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Journal of Food Science and Technology logoLink to Journal of Food Science and Technology
. 2012 Feb 3;51(6):1066–1075. doi: 10.1007/s13197-012-0629-8

Effect of pentosans addition on pasting properties of flours of eight hard white spring wheat cultivars

Saqib Arif 1,✉, Tahira Mohsin Ali 2, Qurat ul Afzal 1, Mubarik Ahmed 1, Asim Jamal Siddiqui 3, Abid Hasnain 2
PMCID: PMC4033747  PMID: 24876638

Abstract

The effects of water extractable pentosans (WEP) and water unextractable pentosans (WUP) on pasting properties in flours of eight different hard white spring wheat (HWSW) cultivars was studied. WEP and WUP isolated from a hard wheat flour were added to each of the cultivars at 1% and 2% level. The results indicated that WEP exhibited a pronounced effect on pasting properties as compared to WUP and variety. Univariate analysis of variance (ANOVA) was used to evaluate sources of variation. The variety significantly (P < 0.001) influenced all the pasting parameters. WUP caused significant (P < 0.001) variation in paste viscosities (except breakdown). WEP influenced more pronouncedly the hot paste, cold paste, breakdown and setback viscosities with F values—221.802, 214.286, 98.073 and 120.159, respectively. Variety-by-WEP interaction exhibited significant (P < 0.01) influence on pasting time, peak, hot paste and cold paste viscosities. Whereas, variety-by-WUP interaction only significantly (P < 0.001) influenced the pasting- time and -temperature. Duncan’s test was used to analyze the significant difference (P < 0.05) within the variety. The results revealed that WUP did not induce significant (P < 0.05) influence on all the pasting parameters, whereas, WEP influenced significantly (P < 0.05) the paste viscosities of some of the varieties. It was also found that the addition of WEP remarkably reduced the setback, hot paste, cold paste viscosities and increased the breakdown viscosity in all cultivar flours. The effect of WEP was greater at higher level of supplementation on paste viscosities.

Keywords: Pentosans, Pasting properties, Hard white spring wheat flours

Introduction

Starch is the most abundant component of food. It is the major component of wheat kernel and therefore its behavior during wheat processing is an area of interest for researchers and bakers. A lot of work has been undertaken on the role of wheat starch and its pasting properties in bread making and storage (Toshiki and Paula 1992; Ozkoc et al. 2009; Martin and Hoseney 1991; Zeleznak and Hoseney 1986). Also, starches from other sources such as rye (Buksa et al. 2010; Ragaee and Abdel-Aal 2006), water chestnut (Lutfi and Hasnain 2009; Murty et al. 1962) and sweet potato (Lee et al. 2002) have been studied. In addition to starch, the pasting properties of wheat flours are related to protein, particles size distribution, α-amylase activity and damaged starch (Nagao 1995) and also influenced by presence of other ingredients such as sugar and salt (Wootton and Bamunuarachchi 1980).

Wheat pasting properties would be useful to predict performance of wheat flour during processing and phenomenon of bread staling (Collar 2003). Bakers are often interested to assess as well as control the bread staling. Hydrocolloids or gums are known to influence pasting properties of wheat starch and flour (Rosell et al. 2001) and widely used as antistaling agent in bread making (Davidou et al. 1996; Armero and Collar 1998). Many hydrocolloids like Xanthan gum, guar gum, CMC, gum acacia and locust bean gum have been investigated to exploit their effects on bread staling (Dickinson 2003; Juszczak et al. 2004; Gavilighi et al. 2006; Azizi and Rao 2004). But only few researchers have included pentosans in their studies even though pentosans compete well for water with other constituents of flour and subsequently affect the pasting properties of flour.

