Barley β-Glucans and β-Glucan-Enriched Fractions as Functional Ingredients in Flat and Pan Breads

C H A P T E R

27 Barley β-Glucans and β-Glucan-Enriched Fractions as Functional Ingredients in Flat and Pan Breads Marta S. Izydorczyk, and Tricia McMillan Grain Research Laboratory, Canadian Grain Commission, Winnipeg, MB, Canada

O U T L I N E Introduction

347

Barley β-Glucan-Enriched Fractions in Flatbread

358

Barley β-Glucan Isolates in Bread Products

348

Technological Issues

361

β-Glucan Concentrates and β-Glucan-Enriched Grain Fractions

References

362

349

Barley Flour and β-Glucan-Enriched Grain Fractions in Pan Breads

353

Abbreviations FRF GI DSC CSP

fiber-rich fractions glycemic index differential scanning calorimetry Canadian short process

INTRODUCTION In recent years, the role of diet has expanded from emphasizing survival and hunger satisfaction to using food to promote better health and to manage and reduce the risk of certain chronic diseases. Consumers’ attention on acquiring health-promoting foods and healthy food ingredients continues to increase as the link between diet and health benefits becomes substantiated by positive scientific evidence and clinical trials. This trend has revived interest in some ancient and nutritious, but often neglected, cereals, such as barley. Barley is increasingly incorporated into new and established food products, either as a whole grain or as a grain-derived ingredient (e.g., flour, fiber fraction, concentrate). Barley contains an assortment of phytochemicals with potential health benefits, including phenolic acids, flavonoids, lignans, tocols (vitamin E), phytosterols, and folates (vitamin B), but it is probably best known for its high content of soluble dietary fiber (DF), especially mixed-linkage (1 ! 3, 1 ! 4)-β-D-glucans, commonly known as β-glucans.1,2 β-Glucans have been implicated in attenuating postprandial blood glucose and insulin levels, lowering serum cholesterol levels, and having an effect on certain metabolic syndromes, including appetite control, obesity, hypertension, gut microbiota composition, and modulating immune functions.3–5

Flour and Breads and their Fortification in Health and Disease Prevention https://doi.org/10.1016/B978-0-12-814639-2.00027-7

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© 2019 Elsevier Inc. All rights reserved.

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27. BARLEY β-GLUCANS AND β-GLUCAN-ENRICHED FRACTIONS AS FUNCTIONAL INGREDIENTS IN FLAT AND PAN BREADS

The role of β-glucans in lowering cholesterol and serum lipids has been a subject of numerous studies.3,6 It has been demonstrated that the cholesterol-lowering effect of β-glucans depends on the increased viscosity of the contents of the gastrointestinal tract, which reduces the reabsorption of bile acids, increases the synthesis of bile acids from cholesterol, and reduces circulating low-density lipoprotein (LDL) cholesterol concentration. Elevated levels of total and LDL blood cholesterol are recognized as independent diet-related risk factors of coronary heart disease. Enough positive evidence of the efficacy of barley β-glucans to reduce the risk of coronary heart disease has been found, and, in the United States, Canada, and European Union countries, foods containing barley are allowed to make a health claim. This claim stipulates that 3 g per day of β-glucan soluble fiber (from either whole-grain barley, pearled barley, barley flakes, barley grits, or other barley products), combined with a diet low in saturated fat and cholesterol and high in vegetables, fruit, and grains, are needed to affect cholesterol levels.7–9 The effect of β-glucans on postprandial glucose metabolism is also related to their ability to increase viscosity in the gut, causing a delayed and/or decreased absorption of glucose into the bloodstream.10 This action helps in the prevention and management of type 2 diabetes because slower absorption of glucose after a meal reduces the amount of insulin that must be produced by the pancreas, and blood sugar levels are easier to maintain. The European Food Safety Authority (EFSA)11 permits the claim that consumption of β-glucans from barley as part of a meal contributes to reduction of blood glucose increases after that meal. However, in order to benefit from the claimed effect, 4 g of β-glucans for each 30 g of available carbohydrate should be consumed per meal. Given the evidence supporting the physiological benefits of β-glucans in the human diet, a considerable amount of technological research has gone into developing ways of incorporating these polysaccharides into food products. Typically, white bread is a poor source of DF and is considered to be a high-glycemic food; therefore, incorporation of β-glucans into bread is desirable, and at the same time, an effective way to increase the intake of these polysaccharides because of the high consumption of bread products worldwide. Research has shown that incorporating barley β-glucans into bread without compromising product palatability and marketability and without sacrificing the physiological efficacy of β-glucans, not only at the stage of addition but also after processing, can be a challenging task. This chapter discusses various technological and functional aspects of incorporating different forms of β-glucan preparations into pan and flatbread products.

BARLEY β-GLUCAN ISOLATES IN BREAD PRODUCTS In an attempt to specifically assess the role of β-glucans during various stages of the bread-making process, several baking studies using isolated and purified polymers from barley grain have been conducted. Extraction of β-glucans from barley usually involves several steps, including inactivation of endogenous enzymes in the grain, extraction of grain with water or alkali solutions, removal of contaminating protein and starch from extracts, and precipitation of β-glucans from the purified solutions via ethanol and drying.12–15 Most of the resulting preparations contain between 70% and 85% of β-glucans. Partial replacement of wheat flour with purified water soluble β-glucans significantly increases the farinograph and baking water absorption of dough during mixing (Table 1). This effect is attributed to a high water-absorbing capacity of these polymers, and its magnitude is dependent on the amount of β-glucans in dough and their molecular weight.13,15 Noticeable changes to the dough rheology were reported by Cleary et al.16 who observed higher resistance to extension and lower extensibility in doughs containing 5% of high (510 kDa) and low (160 Da) molecular mass β-glucan preparations. The effects of β-glucans on the rheological properties of wheat doughs are also influenced by the quality of the base wheat flour. Skendi et al.15 reported that β-glucan addition (0.2%–1.4%) improved the extensibility of the poor bread-making quality of the dough somewhat, thus strengthening the gluten matrix and increasing the gas-retention capacity of dough (Table 1). Wang et al.17 pointed to the possible role of β-glucans in improving bread-crumb grain by stabilizing air cells in the bread dough and preventing their coalescence. Inclusion of β-glucans in bread generally results in a significant decrease in loaf volume and height, and the reduction in height and volume worsens with increasing amount and molecular weights of β-glucans (Table 1). However, Skendi et al.15 observed that small improvements in the specific volume of bread are achievable through optimization trials that take into consideration the quality of wheat flour, as well as the level and molecular features of β-glucans used for fortification. It is postulated that the negative effect of β-glucans on loaf volume is due to the combined effects of gluten dilution and disruption of gluten networks. The high water-binding properties of β-glucans interfere with proper hydration of gluten, resulting in underdeveloped gluten networks. Cleary et al.16 proposed that a reduction of steam production during baking as a result of strong water binding of β-glucans also contributes to the decreased loaf volume. The increase in hardness of bread crumbs fortified with β-glucans at a higher level of addition (>1%) has been observed, and various interpretations have been put forward. Rosell et al.18 proposed that the increase in crumb 3. FORTIFICATION OF FLOURS AND BREADS

