Utilization of Microvisco-Amylograph to Study Flour, Dough, and Bread Qualities of Hydrocolloid/Flour Blends

Abstract

Changes in functionality of wheat flour blended with hydrocolloids (alginate, locust bean gum, guar gum, and xanthan) were investigated. Microvisco-amylograph and flour quality analyses were conducted and showed significant (p < 0.05) differences among samples. Correlation of microvisco-amylograph values with other parameters showed that microvisco-amylograph parameters (final viscosity, setback, breakdown, etc.) showed significant (p < 0.05) correlation with other parameters. Microvisco-amylograph breakdown was significantly (p < 0.05) and positively correlated with dough strength and loaf volume. Microvisco-amylograph end of cooling, final viscosity, setback, and breakdown were identified as valuable for determination of flour, dough, and bread qualities as impacted by addition of hydrocolloids.

Keywords:

• Bread
• Carbohydrate
• Farinograph
• Guar
• Wheat

INTRODUCTION

Inclusion of hydrocolloids in food matrices is a common practice among food scientists in order to achieve improvement in food-handling during processing as well as end-product quality. The reasons for addition of hydrocolloids to cereal-based food systems include thickening, stabilization, gelation, and emulsification. Hydrocolloids also help to increase food solid-mass and fiber during formulation of low-calorie cereal products.^[1] It has been shown that the hydrophilic nature of hydrocolloids enhance water the absorption potential of dough and eventually lead to increased production yield^[2] and economic gain.^[3] Hydrocolloids have potential to interact with wheat flour polymers (gluten and starch), thus impacting flour functionality. Improvement of flour functionality by addition of hydrocolloid has been suggested as a better alternative to chemical methods.^[3]

Previous studies have shown that different types of hydrocolloids influence pasting, gelling, and surface physical properties of dough and bread quality. Studies that evaluated the effects of different concentrations of hydrocolloids (alginate, xanthan, locust bean gum (LBG), gum arabic, guar, tragacanth gum, methyl cellulose, and high-methoxyl pectin) on wheat flour/dough characteristics have been conducted.^[2–7] These studies showed that hydrocolloids had the ability to control rheology and modify texture of wheat dough. Addition of hydrocolloids also affect dough gelatinization and retrogradation process; and bread staling was reportedly reduced by addition of hydrocolloids.^[8]

Impact of hydrocolloids on wheat flour functionality is dependent on concentrations and chemical structure of the hydrocolloids used. In this work, different hydrocolloids (xanthan, guar, locust bean, and alginate) were blended with flour in order to investigate possible effects on flour functionality. Xanthan consists of repeating pentasaccharide units (2 glucose, 2 mannose, and 1 glucoronic acid units) with trisaccharide side chains of D-glucoronic acid between 2 D-mannose units. Its molecular weight ranges from 2 – 20 × 10⁶ Da. Xanthan is an anionic hetero-polysaccharide due to the presence of acetic and pyruvic acids. Xanthan does not gel easily due to presence of β 1-4 linkage.^[9,10] Alginate is an unbranched polyuronic saccharide with (1-4) linked α-L-guluronic acid and β-D-mannuronic acid pyronose chain. It is also anionic polysaccharide, with molecular weight range of 0.5 – 1 × 10⁶ Da and gels in presence of Ca ion.^[11] Guar gum is a galactomannan and consists of β-D-mannopyranose backbone with α-D-galactose branches. The high branching of guar is responsible for a high degree of hydrogen bonding and hydration properties. Guar gum also exhibits viscoelastic properties and the molecular weight ranges from 1 – 2 × 10⁶ Da.^[12,13] LBG is also a galactomanan, and consists of a linear chain of mannose substituted with D-glatopyronosyl at every 4th/5th mannose unit. Additionally, LBG contains galactopyronosyl residue side chains.^[14] The molecular weight of LBG ranges between 0.05 – 1 × 10⁶ Da.^[15]

Quality parameters of wheat flour and dough can be measured using farinograph, mixograph, alveograph, amylograph, microvisco-amylograph (MVAG), differential scanning calorimetry (DSC), extensograph, and rapid visco analyzer. Among all these previously mentioned equipments, MVAG is relatively new and has combined the principle of viscograph and amylograph. Initially, the MVAG was developed to counter the need for the large sample quantities required by Brabender amylograph and viscograph. MVAG has additional advantages including increased heating/cooling rates (range 1.5 – 10°C/min), improved precision of sample temperature measurement, built-in self-optimizing temperature control unit, reduced test time, and ease of handling. Results from MVAG were stated to be comparable with amlyograph and viscograph.^[16] In this study, quality parameters of xanthan-, guar-, alginate- and LBG-flour blends have been investigated using MVAG, DSC, farinograph, and texture analyzer. The end-product quality of the hydrocolloid-flour blends was also determined by baking pup loaves. Correlation between MVAG parameters and other quality parameters was also carried out.