Pentosans and hemicelluloses are the major component of cell walls of cereal grains and varies between 4% and 8% in wheat (Hong et al. 1989; Saulnier et al. 1995). Pentosans positively affect shelf life of breads either by directly interacting with starch (Benamrouche et al. 2002; Devesa and Martinez-Anaya 2003) or by curtailing the availability of water during retrogradation (Biliaderis et al. 1995). Water soluble pentosans had detrimental effects on starch gelation (Santos et al. 2002). Some researchers have found the increasing effect of pentosans on peak viscosity, and the effect was greater by adding water extractable pentosans than water unextractable pentosans (El-Wakeil et al. 1976). Others have found no effects of pentosans on pasting properties of wheat flour (Kim and D’Appolonia 1977b). The discrepancies in results could be due to the different sources from which pentosans were isolated. Tao and Pomeranz (1967) reported that durum pentosan decreases peak viscosity, whereas, pentosans from other flour varieties (including hard red winter, hard red spring, soft red winter and club wheats) either increased or had no effects on peak viscosity. Other factors could be difference in isolation procedures of pentosans; level of supplementation and the quality of base flours.

The pasting properties of wheat are largely related to cultivar (Bhattacharya et al. 1997; Singh et al. 2011; Massaux et al. 2008), irrigation practices and sowing time (Singh et al. 2010). Despite the significance of flour pasting properties and role of pentosans, no extensive study had been undertaken on Pakistani wheat cultivars. The present study had therefore been emphasized to study the effects of pentosans on pasting properties of HWSW flours.

Materials & methods

Eight hard white spring wheat cultivars namely TJ-83, Abadgar, Anmol, TD-1, Moomal, Imdad, SKD-1 and Mehran were grown at two locations Hyderabad and Nawabshah-Sindh in Pakistan. Both the locations have almost identical agro-ecology and are about 120 km distance to each other. Hyderabad lies 25.36° latitude and 68.36° longitude whereas Nawabshah lies 26.25 and 68.41° latitude and longitude, respectively. The environmental factors including maximum temperature, minimum temperature and precipitation for the crop period (about 15Nov to 15May, 2008) was found to be 30.0 °C, 15.8 °C and 1.3 mm for Hyderabad and 31.9 °C, 10.4 °C and 0.12 mm for Nawabshah respectively. Both the areas are irrigated and canal-fed and are rich and known for wheat cultivation. On harvest, the wheat representing different genotypes were randomly sampled, mixed and divided to form representative laboratory samples.

In laboratory, samples were mixed thoroughly using precision electronic divider and thereafter cleaned manually using appropriate sieves. Wheat grain was milled into flour with the help of Brabender Quadramat Junior Mill, in accordance to the procedure of AACC 26–50 (2000). Wheat was conditioned to 15% moisture for 18 h before milling. The feeding rate was kept at about 100 g/min.

Isolation of WUP and WEP

The WEP and WUP fractions of pentosans were isolated from a commercially available hard wheat variety “Inqlab”. Water-unextractable pentosans were isolated following the procedure of Wang et al. (2003) with slight modifications. The resultant starch slurry was passed twice through a muslin cloth before sieving through a 32 μm mesh size standard sieve. Further steps of isolation and purification of WUP including incubation for 16 h at 30 °C after adding α-amylase, freeze drying and grinding were adapted as described by Wang et al. (2003). For the extraction of WEP, procedure given by Cleemput et al. (1995) was followed.

Pasting properties

Both the isolated materials (WUP and WEP) were substituted at the rate of 1% and 2% to HWSW flours separately. The samples including control and pentosan substituted were analyzed for pasting properties using Brabender Microviscoamylograph (Model # 803201, Brabender, Germany), equipped with 300 control moment gyroscope (cmg) sensitivity cartridge. Sample slurry (15%) w/v was subjected to heating cycle from 40 to 95 °C at a heating rate of 3 °C/min. The slurry was held at this temperature for 10 min and was subsequently cooled back to 50 °C/min at a cooling rate of 3 °C/min. The slurry was held at this temperature for 10 min. The speed of rotation of bowl was fixed at 75 rpm. Peak viscosity (PV), pasting temperature (PT), time to reach peak viscosity (TTP), hot paste viscosity (HPV), cold paste viscosity (CPV), breakdown (BD) and setback (SB) viscosities were recorded from resulting amylograph.

