fiber [1]. Among the NSPs commonly found in seeds and grains are arabinoxylans, β-glucans, cellulose, galactomannans, arabinogalactans, xyloglucans, and pectic polysaccharides [2]. The structure of NSPs varies considerably, depending on the type of plants in which they occur.

The examination of the influence of NSPs on the technological properties and quality of bread is very complex. The dough is a complex multi-component system in which (during mixing, fermentation, baking, and subsequent storage of bread) interactions between components lead to numerous chemical, biochemical, or microbiological reactions. In addition, it should be underlined that these reactions take place in a completely different way in traditional or gluten-free bread obtained by direct or sourdough methods. In such a complex environment as dough, unequivocally showing the role of individual compounds and their properties, the determination of the quality of bread is difficult. So, despite a lot of research carried out in this area, it has still not been possible to clarify what structure and properties of NSPs are particularly beneficial for obtaining bread of the highest quality.

The studies conducted to date have shown that NSPs, such as AXs, β-glucans, and others, significantly affect flour’s water absorption, dough yield, bread volume, moisture content, and hardness of the bread crumb, and other quality parameters of bread obtained using different baking technologies. However, the influence of the structural composition and molar mass of polysaccharides and the mechanisms of their effect in shaping bread quality are still unexplained.

In order to study the role of NSPs in bread baking, there is a need to extract them from various raw materials in significant quantities. On a laboratory scale, this is a complicated and time-consuming process; hence many researchers, in order to study the role of individual hydrocolloids in baking, choose to purchase commercially available preparations. Industrially obtained hydrocolloids may be poorly purified and therefore contaminated with associated substances, or as a result of purification and the technological process used, they often undergo significant modifications, including partial degradation in the process of obtaining them, so that they often do not reflect the structure and properties of native hydrocolloids. There is also frequently a lack of adequate characterization of commercial preparations performed by defined and recognized methods. The variety of commercially available preparations of non-starch polysaccharides is limited, which also hinders research on their potential application in bread baking.

In the literature to date, there is a noticeable lack of reports that summarize current information on the properties and role of NSPs in bread baking. The purpose of this review is to present the properties and function of NSPs in bread baking, with particular emphasis on AXs and β-glucans.

2. Definition and Occurrence of Cereal NSPs

Arabinoxylans (AXs) are built from a skeleton composed of xylose residues which may be substituted with arabinose residues at the positions of C(O)-3 (monosubstituted xylose residues) and C(O)-2 and C(O)-3 (disubstituted xylose). The arabinose residues in AX molecules can be further substituted with phenolic acid molecules, in particular ferulic acid. In cereal grains (Table 1), the highest AX contents were found in rye grain (8–12%), but AXs are also present in relatively high amounts in grains of wheat 0.8–9%, corn 4.8–5.6%, rice 2.97–6.84%, barley 1.2–10.5% and oats 1.2–11.6% [2,3,4,5,6,7,8,9,10,11,12,13,14,15].

β-glucans consist of long, linear chains composed of glucose residues linked in the cell walls of cereal grains and seeds by β-(1→4) and β-(1→3) glycosidic bonds, while in the cell walls of fungi by β-(1→3) and β-(1→6) glycosidic bonds [16,17,18,19]. Generally, there are trimonomeric and tetramonomeric segments in β-glucan molecules, i.e., containing three or four β-(1→3) linked glucose molecules. In cereal grains, trimonomeric segments of β-glucans account for 58–72%, while tetramonomeric segments account for 20–34% [20]. Fungal β-glucans are composed of segments consisting mainly of three β-(1→3) linked glucose molecules and, in small amounts, segments of two or four β-(1→3) linked glucose units [21,22]. As summarized in Table 1, the highest number of β-glucans (6.6%) was determined in the grain of cereals such as oats and barley [13,18,23,24,25,26]. β-glucans are especially abundant in the outer parts of the grain. Therefore, their content in bran is especially high (Table 1). These polymers are found in smaller amounts of 0.12–2.6% in rye and wheat grains in amounts of 0.4–1.3% in corn and rice grains [16,27,28,29]. β-glucans are also found in the cell walls of fungi in the amount of 4.71–56% d.b. of dried mushrooms [19,30,31,32,33,34]. Shiitake mushrooms (Lentinus edodes) and some members of the oyster mushroom family, especially Pleurotus spp., are considered to be among the most important sources of β-glucans, and their content in these mushrooms ranges from 10–56% d.b. [19,32,33,34].

Cellulose is formed by long linear chains of glucose linked by β-(1,4) glycosidic bonds. Due to its linear structure, cellulose is insoluble in water and resistant to digestive enzymes. The average cellulose content reported in the literature in barley grain is 1.4–4.7%, in rye 1.3–11.8%, and 1.67–14.1% in wheat grain [35,36,37,38,39]. It must be noted that the determination of cellulose content is complicated due to complex structure, poor solubility, and application of non-specific analytical methods for the determination of their content. Therefore, the reported values should be considered proximate.

Galactomannans are heterogeneous polysaccharides composed of a backbone of mannose residues linked by β-(1–4) glycosidic bonds with attached galactose residues via α-(1–6) glycosidic bonds. They differ in the ratio of mannose to galactose content. Galactomannans are mainly obtained from the endosperm of the seeds of many dicotyledonous plants, especially species of plants within the Leguminosae family. The highest amounts of galactomannans are found in carob gum (27–33%), fenugreek seed gum (25.5–32.8%), and guar gum (28.6–34.6%) [2,40,41,42,43,44]. Galactomannan content in cereals has not been reported.

Glucomannans have been found as a minor component in cereal grains. These NSPs are composed of glucose and mannose units [2].

Arabinogalactans consist of galactan chains with attached arabinose residues. Arabinogalactans are present in the cell walls of cereal grains, and their content (Table 1) ranges from 0.3% to 1.5% [45,46,47]. There are two types of arabinogalactans: type I and type II. Type I arabinogalactans are more common in nature than type II. The two types are distinguished from each other by their molecular structure. Arabinogalactan of type II is characterized by a more extended structure, as the galactan chains, in which galactose residues are linked by 1→3 glycosidic bonds, are attached to short galactan chains linked by 1→6 glycosidic bonds, which in turn are linked by further ranching in the form of arabinose residues, linked by (1→3) and/or (1→5) glycosidic bonds. In type I arabinogalactans, the molecule is built from a galactan chain with arabinose residues attached via (1→4) glycosidic bonds [48,49,50].

