Food Research International 64 (2014) 677–682

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Food Research International

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Effects of malting on molecular weight distribution and content ofwater-extractable β-glucans in barley

Ombretta Marconi a,⁎, Ivan Tomasi a, Laura Dionisio b, Giuseppe Perretti b, Paolo Fantozzi b

a Department of Agricultural, Food and Environmental Science, University of Perugia, Via San Costanzo, 06126 Perugia, Italyb Italian Brewing Research Centre, University of Perugia, Via San Costanzo, 06126 Perugia, Italy

⁎ Corresponding author. Tel.: +39 0755857926.E-mail address: ombretta.marconi@unipg.it (O. Marco

http://dx.doi.org/10.1016/j.foodres.2014.07.0350963-9969/© 2014 Elsevier Ltd. All rights reserved.

a b s t r a c t

a r t i c l e i n f o

Article history:Received 19 May 2014Accepted 23 July 2014Available online 31 July 2014

Keywords:β-GlucansBarleyMaltingβ-GlucanaseMolecular weight distributionHigh-performance size-exclusionchromatography

In the beer industry β-glucans are extensively studied non-starch polysaccharides due to their ability to increasethe viscosity of solutions and to form gels. The current study was designed to determine the total and water-soluble β-glucan contents of barley during malting. Total and water-soluble β-glucans were analyzed from twodifferent malts that originated from the same barley but varied in germination time from 36 h (malt A) to 72 h(malt B). Water-soluble β-glucans were also characterized using high-performance size-exclusion chromatogra-phy with triple-detector analysis (HPSEC-TDA) to evaluate the variation in molecular weight distributions,intrinsic viscosity, radius of gyration, Mark–Houwink parameters and polydispersity and thus the overall struc-tural changes during malting. Total β-glucan content decreased from barley to malt due to the action of β-glucanase and was greatest in malt B (where 92% of β-glucans were degraded) which highlights the influenceof germination time. β-Glucan solubility increased during malting, again particularly in malt B, where most ofβ-glucans became soluble. The β-glucanase activity also affected the molecular weight of the polymers whichranged from 298 · 103 g/mol in barley to 293 · 103 and 218 · 103 g/mol in malts A and B respectively. The molarmass of the most abundant fraction decreased from barley (256 · 103 g/mol) to malt A (112 · 103 g/mol) andmalt B (89 · 103 g/mol), again highlighting the effect of the longer germination time. Proceeding from barleyto malt, the cumulative molar mass distribution function confirmed that the weight fraction of polymersbelow 200 · 103 g/mol increased, while the high molecular weight fraction (between 200 · 103 g/moland 400 · 103 g/mol) decreased. Moreover, the presence of a higher molecular weight fraction (14–16%)beyond 400 · 103 g/mol which does not change during malting was observed. The Mark–Houwink con-stants α and log k confirmed the random coil conformation of soluble β-glucans and showed an increasein the compactness of the macromolecules from barley to malts.

© 2014 Elsevier Ltd. All rights reserved.

1. Introduction

Barley is a traditional raw material used for brewing. β-Glucans arethe main components of the cell walls of the endosperm howeverother constituents such as arabinoxylan, cellulose, glucomannan, pro-tein and phenolic compounds are also present (Beer, Wood, & Weisz,1997; Holtekjølen, Uhlen, Bråthen, Sahlstrøm, & Knutsen, 2006; Wood,Weisz, & Blackwell, 1991).β-Glucans are a family of non-starch polysac-charides composed of linear chains of glucose residues polymerizedthrough β-1–3 and β-1–4 linkages. β-1–4 linkages occur in groups oftwo to four while β-1–3 linkages occur singly. Therefore, the structureis dominated by β-1–3-linked cellotriosyl and cellotetraosyl units. Therest of the structure consists of longer blocks of 4–15 1–4-linked β-D-glucopyranosyl units.