MATERIALS AND METHODS

Materials

Hard red spring wheat variety Glenn was grown at Casselton, ND and grown in 2012. Wheat was milled on a Buhler Type MLU-202 laboratory mill. The flour moisture, ash (14% moisture basis) and protein (14% moisture basis) contents were 14.0, 0.44, and 14.2%, respectively. Alginate, locust bean, guar, and xanthan were obtained from Sigma-Aldrich. Blends of flour and each hydrocolloid were prepared at 0.5, 1.0, and 2.0% (w/w) levels of hydrocolloid addition.

Pasting Properties

The pasting properties of the flour/hydrocolloid blends were determined using the Brabender MVAG (Braebender, Duisburg, Germany). Fifteen grams of flour was weighed on a 14% moisture basis and shaken with 110 g water. The slurry was stirred in the MVAG at 250 rpm. The slurry was heated from 50 to 95°C at 6°C/min and then held at 95°C for 5 min. The slurry was then cooled back to 50°C at 6°C/min and held for 2 min. Peak viscosity, hot paste viscosity (HPV), end of cooling, final viscosity, breakdown, and setback values were all determined and reported in Brabender units (BU). The peak viscosity was the first maximum viscosity of the slurry. The HPV was the minimum viscosity during the hold period. The end of cooling was the viscosity of the slurry at the end of the cooling period. The final viscosity was the viscosity of the slurry at the end of the test. The breakdown is defined as the difference between peak viscosity and HPV. The setback is defined as the difference between the peak viscosity and the viscosity at the end of cooling.

Gelatinization Properties

Gelatinization of the samples was determined using a DSC (Waltham, MA, USA) according to the method of White et al.^[17] The samples (3.5 mg) were weighed into aluminum pans. Water (8 μL) was added and the pan hermetically sealed. This concentration of sample in water allows for the formation of a single gelatinization peak without over dilution of the sample.^[17] The samples in pans were stored at room temperature (≈25°C) overnight prior to analysis. The samples were heated along with an empty reference pan from 10 to 100°C at a rate of 10°C/min. The onset, peak and end temperatures (°C) were determined, as well as peak height (mW), peak area (mJ), and enthalpy of gelatinization ΔH_g (J/g).

Dough Quality

Farinograph (Brabender, Duisberg, Germany) analysis was done according to AACC Method: 54–21.02; with 50 g bowl. Absorption was expressed on 14% moisture basis. Flour (50 g weighed on 14% mb) and water was mixed in a 50 g bowl and the farinograph curve was recorded electronically. The parameters determined by the farinograph were, flour water absorption (FWA, percent on 14% moisture basis), peak time (min), mixing stability (min), mixing tolerance index (MTI; BU) and farinograph quality number (FQN, mm). The FQN is the distance in mm, along the time axis from the point of water addition to the point where the height in the center of the curve has dropped 20 BU. Dough strength was also measured using Kieffer micro-extensibiltiy rig (Texture Technologies, Hamilton, MA, USA) to determine extensibility (distance dough stretches before rupture in mm) and resistance to extension (force exerted by dough on hook in grams).^[18] The stickiness of the dough was measured using a dough extrusion rig (Texture Technologies, Hamilton, MA, USA) and texture analyzer (Texture Technologies, Hamilton, MA, USA) according to the method of Chen et al.^[19] After extruding approximately 2 mm of dough from the extrusion apparatus a 25 mm acrylic probe was used to compress the extruded dough. During and after compression the stickiness (grams), work of adhesion (gs), and cohesiveness (mm) of the dough was measured. The stickiness was determined as the force (grams) required to separate the dough from the probe after compression. The work of adhesion was defined as the force exerted by the dough pulling on the probe during the time the probe is being pulled up away from the dough. The cohesiveness of the dough is the distance from the time the probe begins to pull away from the dough until the probe detaches from the dough. Dough for extensibility and stickiness measurements were mixed using a 25 g pin mixer with the water absorption determined by the farinograph measurement.