Xyloglucans are the general name for linear NSPs consisting of chains of glucans made up of glucose residues linked by β-(1–4) glycosidic bonds that are substituted with xylose. The content of xyloglucans in quinoa and amaranth grains was about 30% of the insoluble fraction of dietary fiber [2,51,52]. So far, the content of xyloglucans in other cereals has not been analyzed.

Pectic polysaccharides are composed of galacturonic acid molecules linked by α-(1→4) glycosidic bonds, most often with attached rhamnose residues, but also galactose, arabinose, xylose, fucose, or glucuronic acid. The average content of pectic polysaccharides in wheat, corn, and rice grains is 0.24–0.25% [53]. In quinoa grain, it is 4.68%, while in barley grain, it is 2.41% [54]. Some carboxyl groups in the galacturonic acid chain occur as methyl esters, and two types of pectins are distinguished: high methoxyl and low methoxyl. Additionally, protopectin is also present [55,56,57]. High methoxyl pectins contain >50% methanol-esterified carboxyl groups, while low methoxyl pectins contain <50% methanol-esterified carboxyl groups [58]. In cereal grains, high methoxyl pectins account for 28.7–36.4% of the total pectin content, and low methoxyl pectins account for 30.9–35.2% of the total pectin content. The remaining pectin content consists of protopectins, which are water-insoluble pectic substances (32.3–36.5%) [59,60].

Table 1. Content of non-starch polysaccharides in cereal grains.

Non-Starch Polysaccharides	Source	Content [%]	References
Arabinoxylans	Wheat grain	4.1–9	[5]
	Endosperm of durum wheat grain	1.5–1.8	[14]
	Endosperm of wheat grain	0.8–0.9	[10]
	Whole wheat flour	3–5	[46]
	Endosperm of barley grain	1.2–1.3	[10]
	Barley bran	10.5	[8]
	Barley flour	2.9–4.8	[11]
	Whole rye grain	7.6	[3]
	Whole rye grain	8.6	[7]
	Whole rye grain	7.1–12.2	[9]
	Endosperm of rye grain	2.2–2.4	[10]
	Endosperm of oat grain	1.2	[4]
	Oat bran	5.2	[4]
	Whole oat grain	11.6	[13]
	Corn grain	4.8–5.6	[6]
	Rice grain	2.97–6.84	[12]
β-glucans	Endosperm of durum wheat grain	0.12–0.16	[14]
	Durum wheat bran	0.71–0.8	[14]
	Wheat bran	2.6	[27]
	Wheat grain	1–2	[16]
	Wheat bran	2.15–2.51	[29]
	Whole barley flour	4.6	[25]
	Barley grain	3.9–6.6	[24]
	Barley bran	7.7–15.4	[23]
	Different varieties of barley	3.43–6.11	[18]
	Barley grain	3.9–5.9	[26]
	Rye grain	2.3	[3]
	Rye grain	<1	[16]
	Oat grain	3.4	[13]
	Oat bran	4.5–8.5	[23]
	Oat grain	4.4–6.1	[24]
	Rice grain	0.4–0.9	[28]
	Corn grain	0.5–1.3	[28]
Cellulose	Wheat grain	14.1	[38]
	Wheat grain	1.67–3.05	[39]
	Barley grain	4.29	[35]
	Barley grain	1.4–4.7	[36]
	Rye grain	1.3	[37]
	Rye grain	11.8	[39]
Arabinogalactans	Wheat flour	0.5–1	[46]
	Wheat bran	1–4.5	[46]
	Wheat flour	0.27–0.38	[45]
	Hulled barley	1.32–1.45	[47]
Pectic polysaccharides	Quinoa grain	4.68	[54]
	Barley grain	2.41	[54]
	Wheat meal	0.25	[53]
	Wheat bran	0.35	[53]
	Rice meal	0.25	[53]
	Corn meal	0.24	[53]

Table 1. Content of non-starch polysaccharides in cereal grains.

Non-Starch Polysaccharides	Source	Content [%]	References
Arabinoxylans	Wheat grain	4.1–9	[5]
	Endosperm of durum wheat grain	1.5–1.8	[14]
	Endosperm of wheat grain	0.8–0.9	[10]
	Whole wheat flour	3–5	[46]
	Endosperm of barley grain	1.2–1.3	[10]
	Barley bran	10.5	[8]
	Barley flour	2.9–4.8	[11]
	Whole rye grain	7.6	[3]
	Whole rye grain	8.6	[7]
	Whole rye grain	7.1–12.2	[9]
	Endosperm of rye grain	2.2–2.4	[10]
	Endosperm of oat grain	1.2	[4]
	Oat bran	5.2	[4]
	Whole oat grain	11.6	[13]
	Corn grain	4.8–5.6	[6]
	Rice grain	2.97–6.84	[12]
β-glucans	Endosperm of durum wheat grain	0.12–0.16	[14]
	Durum wheat bran	0.71–0.8	[14]
	Wheat bran	2.6	[27]
	Wheat grain	1–2	[16]
	Wheat bran	2.15–2.51	[29]
	Whole barley flour	4.6	[25]
	Barley grain	3.9–6.6	[24]
	Barley bran	7.7–15.4	[23]
	Different varieties of barley	3.43–6.11	[18]
	Barley grain	3.9–5.9	[26]
	Rye grain	2.3	[3]
	Rye grain	<1	[16]
	Oat grain	3.4	[13]
	Oat bran	4.5–8.5	[23]
	Oat grain	4.4–6.1	[24]
	Rice grain	0.4–0.9	[28]
	Corn grain	0.5–1.3	[28]
Cellulose	Wheat grain	14.1	[38]
	Wheat grain	1.67–3.05	[39]
	Barley grain	4.29	[35]
	Barley grain	1.4–4.7	[36]
	Rye grain	1.3	[37]
	Rye grain	11.8	[39]
Arabinogalactans	Wheat flour	0.5–1	[46]
	Wheat bran	1–4.5	[46]
	Wheat flour	0.27–0.38	[45]
	Hulled barley	1.32–1.45	[47]
Pectic polysaccharides	Quinoa grain	4.68	[54]
	Barley grain	2.41	[54]
	Wheat meal	0.25	[53]
	Wheat bran	0.35	[53]
	Rice meal	0.25	[53]
	Corn meal	0.24	[53]

3. Properties of NSPs

The basic properties of NSPs include solubility, water-binding capacity, formation of high-viscosity solutions, and ability to cross-link and decrease the surface tension [61,62]. The properties of NSPs are summarized in

Table 2. Properties of non-starch polysaccharides occurring in cereal-based products.