Statistical analysis

All the analytical tests were replicated four times for the randomized samples collected from the experimental locations. A 3-way ANOVA for a factorial design (the factors were variety at 8 levels and WEP or WUP at 3 levels each including control) was performed to analyze the sources of variation in pasting properties of HWSW flours. Duncan’s test (at P < 0.05) was used to separate varieties within treatments (control, 1% and 2%) and also to calculate significant differences of pentosan substituted flours from control. All the statistical analysis was undertaken using SPSS software (SPSS version 17, Inc., USA).

Results and discussion

Table 1 depicts the ANOVA analysis to determine the effects of varietal differences, WEP and WUP on pasting properties of HWSW flours. It is evident that 70–90% of total variation in peak, hot paste, cold paste, breakdown and setback viscosities are a result of varietal differences, WEP and WUP influence. For pasting- temperature and -time the model explained the variation to a lesser degree. The results for individual parameters are discussed as under.

Table 1.

Analysis of variance of pasting parameters of flours of different HWSW varieties

Source Pasting temperature(°C) Time to reach peak viscosity (min) Viscosity (BU)
Peak Hot paste Cold paste Breakdown Setback
R 2 0.45 0.48 0.70 0.90 0.90 0.81 0.84
Corrected Model F value 2.526*** 2.831*** 7.009*** 28.083*** 26.643*** 13.073*** 16.503***
Variety (V) F value 4.067*** 4.700*** 9.379*** 8.677*** 12.966*** 9.668*** 4.856***
WUP F value 0.541 ns 0.360 ns 9.761*** 21.029*** 13.775*** 1.185 ns 13.609***
WEP F value 1.445 ns 3.620* 16.399*** 221.802*** 214.286*** 98.073*** 120.159***
V × WUP F value 3.439*** 3.300*** 1.662 ns 1.108 ns 1.039 ns 1.607 ns 1.303 ns
V × WEP F value 1.785* 2.364** 2.914** 3.691*** 2.710** 1.721 ns 1.114 ns
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F values used type III mean squares; ns, non-significant; *, P < 0.05; **, P < 0.01; and ***, P < 0.001

HWSW hard white spring wheat; WEP water-extractable pentosan; WUP water-unextractable pentosan

Pasting temperature

Pasting temperature (PT) is the temperature at which the first rise in viscosity is recorded on a viscoamylograph. The results have indicated that neither WEP nor WUP had significant effect on PT of HWSW flours (Table 1). However, the significant variation in PT was caused by the varietal differences, variety-by-WEP and variety-by-WUP interaction. The HWSW flours, investigated in this study, had comparable PT values (Table 2). The lowest (56.8 °C) and highest (59.9 °C) values were found in varieties Moomal and Abadgar, respectively. In all the varieties except Abadgar and SKD-1, the WEP was found to have marginally increased (0.2–6%) the PT as shown in figure 1(a). Both these varieties exhibited decrease in PT for WEP and WUP substituted flours that is unexplainable and suggests further investigation to reach any meaningful conclusion. Such marginal decrease in PT had also been reported by Rao et al. (2007) who used rice and ragi origin WEP for addition in wheat flour.

Table 2.

Pasting temperature (°C) of control and pentosan substituted flours obtained from different HWSW varieties

Sample Control 1% WUP 2% WUP 1% WEP 2% WEP
TD-1 57.2 ± 0.1A 57.8 ± 1.8A 61.6 ± 5.4Aa 59.1 ± 0.4A 58.8 ± 0.6A
Imdad 57.5 ± 1.2A 58.5 ± 1.0AB 57.4 ± 0.6A 58.4 ± 1.3A 57.8 ± 0.2A
Mehran 57.6 ± 1.1A 62.1 ± 3.4Ba 57.4 ± 2.4A 58.5 ± 0.1A 58.2 ± 1.8A
Abadgar 59.9 ± 4.1A 58.0 ± 0.5A 57.5 ± 0.6A 58.1 ± 0.1A 56.7 ± 0.7A
Moomal 56.8 ± 0.2A 56.8 ± 0.8A 56.8 ± 0.6A 56.9 ± 0.2A 58.3 ± 0.9A
Anmol 57.3 ± 0.1A 57.7 ± 0.1A 57.9 ± 1.5A 58.4 ± 0.9A 58.6 ± 0.4A
SKD-1 59.5 ± 1.3A 58.8 ± 0.1AB 57.9 ± 0.2A 58.3 ± 1.2A 58.5 ± 1.8A
TJ-83 58.5 ± 0.1A 58.0 ± 1.8A 60.1 ± 0.5A 62.0 ± 8.2A 58.7 ± 1.4A
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Values are Means±SD (n = 4)