End-Product Quality

The end-product quality was assessed by baking pup loaves according to approved method 10–09.01,^[20] with some modifications. Fungal amylase was used in place of malt powder and instant dry yeast was used instead of compressed yeast to improve consistency of these ingredients. Ammonium phosphate (5 ppm) was added to improve yeast function. Fermentation was shortened to 2 h. During and after the test baking procedure, the mix time (min), baking water absorption (percent of 100 g flour based on 14% moisture content) and loaf volume (cc) were determined.

Statistical Analysis

Analysis was conducted in duplicate, except for farinograph measurement for which a single analysis was done. ANOVA was conducted with completely random design (CRD) using SAS v.9.3. Least significant difference (LSD) at α = 0.05 was determined for mean separation. Excel was used to calculate the correlation coefficients and significance was determined at 5, 1, and 0.1% using Pearson’s two-tailed r-values with df = 11.

RESULTS AND DISCUSSION

Effect of Hydrocolloids Addition on MVAG Parameters

The pasting properties (see Table 1) of wheat flour and hydrocolloid-wheat flour blends were measured using MVAG. According to Linlaud et al.,^[2] incorporation of hydrocolloids into flour led to rheological changes in dough, the degree of which is dependent on the structure (type) and concentration of hydrocolloids. Similarly, we observed that addition of hydrocolloids into wheat flour significantly (p < 0.05) affected the pasting properties dependent on type and concentration of the hydrocolloids.

TABLE 1 Pasting properties of wheat flour/hydrocolloid blends

Hydrocolloid	Concentration (% w/w flour basis)	Peak (BU)	Hot paste viscosity (BU)	End of cooling (BU)	Final viscosity (BU)	Breakdown (BU)	Setback (BU)
None	—	1060.5	1019.5	1332.5	1241.0	41.0	221.5
Alginate	0.5	886.0	837.5	1181.0	1094.5	48.5	257.0
	1.0	896.5	879.5	1153.5	1078.5	17.0	199.0
	2.0	1007.0	995.5	1220.0	1151.0	11.5	155.5
LBG	0.5	1061.5	1023.5	1339.0	1249.5	38.0	226.0
	1.0	1082.5	1030.5	1315.5	1219.5	52.0	189.0
	2.0	1169.0	1123.5	1379.5	1318.5	45.5	195.0
Guar	0.5	1066.0	1033.5	1320.5	1244.0	32.5	210.5
	1.0	1102.0	1053.0	1324.0	1262.5	49.0	209.5
	2.0	1247.0	1111.5	1468.5	1412.0	135.5	300.5
Xanthan	0.5	832.5	782.5	1305.0	1190.0	50.0	407.5
	1.0	889.0	824.5	1314.0	1198.5	64.5	374.0
	2.0	1055.0	953.5	1230.0	1158.0	101.5	204.5
LSD (p < 0.05)		55.6	38.3	33.8	37.9	61.3	29.2

Breakdown = peak viscosity—Hot paste viscosity;

Setback = final viscosity—Hot paste viscosity;

LBG: locust bean gum.

Peak values (maximum viscosity) describe the swelling of starch granule prior to physical break down of starch granules.^[21] Increase in viscosity has been associated with occurrence of polymer complexes formed from interaction of hydrocolloids with certain leached amylose molecules and low-molecular-weight amylopectin molecules during starch pasting.^[22,23] Peak values of flour pastes were affected differently by addition of hydrocolloids. The result (Table 1) shows that peak value range from 886.0–1247.0 BU. This range was lower than previously reported,^[3] which might be due to the lower concentrations of hydrocolloids (0.5–2.0 g/100 g flour) employed in this experiment compared to the previous study (5 g/100 g flour). Compared to control flour without hydrocolloid addition, the peak values of anionic hydrocolloid-flour (xanthan- and alginate-flour) blends were lower, while that of galactomannan-flour (guar and LBG-flour) blends were higher. Repelling forces between negative charge groups in flour polymers and that of anionic hydrocolloids might be responsible for decrease in peak viscosity, as previously explained for potato starch.^[22] In line with data reported by Rojas et al.^[7] addition of guar gum to flour increased the peak viscosity. However, in previous studies alginate and xanthan reportedly increased peak viscosity of wheat flour paste.^[7,21] The reason for this difference might be due to difference in structure of hydrocolloids. For instance, alginate with high guluronic acid region (which allows gel formation in presence of Ca⁺⁺ or H⁺ ions) enhanced viscosity while alginate with high alternated mannuronic-guluronic acid region reduced viscosity.^[11] The peak viscosity increased as concentrations of the hydrocolloids in flour blends increased. Guar, followed by LBG, displayed most effective impact on peak viscosity. This is in agreement with previous finding that guar resulted in a larger increase of peak viscosity compared to other hydrocolloids.^[3,24]