The presence of β-1–3 linkages forms twists in the chains that influ-ence the stability and affinity of β-glucans to form aggregates and,

ni).

consequently, their solubility. The published research on the relationshipbetween β-glucan solubility and these linkages is limited (Ahmad,Anjumb, Zahoorb, Nawazc, & Dilshadd, 2012). The structural features ofβ-glucans also appear to be important factors for other physical proper-ties such as viscosity and gelation. In fact, the ability of β-glucans toform gels depends on their concentrations, molecular weight distribu-tions, and structures. Some studies have shown that gelation ratedeclines with decreasing concentration and increasing molar mass ofβ-glucans by affecting the probability of contact between the coils(Böhm&Kulicke, 1999; Lazaridou, Biliaderis, & Izydorczyk, 2003). How-ever, higher molecular weight gels showed an increase in gel strengthas well as a decrease in gel brittleness (Lazaridou et al., 2003). Further-more, gelation rate has been correlated with polydispersity and in par-ticular with averagemolecular weight values that are predominantly inthe low molecular weight tail of the molar mass distribution (Böhm &Kulicke, 1999). Finally, the structures of β-glucans also contribute togel formation according to the DP3/DP4 ratio as well as the amount ofβ-(1 → 3) glucosidic linkages which enhance gelation rate and elastic-ity (Tosh, Wood, Wang, & Weisz, 2004).

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Total content of β-glucans in barley normally ranges from 2 to 8%and depends on both genetic and environmental factors. About 66% ofthe barley β-glucans are in soluble form, although the factors influenc-ing their solubility are not fully known (Lee & Bamforth, 2009). Someparameters such as temperature, solvent type, extraction time andenzymatic treatment can influence the yield and structural characteris-tics of soluble β-glucans (Ahmad et al., 2012; Bhatty, 1993; Izydorczyk,Storsley, Labossiere, MacGregor, & Rossnagel, 2000). Ideally barley maltused for beer production should have low levels of β-glucans, lowviscosity, high extractability, friability, and diastatic power, as well as alow level of total nitrogen and an average level of soluble nitrogen(Kunze, 2004). During malting β-glucans are degraded by the actionof endo-β-glucanase into soluble compounds (Wang, Zhang, Chen, &Wu, 2004) but little is known about the structural andmolecularweightchanges during this process. Soluble β-glucan levels in worts and beersproduced from slightly modified malts are too high, highlighting thecritical importance of the malt modification process (Lee & Bamforth,2009) which may lead to subsequent problems during filtration andresult in low production yields (Jin, Speers, Paulson, & Stewart, 2004;Speers, Jin, Paulson, & Stewart, 2003). However, the underlying causeof problems with wort and beer filtration is not clear because it couldbe due to the concentration of β-glucans or their structure and molecu-lar weight which influence the β-glucan gel formation.

This studywas conducted in order to evaluate the effects of differentmalting conditions on both total and water soluble levels of β-glucansand to highlight the differences between barley and malt β-glucans.Themolecular characterization of β-glucan extracts was also investigat-ed to elucidate structural and physical changes to β-glucans duringmalting and collect valuable information to improve the brewingprocess starting from row materials.

2. Materials and methods

2.1. Barley processing and malting procedure

Malting was conducted in a micro-malting pilot plant provided bythe Italian Brewing Research Centre (CERB, University of Perugia,Perugia, Italy). The plant included 4 independent steeping/germinationtanks as well as 4 independent drying tanks and each tank had thecapacity to hold 4 drums filled with 0.5 kg of sample.

The barley was steeped twice; once at 18 °C for 5 h followed by anair rest at 17 °C for 16 h and then again at 16 °C for 4 h followed by anair rest at 16 °C for 24 h. Germination was conducted at 15 °C for 36 hto obtain greenmalt A and for 72 h to obtained greenmalt B. The kilningprogram was 15 h at 55 °C, 4.5 h at 72 °C and finally 3.5 h at 82 °C.