Properties	Non-Starch Polysaccharides	Main Conditions of Determination	Result	References
Solubility	Arabinoxylans	H2O 15 min., 30 °C Deionized water 1 h, 20 °C	30–40%	[63]
			18–23%	[64]
		[NA]	10–18.5%	[65]
	β-glucans	Deionized water	53.4–57.2%	[66]
		[NA]	27–78%	[67]
	Galactomannans	Deionized water	62.7–82.7%, solubility increased with temperature 25–80 °C	[68]
Water-binding capacity	Arabinoxylans	[NA]	15 g/g	[69]
		Measuring the amount of “defrosted” water at 30 °C	0.38 g/g	[70]
		Farinograph	After adding 1%, AXs to rye flour type 1150 and 720, these flours bound 2.5% and 8% more water, respectively. After adding 2% of AX flour bound 7.6% and 18.8% more water, respectively.	[71]
		Centrifuge method	1.58 g water/g AXs	[72]
		Centrifuge method	13.3 g to 16.13 g of water/g cellulose-rich AX fraction	[73]
	β-glucans	Centrifuge method	2.91 g/g d.b.—enzymatic extraction 3.10 g/g d.b.—acid extraction 3.28 g/g d.b.—alkaline extraction 3.79 g/g d.b.—extracted with water at 55 °C	[74]
			6.14–6.74 g/g	[66]
	Galactomannans	Centrifuge method	Galactomannans bound 42.5–47% of water depending on the maturity of the sugar palm nut	[75]
Viscosity	Arabinoxylans	Ubbelohde capillary viscometer at temperature 25 °C	2.81–4.23 dL/g	[61]
			Soluble AX 1.96–2.18 dL/g Insoluble AX 2.04–2.59 dL/g	[76]
	β-glucans		0.28 dL/g to 5.2 dL/g	[77]
			1.7–7.2 dL/g	[78]
	Galactomannans	Viscosity measurements at 25 °C	9.7–14.3 dL/g	[79]
		Ubbelohde capillary viscometer at 25 °C	12–12.5 dL/g at Mw of 2,720,000–2,790,000 g/mol	[80]
	Arabinogalactan	Ubbelohde capillary viscometer at 25 °C	0.045 to 0.062 dL/g	[61]
	Pectin		0.64 to 1.07 dL/g	[81]
			0.75 to 5.9 dL/g	[82]
Cross-linking	Arabinoxylans	Horseradish peroxidase + hydrogen peroxide	The Mw was 505,000 g/mol, and the viscosity was 2.90 dL/g	[83]
		Horseradish peroxidase + hydrogen peroxide	The initial Mw was 240,000–400,000 g/mol; after cross-linking, the Mw increased to 520,000–770,000 g/mol.	[9]
		Laccase	The Mw was 440,000 g/mol, and the viscosity was 3.6 dL/g	[84]
		Laccase, pH 5.5, 25 °C	The Mw was 508,000 g/mol	[85]
		1M sodium phosphate buffer (pH = 6) at 25 °C hydrogen peroxide and horseradish peroxidase	The Mw was 243,500 g/mol and 191,100 g/mol. The intrinsic viscosity was 2.3 dL/g and 1.6 dL/g.	[86]
		Laccase	Initial Mw was 128,000 g/mol, and after cross-linking, it was 159,000 g/mol.	[87]
	β-glucans	Ethylene glycol diglycidyl ether in the presence of 4% sodium hydroxide	Only elasticity was tested.	[88]
Surface Tension	Arabinoxylans	Alveolar tensiometer	Decrease in surface tension from 72 mN/m to about 52 mN/m, at concentration 0.6–1.5%	[61]
	β-glucans	Analysis of the profile of an axially symmetrical drop shape	Decrease in surface tension after 8 min <10 mN/m at a concentration of 1%. Decrease in surface tension in the presence of 0.5% β-glucans was less than 1 mN/m.	[89]
	Galactomannans	The Du Nouy ring method	Decrease in surface tension from 72 mN/m to 61 mN/m at a concentration of 0.5%.	[90]
	Pigeon pea polysaccharide (arabinogalacatan) Lemon pectin	The Du Nouy ring method with a tensiometer	Decrease in surface tension from 72 mN/m to approx. 50 mN/m at a concentration of 1.5%	[91]
			Decrease in surface tension from 72 mN/m to 53 mN/at a concentration of 1.5%	[91]
Molar mass (Mw)	Arabinoxylans	SEC a	240,000–400,000 *	[9]
		SEC	500,000 *	[92]
		SEC	820,000–1,220,0000 **	[93]
		SEC	244,000–491,000 *****	[6]
		SEC	2,000,000 *	[7]
		SEC	381,000 ****	[94]
		SEC	276,000–877,000 **	[8]
		SEC	176,000–260,980 ****	[76]
		SEC	197,800–294,640 *	[76]
		SEC	253,000 ******	[95]
		SEC	24,400–232,000 ******	[96]
	β-glucans	Based on viscosity	1,500,000 ***	[97]
		SEC	1,200,000 ***	[98]
		SEC	1,400,000–1,800,000 ***	[99]
		SEC	1,160,000 ***	[20]
		SEC	250,000 ***	[100]
		SEC	270,000–780,000 ***	[101]
		SEC	203,000 ***	[102]
		SEC	2,060,000–2,300,00 0***	[103]
		SEC	440,000–2,340,000 **	[104]
		SEC	187,000–338,000 **	[20]
		SEC	450,000–1,320,000 **	[26]
		SEC	250,000 **	[105]
		SEC	200,000–300,000 **	[106]
		SEC	606,400–698,500 **	[66]
		SEC	487,000 ****	[29]
		SEC	970,000 *	[7]
		SEC	172,000 ***	[107]
		SEC	743,000 **	[107]
		SEC	635,000 ****	[107]
	Galactomannans	SEC	1,418,000 ^	[108]
		SEC	1,490,000 ^	[90]
		SEC	1,170,000–1,810,000 ^	[42]
	Arabinogalactans (Mongolian Larchwood)	Based on viscosity	16,000	[109]
	Arabinogalactans (rhizome of Polygonatum sibiricum)	Based on viscosity	141,000	[110]
	Xyloglucans (Azuki bean seeds)	Based on viscosity	420,000	[111]
		SEC	98,000	[112]
	Xyloglucans from tamarind seeds	SEC	450,000–830,000	[113]
	Xyloglucans from Detarium senegalense seeds	SEC	630,000–1,660,000	[82]
	Pectins (obtained from various fruits and vegetables)	SEC	61,000–182,000	[114]
		SEC	153,800–247,100	[114]

^a Size Exclusion Chromatography (SEC); * rye grain; ** barley grain; *** oat grain; **** wheat grain; ***** maize grain; ****** rice grain; ^ fenugreek seeds.