Different capital letters within column are significantly different at P < 0.05

ameans significant difference from control at P < 0.05

HWSW hard white spring wheat; WEP water-extractable pentosan; WUP water-unextractable pentosan

Fig. 1.

Fig. 1

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The magnitude of increase or decrease (in percentage) in pasting parameters of HWSW (hard white spring wheat) flours due to addition of water-extractable pentosan. (n = 4)

The effect of WUP on PT in different varieties did not exhibit any uniform pattern and may be an indirect reflection of varietal composition or supplementation level or any other reason.

Peak viscosity

Peak viscosity (PV) is the equilibrium point between swelling and rupture of starch granules (Newport Scientific 1995). It was found that PV of different HWSW flours ranged between 962BU and 1252BU with the highest and lowest values exhibited by the varieties TJ-83 and Mehran respectively (Table 3).

Table 3.

Peak viscosity (BU) of control and pentosan substituted flours obtained from different HWSW varieties

Sample Control 1% WUP 2% WUP 1% WEP 2% WEP
TD-1 1054 ± 77AB 1101 ± 43AB 1044 ± 40A 1001 ± 95A 962 ± 31AB
Imdad 1104 ± 10ABC 1233 ± 28B 1132 ± 26A 1107 ± 16A 906 ± 28AB
Mehran 962 ± 13A 1036 ± 49A 981 ± 27A 984 ± 23A 935 ± 26AB
Abadgar 1134 ± 97ABC 1094 ± 49AB 973 ± 46A 926 ± 34A 870 ± 7A a
Moomal 1011 ± 26A 1202 ± 11B 1078 ± 64A 1014 ± 19A 994 ± 79AB
Anmol 1221 ± 13BC 1215 ± 11B 1165 ± 19A 1126 ± 25A 1088 ± 11AB
SKD-1 1110 ± 50ABC 1245 ± 11B 1170 ± 99A 1179 ± 33A 1092 ± 43AB
TJ-83 1252 ± 62 C 1218 ± 18B 1154 ± 37A 1036 ± 42A 1123 ± 50B
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Values are Means±SD (n = 4)

Different capital letters within column are significantly different at P < 0.05

ameans significant difference from control at P < 0.05

HWSW hard white spring wheat; WEP water-extractable pentosan; WUP water-unextractable pentosan

Varietal differences, WEP, WUP and variety-by-WEP interaction contributed significantly in the variation of PV of HWSW flours (Table 1). Lin and Czuchajowska (1997) also found the significant effect of variety on peak viscosity. The results of present study revealed that the supplementation level of pentosan influences the PV of wheat flour. At 1-percent concentration, both types of pentosans exhibited a similar pattern (whether increase or decrease) on all cultivar flours except TD-1. However, the magnitude of influence was found to be different in each of the variety. Results also reflect that at 2% concentration levels, the WEP exhibited a negative impact on PV of all the cultivars (1.6–23.3% decrease in PV) whereas WUP was found to impart variable influence on PV in the tested varieties (Figure 1b and 2b).

Fig. 2.