Similar to peak viscosity, HPV was lower in anionic hydrocolloid-flour blends (alginate and xanthan-flour blends) but higher in LBG- and guar-flour blends, compared to unblended flour. As concentration of each hydrocolloid increased, their respective HPV increased. High HPV value suggests high stability of starch granules at cooking temperature. As expected, HPVs for all samples were lower than their corresponding peak viscosity. This is due to physical breaking down of gel at high temperature during the first holding period. The extent of loss of viscosity is depicted by breakdown. Breakdown values increased as concentration of guar and xanthan increased; however, it reduced as concentrations of alginate increased. Guar, followed by xanthan, each at 2.0 g/100 g gave significantly (p < 0.05) higher breakdown values compared to the flour only, while the largest effect was observed in guar-flour blend. This result is in agreement with previous findings of Alam et al.^[3] that addition of guar to flour resulted in higher breakdown. Increase in breakdown values mean that the starch granules become less resistance to thermal treatment and mechanical shear.^[25] Therefore, addition of alginate strengthened resistance of flour to thermal treatment and mechanical shear, although alginate blends had low peak viscosity and HPV values. Interestingly, blends with low Mw and linear or less branched hydrocolloids (alginate and LGB) exhibited low breakdown value while blends with branch hydrocolloids (xanthan and guar) exhibited high breakdown value. A possible explanation is that linear or less branched hydrocolloids possess large surface area and were able to maintain paste conformation.

Compared to HPV, cooling of samples resulted in increase of their corresponding viscosities. The end of cooling and final viscosities of the blends varied significantly (p < 0.05) and were lowered than that of control except 2.0 g/100 g guar- and LBG-flour blends. Difference between the final viscosity and HPV is a measure of paste retrogradation and is referred to as setback. Setback values of samples vary significantly (p < 0.05). Although, 0.5 g/100 g concentration of alginate-, xanthan-, and LBG-flour blends and 1 g/100 g xanthan-flour blend, exhibited higher setback values compared to control, further increase in concentration of lead to decrease in setback values. Higher concentration of xanthan has also been reported to reduce setback of flour.^[3] Higher concentration of guar caused increase in setback values, a result that is in line with that of Rojas et al.^[7] but contradict that of Alam et al.^[3] Retrogradation is as a result of re-association of amylose that diffused outside starch granules during cooling. Therefore, the presence of hydrocolloids exhibited different interaction with amylose during re-association which changed the setback values.

Effect of Hydrocolloids on Gelatinization of Flour

Gelatinization properties of samples were investigated using DSC and the results are presented in Table 2. The results showed that there was significant (p < 0.05) difference among the DSC parameters. There was slight delay in starch gelatinization (due to high T_o) with 1.0 g/100 g alginate, 0.5 and 1.0 g/100 g LBG, and 0.5 g/100 g guar-flour blends, while the other hydrocolloids-blends resulted in slightly earlier starch gelatinization compared to control. Onset temperatures of the hydrocolloid-flour blends were not significantly (p < 0.05) different from the control (flour without hydrocolloid) sample. A slight delay in gelatinization temperature of the flour system has been reported when dietary fiber was incorporated.^[7,26] Availability of water for uptake by starch granules during gelatinization might have been affected due to presence of hydrocolloids in the blends, which lead to alteration in onset temperature. Limitation of available water might have led to increased gelatinization temperature of flour.^[6,27]

TABLE 2 Gelatinization of flour/hydrocolloid blends

Hydrocolloid	Concentration (%w/w flour basis)	Onset (To) (°C)	Peak (Tp) (°C)	Peak height (Hp) (mW)	End (Tc) (°C)	Area (mJ)	Δ HG (J/g)
None	—	64.80	69.16	0.39	74.49	14.63	4.17
Alginate	0.5	63.86	68.55	0.64	73.57	24.55	7.02
	1.0	65.83	69.56	0.32	73.81	9.17	2.61
	2.0	64.53	68.89	0.38	73.38	13.44	3.83
LBG	0.5	65.04	68.70	0.48	73.23	14.52	4.19
	1.0	65.09	68.80	0.44	73.07	12.83	3.67
	2.0	63.51	68.83	0.51	75.15	22.27	6.33
Guar	0.5	64.95	68.81	0.44	73.29	12.78	3.63
	1.0	64.50	68.53	0.45	72.81	13.90	3.98
	2.0	64.06	68.55	0.54	73.54	19.42	5.59
Xanthan	0.5	64.18	68.64	0.55	73.52	20.06	5.71
	1.0	64.37	68.98	0.60	74.56	23.51	6.75
	2.0	64.32	69.40	0.58	75.78	25.89	7.35
LSD (P < 0.05)		1.51	0.81	0.19	1.87	9.04	2.57

LBG: locust bean gum;

Δ H_G: enthalpy of gelatinization.