.

3.1. Solubility

The solubility of NSPs depends on their molecular structure. Any structural feature that hinders intermolecular association, such as molecular branching or the presence of carboxyl, sulfate, or phosphate groups, leads to higher solubility [115]. Structural features that promote intermolecular association, affecting poor solubility, include the presence of linear chains in the molecule, high molar mass, and other regular structural features [2,116].

AXs are generally classified into two fractions: water-soluble and water-insoluble. The solubility of AXs in water depends on the degree and pat tern of substitution, the ratio of arabinose to xylose, and the molecular weight. It has been shown that the removal of arabinose residues from the AX chain results in reduced solubility [117]. Water-insoluble AXs are bound to substances found in the cell wall, such as proteins, lignin, or cellulose [117,118]. Water-soluble AXs are loosely bound at the cell wall surface [117,119]. The solubility of AX (Table 2) from wheat flour is typically 30–40% [63], while that of rye whole-grain flour is 18–23% [64]. The solubility of AXs from barley grain was 10–18.5% [65]. However, it should be noted that the observed differences in the determined solubility of AXs may be due to the extraction conditions applied, the differences in the composition of obtained preparations, and the differences between methods used for solubility determination [64,65].

The solubility of β-glucans is affected by the ratio of trisaccharide to tetrasaccharide units because if the ratio is smaller, the solubility will be higher [120]. The solubility of β-glucans from oat grains is higher in hot water than in cold water, so food processing steps that require moisture and heat are likely to increase the solubility of β-glucans [121]. The solubility of β-glucans has been shown to increase during bread baking as well [122]. However, a decrease in the solubility of β-glucans has been observed for foods stored frozen for longer periods of time [123]. It was shown that the solubility of β-glucans increased along with decreasing in the molecular weight (reducing Mw from 2,200,000 g/mol to 400,000 g/mol). However, β-glucan molecules with low molecular weight (120,000 g/mol) show the ability to form insoluble aggregates [124,125]. As reported in the literature (Table 2), the solubility of β-glucans isolated from oat grain is 27–78%, while barley grain is 53.4–63% [66,67].

The solubility of galactomannans depends on the degree of substitution of mannose chains by galactose residues. A larger degree of substitution results in a greater solubility of the molecules. Galactomannans, in which galactose residues are attached to each mannose molecule, form such a large steric hindrance that they dissolve easily in cold water. In galactomannans, in which a galactose residue is attached to every fourth mannose molecule, there are difficulties dissolving in cold water, but such molecules dissolve easily in hot water. The presence of more side chains in galactomannan molecules, which keep the main mannose chains far enough apart, contributes to the greater solubility of galactomannan molecules. On the other hand, galactomannans with fewer side chains (larger mannose-to-galactose ratio) can interact with other polysaccharides due to their long blocks of unsubstituted mannose units [126,127]. Information on the degree of solubility of galactomannans from cereal grains is lacking in previous research studies. However, the solubility of locust bean gum was tested and amounted to 62.7–82.7% [68].

Arabinogalactans are NSPs most often extracted in the form of arabinogalactan peptide. Arabinogalactan peptide comprises about 92% of a polysaccharide, while the peptide part accounts for 8% [128]. The solubility of arabinogalactans from cereal grains was not reported.

The solubility of pectins is related to their degree of polymerization and the number and distribution of carboxyl groups. The solubility of pectin increases along with a decrease in its molar mass and an increase in the esterification of carboxyl groups. The solubility of pectin is also clearly influenced by pH and solution temperature [129,130,131]. In previous literature studies, the solubility of cereal pectins has not been determined.

Xyloglucans are soluble in water [113], but the solubility of cereal grains xyloglucans was not reported.

3.2. Water-Binding Capacity

NSPs show hydrophilic properties so that they can bind water. The water-binding capacity results from the interaction of water with NSP molecules through the formation of hydrogen bonds or dipole interactions [132,133].

AXs show a strong tendency to bind water (Table 2), especially the water-soluble ones [70,72,134]. The addition of water-soluble AXs in the amount of 0.5–1.3% to wheat flour led to the binding of 11–12% more water compared to the flour without the addition of these polysaccharides [134]. Water-soluble AXs derived from wheat flour are able to bind an average of 0.38 g water/g d.b. [70], whereas AXs derived from rye grains are able to bind 1.58 g water/g [72]. According to other literature data, it has also been shown that AXs from wheat flour is able to bind even 15 g of water/g [69]. Cellulose-rich AX from wheat bran is able to bind from 13.3 g to 16.13 g of water [73].

Depending on the extraction method (Table 2), the amount of water bound by β-glucans from barley grain ranged from 2.91 g/g d.b. using enzymatic extraction to 3.79 g/g d.b. using hot water extraction [74]. Other literature studies reported that the water binding capacity of β-glucans from barley grain was 6.14–6.74 g water per 1 g of β-glucans [66]. The significant differences in the obtained results were probably due to the use of other barley grain varieties.

It must be noted that determined values of water-binding capacity are proximate and strongly affected by methods of NSPs extraction, but also by differences in methods used for the determination of this parameter.

3.3. Viscosity

The viscosity of aqueous solutions of AXs depends on the length of the chains of the molecules, the molar mass, the degree and pattern of substitution of the main chain (backbone) composed of xylose residues with arabinose molecules, and the presence of attached ferulic acid [117]. There are two types of soluble AXs: arabinoxylan I and arabinoxylan II [135]. The first one contains a chain of xylose residues that is substituted in 50% by arabinose residues at the O-3 position. Arabinoxylan II consists of a chain of xylose residues that are substituted in 60–70% by arabinose residues at the O-2 and O-3 positions. Arabinoxylan type II molecules show a stronger correlation with viscosity than arabinoxylan type I [135]. As it was shown in Table 2, the intrinsic viscosity of aqueous solutions of AXs ranges from 1.96 dL/g to 4.23 dL/g [61,76].

β-glucans also have the ability to increase the viscosity of aqueous solutions. Based on the literature, the viscosity of β-glucans is affected by the method of extraction, molar mass, temperature, pH of the solution, concentration, and aggregation ability [2,20,100,116]. As shown in Table 2, the intrinsic viscosity of β-glucan water solutions typically ranges from 0.28 dL/g to 7.2 dL/g [77,78].