Throughout these procedures samples were collected for analysisduring steeping, germination and at the end of kilning.

2.2. Barley and malt analysis

2.2.1. Barley and malt quality attributesQuality attributes important for malting barley (such as grain mois-

ture, protein content, germinative energy and water sensitivity) weredetermined using Analytica EBC methods (European Brewery Conven-tion, 2007). Specifically malt quality was assessed using the followingmethods:

• Moisture content (%): EBC method 4.2.• Extract yield (% dm) and saccharification time (min): EBC method4.5.1.

• Total nitrogen content (% dm): EBC method 4.3.1.• Kolbach index: EBC method 4.9.1.• Free amino nitrogen content (g/100 g): EBC method 4.10.• Viscosity (cP at 20 °C and 8.6 °P): EBC method 4.8.• Apparent final attenuation (%): EBC method 4.11.1.• Diastatic power (°WK): EBC method 4.12.

• pH: EBC method 8.17.• Malt color: EBC method 4.7.1.

2.2.2. Determination of total and water-soluble β-glucan contentsTotal β-glucan content in barley, intermediate malting samples and

in malt was measured according to the enzymatic method of McClearyand Glennie-Holmes (1985) using a commercial assay kit (MegazymeInternational Ireland, Bray, Ireland). Soluble β-glucans were measuredusing a new method of extraction described below and the resultswere expressed on a dry weight basis. β-Glucan solubility was calculat-ed as soluble β-glucans / total β-glucans ∗ 100.

2.2.3. Extraction of water-soluble β-glucansWater-soluble β-glucans were extracted in triplicate by the proce-

dures of Colleoni-Sirghie, Kovalenko, Briggs, Fulton, and White (2003)and Andersson, Fransson, Tietjen, and Åman (2009) with a few modifi-cations. The sample flour (10 g) was defatted in a Soxhlet system by2-propanol:petroleum ether (2:3) for 6 h and stored dry overnight.Then, 1 g of defatted sample was incubated in 5mL of 50% aqueous eth-anol in a water bath at 80 °C for 15 min. After cooling to room temper-ature, 5mL of 50% ethanol were added, and the sample was centrifugedfor 10min at 1000 g. The supernatant was discarded, and the pellet waswashed with 10 mL of 50% ethanol, followed by centrifugation anddecantation. The pellet was suspended in 20 mL of distilled water, and50 μL of thermostable α-amylase (3000 units/mL, Megazyme Interna-tional Ireland, Bray, Ireland) were added. The sample was mixed andincubated for 90 min at 80 °C with occasional mixing. After cooling toroom temperature, 43 μL of amyloglucosidase (140 units/mL, MegazymeInternational Ireland, Bray, Ireland) were added, and the sample wasincubated at 60 °C overnight. The sample was cooled and centrifugedfor 15 min at 1500 g. An aliquot of 15 mL of supernatant, 450 μL of0.5 M sodium phosphate, 1 mg of pancreatin (P7545, Sigma Aldrich,St. Louis, U.S.A.), and 43 μL of xylanase (2300 units/mL, Megazyme In-ternational Ireland, Bray, Ireland) were mixed and incubated for 2 h at40 °C under occasional stirring. β-Glucans were precipitated by adding22.5mL of ethanol and incubating overnight at 4 °C. The precipitatewasisolated by centrifugation (1000 g, 10 min) and resolubilized in 2.5 mLof 0.1 M sodium nitrate containing 0.05% NaN3, at 80 °C for 1.5 h undermagnetic stirring. The sample was centrifuged for 10 min at 18,000 gand filtered through a 0.45 μm filter for immediate high-performancesize-exclusion chromatography (HPSEC) analysis.