The peak temperature of control (flour without hydrocolloid) was higher than all hydrocolloid-flour blends except for 2 g/100 g xanthan-flour and 1 g/100 g alginate-flour blends. Linlaud et al.^[4] has also reported lower peak temperature of 1% xanthan-flour dough compared to the control. However, the peak temperature of 1 g/100 g alginate-flour blends was reported to be lower than the control.^[7] At all concentrations, the peak height (H_P) of LBG-, guar-, and xanthan-flour blends were consistently higher than that of control. Among the alginate-flour blends, only 0.5 g/100 g alginate-flour blend exhibited higher H_p. Reduction in H_p has been associated with limitation in water availability for starch gelatinization.^[6,27] Alginate potentially exhibited strong water binding effect, thus reduce water availability during gelatinization of starch. Lowest H_p value was observed for 1.0 g/100 g alginate-flour blend. The conclusion/end temperature (Tc) for the samples is between 72.81–75.78°C, a range which falls within the range reported in similar work of Rojas et al.^[7] The T_c of the hydrocolloids-flour blends were lower than that of control, with the exception of 2.0 g/100 g LBG, 1.0 and 2.0 g/100 g xanthan.

According to Table 2, the presence of hydrocolloids exhibited different effects on peak area (starch granules transition) and enthalpy of gelatinization (ΔH_G). Increasing the concentration of xanthan consistently increased transition and ΔH_G of starch granules. Also, the highest concentration (2 g/100 g) of LBG and guar, and the lowest concentration (0.5 g/100g) of alginate, resulted in increased starch granules transition and ΔH_G. Compared to previous work, addition of 1% hydrocolloids reduced ΔH_G,^[7] which is in line with what was observed for alginate, LBG, and guar, but not xanthan.

Effect of Hydrocolloids on Dough Quality Measured by Farinograph

Farinograph is among the most popular and accepted device for assessment of dough physical properties and could be used to investigate the influence of additives.^[28] FWA depicts the amount of water absorbed by dough to reach a minimum viscosity of 500 BU. Farinograph was used to measure dough quality of samples and the (Table 3) result shows that the dough quality was affected differently by addition of the different hydrocolloids. Effect of hydrocolloids on FWA depends on both the concentration and type of hydrocolloid. Addition of alginate, xanthan, and LBG caused increased FWA, while FWA was similar to the control with the addition of guar gum. In agreement with this result, xanthan and LBG were reported to cause increase, while guar caused less increase in FWA of flour.^[2] Another report stated that addition of LBG reportedly increased FWA,^[29] which is constant with our results. Variation in FWA can be associated with differences in intrinsic water absorption ability of the hydrocolloid that interferes with the availability of water to flour gluten and starch.^[2] Therefore, it is suggested that LBG, alginate, and xanthan, but not guar, could be added for improvement of FWA of dough.

TABLE 3 Dough quality of flour/hydrocolloid blends

Hydrocolloid	Concentration (% w/w flour basis)	Absorption (FWA, 14% mb)	Peak time (min)	Stability (min)	MTI (BU)	Quality number (FQN, mm)
None	—	63.3	12.7	25.7	6	300
Alginate	0.5	66.7	21.5	18.0	12	284
	1.0	68.7	21.5	12.8	21	279
	2.0	71.4	26.9	13.1	0	300
LBG	0.5	65.1	19.0	25.5	10	300
	1.0	66.9	17.3	22.0	9	289
	2.0	69.9	17.0	19.7	10	283
Guar	0.5	63.6	26.0	39.5	12	425
	1.0	62.6	20.5	44.3	6	463
	2.0	64.8	31.9	43.5	3	465
Xanthan	0.5	65.9	22.0	24.0	10	328
	1.0	67.5	26.8	28.7	7	371
	2.0	71.7	17.7	34.3	6	438

LBG: locust bean gum; FQN: farinograph quality number; FWA: farinograph water absorption;

14% mb: 14% moisture basis;

MTI: mixing tolerance index.