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β-GLUCAN CONCENTRATES AND β-GLUCAN-ENRICHED GRAIN FRACTIONS

TABLE 1

Properties of Bread Supplemented With Isolated β-Glucans Farinograph

Dough rheology

Isolate

Water absorption (%, 14% mb)

Dough development time (min)

Resistance to extension

Extensibility (mm)

Loaf volume

References

Control

58.4

5.7

–

–

768 mL

Cavallero et al.12

+20% WF

67.0

8.2

–

–

Control

385 mL

33.34 g

29.83

212 mL

a

a

+5% HMW

–

–

74.28 g

22.30

100 mL

+5% LMW

–

–

49.18 g

23.75

118 mL

Control

62

–

–

–

905 mL

+0.5% BG

69

–

–

–

855 mL

+1.0% BG

75

–

–

– b

Cleary et al.16

Jacobs et al.14

765 mL b

Control-Dion

50.3

1.8

103 BU

241

2.46 mL/g

+0.2% BG-100

52.6

4.5

148 BU

202

2.69 mL/g

+0.6% BG-100

52.8

4.8

118 BU

215

2.88 mL/g

+1.0% BG-100

52.8

4.7

95 BU

222

2.29 mL/g

+1.4% BG-100

53.0

5.3

188 BU

195

2.26 mL/g

Skendi et al.15

a

Resistance to extension (mean max force, g) and extensibility (mean distance at max force, mm) of doughs were measured using a TA-XT2 texture analyzer. After 135 min resting time in fermenting cabinet, each dough piece was stretched in the Brabender Extensograph by a hook until rupture. The stretching force was recorded as a function of time, and the resistance to constant deformation after 50 mm stretching (R50) and the extensibility were obtained. BG, water extracted β-glucan (85% β-glucan); BG-100, commercial concentrate (84.5% β-glucans, 100 kDa); Dion, poor bread making quality wheat flour; HMW, high-molecular-weight β-glucans (95%, 510 kDa); LMW, low-molecular-weight β-glucans (95%, 160 kDa); WF, water extracted fraction (33.2% β-glucan). b

firmness may be a consequence of the thickening of walls surrounding the gas cells that occurs upon the addition of hydrocolloids into bread formulas. Furthermore, an increase in bread firmness may be a consequence of a decrease of the total area of the gas cells in bread containing β-glucans; indeed, the greatest crumb firmness is usually observed in breads with the lowest loaf volume. Also, water promotes starch recrystallization, and the water content of β-glucanenriched breads is generally higher than that of control breads. However, the role of β-glucans in starch retrogradation and bread firmness is not entirely clear. Skendi et al.15 did not report an increase in starch retrogradation (using differential scanning calorimetry measurements) with the addition of β-glucans, and Gill et al.19 proposed that β-glucans added to wheat flour reduce swelling and solubilization of starch during baking, thereby reducing bread firmness. The effectiveness of barley β-glucan inclusion on the in vitro digestibility of breads was studied by measuring the amount of reducing sugars released during enzymatic digestion of control and β-glucan-supplemented breads.13, 16 Both studies reported significant reduction of sugars during in vitro digestion of breads prepared by replacing 5% of wheat flour with purified β-glucan preparations. These effects were partly attributed to the inhibition of enzyme accessibility to starch polymers due to the increased digesta viscosity, altered rheological properties of breads containing β-glucans, or both. Scanning electron micrographs of in vitro digests of bread containing barley β-glucan illustrated the more compact structure of bread and the retention of undigested starch granules compared to control breads.16 Cavallero et al.12 demonstrated a potential to regulate, in vivo, sugar release from breads containing β-glucans; a significant reduction in the area under the blood glucose curve and delay in the mean peak of blood glucose was observed in human subjects who consumed bread supplemented with 20% of barley β-glucans.

β-GLUCAN CONCENTRATES AND β-GLUCAN-ENRICHED GRAIN FRACTIONS Pure β-glucan isolates obtained via the traditional extraction procedures described previously are not suitable for commercial applications because the procedures are time-consuming and costly. Recently, however, several β-glucan concentrates obtained by novel, simplified, and presumably less expensive commercial methods were introduced to the market. The level of β-glucan enrichment and physicochemical properties of β-glucans (including molecular weight, solubility, and viscosity) in these products vary depending on specific treatments employed during the extraction and purification procedures. For example, Nutrim, a product prepared by subjecting an aqueous suspension of 3. FORTIFICATION OF FLOURS AND BREADS

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27. BARLEY β-GLUCANS AND β-GLUCAN-ENRICHED FRACTIONS AS FUNCTIONAL INGREDIENTS IN FLAT AND PAN BREADS

µ

µ

µ µ

FIG. 1 Roller-milling flow for the original and enriched FRFs from whole barley. B, break passage; PM, pin mill; S, sizing passage; SD, shorts duster.