Fig. 2

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The magnitude of increase or decrease (in percentage) in pasting parameters of HWSW (hard white spring wheat) flours due to addition of water-unextractable pentosan (n = 4)

Yin and Walker (1992) found a significant effect of pentosan on RVA peak viscosity of starch and reported that PV of starch decreases with the addition of water soluble pentosans. The results of Yin and Walker (1992) are not comparable to this study as they were related to a single commercial starch sample while a range of eight varieties were evaluated in the present study. The pasting properties of starch may not necessarily correspond to that of flour (Meredith and Pomeranz 1982; Lin and Czuchajowska 1997). In another study (Rao et al. 2007) reported that the peak viscosity of wheat flour increased with the addition of water-soluble non-starch polysaccharide obtained from other sources—rice and ragi. In the present study, the pentosans were isolated from wheat flour. Hence, the differences in results could be a result of different analytical technique; nature of sample; source and isolation procedure of pentosans; number of samples analyzed etc.

Time to reach peak viscosity

Time to reach Peak Viscosity (TPV) indirectly reflects the time required for cooking. The increase in time to reach peak viscosity indicates the utilization of more energy to gelatinize starch granules. This eventually results in an increase in the energy cost. It was found that flours of all varieties (except SKD-1) required more than 15 min to reach their maximum viscosity. However, flour of variety SKD-1 took least time span (13:50 min) to reach peak viscosity (Table 4). WEP and varietal difference had significant effect on TPV. Whereas, WUP caused negligible variation (F = 0.360, P = 0.698). Variety-by-WUP and variety-by-WEP interaction contributed significant variation in TPV.

Table 4.

Time to reach peak viscosity (min) of control and pentosan substituted flours obtained from different HWSW varieties

Sample Control 1% WUP 2% WUP 1% WEP 2% WEP
TD-1 15.2 ± 1.6AB 14.5 ± 0.5A 15.2 ± 1.3A 14.6 ± 0.8AB 14.5 ± 0.5AB
Imdad 15.6 ± 0.5AB 16.1 ± 0.4A 15.2 ± 0.3A 15.6 ± 0.1B 15.3 ± 0.3B
Mehran 15.5 ± 1.2AB 15.4 ± 1.3A 14.2 ± 1.1A 14.2 ± 0.1A 14.2 ± 0.1A
Abadgar 15.0 ± 0.4AB 15.5 ± 2.0A 15.4 ± 0.7A 15.4 ± 0.1B 14.5 ± 0.5AB
Moomal 15.4 ± 0.6AB 15.4 ± 0.6A 15.5 ± 0.5A 15.4 ± 0.1B 15.3 ± 0.1B
Anmol 16.3 ± 0.1B 15.2 ± 0.3A 15.6 ± 0.3A 15.3 ± 0.1B 15.1 ± 0.5AB
SKD-1 13.5 ± 0.8A 15.3 ± 1.3A 15.6 ± 0.7A 15.4 ± 0.1B 15.1 ± 0.2B
TJ-83 15.4 ± 0.8AB 15.3 ± 1.2A 15.3 ± 1.2A 15.5 ± 0.1B 15.0 ± 0.6AB
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Values are Means±SD (n = 4)

Different capital letters within column are significantly different at P < 0.05

ameans significant difference from control at P < 0.05

HWSW hard white spring wheat; WEP water-extractable pentosan; WUP water-unextractable pentosan

A scrutiny of figure 1(c) reveals that at 1% level of addition of WEP caused inconsistent effect on TPV. However at 2% WEP addition, with the exception of SKD-1 all the varieties exhibited a decrease in TPV values.

Hot paste and cold paste viscosity

Hot paste viscosity is the viscosity measured after providing flour slurry a holding period of 10 min at 95 °C. Cold paste viscosity (CPV) is the viscosity measured after holding the slurry at 50 °C for 10 min. All cultivar flours were found to vary in their HPV (351–671BU) and CPV (865–1187BU) values (Tables 5 and 6). The lowest value was exhibited by the flour of variety Mehran.

Table 5.