Dough development time (peak time) is the time required for flour dough to reach maximum consistency from beginning of kneading. The farinograph peak time of all hydrocolloid-flour blends were higher compared to unblended wheat flour. Increase in concentration of alginate caused increase in peak time while increase concentration of LBG caused decrease in peak time. The results agreed with previous work which stated that incorporation of xanthan caused increase in dough development time while increased concentration of LBG caused reduction in this parameter.^[2] Addition of hydrocolloids in flour matrix requires more time for proper dough development which might consequently increase processing time and operation cost.

Dough stability measures the length of time that the dough can maintain consistency and indicates strength of dough. Increase in dough stability was observed when guar and xanthan were added, but not for alginate or LBG flour blends. Increasing the concentration of guar and xanthan caused increase in dough stability while increasing the concentration of alginate and LBG led to decrease in stability of dough. Similarly, previous reports showed that addition of xanthan and guar resulted in increased dough stability due to strengthening-tendency of gluten in flour.^[2,5,21] Also, previous studies showed that addition of LBG led to reduction in dough stability^[2] in agreement with our result. However, addition of alginate has been shown to result in increased dough stability^[21] contrary to our result.

The difference in BU at the top of the curve at the peak time and the value at the top of the curve at 5 min after peak time is referred to as MTI. MTI shows the level of softening during mixing. MTI increased with addition of hydrocolloids compared to unblended flour. Increase in the concentration of alginate from 0.5 to 1.0 g/100 g caused great increase in MTI values; however, further increase in alginate concentration to 2.0 g/100 g reduced MTI value to zero. Increase in concentration of xanthan and guar caused reduction in MTI value of blends while increased concentration of LBG did not affect MTI value. Decrease in MTI value has also been reported with addition of xanthan into flour.^[5] FQN increased with increase in guar and xanthan concentration but increase in LBG concentration caused decrease in FQN value. FQN value of alginate-flour blends at 0.5 and 1.0 g/100 g alginate were lower than that of unblended flour while at 2.0 g/100 g alginate FQN value was equal to unblended flour. Overall, strongest dough for bread making purpose was observed in guar-flour blends due to high stability, low MTI, and high FQN.

Effect of Hydrocolloids Addition on Dough Strength and Extensibility

Extensibility and strength (resistance to extension) of dough is greatly dependent on protein, especially gluten quality. Change in extensibility as a result of addition of hydrocolloids suggested the possibility of hydrocolloid-gluten interaction. In food systems, hydrocolloid-protein union can cause changes in electrostatic and hydrophobic effects consequently leading to alteration in protein conformation.^[4] Addition of hydrocolloids affected dough resistance to extension and dough extensibility (Fig. 1) significantly (p < 0.05). Resistance to extension is the maximum amount of force exhibited by the dough against extension.^[30] Resistance to extension of control flour was not significantly different from flour blends with 0.5 g/100 g alginate or xanthan. However, resistance to extension of 0.5 g/100 g of guar or LBG was significantly (p < 0.05) lower compared to control sample. Increase in concentration of alginate reduced resistance to extension while increase in concentration of LBG, xanthan, and guar increased resistance to extension. Xanthan exhibited the most pronounced effect on resistance to extension of dough. In line with this result, xanthan was reported to show highest resistance to extension.^[21,31]

Dough extensibility measures the degree of dough deformation before rupture.^[30] Dough extensibility of the control sample was lower than hydrocolloid-flour blends (except for that of xanthan) at 0.5 g/100 g hydrocolloid concentration. The lowest concentration, 0.5 g/100 g, of guar showed most significant effect on dough extensibility. Increase in concentration of all the hydrocolloids cause reduction in dough extensibility. Extensibility tests have long been associated with baking performance and final product quality. This is because interaction between resistance and extensibility is indirectly responsible for the extent of dough expansion during fermentation process. Dough with low ratio of resistance to extensibility has been stated to result in high volume of baked products.^[28] This is in line with our result where hydrocolloid-flour blends (LBG and 0.5 g/100 g guar) with high extensibility and low resistance enhanced bread loaf volume. Good resistance and extensibility is desired for good bread dough.^[21]