barley flour to high-temperature mechanical shearing in the presence of thermostable α-amylase, followed by centrifugation and drum-drying, contains only 5%–15% of β-glucans. Other products, including an enzymatically produced Viscofiber or warm water-extracted Cerogen, were reported to contain 50% and 70%–90% β-glucans, respectively.20 Some of these commercial β-glucan products contain substantial amounts of β-glucans and were shown to deliver specific health benefits in clinical studies.21 However, despite being generally regarded as safe, the concentrates of β-glucan obtained by wet extraction may not qualify for allowing health claims in some countries. The alternative sources of β-glucans are fractions obtained by dry grain fractionation processes, such as milling, pearling, sieving, and/or air classification. The nonuniform distribution of components within the barley kernel allows fractionation by physical means into products enriched in various constituents, including β-glucans and arabinoxylans. Such naturally obtained products may be more desirable food ingredients for health-conscious consumers than products obtained through chemical processes. Izydorczyk et al.22 developed and optimized roller-milling flow conditions for the production of barley flour and a coarse fiber fraction (known as shorts) that originates mainly from the endosperm cell walls and contains large amounts of β-glucans, bioactives, and other DF constituents. This fraction, designated as a fiber-rich fraction (FRF) in barley milling, potentially has more value as a functional food ingredient than barley flour that is enriched mainly in starch. The milling flow, as shown in Fig. 1, consists of break passages through four sets of corrugated rolls. Following the fourth break, the ground product is put through two sieves with different apertures, and the coarse material retained on the sieves is directed to a shorts duster. The impact action occurring in the shorts duster effectively cleans the fiber by releasing starch granules that are encapsulated in the endosperm cell walls. The next stages of fiber refinement include a single passage through sizing rolls, sieving, and another shorts duster passage. The original FRF can be further enriched by additional pin-milling, sieving, and another shorts duster passage. Depending on the barley genotype, the β-glucan content of the enriched FRF obtained using this expanded rollermilling flow design ranged from 21% to 27% (Table 2). A major benefit of the dry separation technologies is that the cell wall structures remain intact, so there is very little chance of altering the physicochemical properties of β-glucans. Also, in contrast to β-glucan isolates or commercial β-glucan concentrates, barley FRF has the added benefit of containing other DF and bioactive components, as well as being obtained by a chemical-free process. If barley is not pearled before milling, the FRF contains not only the endosperm cell walls, but also portions of the outer grain layers, specifically pericarp, aleurone, and subaleurone tissues (Fig. 2A and B). Compared to the original FRF (150–500 μm) (Fig. 2A), the enriched FRF consist of smaller particles (100–300 μm) with fewer starch granules (Fig. 2B); the particles generally have irregular shape and porous structure (Fig. 3). Both the original and the enriched FRF from two barley cultivars (CDC Fibar and HB08302) contained higher amounts of β-glucan, arabinoxylans,

3. FORTIFICATION OF FLOURS AND BREADS

351

β-GLUCAN CONCENTRATES AND β-GLUCAN-ENRICHED GRAIN FRACTIONS

TABLE 2 Composition and Properties of FRFs Obtained From Hull-less Barley Genotypes CDC Fibar

HB08302

Properties and composition

Whole barley

Original FRF

Enriched FRF

Whole barley

Original FRF

Enriched FRF

Yield (%)

NA

38

19

NA

36

16

Brightness, L*

NA

82.8

85.7

NA

81.9

84.3

Swelling (mL/g)

NA

13.1

16.9

NA

10.0

13.9

Particle size, d0.5 (μm)

NA

300.6

171.8

NA

272.0

175.3

Total β-glucan (%)

10.8

17.4

27.0

7.7

13.0

21.0

Soluble β-glucan (%)

5.4

8.3

12.1

3.4

5.5

8.3

Total arabinoxylans (%)

4.2

8.2

10.0

4.7

10.3

13.0

Starch (%)

52.3

34.4

24.3

56.2

36.4

23.9

Protein (%)

15.8

17.8

15.7

12.7

14.4

13.3

Ash (g/kg)

22.4

32.2

36.6

20.7

31.9

37.6

Mn (mg/kg)

18.3

22.1

18.7

18.5

19.4

17.1

Zn (mg/kg)

29.5

37.7

39.6

23.6

33.2

39.6

Fe (mg/kg)

55.6

79.6

91.8

44.1

66.6

83.4

Ca (mg/kg)

221

227

224

228

300

279

Mg (mg/kg)

1500

2330

2700

1390

2330

2830

P (mg/kg)

4070

6600

7670

4300

6400

7900

Total ferulics (μg/mg)

0.82

1.45

1.50

0.79

1.57

2.08

Vitamin B3 (mg/100 g)

8.2

13.1

15.7

9.3

14.5

18.9

Vitamin E (mg/100 g)

0.96

1.32

0.98

0.43

0.77

0.51

CDC Fibar, hull-less barley with waxy starch; HB08302, an experimental hull-less barley line with high-amylose starch.

protein, manganese (Mn), zinc (Zn), iron (Fe), calcium (Ca), magnesium (Mg), phosphorus (P), total ferulic acids, and vitamins B3 and E than the respective whole-grain samples (Table 2). Although the yield for the enriched FRF decreased, the refinement steps increased the content of β-glucan, arabinoxylans, total ferulics, and vitamin B3, as well as Zn, Fe, Mg, and P. The enriched FRFs were also slightly brighter and contained fewer dark specs than their original counterparts. Grain fractions enriched in β-glucans can also be produced by applying air classification to barley ground by either pin or hammer milling. Andersson et al.23 air-classified ultrafine barley flour from several barley varieties (with β-glucan content ranging from 3.8% to 7.2%) into five fine fractions (F1–F5) and one coarse fraction

FIG. 2

Light photomicrographs of sections of the original (A) and enriched (B) FRF stained with PAS/calcofluor. 3. FORTIFICATION OF FLOURS AND BREADS

FIG. 3 SEM of barley original FRF.

Ultrafine barley flour Fine fraction F1

16,000 rpm

Coarse fraction C1 Fine fraction F2

12,000 rpm

Coarse fraction C2 Fine fraction F3

8000 rpm

Coarse fraction C3 Fine fraction F4

4000 rpm

Coarse fraction C4 Fine fraction F5

2000 rpm

Coarse fraction C5

FIG. 4 Flow of air classification of impact-milled barley flour. Fine (F1–F5) and coarse fractions (C5) obtained by decreasing wheel speed (16,000–2000 rpm). Modified from Andersson AAM, Andersson R, Åman P. Air classification of barley flours. Cereal Chem 2000;77(4):463–7.