Hot paste viscosity (BU) of control and pentosan substituted flours obtained from different HWSW varieties

Sample Control 1% WUP 2% WUP 1% WEP 2% WEP
TD-1 550 ± 12A 542 ± 21AB 431 ± 21A 242 ± 38AB a 142 ± 57A a
Imdad 616 ± 31A 666 ± 25BC 586 ± 48A 372 ± 26AB a 207 ± 57A a
Mehran 351 ± 14B 473 ± 78A 315 ± 38A 242 ± 69AB a 165 ± 54A a
Abadgar 612 ± 51A 685 ± 83 C 540 ± 38A 302 ± 59AB a 211 ± 37A a
Moomal 510 ± 63AB 672 ± 21BC 525 ± 28A 431 ± 41B 330 ± 19A a
Anmol 671 ± 16A 732 ± 62 C 606 ± 29A 351 ± 42AB a 238 ± 32A a
SKD-1 549 ± 1A 635 ± 52BC 581 ± 45A 342 ± 47AB a 245 ± 44A a
TJ-83 604 ± 4A 621 ± 64BC 587 ± 46A 206 ± 36A a 190 ± 20A a
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Values are Means±SD (n = 4)

Different capital letters within column are significantly different at P < 0.05

ameans significant difference from control at P < 0.05

HWSW hard white spring wheat; WEP water-extractable pentosan; WUP water-unextractable pentosan

Table 6.

Cold paste viscosity (BU) of control and pentosan substituted flours obtained from different HWSW varieties

Sample Control 1% WUP 2% WUP 1% WEP 2% WEP
TD-1 1054 ± 63AB 1048 ± 46AB 916 ± 3AB 682 ± 69AB a 426 ± 61A a
Imdad 1190 ± 33B 1227 ± 18BC 1144 ± 60B 913 ± 55 C 665 ± 60A a
Mehran 865 ± 58A 982 ± 34A 802 ± 61A 661 ± 32A 484 ± 56A a
Abadgar 1152 ± 58B 1261 ± 38 C 1097 ± 57B 840 ± 15ABC a 666 ± 63A a
Moomal 1048 ± 60AB 1209 ± 20BC 1040 ± 29B 937 ± 69 C 816 ± 20A
Anmol 1187 ± 42B 1213 ± 59BC 1124 ± 52B 891 ± 1BC a 675 ± 68A a
SKD-1 926 ± 51A 1060 ± 39AB 1036 ± 52B 780 ± 59ABC 614 ± 46A a
TJ-83 1052 ± 55AB 1085 ± 7ABC 1025 ± 10AB 638 ± 56A a 524 ± 64A a
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Values are Means±SD (n = 4)

Different capital letters within column are significantly different at P < 0.05

ameans significant difference from control at P < 0.05

HWSW hard white spring wheat; WEP water-extractable pentosan; WUP water-unextractable pentosan

It is apparent that variety, WEP, WUP and variety-by-WEP interaction significantly influenced the HPV and CPV of HWSW flours (Table 1). However, WEP contributed much greater variation in HPV and CPV of HWSW flours when compared to variety and WUP. It was found that both fractions of pentosans exhibited different types of impacts on HPV and CPV. The WEP considerably reduced the HPV and CPV of all cultivar flours, whereas, WUP induced irregular changes in HPV and CPV values. This may be a result of hydrophilic nature of WEP that increases the rupturing tendency among starch granules during isothermal phase or under induced mechanical stress while they are suspended in flour. Moreover, WEP weakens the gelling tendency of wheat flour possibly by hindering the reassociation of amylose molecules while they aggregate on cooling. Rao et al. (2007) reported an increase in HPV and CPV values when the water-soluble non-starch polysaccharides obtained from rice and ragi were added at 0.5% level to a wheat flour sample. This is in contrast to present study in which pentosans were isolated from a hard-type wheat flour and were substituted at 1% and 2% levels to eight different genotypes of HWSW. The differences in pentosan source; supplementation level; number and quality of wheat flour samples analyzed might be the possible reasons for contrary results.

As shown in figure 1(d), the magnitude of reduction in HPV at 1%WEP varied from variety to variety in the range of 15 and 66%. The highest reduction was observed in the variety TJ-83, followed by TD-1 (56%) and Abadgar (51%). At 2% supplementation level, the reduction (35%–74%) was found to have further increased with maximum decrease in variety TD-1.