Galactomannans have the ability to form highly viscous aqueous solutions at relatively low concentrations, which are only slightly affected by pH, ionic strength, and heat treatment. The viscosity of galactomannan solutions is characterized by high stability in a wide pH range (1–10.5), mainly due to the neutral character of their molecules [126,127,136]. The intrinsic viscosity of aqueous solutions of galactomannans reported in the literature (Table 2) ranges from 9.7 dL/g to 14.3 dL/g [79,80].

The intrinsic viscosity of aqueous solutions of arabinogalactans was 0.045–0.062 dL/g [61].

Pectin polysaccharides also show the ability to form highly viscous solutions, which depend on the polymer concentration, molar mass and structure, pH, and ionic strength. The viscosity of water solutions of pectins increases with the increase in their molar mass [137]. In addition, the viscosity of pectic polysaccharide solutions is affected by pH. This is due to a change in the molecular conformation of polysaccharide chains under the influence of the electric charge of polysaccharides [138]. In an acidic environment, the dissociation of the carboxyl groups of the galacturonic acid residues is reduced, the electrostatic repulsive forces between the pectin chains are lower, and consequently, the viscosity of the aqueous solution of such polysaccharides will be higher than the aqueous solutions of polysaccharides with a neutral or alkaline pH [139]. Low-methylated pectic polysaccharides gel over a wide pH range (3.5–8.5), while high-methylated pectic polysaccharides gel at acidic pH (<3.6) [139,140,141]. The intrinsic viscosity of aqueous solutions of pectic polysaccharides obtained from fruits ranges from 0.64 dL/g to 5.9 dL/g [81,82]. The literature lacks information on the viscosity of aqueous solutions of arabinogalactans, xyloglucans, and pectic polysaccharides from cereal grains.

3.4. Cross-Linking

Under oxidizing conditions and in the presence of free radicals, adjacent AX molecules can form a covalent bond between ferulic acid residues, becoming cross-linked [142,143]. Cross-linking of AX is most often carried out using agents that generate free radicals: the peroxidase/hydrogen peroxide system (both of these components occur naturally in flour and yeast) or the enzyme laccase [143]. During the enzymatic coupling reaction, monomeric ferulic acid is oxidized and converted into isomers of dehydrodiferulic acid or dehydrotriferulic acid [144]. The cross-linking efficiency of AX is affected by their molecular structure, i.e., molar mass, the degree of substitution of the xylan skeleton with arabinose residues, and the content and distribution of ferulic acid in the molecules. The greater number of ferulic acid residues in the polysaccharide backbone, the more covalent cross-links can be generated. The total content of ferulic acid in AX molecules from cereal grains is estimated to be 0.4–450 mg/100 g [9,145,146,147,148,149,150]. As a result of cross-linking, NSPs of high molar mass and, consequently, high viscosity is obtained [151]. The weight average molar mass of AX cross-linked with horseradish peroxidase and hydrogen peroxide ranges from 191,000 g/mol to 720,000 g/mol [9,83,86,110], and the weight average molar mass of laccase cross-linked AX ranges from 159,000 g/mol to 508,000 g/mol [84,85,87]. However, presented values of molar mass (Table 2) seem to be tentative and underestimated because problems with the solubility of large molecules formed after cross-linking are reported [9].

Paramylon, which are β-glucans extracted from euglenin cells, and kurdlan, which are β-glucans produced by a strain of the bacteria Alcaligenes faecalis strain, were cross-linked using ethylene glycol diglycidyl ether (EDGE) in the presence of 4% sodium hydroxide, yielding compounds with greater hydrophilic properties (greater ability to form a gel). Cross-linked β-glucans are obtained by breaking the hydrogen bonds in the chains of the molecules, so new hydroxyl groups are created [88].

So far, data concerning cross-linking of arabinogalactans, xyloglucans, and pectic polysaccharides of cereal origin have not been reported.

3.5. Surface Tension

Surface tension is created by cohesive interactions between water molecules. Active surfactants interrupt the interactions of cohesion forces between water molecules, which consequently leads to a reduction in the surface tension of water [152]. This is important because the adhesion of liquid food, dough, and food emulsions to processing equipment, packaging, and resulting residues cause significant economic losses [153].

It was reported (Table 2) that AX in the amount of 0.2% to 1.6% reduces the surface tension of water from 72 mN/m to about 52 mN/m [61].

β-glucans reduce the surface tension of water, but only to a small extent. The higher the concentration of β-glucans used, the more the surface tension decrease is observed. The decrease in surface tension in the presence of 1% β-glucans was approximately 10 mN/m, whereas the decrease in surface tension in the presence of 0.5% β-glucans was less than 1 mN/m [89].

In the presence of 0.4–0.5% galactomannans obtained from fenugreek seeds, the surface tension of water was reduced from 72 mN/m to 61 mN/m [90].

Pectin polysaccharides from citrus peel and pigeon pea (probably arabinogalactan) also showed the ability to lower surface tension [91]. With the addition of 1.5% pigeon pea polysaccharides, the surface tension decreased from 72 mN/m to about 50 mN/m, and with the addition of 1.5% citrus peel pectin, from 72 mN/m to 53 mN/m [91].

The influence of arabinogalactans, xyloglucans, and pectic polysaccharides from cereal grains on the surface tension of water was not reported.

3.6. Molar Mass

NSPs of natural origin are polydisperse in terms of molar mass, i.e., the size of their molecules is not uniform [115].

The weight average molar mass of cereal AX (Table 2), determined mainly by Size Exclusion Chromatography (SEC), is typically in the range of 197,800–2,000,000 g/mol for rye, 176,000,000–381,000 g/mol for wheat, and 276,000–1,220,000 g/mol for barley grains, 244,000–491,000 g/mol for corn, 24,400–232,000 g/mol for rice [6,7,8,9,76,83,92,93,94,95,96].

Among the β-glucans occurring in cereal grains (Table 2), oat β-glucans have a molar mass of 172,000 g/mol to 2,300,000 g/mol [20,97,98,99,100,101,102,103,107], while the molar mass of barley β-glucans ranges from 187,000 g/mol to 2,340,000 g/mol [20,26,66,104,105]. The weight average molar mass of β-glucans from wheat grain is estimated to be 487,000–635,000 g/mol, while from rye grain is 970,000 g/mol [7,29,107].