(C1) (Fig. 4). The highest β-glucan concentrations were found in F5 and C1 fractions (7%–12%), demonstrating 1.7fold to 2.1-fold enrichment of these polysaccharides compared to whole-grain flour. However, the yields of fractions enriched in β-glucans (F5 and C1) were relatively low (about 11%–22%). Ferrari et al.24 applied double micronization to barley grain to obtain sufficiently fine particles that were then sorted into a series of coarse/fine fraction pairs by air classification (Fig. 5). This approach was tested on two hull-less barleys with different starch types: cultivar Priora with normal starch and CDC Alamo with waxy starch; and this resulted in β-glucan-enriched coarse flour fractions (CF2) with a yield of about 30% and a twofold increase in β-glucan concentration compared to whole grain (Table 3). Successful separation and concentration of grain components via air classification depend on such parameters as particle size distribution and fat content of the material to be air-classified. Good yield (62%) with 1.58-fold enrichment of β-glucans was obtained for a high-β-glucan barley variety, Prowashonupana (originally containing 17%–19% β-glucan and 6% fat) when defatting of grain was conducted before processing.25 Parameters such as β-glucan content in barley grain, the presence of hull, and starch characteristics may also affect the grinding and segregation processes. Further optimization of the dry fractionation processes is still needed in order to obtain fractions concentrated in target components and to reduce the costs associated with power consumption.

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BARLEY FLOUR AND β-GLUCAN-ENRICHED GRAIN FRACTIONS IN PAN BREADS

Micronized barley (2x)

Air classification (valve =220)

Fine fraction FF1

Coarse fraction CF1

Air classification (valve = 190)

Fine fraction FF2

Coarse fraction CF2

FIG. 5 Flow of the air-classification process for enrichment of β-glucans in barley fractions. Modified from Ferrari B, Finocchiaro F, Stanca AM, Gianinetti A. Optimization of air classification for the production of β-glucan-enriched barley flours. J Cereal Sci 2009;50(2):152–8.

TABLE 3

Yield and DF Contents in Barley Flour Fractions Obtained by Air Classification of Micronized Grain

Barley genotype

Flour fraction

Yield (%)

TDF (%)

β-Glucan (%)

CDC Alamo

Micronized

–

12.8

7.8

CF1

10.4

25.5

11.1

CF2

28.4

25.5

15.6

FF2

61.2

3.8

2.3

Micronized

–

11.5

5.4

CF1

16.5

23.4

8.1

CF2

29.8

21.8

11.2

FF2

53.7

3.3

3.0

Priora

CF1 and CF2 fractions are the coarse fractions from the first and second air classification, respectively; FF2 is the fine fraction from the second air classification as shown in Fig. 5. TDF, total dietary fiber. Modified from Ferrari B, Finocchiaro F, Stanca AM, Gianinetti A. Optimization of air classification for the production of β-glucan-enriched barley flours. J Cereal Sci 2009;50(2):152–8.

BARLEY FLOUR AND β-GLUCAN-ENRICHED GRAIN FRACTIONS IN PAN BREADS Although the addition of β-glucans to bread has the potential to improve its nutritional benefits, its incorporation at the level recommended by various jurisdictions (i.e., 0.75 g of β-glucan per serving) has proved to be challenging, resulting in lower product quality and reduced consumer acceptability. In the bread-making process, replacement of wheat flour by large amounts of nongluten-forming flours such as barley can seriously constrain dough viscoelasticity and the gas-retention capacity of blended dough matrices. Weakened gluten networks often lead to impaired technological and sensory quality of bread in terms of volume, texture, appearance, color, and taste. Although satisfactory bread products supplemented with barley flour have been produced, often the level of supplementation is too small to achieve any significant increase of β-glucan concentration in the final product, and consequently the desired health benefits. For example, Sullivan et al.26 reported that incorporation of up to 50% of barley flour obtained by roller-milling of pearled barley (with 10% w/w of the outer layers removed) into bread had no significant negative effects on bread acceptability. However, to meet the recommended 0.75 g β-glucan dose per serving, it was calculated that about six slices of bread from a standard 800 g loaf would have to be consumed, exciding by far consumers’ preferences and habits. Bread with 100% barley flour was made by using elevated levels of water, malt flour, and margarine (Fig. 6).27 The authors calculated that intake of four slices of this barley bread should deliver a sufficient amount of β-glucans to meet the health claim requirements. However, the use of malt flour in the bread formulation could significantly decrease the molar mass of β-glucans due to the high concentration of β-glucanases in malt, and consequently negatively affect the efficacy of these polysaccharides. 3. FORTIFICATION OF FLOURS AND BREADS

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27. BARLEY β-GLUCANS AND β-GLUCAN-ENRICHED FRACTIONS AS FUNCTIONAL INGREDIENTS IN FLAT AND PAN BREADS

FIG. 6 Appearance of bread made from 100% barley flour according to the optimized procedure with sufficient β-glucan according to the EFSA health claim. Reproduced with permission from Kinner M, Nitschko S, Sommeregger J, et al. Naked barley—optimized recipe for pure barley bread with sufficient beta-glucan according to the EFSA health claims. J Cereal Sci 2011;53(2):225–30.

Compared to white or whole-barley flour, β-glucan-enriched grain fractions have the advantage of elevated levels of β-glucans and other bioactive components, and as a result, lower supplementation levels can be used to achieve the desired health benefits. We assessed the potential of the original and enriched FRF from waxy and high-amylose, hullless barley cultivars (CDC Fibar and HB08302) as functional ingredients in bread prepared by the Canadian short process (CSP). The formula included wheat flour (100 g), whey (4 g), shortening (3 g), yeast (3 g), sugar (4 g), salt (2.4 g), and ascorbic acid (150 μg). To obtain the U.S. Food and Drug Administration (FDA) recommended dosage of 0.75 g of β-glucan per two-slice serving, 10% and 13% of white-wheat flour was replaced with the original FRF from CDC Fibar and HB08302, respectively. Because of the higher concentration of β-glucans in the enriched FRF, the replacement level was reduced to 6% and 8% when using the enriched FRF from CDC Fibar and HB08302, respectively. In each case, the water absorption of the FRF-supplemented doughs was higher than that of 100% white flour, but comparable to that of the 100% whole-wheat flour (Table 4). As a consequence of higher baking absorption, the barley FRF-supplemented loaves and the 100% whole-wheat loaves were heavier than the white-flour control. The loaf volume of breads supplemented with original FRF was reduced by approximately 20%–22% compared to the white-flour bread, and by 7%–10% compared to the 100% whole-wheat-flour bread (Table 4). The crumb structure of breads containing the original FRF scored higher (by visual evaluation) than that of the 100% whole-wheat bread, but slightly lower than that of the white bread (Table 4). Replacement of wheat flour with the enriched FRF preparations significantly improved the overall quality of the TABLE 4