It was also found that the magnitude of CPV reduction also varied among varieties upon the addition of same level of WEP (Figure 1e). At 1-percent supplementation level, the percent reduction varied between 11 and 39%. The highest CPV reduction was found in variety TJ-83. At 2-percent level, further decrease (22–60%) was found in CPV of all varieties. At this concentration level, the maximum decrease was found in the CPV of variety TD-1 followed by TJ-83. The CPV reduction with increasing WEP concentration reflects a further weakening in the paste stability. It is evident that the increase in WEP molecules may have more strongly hindered the reassociation of amylose molecules upon cooling and resulted in further reduction in CPV.

Breakdown viscosity

Breakdown viscosity (BD) is the measure of fragility of starch granules. The BD viscosities of flours varied insignificantly between 487 BU to 644 BU (Table 7). Singh et al. (2010) investigated the relationship between the BD viscosities of flours with the climatic conditions and found the decrease in breakdown viscosity in wheat cultivated under rain-fed conditions. In the present study, the highest breakdown viscosity was found in the flour of variety TJ-83 followed by Mehran, SKD-1 and Anmol (Table 7). It is evident that the variety and WEP contributed significant variation in BD viscosity of HWSW flours. WUP, variety-by-WEP and variety-by-WUP interaction did not cause significant variation in BD viscosity (Table 1).

Table 7.

Breakdown viscosity (BU) of control and pentosan substituted flours obtained from different HWSW varieties

Sample Control 1% WUP 2% WUP 1% WEP 2% WEP
TD-1 504 ± 34A 559 ± 22BC 612 ± 62A 759 ± 56AB a 820 ± 54BCDa
Imdad 487 ± 29A 563 ± 47BC 546 ± 73A 735 ± 11AB a 698 ± 51AB a
Mehran 610 ± 18A 561 ± 31BC 665 ± 60A 742 ± 54AB 770 ± 50ABC
Abadgar 522 ± 67A 410 ± 33A 433 ± 66A 624 ± 93AB 660 ± 43A
Moomal 501 ± 48A 528 ± 27BC 554 ± 64A 583 ± 10A 664 ± 30A
Anmol 556 ± 19A 481 ± 48AB 557 ± 50A 774 ± 17AB a 850 ± 44CD a
SKD-1 560 ± 52A 609 ± 59 C 588 ± 57A 838 ± 20B a 847 ± 1CD a
TJ-83 644 ± 53A 598 ± 47 C 567 ± 13A 830 ± 16B 932 ± 31D a
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Values are Means±SD (n = 4)

Different capital letters within column are significantly different at P < 0.05

ameans significant difference from control at P < 0.05

HWSW hard white spring wheat; WEP water-extractable pentosan; WUP water-unextractable pentosan

The influence of WEP was found consistently positive on BD of all the cultivar flours. Whereas, the effect of WUP on BD values was found to be inconsistent and possibly regulated by the concentration of WUP and genotype of wheat flour. There is every likelihood that the presence of WEP being hydrophilic exerts more stress on wheat starch granules that may result in rapid decline in viscosity of wheat flour suspensions. Sasaki et al. (2000) studied the influence of non-starch polysaccharide on gelatinization properties of wheat starch. They found higher breakdown values in non-starch polysaccharide added starch as compared to starch without such addition.

Despite that WEP effect on BD viscosity was found to be positive at both the levels of fortification, but the magnitude of effect was found to be inconsistent and possibly dependent on the concentration of WEP and genotype of wheat. At 1% concentration, the increase in BD values varied between 16% and 51% higher to the BD values of control flours (Figure 1f). The BD values exhibited a further increase and reached up to 63% when WEP supplementation was increased to 2% level.

The WUP at both levels of concentrations, exhibited similar type of influence (whether positive or negative) on all the varieties except Mehran (Figure 2f).

Setback viscosity

Setback viscosity is the measure of retrogradation tendency of starch granules (Abd Karim et al. 2000). After gelatinization, the leached out linear amylose chains starts reassociating with each other on cooling that subsequently results in increased viscosity of flour pastes. Retrogradation of starch is a good indicator of bread staling. The setback value of all cultivar flours (except Imdad) was found to range between 459 and 571BU. The SB viscosity of Imdad had SB viscosity (641BU) was found exceptionally higher than all the other varieties (Table 8).