2.2.4. Characterization of water-soluble β-glucansPurified β-glucans were fractionated by HPSEC and characterized by

a triple detector (TDA). The systemwas kept at 40 °C andwas composedof a Knauer 1050 solvent delivery system, an HTA 300 L autosamplerwith a 100 μLmounted loop, a TSK PWXL guard column and two seriallyconnected columns (TSKgel G5000PW, TSKgel G4000PW, Tosoh Corpo-ration, Tokyo, Japan). The eluent was 0.1 M NaNO3 containing 0.05%NaN3 injected at a flow rate of 1 mL/min. The TDA was a Viscotek 270model (Malvern Instruments Ltd., Malvern, United Kingdom) (low andright angle light scattering, and differential 4-capillary viscometer) anda serially-connected Viscotek VE3850 refractive index detector kept at35 °C. Raw data were analyzed using Viscotek OmniSEC software. TheHPSEC-TDA provides data for multiple polymer properties such as mo-lecular weight distributions (Mw, Mn, Mz), intrinsic viscosity [η], radiusof gyration (Rg),Mark–Houwink parameters (α, log k) and polydispersi-ty (Pd) asMw/Mn ratio.Molecularweight distributionwas calculated byperforming a multi-detector homopolymer calibration using polyethyl-ene oxide (PEO 22 K, PolyCAL standard, Viscotek) as a narrow standardand using a refractive index increment (dn/dc) of 0.132. The methodwas validated by analyzing a dextran (Dextran 70 K, PolyCAL standard,Viscotek) as a broad standard and using a dn/dc of 0.139. The methodwas further tested using 650 kDa and 229 kDa molecular weight β-glucan standards (Megazyme International Ireland, Bray, Ireland) usinga dn/dc of 0.146. These calibrations allowed for the quantification of

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Fig. 1. Variation in total and water-soluble β-glucan contents during malting with germi-nation periods of 3 days (panel A) or 1.5 days (panel B). Solubility (%) was calculated as(water-soluble β-glucans / total β-glucans) · 100 (B: barley; S1: 1st day of steeping; S2:2nd day of steeping; G1: 1st day of germination; G1.5: 1.5 days of germination; G2: 2ndday of germination; G3: 3rd day of germination; MA: malt A; MB: malt B).

679O. Marconi et al. / Food Research International 64 (2014) 677–682

soluble β-glucan content in the sample which was used to calculate ini-tial β-glucan content as a percentage of dry mass.

2.2.5. Evaluation of beta-glucanase activityMalt β-glucanase activity in intermediate malting samples and in

malt was measured according to the enzymatic method of McClearyand Shameer (1987) using a commercial assay kit (Megazyme Interna-tional Ireland, Bray, Ireland).

2.2.6. Statistical analysisStatistical analysiswasperformedusing SigmaStat software (version

11; Jandel Scientific, San Rafael, U.S.A.). Comparisons of the differentmatrices were made by one-way repeated measures analysis ofvariance.

3. Results and discussion

Barley was malted in two different ways for this study. The steepingand kilning steps were performed in the samemanner for both maltingtrials while the germination times were 1.5 days (malt A) or 3 days(malt B). The quality parameters of the barley grains and both maltsare reported in Table 1. The quality attributes of malts A and B weresimilar and the friability value and Kolbach index showed a high levelof modification.

Next the influence of themalting process on the β-glucanswas eval-uated. The total β-glucan content was determined by the enzymaticmethod of McCleary and Glennie-Holmes (1985), while the water-soluble ß-glucan content was evaluated using a specific method basedon HPSEC-TDA after extraction from the solid matrix. The water-soluble β-glucan extraction from barley andmalt was optimized by tak-ing into account the procedures of Colleoni-Sirghie et al. (2003) andAndersson et al. (2009) for oat and rye respectively. Heated treatmentwith 2-propanol/petroleum ether was carried out to inactivate endoge-nous β-glucanase (Colleoni-Sirghie et al., 2003) and also to removepolar lipophilic compounds that could interfere with the chromato-graphic analysis. Starch, dextrins and protein were also removed by en-zymatic treatment. A treatment with xylanase was also added becauseduring the hot water extraction some soluble arabinoxylanwas extract-ed with β-glucan. This fact was confirmed by the analytical determina-tion of the malt water soluble β-glucan content with and withoutxylanase treatment which yielded 0.192 g/100 g and 0.297 g/100 g,respectively (data not shown).