Quality Characteristics of Wheat and Barley FRF-Supplemented Breads Visual assessment Water absorption (%)

C-cell parameters

Loaf volume (cm3)

Loaf weight (g)

Crumb Appearance texture

Brightness, L*

No. of cells

Cell diameter (mm)

Cell wall thickness (mm)

Nonuniformity

CONTROL LOAVES 100% white flour

65

2210

286

7.5

6.5

85.0

5777

2.498

0.476

2.944

100% wholewheat flour

73

1910

304

6.0

5.5

72.9

4712

2.790

0.494

1.818

+10% original FRF 74

1770

300

5.5

5.8

77.5

4551

2.427

0.490

3.143

+6% enriched FRF 74

2060

302

7.5

5.8

81.7

5308

2.396

0.482

1.567

+13% original FRF 73

1720

303

6.5

6.0

78.5

4682

2.375

0.484

3.200

+8% enriched FRF 74

2020

308

7.5

6.2

82.1

5247

2.404

0.483

1.567

FRF-SUPPLEMENTED LOAVES CDC FIBAR

HB08302

3. FORTIFICATION OF FLOURS AND BREADS

BARLEY FLOUR AND β-GLUCAN-ENRICHED GRAIN FRACTIONS IN PAN BREADS

355

FIG. 7 Control loaves and barley FRF-supplemented breads. (A) 100% white flour, (B) 100% whole-wheat flour, (C) 6% CDC Fibar-enriched FRF, and (D) 8% HB08302-enriched FRF.

supplemented bread compared to the bread supplemented with the original FRF. The most striking improvements were in the loaf volume, appearance, crumb structure, and color of the bread (Table 4). The loaf volume of bread supplemented with both enriched FRFs was superior to that of 100% whole-wheat bread, and when compared to white-flour bread, the volume was reduced by only 6%–9% (Fig. 7). The loaf volume of breads supplemented with the enriched FRF was superior to breads containing the original FRF. The number of cells in bread slices increased substantially when the enriched rather than the original FRF was used. Overall, the FRF-supplemented breads exhibited slightly finer crumb structure than wheat breads, as indicated by the lower diameter of the cells in the former. The cell-wall thickness in the FRF-supplemented breads was higher than that in white-flour bread, but lower than that in the whole-wheat-flour bread. The enriched FRF only slightly decreased the cell diameter or the wall thickness of bread, but substantially improved the texture uniformity of bread slices compared to bread supplemented with the original FRF. A significant improvement in brightness of the bread supplemented with the enriched FRF (Table 4) was a definite advantage because often, breads containing barley ingredients are characterized as having a grayish tint. 3. FORTIFICATION OF FLOURS AND BREADS

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27. BARLEY β-GLUCANS AND β-GLUCAN-ENRICHED FRACTIONS AS FUNCTIONAL INGREDIENTS IN FLAT AND PAN BREADS

TABLE 5 Nutritional Information and Technological and Sensory Characteristics of Wheat and Wheat/Barley (60/40) Blended Breads Nutritional information/technological and sensory characteristics

WT Nutrient (per 100 g)

WT/CB Nutrient (per 100 g)

WT/HBGB Nutrient (per 100 g)

Protein (g)

7.89b

7.31a

8.10b

Ash (g)

0.35a

0.56b

0.96c

Total DF (g)

1.15a

4.01b

11.91c

Soluble DF (g)

0.36a

1.24b

3.69c

Insoluble DF (g)

0.79a

2.77b

8.22c

β-Glucan (g)

0.11a

1.51b

3.23c

RS (g)

1.8a

4.4b

7.0c

Digestible carbohydrates (g)

45c

39b

25a

RDS (g)

58.5c

53.1b

34.7a

SDS (g)

7.5b

3.4a

9.3c

Expected GI

94b

91b

85a

Volume (mL)

1890

1480

1360

Hardness (N)

3.9a

3.3a

7.5b

0.84c

0.72a

0.77b

2.0b

1.4a

1.4a

Cells/cm

50.76b

52.88c

47.36a

External appearance (0 10)

7a

6a

7a

Aroma intensity (0–10)

6a

7a

7a

Taste intensity (0–10)

4a

6b

6.5b

Firmness (0–10)

3a

3a

4a

Overall acceptability (0–10)

6.5a

7.5a

7a

Cohesiveness 2

Mean cell area (mm ) 2

WT, wheat flour; CB, commercial barley flour; HBGB, high β-glucan barley flour. Within rows, values with the same following letter do not differ significantly from each other (P > .05). Modified from Collar C, Angioloni A. Nutritional and functional performance of high β-glucan barley flours in breadmaking: mixed breads versus wheat breads. Eur Food Res Technol 2014;238(3):459–69.

Collar and Anglioloni28 compared the potential of a high β-glucan barley flour of superior nutritional value and a regular commercial barley flour in blends with wheat flour for making nutritious breads with high functional and sensory standards. The high β-glucan barley flour, known under the brand name of Sustagrain, is produced from a unique barley variety, Prowashonupana, with ultrahigh fiber and β-glucan content (30% and 15%, respectively). Here, 100 g of wheat flour or wheat-barley blended flours (60/40 w/w) were mixed with water (63% for wheat and 80% for blends), compressed yeast (4% flour basis), salt (1.5%), vegetable fat (4%), sugar (1%), commercial sourdough (3%), gluten (2%), carboxymethylcellulose (1%), and calcium priopionate (0.5%) in a mixer at 60 revolutions/min for 10 min up to optimum dough development. Fermented doughs were obtained by bulk fermentation, dividing, rounding, molding, and proofing, and then baked at 220°C. The addition of either commercial barley flour or high β-glucan flour significantly decreased the bread volume (22%) and crumb cohesiveness (14%), and increased crumb hardness (Table 5). The crumb quality of barley-supplemented breads decreased in terms of lower cell size and thicker cell walls, but crumb pore uniformity and crumb grain structure were not significantly affected (Table 5). Despite the diminished technological attributes, blended breads scored higher than wheat bread in both taste intensity and overall acceptability. The high β-glucan-flour-supplemented bread showed appealing nutritional quality in terms of lower digestible starch, high soluble and insoluble DF, β-glucan, and resistant starch (RS). The lowest rapidly digestible starch content and highest slowly digestible starch and RS content were observed for the blend of wheat/ high β-glucan barley flours, leading to a significantly lower glycemic index (GI; Table 5). The authors postulated that the incorporation of high β-glucan barley flour into wheat-bread formulations reduced starch hydrolysis due to the

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BARLEY FLOUR AND β-GLUCAN-ENRICHED GRAIN FRACTIONS IN PAN BREADS

357

FIG. 8 SEM micrographs of barley FRF-supplemented bread dough. Discrete cell-wall fragments are visible in the FRF-supplemented dough, giving it an appearance of a composite with particles of texture different than the matrix.