The molar mass of arabinogalactans, xyloglucans, and pectins of cereal origin has not been analyzed. The weight average molar mass of galactomannans from fenugreek seeds is estimated to be 1,170,000–1,810,000 g/mol [42,90,108]. The weight average molar mass of arabinogalactans from Mongolian larch is 16,000 g/mol, and from Polygonatum sibiricum rhizome is 141,000 g/mol [109,110]. The weight average molar mass of xyloglucans from azuki bean seeds ranges from 98,000 g/mol to 420,000 g/mol, while from tamarind seeds and Detarium senegalense seeds is 480,000–2,400,000 g/mol [111,112,113]. It has been shown that the average molar mass of fruit pectins ranges from 61,000 g/mol to 247,000 g/mol [82,114].

3.7. Modifications of NSPs

Modifications of polysaccharides include changing their structure using chemical, physical and biotechnological methods in order to obtain compounds with desired properties. The most commonly used modifications are cross-linking and hydrolysis.

Cross-linking of AX results in an increase in molar mass, an almost 100-fold increase in the viscosity of their solutions compared to unmodified ones, and an increase in the water-binding capacity of these polysaccharides [151]. AX molecules are subjected to the crosslinking process due to the presence of ferulic acid molecules in their structure, with the help of which the AX molecules are linked [9,83,86,110]. The addition of cross-linked AX to bread dough causes an increase in the water absorption of flour, reduces the hardness of the bread crumb, and improves organoleptic properties [83,154,155]. Information on cross-linking of other non-starch polysaccharides from cereal grains is scarce.

Another frequently used method of modifying NSPs is their partial enzymatic hydrolysis, for which enzymes naturally present in the grain and/or seeds can be used. Enzymatic hydrolysis of AX is most often carried out using the endo-1,4-xylanase enzyme. As a result of hydrolysis, the molecules are divided into smaller fragments [156]. Hydrolyzed AX are characterized by lower molar mass and higher solubility, and their aqueous solutions have lower viscosity compared to native or cross-linked AX [9,83]. Hydrolysis of β-glucan chains leads to changes in the structure of the molecules; as a consequence of such modifications, the molar mass of β-glucan and the viscosity of their solutions are reduced [157]. Enzymatic hydrolysis of oat grain β-glucans using a commercial cellulase resulted in a decrease in the molar mass of β-glucans. As a result of reducing the molar mass of β-glucans, their solubility increased by 78–100% compared to non-hydrolyzed β-glucans. In contrast, the water-holding capacity of hydrolyzed β-glucans decreased by 60–76% compared to non-hydrolyzed β-glucans [158]. β-glucans from bran and oat flakes were also modified using lichenase. As a result of this modification, oligosaccharides with a degree of polymerization (DP) ≥ 3 (but lower than DP < 10) were obtained. The hydrolysis of β-glucans with lichenase positively influenced the yield of these polysaccharides from the soluble fraction of dietary fiber [159].

It is worth noting that above mentioned modifications of NSPs may also occur naturally in dough during the breadmaking process because the modifying agents are naturally present in dough ingredients. Observing the strong impact of such modifications on the molecular properties of NSPs, it may be expected that they may have a high impact on the process and properties of the final product. However, further research is needed to reveal and characterize the modifications, their mechanism, and their effect on the whole breadmaking process.

4. The Role of NSPs in Bread Making

4.1. The Influence of NSPs on the Water Absorption of Flour

Flour water absorption is an important parameter determining the amount of water bound by flour ingredients, including, in particular, starch, NSPs, and proteins [160]. NSPs affect the water absorption of flour due to their high water-binding capacity [161].

In studies conducted to date (

Table 3. Effect of the addition of NSPs on the water added to the dough and on quality features of bread.

Non-Starch Polysaccharides	Type of Bread	Addition to Dough [%]	Increase in the Water Addition to Dough [%] *	Increase in Bread Volume	Decrease in Crumb Hardness	Increase in Crumb Moisture	References
Arabinoxylans	Rye	0.5	1–5	up to 16%	up to 14%	up to 1%	[163]
	Rye	1–2	2.5–19	-	-	-	[71]
	Wheat	0.5–1.3	11–13	positive effect	-	up to 29%	[134]
	Wheat	0.25–0.5	-	positive effect	positive effect	positive effect	[15]
	Gluten-free	3–6	up to 10	up to 20.5%	-	up to 9%	[155]
Cross-linked arabinoxylans Hydrolyzed arabinoxylans Cross-linked, hydrolyzed, and unmodified arabinoxylans	Rye	1–12	3–95	up to 18%	up to 88%	up to 62%	[83]
	Rye	1–15	0.2–22	up to 55%	up to 92%	up to 33%	[83]
	Rye	1	5–18	up to 34%	depends on modification	up to 4.5%	[154]
β-glucans	Wheat	0.2–1.4	5–13	up to 37%	-	up to 6.5%	[164]
	Wheat	2.5–10	6–19	-	-	-	[165]
	Wheat	0.8–1.2	9–1	negative effect	-	up to 8%	[166]
	Gluten-free	1–2	-	up to 16.5%	-	-	[170]
Galactomannans	Wheat	5–10	18.5–35.5	negative effect	up to 21%	-	[168]

* water addition to obtain the same optimum consistency. - lack of information.

), it has been shown that the addition of AXs to wheat, rye, and gluten-free dough (in amounts up to 6%) significantly increases water addition to dough needed to obtain the same optimal consistency [83,155]. It has also been shown that the effect of AXs on flour water absorption depends on the structural characteristics of AXs, such as the degree of branching, A/X ratio, the degree of substitution with ferulic acid molecules and cross-linking, and their molar mass [9,83,154,162]. However, there is a lack of information on comparing the effect of structural properties and molar mass of AXs on the water absorption of wheat flour during dough making by direct and sourdough methods.

As shown in Table 3, after adding AXs in the amount of 0.5% to rye dough, it bound 1–5% more water [163]. After adding AXs in the amount of 1% to rye flour type 1150 and 720, these flours bound 2.5% and 8% more water, respectively. However, after adding AXs in the amount of 2%, they bound 8% and 19% more water, respectively [71]. The addition of AXs in the amount of 0.5–1.3% resulted in increased water absorption of wheat flour by 11–13% [134].