Effects of Addition of Hydrocolloids on Dough Stickiness

Addition of hydrocolloids caused significant (p < 0.05) effect on stickiness, work of adhesion and cohesiveness of dough (Fig. 2). All the hydrocolloids at 0.5 g/100 g caused increase in dough stickiness, work of adhesion, and cohesiveness of dough, compared to control. Apart from guar, increase in concentration of hydrocolloids caused increase in dough stickiness, work of adhesion, and cohesiveness of dough. Previous work has also shown that addition of xanthan induced increase in dough resistance to extension.^[31] Increase in work of adhesion might be responsible for similar increase in dough stickiness. Alginate contributed mostly to increase in dough stickiness, work of adhesion and cohesiveness of dough. High dough stickiness may cause difficulties in machinability, in particular during automated bread-making process.^[32]

Increase in concentration of guar caused reduction in dough stickiness, work of adhesion, and cohesiveness of dough. Reduction in surface properties of dough (adhesiveness and/or stickiness) is very important since they affect dough readiness for large scale processing.^[31] High dough cohesiveness is essential for higher specific volume and softer bread.^[31]

Effect of Hydrocolloids on Bread Quality

Addition of hydrocolloids to wheat flour had significant effects on the end-product quality (Table 4). The nature of the effect is dependent on both the type and concentration of hydrocolloids. Hydrocolloid-flour blends require increased mixing time compared to unblended flour and mixing time gradually increased as the concentration of all hydrocolloids increased, except in guar-flour blends. Similarly, bake absorption was higher in hydrocolloid-flour blends compared to unblended and increase of hydrocolloid concentrations also increased the bake absorption. Among the hydrocolloid-flour blends, 0.5 and 1.0 g/100 g guar and all concentrations of LBG-flour blends gave higher loaf volume compared to unblended flour. Similar results have been reported by Ribotta et al.,^[33] with the addition of 0.5 g/100 g guar. Addition of xanthan and alginate reduced loaf volume in accordance with previous findings.^[21,35] However, contrary to our findings, Sharadanant et al.^[29] reported that LBG reduced loaf volume while Rosell et al.^[21] reported that xanthan increased specific loaf volume compared to control.^[29] Increase in concentration of guar, xanthan, and alginate in hydrocolloid-flour blends caused decreased in loaf volume while increase in LBG concentration caused increased in loaf volume. Hydrocolloid-flour blend with 0.5 g/100 g guar gave highest loaf volume which might be due good compatibility with gluten during gluten-network formation.^[4] Also, the 0.5 g/100 g blend had the highest cohesiveness (Fig. 2b), which is reflected in this sample having the highest loaf volume.

TABLE 4 End-product quality of flour/hydrocolloid blends

Hydrocolloid	Concentration (% w/w flour basis)	Mix time (min.)	Bake absorption (14 % mb)	Loaf volume (cc)
None	—	4.5	65.2	970.0
Alginate	0.5	4.5	68.5	957.5
	1.0	4.8	68.9	967.5
	2.0	5.5	72.0	912.5
LBG	0.5	4.5	66.3	985.0
	1.0	5.0	67.7	1027.5
	2.0	5.1	71.6	1012.5
Guar	0.5	4.8	64.8	1037.5
	1.0	4.4	64.8	972.5
	2.0	4.9	68.0	865.0
Xanthan	0.5	4.6	68.4	950.0
	1.0	5.1	70.5	887.5
	2.0	5.5	74.0	800.0
LSD (p < 0.05)		0.4	1.1	68.8

LBG: locust bean gum;

14% mb: 14% moisture basis.

FIGURE 1 Strength of flour/hydrocolloid dough. Samples with 0.5, 1.0, and 2.0% hydrocolloid, columns of the same color with the same letter are not significantly (p < 0.05) different. LBG: locust bean gum.

FIGURE 2 Stickiness of flour/hydrocolloid dough. Samples with 0.5, 1.0, and 2.0% hydrocolloid, columns of the same color with the same letter are not significantly (p < 0.05) different. LBG: locust bean gum.

Correlation Between MVAG and Dough and Bread Qualities

Correlation analysis was conducted between MVAG parameters and loaf volume, DSC, farinograph, texture analyzer parameters. According to Table 5, MVAG peak viscosity and HPV lack significant correlation with all other parameters. MVAG end of cooling was significant (p < 0.05) and positively correlated (r = 0.60) with farinograph stability but had significant (p < 0.05) negative correlation with dough stickiness and work of adhesion with correlation coefficients of –0.67 and –0.66, respectively. Similarly, MVAG final viscosity was significantly (p < 0.05) and positively correlated (r = 0.63) with farinograph stability. However, MVAG final viscosity was significantly (p < 0.05) and negatively correlated with dough stickiness and work of adhesion with correlation coefficients of –0.59 and –0.57, respectively. This suggested that viscosity of dough at 50°C as measured by MVAG has close relationship with farinograph stability, stickiness, and work adhesion of dough of hydrocolloids-flour blends.