Light micrographs of barley FRF-supplemented breads. (A) Bread stained with Calcofluor indicating the presence of β-glucans (lighter spots); (B) bread showing autofluorescence due to the presence of arabinoxylans in the aleurone cell walls.

FIG. 9

presence of viscous DF components (β-glucans), higher protein, and lower starch in the blended breads. Therefore, the addition of high β-glucan barley flour to common wheat flour highly enhanced the health benefits and sensory appreciation of breads, while generally preserving the technological properties. The mechanisms by which the barley FRFs or high β-glucan barley flour affect the dough rheology and bread textural attributes are complex, and the overall effects depend on the interactions among water, protein, starch, and fiber polysaccharides at the microscopic and molecular levels. As shown in Fig. 8, discrete cell wall fragments are visible in the FRF-fortified dough, giving it the appearance of a composite with particles of texture that differ from the matrix. In bread, both the β-glucan-containing endosperm cell-wall fragments (Fig. 9A) and the arabinoxylan-rich aleurone cell walls (Fig. 9B) can still be detected, although the fiber particles appear smaller and distorted, indicating their partial solubilization. The potential mechanisms by which insoluble fiber ingredients, such as bran, exert negative effects include gluten dilution, water entrapment, and mechanical disruption of gluten films during mixing, proofing, or the early stages of baking.29 Rieder et al.30 explored the potential of sourdough to improve the quality of breads supplemented with wholebarley flour (40% substitution level). Barley flour was mixed with water and fermented with a Lactobacillus plantarum strain. The use of sourdough (20% substitution level) improved the dough structure, bread volume, form ratio, and gas-retaining ability of breads made with the addition of whole-grain barley flour. The positive effect of sourdough was attributed to a particle softening effect, as previously observed for wheat bran.31 The softening of bran particles during fermentation may result in less mechanical disruption of the gluten network and gas cell in the dough. From a physiological standpoint, increased solubilization of β-glucan in a food product and/or during the passage through the gastrointestinal tract is highly beneficial. The amount of β-glucan ingested accounts for only part of the physiological effects; water solubility and the high molecular weight of β-glucans contribute to increased viscosity of digesta in the gastrointestinal tract, and these properties of β-glucans are critical for their health benefits.6, 32 Whereas the increased solubility of β-glucans that might occur during bread preparation and baking is beneficial, a decrease of

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27. BARLEY β-GLUCANS AND β-GLUCAN-ENRICHED FRACTIONS AS FUNCTIONAL INGREDIENTS IN FLAT AND PAN BREADS

TABLE 6

Extractability and Molecular Mass of β-Glucans Obtained by In Vitro Digestion of FRF and FRF-Supplemented Breads Extractability of β-glucans (% of total)

Molecular mass (g/mol)

Enriched FRF

55.6

279,000

Bread + enriched FRF

33.0  3.9

247,200

Enriched FRF

39.7

287,300

Bread + enriched FRF

40.4  4.3

495,500

CDC FIBAR

HB08302

the molecular weight of these polymers is detrimental. The degradation of β-glucans appears to occur mainly during dough mixing, proofing, and fermentation, partly due to activation of endogenous β-glucanases, and to a lesser extent during baking.33 Thus, to retain the high molecular weight of β-glucans, the mixing and fermentation time should be as short as possible, and the β-glucanase activity in any ingredient used in baking should be eliminated by appropriate methods. In our studies, the FRFs used for baking were obtained from sound barley grain with no detectable β-glucanase activity, and wheat flour was also derived from unsprouted wheat. CSP is a no-time mechanical dough-development baking procedure involving fast mixing, followed by short rest (15 min) and relatively short 70-min proof at 37.5°C.34 The rich formula of the CSP dough was altered in our study by omitting the malt extract to avoid the addition of β-glucan-degrading enzymes. As a consequence, the molecular weight of β-glucans extracted from the FRF-enriched breads after in vitro digestions with α-amylase, pepsin, and pancreatin was preserved and comparable to or even higher than that of β-glucans extracted from the FRF under similar conditions (Table 6). Rieder et al.35 recommended a few other strategies for minimizing the molecular-weight reduction of β-glucans during bread-making. The authors incorporated barley flour into already fermented wheat dough or omitted fermentation and shortened proofing time. The altered fermentation and proofing stages were compensated for by adding more yeast and sucrose, which resulted in the production of good-quality barley bread containing high-molecular-weight β-glucans. The use of barley ingredients with bigger particle size, like coarse barley flour or intact barley flakes, also preserved the high molecular weight of these polysaccharides in bread.

BARLEY β-GLUCAN-ENRICHED FRACTIONS IN FLATBREAD Compared to pan or hearth bread, flatbreads have modest flour-quality requirements, and their appeal is not derived from an aerated structure. Also, flatbreads have been made from various grains, and consumers generally have greater tolerance for different colors or tastes of these products. From a technological standpoint, flatbreads are better vehicles for delivering high DF ingredients into the diet, and they appear suitable for inclusion of β-glucans or barley fiber fractions. Barley flour has been successfully incorporated into single-layer flatbreads, including chapatis and Turkish bazlama bread, but only a moderate increase of β-glucan in these products was achieved. Thondre and Henry36 showed that supplementation of whole-wheat flour with a commercial barley β-glucan fiber preparation created a palatable chapatis for diabetic patients, and the GI of chapatis with 4 g of β-glucan per serving was significantly reduced. We have tested the potential of barley FRF as functional ingredients in two-layer flatbread.37 The study was designed to investigate the effect of particle size of the FRF preparations on the technological and nutritional characteristics of flatbreads. It was postulated that apart from the chemical composition of fiber preparations, the properties that are technologically and nutritionally relevant include the particle size, bulk volume, surface characteristics, hydration, and rheological properties. The original FRFs were obtained according to the milling flow shown in Fig. 1. A portion of the FRF was subsequently pin-milled but not subjected to any further processing or sieving. As a consequence, the composition of the original and pin-milled FRF remained the same (Table 7). In addition to reducing particle size, pin-milling slightly increased the water solubility of β-glucans and arabinoxylans and increased the viscosity of FRF water slurries, but decreased their swelling capacity. The particle size reduction was expected to improve the solubility of fiber components by increasing the surface area of particles. It appears,