Table 8.

Setback viscosity (BU) of control and pentosan substituted flours obtained from different HWSW varieties

Sample Control 1% WUP 2% WUP 1% WEP 2% WEP
TD-1 459 ± 15A 615 ± 13AB 537 ± 62A 438 ± 68A 258 ± 15A a
Imdad 641 ± 40B 657 ± 32B 610 ± 61A 553 ± 23A 387 ± 79A a
Mehran 492 ± 35A 580 ± 43AB 509 ± 34A 438 ± 17A 286 ± 16A
Abadgar 571 ± 20AB 650 ± 62B 622 ± 2A 567 ± 68A 397 ± 19A a
Moomal 571 ± 11AB 609 ± 54AB 578 ± 11A 517 ± 62A 454 ± 37A
Anmol 564 ± 4AB 588 ± 22AB 578 ± 55A 551 ± 13A 423 ± 36A
SKD-1 498 ± 36A 543 ± 6A 569 ± 62A 464 ± 35A 336 ± 38A
TJ-83 508 ± 10A 568 ± 53AB 560 ± 25A 481 ± 4A 343 ± 23A a
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Values are Means±SD (n = 4)

Different capital letters within column are significantly different at P < 0.05

ameans significant difference from control at P < 0.05

HWSW hard white spring wheat; WEP water-extractable pentosan; WUP water-unextractable pentosan

Variety, WEP and WUP contributed significant variation in SB viscosity. But WEP caused much greater effect on setback when compared to variety and WUP (Table 1). Figure 1(g) and 2(g) clearly indicates that both type of pentosan influences differently on setback values of each cultivar flour. WEP reduced the setback viscosity whereas WUP was found to have increased the setback value of flour. The reduction in setback viscosities of flours indicates that WEP possess the ability to reduce the staling tendency of wheat flours. WEP being hydrophilic in nature possibly binds the water molecules that interacts with solubilized amylose chains to curtail the reassociative tendency of amylose chains. Based on the low firmness values, it has been found in previous reports that pentosan reduce the starch retrogradation and bread staling (Kim and D’Appolonia 1977a; b); Jankiewicz and Michniewiez 1987). Schiraldi et al. (1996) explored the role of water-soluble pentosans besides other ingredients in bread staling through DSC and confirmed an indirect anti-staling role of soluble pentosans. Gul and Dizlek (2008) also reported that pentosan decreases the staling rate of bread by retarding the starch retrogradation.

The setback value of flours was found to have reduction in a non-linear fashion with the increasing concentration of WEP. At 1% concentration level, the reduction in setback value varied between 2 and 14% (Figure 1g). The degree of reduction also increased with increasing pentosan concentration (2% level) and the setback values reduced upto 44%. It was also found that the WUP insignificantly increased the setback viscosities of all varieties except Imdad (Figure 2g). Only 5% reduction in setback value of variety Imdad was found at the addition of 2% WUP substitution level. The WUP possibly facilitated the reassociation of amylose chains upon cooling after gelatinization that subsequently increased the viscosity of flour pastes.

Conclusion

The results have indicated that water-extractable and water-unextractable pentosans exhibited different impacts on various pasting parameters between varieties as well as within the variety. The effects of WEP were more pronounced as it caused significant variation in all pasting properties except PT. WEP induced considerable reductions in hot paste, cold paste and setback viscosities and increased the breakdown viscosities of all cultivar flours. The magnitude of increase or decrease however varied from cultivar to cultivar. WUP did induce significant variation in viscosity attributes (except BD) but to a lesser degree comparing to WEP. The variable type of effect of WUP did not reveal meaningful findings. Both the pentosan fractions were found to have produced inconclusive and inconsistent responses on PV and TPV, whereas, WEP marginally increased the PT of almost all cultivar flours.

It is most likely that substitution of WEP in flour may have significantly reduced retrogradation process of starch granules. The process is known to cause syneresis in food gels intended for refrigerated storage and could improve their stability and also prevent staling of bread.

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