Total and soluble β-glucan contents and solubility during themalting trials are presented in Fig. 1. Both total and soluble β-glucancontents decreased during malting. In barley total β-glucan contentwas 3.79 g/100 g and about 34% of this was in soluble form. Duringthe first day of steeping total β-glucan content did not decrease howev-er by the end of steeping they had reduced by about 33%. At the end ofgermination, 73% of total β-glucan content was degraded in malt A,

Table 1Quality attributes of the barley and malts (means ± standard deviations of duplicates).

Barley Malt A Malt B

Moisture (%) 9.3 ± 0.5 3.7 ± 0.4 3.9 ± 0.4Germinative energy (%) 90 ± 7 – –

Total protein (% dm) 7.3 ± 0.6 6.8 ± 0.6 6.9 ± 0.6Extract yield (% dm) – 82.4 ± 0.8 82.5 ± 0.8Saccharification time (min) – 10–15 10–15Viscosity (cP at 8.6 °P) – 1.52 ± 0.03 1.52 ± 0.03Final attenuation (%) – 79.5 ± 1.8 80.4 ± 1.8Total nitrogen (% dm) – 1.10 ± 0.10 1.10 ± 0.10Kolbach index – 38.9 ± 1.4 39.0 ± 1.4Free amino nitrogen (g/100 g dm) – 0.10 ± 0.02 0.10 ± 0.02Diastatic power (°WK) – 143 ± 26 171 ± 29Color (EBC-U) – 6.2 ± 0.8 6.0 ± 0.8Friability (%) – 95 ± 3 97 ± 3

dm: dry matter; cP: centipoise; WK: Windisch–Kolbach units.

while 92% was degraded in malt B. These results suggest that total β-glucan content depends significantly on germination time and theyalso suggest that β-glucanase is most active during late steeping andreaches its maximum activity during germination which is in agree-ment with a previous report (Kuntz & Bamforth, 2007).

With regard to water-soluble β-glucans, no reduction in theircontent was observed during steeping while a reduction of about 70%and 80% was observed at the end of germination for malts A and Brespectively. Otherwise the two malts displayed significantly differentβ-glucan solubilities. Specifically the longer germination time increasedβ-glucan solubility from about 50% to 78% frommalt A tomalt B, reveal-ing that in malt B most β-glucans are water soluble.

The molecular properties of water-soluble β-glucans were investi-gated by HPSEC-TDA and the data are reported in Table 2. The averagemolecular weight of the samples decreased during malting from298 · 103 g/mol for barley to 196 · 103 and 158 · 103 g/mol for greenmalt A and green malt B, respectively. The Mw of malts A and B were293 · 103 and 218 · 103 g/mol. The differential molecular weight distri-bution function can correlate Mw changes and enzymatic activity dur-ing malting. The differential distribution function can also be utilizedto determine molar mass minimums and maximums as well as themolar mass of the most abundant fractions. The distribution functionexpressing the amount of material as the weight fraction is called

Table 2Molecular properties of water-soluble beta-glucans during malting (means of triplicates).

Mw(·103 g/mol)

Pd [η](dL/g)

Rg(nm)

α log k

Barley 298a 1.41a,d 4.100a 32a 0.62a,b −2.77a

Steeping (1 day) 223b 1.55b,c 3.136b 24b 0.67a −3.05a

Steeping (2 days) 168d 1.51a,b,c 2.776b,c 20b 0.69a −3.15a

Germination(1 day)

165d 1.56b,c 2.520c,d 19b 0.67a −3.04a

Germination(1.5 days)plus kilning

196c 1.54b,c 2.390d 17b 0.63a,b −2.93a

Malt A 293a 1.59 b,c 2.310d,e b15 0.55a,b −2.60a

Germination(2 days)

170d 1.31d 1.773f b15 0.62a,b −2.93a

Germination(3 days)plus kilning

158d 1.48a,b,c 1.987e,f b15 0.59a,b −2.34a

Malt B 218b,c 1.49c 1.820f b15 0.54b −2.56a

Values in the same column followed by the same letter are not statistically different(P b 0.05).Mw: average molecular weight; Pd = polydispersity (Mw/Mn); [η]: intrinsic viscosity;Rg: radius of gyration; α and k: slope and intercept in the Mark–Houwink equation.