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TABLE 7 Barley type/FRF

Composition and Physicochemical Properties of Barley Fiber-Rich Fractions (FRF) Before and After Pin Milling (PM)a Total Water-soluble β-glucans (%) β-glucans (%)b

Total arabinoxylans (%)

Water-soluble arabinoxylans (%)b

Swelling capacity Proteins (%) Starch (%) (ml/g)

Brightness, L*

Particle size, d0.5 (μm)

8.93  0.05

10.11  0.04

1.41 (13.9)b

19.1  0.1

9.09c

79.02e

204

d

8.16

d

80.59

139

10.95b

84.00c

220

NORMAL N-FRF

4.55 (50.9)c c

N-FRF-PM

36.2  0.3

a

1.47 (14.5)

4.79 (53.6)

WAXY W-FRF

13.84  0.30

8.87  0.00

6.88 (49.7)a a

W-FRF-PM

20.0  0.1

0.87 (9.8)e

38.1  0.2

e

c

0.91 (10.3)

7.21 (52.1)

b,c

9.28

84.95

155

12.04a

85.46b

220

a

a

164

HIGH AMYLOSE HA-FRF

14.06  1.10

9.98  0.28

6.25 (44.5)b a

HA-FRF-PM

19.5  0.1

0.99 (9.9)d

36.4  0.2

c

1.06 (10.6)

6.90 (49.1)

11.89

86.83

Means in columns followed by a different letter(s) are significantly different (P  .05) as determined by Duncan’s multiple range test. The values in parentheses indicate solubility expressed as a percentage of either total β-glucans or arabinoxylans, respectively. HA, high amylose; N, normal; PM, pin mill; W, waxy. a

b

TABLE 8

Quality Characteristics of Barley Fiber-Rich Fraction (FRF)-Supplemented Flat Breadsa Dough handling scoresb

Flat bread

Texture Bread scoresb Water c d absorption (%) Division Sheeting Appearance Diameter Crumb Aroma Brightness, L* Hardness (kg) Chewiness

Controle

57c

4.25

4.25

4.25

5.0

3.75

4.75

74.09

0.47c

0.36d

+N-FRF

68a

4.25

4.25

4.25

5.0

3.5

4.5

68.96

0.54a,b,c

0.47a,b,c,d

+N-FRF-PM

68a

4.0

4.25

4.25

5.0

3.5

4.25

67.45

0.54a,b,c

0.48a,b,c

+W-FRF

64b

4.0

4.0

4.25

5.0

4.0

4.25

69.01

0.52b,c

0.45b,c,d

+W-FRF-PM

64b

4.25

4.5

4.25

5.0

4.0

4.5

71.84

0.49b,c

0.42c,d

+HA-FRF

67a

4.0

4.0

4.25

5.0

4.0

5.0

74.31

0.62a,b

0.54a,b

4.25

4.25

4.5

5.0

4.0

4.75

73.22

0.66a

0.58a

+HA-FRF-PM 67a

Means in columns followed by a different letter(s) are significantly different (P  0.05) as determined by Duncan’s multiple range test. Each quality parameter was given a score from 0 to 5. c Division is the step in flat bread processing in which the dough was cut into five 125 g pieces after fermentation and before sheeting. d Sheeting is the step in flat bread processing in which the dough is pinned into circular sheets followed by proofing and then baking. e Control flat bread consisted of 80% straight grade Canadian Western Red Spring wheat flour and 20% whole wheat flour. HA, high amylose; N, normal; PM, pin mill; W, waxy. a

b

however, that the reduction of particle size of FRF preparations caused a collapse of the porous fiber structure, making it unable to absorb as much free water as rough fiber. Flatbreads were prepared by mechanically mixing the ingredients, which included wheat flour (100 g; a blend of 80% white flour and 20% whole-wheat flour), salt (1 g), sugar (1 g), and fresh compressed yeast (1.5 g), followed by fermentation (45 min at 30°C), division, rest (10 min), manually pinning the dough into circular sheets, proofing (25 min at 30°C), and baking (540°C for 70 s) in an electric traveling flatbread oven. The FRF-fortified flatbreads were prepared by replacing 20% of white flour with the original and pin-milled FRF. All FRF-containing doughs exhibited higher water absorption, but good handling characteristics at division and sheeting (Table 8). The layer separation during baking was very good, and flatbreads with FRF did not show any tendency for burning (Fig. 10). Characteristics of FRF-fortified breads such as appearance, diameter, crumb structure, and aroma were comparable to those of the control breads (Table 8). However, the addition of FRF increased hardness and chewiness and decreased brightness (L*). The greatest hardness was observed for FRF derived from high-amylose barley, and it was noticed that properties of starches associated with the FRF (especially at a higher level of FRF addition) could also contribute to the

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27. BARLEY β-GLUCANS AND β-GLUCAN-ENRICHED FRACTIONS AS FUNCTIONAL INGREDIENTS IN FLAT AND PAN BREADS

FIG. 10 Barley FRF-supplemented flatbreads coming out of a traveling oven.