The addition of β-glucans to the dough for wheat bread (in the amount of up to 1.4%) resulted in an increase in the water absorption of the flour by up to 5–13%, compared to the flour without the addition of polysaccharides [164]. The addition of β-glucans in the amount of 2.5–10% to wheat flour increased its water absorption from 6% to 19%, compared to bread without the addition of polysaccharides [165]. The addition of β-glucans in the amount of 0.8–1.2% to wheat bread increased the water absorption of the flour by 9–16% [166]. The water absorption of dough is also influenced by arabinogalactans [167] and galactomannans [168,169].The addition of galactomannans in the amount of 5–10% to wheat bread increased the water absorption of the flour by 18.5–35.5% [168].

In the available literature, there is a lack of comparison of the effect of various NSPs of different molar masses on water absorption determined under standardized conditions. The studies conducted so far concerned the characteristics and assessment of the effect of individual polysaccharides on the baking properties, and the use of different conditions for dough preparation and bread baking by different authors makes it impossible to compare the effect of individual polysaccharides. Some NSPs are acidic polysaccharides (containing uronic acids in the molecules), whose effect during the preparation of the dough and baking can be very different, depending on the pH of the environment and on the baking technology used. However, the role of acidic polysaccharides in baking has not been thoroughly investigated.

4.2. The Influence of NSPs on the Yield of Dough

The consequence of the increased water absorption of the flour and the increased addition of water to the dough in order to obtain optimal consistency is its higher yield, which is, from an economic point of view, of great importance for the bakery industry. Even a small addition of NSPs has a positive effect on dough yield, which means that more bread can be produced from the same amount of flour [9,76,83,162,171]. It should be noted that bread obtained from flours with higher water content per 100 g of product is also characterized by lower calorie content. This property can be very desirable for consumers, especially those struggling with diabetes or obesity.

4.3. The Influence of NSPs on Bread Volume

According to the literature, two kinds of bread’s volumes are determined: the volume of bread baked from the same amount of dough and the specific bread volume expressed as bread volume per defined amount (100 g) of flour. The first parameter is commonly used and represents the structural properties of dough. The second one includes the structural properties of dough and also the yield of dough, which is related to the differences in water absorption. It was shown that the addition of AXs (in the range of 1–6%) had a positive effect on the volume of both wheat and rye bread (Table 3). The influence of the molar mass of AXs on the parameter mentioned above depends on the type of dough (wheat, rye) [76,83,134,154,155,163,172,173]. Moreover, in the case of rye bread, the addition of cross-linked AXs in the amounts of up to 3–6% resulted in an increase in bread volume by up to 18%, however at a higher share of such AX bread volume gradually decreased [83]. In the case of the addition of low molar mass AXs (partially hydrolyzed), the most pronounced effect on bread volume was observed when higher amounts of AXs were applied, and the increase in bread volume was up to 55% [83]. In a previous research study, it was shown that the addition of AXs obtained from other sources, such as flax mucilage, effectively improved the volume of gluten-free bread [174]. The analysis of the available literature shows that AXs are particularly promising NSPs in terms of improving not only the volume but also the overall quality of gluten-free bread.

Information on the effect of the addition of β-glucans on the volume of bread is ambiguous, and further research is needed to be able to determine their effect on this parameter clearly. It has been shown that β-glucans have a positive effect on the volume of wheat bread, but this is correlated with their content and molar mass, as well as with the quality of the wheat flour used. The addition of 0.6% of high molar mass β-glucans obtained from barley grain resulted in an increase in the specific volume of wheat bread by as much as 37% [164]. In the case of gluten-free bread, the addition of 1% β-glucans increased the bread volume by 22.4%. On the other hand, the addition of β-glucans to gluten-free bread in the amount of 2% increased the bread volume by 8–16.5% [170]. However, based on some studies, the application of barley grain β-glucans at 5% to wheat bread resulted in a 28% reduction in bread volume [175], and the addition of both high and low molar mass β-glucans to wheat bread at the level of 4.5% resulted in a 53% and 44% decrease in bread volume, respectively [176]. It must be noted that in some research works, there is no information regarding compensation of higher water absorption caused by the addition of NSP, by additional amounts of water applied, and in the cases where this was not performed the dough could be too dense, and as a consequence the observed bread volume from the same amount of dough is lower compared to bread without the addition of NSPs.

In the available literature, there are indications of the potential of other NSPs, such as galactomannans. For example, the addition of galactomannans from locust bean seeds at 2% to wheat bread increased its volume by 12% [169].

4.4. The Influence of NSPs on Bread Crumb Moisture

The addition of NSPs with a specific molecular structure to the dough may increase the water absorption and yield of the dough, which also results in the desired, higher moisture content of the bread crumb [134,154,162,167]. It has been shown (Table 3) that AXs with a higher molar mass has a greater effect on crumb moisture than those with a lower molar mass [46,76,83,134].

The addition of 0.5–6% AXs to wheat and gluten-free bread increased the moisture content of its crumb up to 29%, compared to bread without the addition of AX [90,155]. The addition of cross-linked AXs to rye bread increased the moisture content of its crumb up to 62%, compared to rye bread without the addition of AXs. On the other hand, the addition of hydrolyzed AXs to rye bread increased the moisture content of its crumb by up to 33%, compared to rye bread without the addition of AXs [83].

The addition of β-glucans, especially those with a higher molar mass in the amount of 0.2–1.4%, increased the moisture content of the wheat bread crumb, compared to wheat bread without the addition of β-glucans [164,166]. However, the literature lacks comprehensive studies indicating the role of the type, structure, and molar mass of polysaccharides in shaping the moisture content of the bread crumb.

4.5. The Influence of NSPs on Bread Crumb Hardness

It has been shown (Table 3) that the addition of 0.5–1% AXs to wheat, rye, or gluten-free bread significantly reduces crumb hardness, compared to bread without the addition of NSPs [15,134,154,155,163]. The addition of cross-linked AXs to rye bread in amounts of 1–12% reduced the hardness of the bread crumb up to 88%. On the other hand, the addition of hydrolyzed AXs to rye bread in the amount of 1–15% reduced the hardness of the bread crumb up to 92% [83,154]. This is due to the fact that AXs increase bread volume and crumb porosity and also help retain water in the bread crumb, which consequently affects its hardness [177].

It was shown that the addition of 0.8% β-glucans to wheat bread reduced the crumb hardness after 1 day of bread storage by 30% [166]. Soluble oat fiber containing 70% β-glucans was added to the wheat bread, and the bread with the addition of 10% to 12% of such fiber was characterized by lower crumb hardness compared to the control bread, which was baked without fiber addition [178]. The addition of 2% galactomannans from carob seeds to wheat bread also caused a decrease in crumb hardness [169].