Fig. 3.Molar mass of the largest fraction of water-soluble β-glucans inmalting (B: barley;S1: 1st day of steeping; S2: 2nd day of steeping; G1: 1st day of germination; G1.5: 1.5 daysof germination; G2: 2nd day of germination; G3: 3rd day of germination;MA:malt A;MB:malt B).

600beta-glucanase

680 O. Marconi et al. / Food Research International 64 (2014) 677–682

weight molar mass distribution (Podzimek, 2011). Fig. 2 shows themolar mass distributions for barley, malt A and malt B. The molarmass of the most abundant fraction was 256 · 103 g/mol for barley,112 · 103 g/mol for malt A, and 89 · 103 g/mol for malt B. These resultsagain highlight the effect of the longer germination time. The trend ofthe molar mass of the most abundant fractions of β-glucans duringmalting is presented in Fig. 3. It is worth noting that the molar mass ofthe most abundant fraction clearly decreases from barley duringmalting.

The effects on molar mass may be at least partly explained by theevaluation of the β-glucanase activity duringmalting, which is depictedin Fig. 4. β-Glucanase activity begins during the second day of steepingand increases during germination, reaching its maximum after 1.5 and3 days of germination for malt A and malt B respectively. In the finalmalts the β-glucanase activity is slightly lower, probably because ofthe high temperature reached during the kilning. The increase of theβ-glucanase activity during germination correlates with the decreasesin concentration and molar mass of the most abundant fractions. How-ever, there is a decrease in molar mass of the most abundant β-glucanfractions during the first day of steeping even if β-glucanase activity isnot detectable. These changes in β-glucan molar masses are supportedby changes in other properties such as intrinsic viscosity and gyrationradius (Table 2) but the underlying cause of these changes is not clear.They may be due to the action of other enzymes present in raw barley(Bamforth & Martin, 1980; Bamforth, Martin, & Wainwright, 1979;Forrest & Wainwright, 1976).

Log molecular weight (g/mol)

Wf/d

log

Mw

Mw: 96 x103 Mw: 117 x103Mw: 256 x103Barley Malt AMalt B

Fig. 2. Differential molar mass distribution function of β-glucans extracted from barley,malts A and B.

In Fig. 5 the cumulative molar mass distribution is depicted for bar-ley, malt A and malt B water-soluble β-glucans. The cumulative molarmass distribution allows for the determination of the weight fractionsof polymers below or above certain molar mass limits or within specificmolar mass ranges. In this case the figure shows the weight fraction (orweight percentage) of polymers up to 200 · 103 g/mol, between 200and 400 · 103 g/mol, and over 400 · 103 g/mol. These limits were cho-sen because they best described the weight fraction variation risingfrom barley to malt. In barley 49% of water-soluble β-glucans had amolar mass in the range of 200 to 400 · 103 g/mol while in malts Aand B 54% and 62% of the molar mass was below 200 · 103 g/mol.These data further confirmed the effect of β-glucanase activity duringmalting. It is interesting that about 14–16% of the β-glucans with amolar mass over 400 · 103 g/mol did not change during the maltingprocess, therefore it was not affected by enzymatic activity. These highmolar mass β-glucans may be found in the wort and final beer andthey could contribute to filtration problems and haze formation.