FIG. 11 SEM micrographs of barley FRF-supplemented flatbreads. (A) Control flatbread (80% white flour/20% whole-wheat flour; (B) flatbread with 20% of barley FRF.

technological properties of breads. Flatbreads supplemented with FRF from high-amylose barley displayed slightly denser crumb structure than the control bread or bread fortified with FRF from waxy barley (Fig. 11). Some differences in the quality characteristics of flatbreads supplemented with FRFs from various barley types were also observed (Table 8). However, the quality and texture of supplemented breads were not significantly influenced by pin-milling of the FRF preparations. The addition of 20% of FRF significantly increased the amount of total and soluble β-glucans in flatbreads. Assuming that a single flatbread constitutes one serving, the FRF-supplemented breads would provide between 1.84 and 2.97 g of total β-glucans and between 0.58 and 1.42 g of water-soluble β-glucans, depending on the origin of the FRF preparations (Table 9). With the exception of the waxy barley FRF preparations that showed a slight decrease, the water solubility of β-glucans was higher in flatbreads containing pin-milled FRF compared to the original FRF preparations. The addition of FRF also significantly increased the content of total arabinoxylans in the flatbreads. The amount of water-soluble arabinoxylans, on the other hand, changed little with the addition of barley FRF, indicating the insoluble nature of these polysaccharides in barley. The results of the in vitro digestibility of starch showed that the inclusion of barley FRF into flatbread significantly decreased the solubilization and digestibility of starch at two different time intervals (Table 9). The pin-milled FRF exerted a slightly greater effect than the original FRF in most cases. The reduction in starch digestibility of FRF-supplemented flatbreads might be associated with the ability of fiber constituents to restrict the enzyme accessibility to the food, either by changing (compacting and/or hardening) the food structure or by physically entrapping starch granules in their mucilaginous matrix. Brennan and Samyue38 postulated that the digestion of starch and sugar release from foods might be delayed

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TECHNOLOGICAL ISSUES

TABLE 9 Nutritional Characteristics of Barley Fiber-Rich Fraction (FRF)-Supplemented Flat Breadsa β-Glucans (%)

Arabinoxylans (%)

Digestible starch (g/g)

Flat bread

Total

Water-solubleb

Total

Water-solubleb

15 min

60 min

Control

0.23d

0.09g

2.40b

0.71b

0.203a

0.436a

+N-FRF

1.85c

0.58f

4.90a

0.91a

0.184b

0.374c

+N-FRF-PM

1.84c

0.62e

4.50a

0.91a

0.172c

0.368c

+W-FRF

2.70b

1.22c

3.70a

0.68c

0.177b,c

0.384b

+W-FRF-PM

2.74b

1.10d

3.90a

0.65c

0.161d

0.352d

+HA-FRF

2.91a

1.31b

4.47a

0.75b

0.180b

0.352d

+HA-FRF-PM

2.97a

1.43a

4.20a

0.71b

0.164d

0.348d

Means in columns followed by a different letter(s) are significantly different (P  .05) as determined by Duncan’s multiple range test. Water-soluble β-glucans and arabinoxylans were measured after extracting cubes of flat bread in water at 40°C for 120 min. Results are expressed as gram of starch released upon digestion with α-amylase per gram of available starch in flat bread samples. HA, high amylose; N, normal; PM, pin mill; W, waxy. a

b

due to DF constituents adhering to starch granules and possibly increasing the digesta viscosity. The decrease of in vitro starch digestibility due to the presence of β-glucans may indicate reduction of the GI of breads. Jenkins et al.39 showed that in a 50 g carbohydrate food portion (a prototype β-glucan-enriched breakfast cereal and bar), each gram of β-glucan could reduce the GI by 4 units, making it a useful functional food component for reducing postprandial glycemia.

TECHNOLOGICAL ISSUES Consumers’ interest in healthy and low-calorie foods has created the demand and opportunity for innovative DF preparations and their incorporation into new and traditional food products. However, producing functional food products that fulfill expectations in terms of sensory appeal and indeed deliver the expected health benefits is challenging and requires innovative approaches and careful attention throughout the manufacturing process. The source of DF and the type and degree of processing involved in fiber preparation are often key factors influencing its physiological functionality. The physiological benefits of β-glucans are associated not only with their amount, but also with their viscosity-building properties linked to the high molecular weight of these polymers. Because β-glucans are easily degraded by β-glucanases, care has to be taken during the preparation of β-glucan fiber to either choose sound barley or to inactivate the endogenous enzymes in grain by appropriate treatment. Changes to the molecular weight of β-glucans can also occur during bread-making processes such as mixing, and fermentation; keeping these steps as short as possible and avoiding introduction of β-glucanase activity from other ingredients used in the bread formulas are also necessary. Finocchiaro and coworkers40 demonstrated that the effectiveness of bread enriched in barley β-glucans in reducing GI was influenced by the amylose/amylopectin ratio of the barley used in their study. It was shown that the addition (40%) of fiber fraction from the waxy variety, CDC Alamo (2.9% amylose), to bread formula was not as effective as the addition of fiber fraction from Priora (26% amylose) in lowering the GI. Indeed, a positive role of the high amylose/amylopectin ratio in lowering GI in other products was shown previously.41 However, it also appears that a sufficiently high concentration of β-glucans can overcome any counteracting effects of high-amylopectin starch. Several studies demonstrated that the use of waxy barley, Prowashonupana, with a uniquely high concentration of β-glucans, can significantly lower the GI of food products (breads, porridge).28,42,43 In bread-making, the incorporation of a sufficient amount of β-glucans to ensure beneficial physiological impact is often associated with replacing large amounts of wheat flour, and the resulting detrimental technological effects are caused by a dilution of functional gluten proteins. The use of fiber preparations with a high concentration of β-glucans eliminates the necessity of high supplementation levels to achieve the desired β-glucan content in the final product. Several hull-less barley genotypes with high β-glucan content have been bred specifically for food uses and are suitable for production of β-glucan-enriched fiber fractions or high β-glucan barley flour. The adverse

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technological effects in bread manufacture associated with high contents of β-glucan fiber can be counteracted to some degree with the use of strong gluten flours, the addition of vital gluten and surfactants, and the incorporation of hemicellulases. Jacobs et al.14 reported that the addition of xylanase to the sponge-and-dough formulas improved the loaf volume, appearance, and crumb structure of bread fortified with barley FRF and potentially increased the health benefits by increasing the amount of soluble fiber content in the bread. These authors also reported that the method of bread production strongly influenced bread quality; the best-quality FRF-enriched bread was obtained by the sponge-anddough process because the gluten network was allowed to develop fully during the 4 h sponge stage, and the barley FRF were incorporated only at the dough stage. The shorter exposure of FRF to fermentation was also a potential advantage because extended fermentation times might reduce the cholesterol-lowering capacity of β-glucans due to their degradation by β-glucanases.

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3. FORTIFICATION OF FLOURS AND BREADS