In addition, other NSPs may reduce crumb hardness, but the effectiveness of individual polysaccharides and the mechanisms behind this process are not well studied.

4.6. The Influence of NSPs on Bread Aging

Starch retrogradation is believed to be a major contributor to bread staling. The addition of 1% AXs positively affects the preservation of freshness of wheat bread, compared to bread without the addition of these polysaccharides [15,134]. The crumb hardness of rye bread baked from flour type 720 with the addition of AXs after 4 days of storage increased slower compared to control bread baked without the addition of AXs. In addition, the crumb of rye bread with the addition of AXs generally lost moisture more slowly after 4 days of storage, both for bread made of rye flour type 720 and for bread made of rye flour type 1150 [154]. Moreover, AXs, due to the fact that they are characterized by the ability to bind large amounts of water, limit the process of starch recrystallization, which is responsible for bread staling [179].

The addition of β-glucans to wheat bread in the amount of 0.2–1% reduced the moisture loss compared to wheat bread without the addition of polysaccharides [164]. Moreover, the addition of 0.8–1% β-glucans to wheat bread inhibited the increase in bread crumb hardness after 5 days of storage compared to bread without polysaccharides [166].

4.7. The Influence of NSPs on Starch Digestibility

There are indications in the literature that NSPs can effectively inhibit the digestion of starch, lipids, and proteins in the small intestine [2,70,180,181]. Previous attempts to explain this effect point to the increased viscosity of the food matrix due to the presence of NSPs, which limits the contact between digestive enzymes and their substrates, and between nutrients and their absorption in the intestinal mucosa [181,182,183,184].

It has been shown that the presence of high molar mass AXs in bread reduces the digestibility of starch and affects the content of resistant starch in the bread crumb [185], but the mechanisms behind this process have not been fully elucidated. Many studies have shown that NSPs, including AXs and β-glucans, reduce the glycemic index of food, which is desirable for people struggling with, for example, diabetes [186], but the mechanisms of this effect, observed with different intensity depending on the type of bread (wheat, rye, traditional, sourdough, gluten-free), have also not been fully studied.

4.8. The Influence of NSPs on the Human Body

NSPs, through their high water-binding capacity, play an important role in the rapid passage of digestive contents, thus positively influencing the functioning of the digestive system [187].

In addition, the fermentation of NSPs provides short-chain fatty acids (SCFAs), which are responsible for a range of health-promoting properties, including inhibiting the growth of pathogenic organisms, increasing absorption of mineral salts, preventing or alleviating diarrhea [188,189]. Both AXs and β-glucans from cereal have a prebiotic effect because they positively influence the increase in the amount of bifidobacteria, i.e., probiotic bacteria in the colon [190,191]. Both AXs and β-glucans influence innate and acquired immunity, as they are immunomodulators [192,193,194,195]. β-glucan molecules have the ability to bind to pattern recognition receptors found in immune cells (such as granulocytes, monocytes, macrophages, and natural killer cells) [196,197,198]. Due to this characteristic, they also show anticancer activity [199,200]. In addition, AX molecules containing ferulic acid in their structure may exhibit antioxidant activity [201]. β-glucans from fungal cell walls have clinically confirmed therapeutic immunostimulatory properties, including antimicrobial, anti-inflammatory, anti-tumor, and accelerated wound healing [202,203]. NSPs are promising in the control of obesity and diabetes, which are typical diseases of modern society. AXs lower postprandial blood glucose levels, regulate insulin response and stimulate the secretion of postprandial ghrelin, a hormone produced by gastric cells that is called “the hunger hormone” [190,204,205]. AXs increase the viscosity of aqueous solutions, so bread baked with the addition of these polysaccharides is characterized by a reduced glycemic index [206].

Galactomannans obtained from morel (Morchella esculenta) can be used as a potential immunomodulator in the food and pharmaceutical industries [207].

4.9. Negative Effects of NSPs

In the literature, negative effects of NSPs are reported [83,117,166,176,208,209]. Excessive addition of AXs caused high viscosity of dough and reduced bread volume [83,208]. The negative effect of NSPs addition on bread volume was also noted by other researchers [175,176,209], and a possible explanation for these observations lies in the purity of examined preparations of NSPs. Often preparations used for breadmaking are not characterized in detail. In some cases, foreign substances (contaminants) present in preparations may cause negative effects, for example, bran particles linked to extracted NSPs, which may damage gas cells in the bread crumb leading to a reduction in bread volume and an increase in the bread crumb hardness [117].

5. Conclusions

This review summarizes the current state of knowledge regarding the role and impact of NSPs in bread baking, as well as outlines missing information on the above issues. A review of the literature showed that NSPs have interesting properties from the point of view of the baking industry. The solubility of NSPs from cereal grains depends on their molecular structure. NSPs from cereal grains have hydrophilic properties and are able to bind high amounts of water—from 0.38 g to 15 g of water/g d.b. NSPs from cereal grains form viscous solutions and are responsible for the viscosity of different kinds of dough. In the presence of NSPs from cereal grains, the surface tension decreases by up to 20 mN/m. The molar mass of NSPs from cereal grains is in the range of 200,000–2,340,000 g/mol. In cereal grains, the dominant NSPs are AXs and β-glucans. To date, properties of AX and β-glucan are better characterized, but there is a lack or incomplete information on the majority of the above-mentioned properties for NSPs such as galactomannans, arabinogalactans, xyloglucans, and pectin polysaccharides from cereal grains.

The second part of this review summarizes information regarding the role of NSPs in bread making. Even a small share of the NSPs in flour can have a positive effect on the basic parameters of dough, such as water absorption, dough yield, as well as volume, moisture, texture, and aging of bread. The addition of NSPs with a specific molecular structure to the dough may increase water absorption and dough yield, which also results in the desired, higher moisture content of the bread crumb. High molar mass cross-linked AXs or partially hydrolyzed low molar mass AXs have a positive effect on the volume and other properties of bread. Research was also carried out on the effect of the addition of β-glucans and galactomannans, and their positive effect on the hardness of the wheat bread crumb was demonstrated. Moreover, according to literature data, NSPs can effectively inhibit the digestion of starch, lipids, and proteins in the small intestine and, therefore, also prevent obesity or diabetes. In addition, NSPs may also show immunomodulatory effects.

The structure of NSPs determines their properties and functionality in technological processes. However, research, including the role of NSPs and their molecular structure in breadmaking, are complicated and still scarce. The knowledge concerning cereal NSPs, especially modified ones and of defined structure, is incomplete and further research is needed to characterize their functionality in breadmaking.