The polydispersity values (Table 2) showed that the β-glucansextracted from all the samples were polydisperse (Pd N 1.2) indicatingthe broad distribution of these polymers. The intrinsic viscosity [η] of

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Fig. 4. Change in β-glucanase activity during malting (B: barley; S1: 1st day of steeping;S2: 2nd day of steeping; G1: 1st day of germination; G1.5: 1.5 days of germination; G2:2nd day of germination; G3: 3rd day of germination; MA: malt A; MB: malt B).

Mw: 200 x103

Barley: 16%Malt A: 16 %Malt B: 14 %

Barley: 49%Malt A: 30%Malt B: 24%

Barley: 35%Malt A: 54%Malt B: 62%

Mw: 400 x103

(g/mol)

Fig. 5. Cumulative weight fraction of β-glucans extracted from barley, malts A and B.

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the samples decreased during malting from 4.100 to 1.820 (dL/g) forbarley to malt B and showed a variation in the polymer structure. Therelationship between intrinsic viscosity and molar mass is determinedby theMark–Houwink equation. For a polydisperse polymer the intrin-sic viscosity is related to the molar mass distribution. In fact the mostabundant fraction molecular weight of water-soluble β-glucans frombarley to malt did correlate with the [η] showing a correlation coeffi-cient (r) of 0.98. In Fig. 6 the logarithmic Mark–Houwink plots for bar-ley, malts A and B were reported. The high [η] value indicated thatbarley β-glucans were less dense than in malts A and B. The Mark–Houwink constants α and log k undergo a slight variation from barleyto malt. Values of α between about 0.65–0.75 indicate flexible randomcoil polymer molecules in thermodynamically good solvents such asfor barley and intermediate malting samples. Water soluble β-glucansinmalts A and B showed lower values ofαwhich indicates theirmacro-molecules are more compact.

4. Conclusions

In conclusion this work showed that malting condition can affectboth content andmolecular characteristics of the β-glucan. In particularthe total β-glucan content decreases duringmalting due to the action ofβ-glucanase while β-glucan solubility increases during malting and ispositively affected by the germination time. Since the solubilization ofdegraded and undegraded substances occur during mashing process,the knowledge of the characteristics of the β-glucans in the final maltcould be useful to improve or facilitate the mashing (and worth filtra-tion) process (es). As seen in this work, barley β-glucans undergoseveral changes in molecular weight distribution and structure. In fact,the molar mass of the most abundant fraction decreased from about256 · 103 g/mol for barley to 117 · 103 and 96 · 103 g/mol for malts Aand B respectively in good relation with the intrinsic viscosity.

Barley: log K = -2.77 = 0.62Malt A: log K = -2.60 = 0.55Malt B: log K = -2.56 = 0.54

(g/mol)

(dl/g

)

Fig. 6.Mark–Houwink plot for β-glucans extracted from barley,malts A and B ([η]: intrin-sic viscosity; α and k: slope and intercept in the Mark–Houwink equation).

Moreover, the cumulative molar mass distribution of water-soluble β-glucans showed that 49% of water-soluble β-glucans had a molar massin the range of 200 and 400 · 103 g/mol in barley while 54% and 62%of the molar masses were below 200 · 103 g/mol in malts A and B, re-spectively, which also confirms the β-glucanase activity duringmalting.Furthermore, it was found that about 14–16% of the β-glucans withmolar masses over 400 · 103 g/mol did not change during the maltingprocess, therefore they were not affected by enzymatic activity. Thisresult can suggest that a low content of β-glucans is not enough toexclude future filtration problems, that could be ascribed to molecularand hydrodynamic properties (such as molecular weight distributions,gyration radii, intrinsic viscosity and Mark–Houwink parameters) ofthe β-glucans.

Acknowledgments

We thank the Italian Ministry of Research for its financial support ofthe project PRIN 2010 prot. 2010ST3AMX, titled “Process and productinnovation in the barley food chain for the improvement of qualityand environmental sustainability of food and beverages.” We alsothank LabService Analytica srl for their technical support.

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