TABLE 5 Correlation of pasting properties of hydrocolloid-flour blends with other quality parameters

Parameters measured		Peak (BU)	Hot paste viscosity (BU)	End of cooling (BU)	Final viscosity (BU)	Breakdown (BU)	Setback (BU)
DSC	Peak height (mW)	0.14	–0.33	0.16	0.09	0.59*	0.59*
	Area (mJ)	–0.09	–0.27	0.08	0.05	0.57*	0.46
	ΔHG (J/g)	–0.09	–0.27	0.09	0.05	0.57*	0.47
Farinograph	Stability (min.)	0.52	0.38	0.60*	0.63*	0.63*	0.19
	Quality number (FQN)	0.41	0.25	0.40	0.46	0.64*	0.17
Dough texture	Stickiness (g)	–0.31	–0.16	–0.67*	–0.59*	–0.57*	–0.47
	Work of adhesion (g.s)	–0.24	–0.13	–0.66*	–0.57*	–0.44	–0.49
	Resistance to extension (mm)	–0.05	–0.25	–0.02	–0.03	0.65*	0.35
End product quality	Loaf volume (cc)	0.03	0.23	0.08	0.06	–0.64*	–0.27

*Significant different at p < 0.05;

FQN: farinograph quality number; Δ H: enthalpy of gelatinization.

Furthermore, MVAG breakdown had significantly (p < 0.05) positive correlations with DSC peak height (r = 0.59), DSC area (r = 0.57), and ΔH_G (r = 0.57), farinograph parameters (stability, r = 0.63 and FQN, r = 0.64), resistance to extension (r = 65) and loaf volume (r = –0.64). The MVAG breakdown had significant (p < 0.05) negative correlation with dough stickiness (r = 0.57). Although, we have made effort to correlate instrumental parameters obtained from materials with different characteristics (dough and paste), the correlation values revealed that there exists disparity in measurement of dough and paste stabilities. This suggested that hydrocolloids act differently in dough and paste systems. As stated earlier, guar and xanthan contributed to dough stability but not to paste stability, however, alginate contributed to paste stability but not dough stability. This might also be due to difference in interaction of hydrocolloids with flour polymers at different conditions. High farinograph stability in guar- and xanthan-flour blends suggest their propensity toward interacting with gluten in dough system than with leached amylose in paste system where they record high MVAG breakdown value. Alginate may have had higher tendency to interact with leached amylose in the paste systems than with gluten in dough system.

The MVAG set back was only significantly (p < 0.05) correlated with DSC peak height (r = 0.59). A previous report has also shown that water concentration (DSC peak height) is proportional to rate of retrogradation (setback value).^[34] However, this was in contrary to previous work^[7] that stated that there was no correlation between DSC parameters and those of amylograph. The reason for this might be difference in equipment used; newly developed MVAG used in this study operates at micro scale that ensures proximate contact of probe with sample, as well as having a different heating profile. MVAG makes use of a specially designed stirrer with geometry that ensure proper sample mixing that disallowed starch particles sedimentation.^[16]

CONCLUSION

Addition of different type of hydrocolloids to flour displayed different effects on dough and bread quality. Each hydrocolloid has desirable and undesirable effects on flour and final product quality alginate is most suitable at reducing retrogradation of starch but reduced loaf volume and dough machinability. Guar enhanced dough stability, scored high in FQN and increased loaf volume but contributed to higher breakdown of dough. Xanthan enhanced water absorption potential of flour and improved dough stability but, reduced paste stability and loaf volume. LBG increased loaf volume but, reduced paste and dough stability. MVAG parameters (end of cooling, final viscosity, set back, and most especially breakdown) showed significant (p < 0.05) correlation relationships with some parameters obtained from other instruments. Positive correlation between MVAG values and DSC parameters showed that there is relationship between change in viscosity and water availability for starch gelatinization. Therefore, MVAG setback and most especially breakdown were found to be useful to explain thermal properties of dough. MVAG end of cooling final viscosity and breakdown values also provided insight into farinograph dough stability and dough textures. Furthermore, MVAG breakdown exhibited negative correlation with loaf volume. Therefore, MVAG breakdown value can be valuable to predict the quality of loaf volume of bread made from hydrocolloid-flour blends. This research work has been able to show the suitability of MVAG for measuring flour qualities.