Patent Application: US-17338505-A

Abstract:
solutions and methods of preparing aqueous solutions containing beta - glucans and gums are described . the solutions demonstrate enhanced rheological properties including improved shear tolerance that provide improved viscosity characteristics enabling the use of the solutions in a number of applications including the beverage industry .

Description:
( 1 ) to investigate the rheological properties of aqueous solutions of barley β - glucan ( bg ) and binary gum blends consisting of bbg and commonly used food gums , namely xanthan ( xan ), guar gum ( gug ), locust bean gum ( lbg ), konjac gum ( kog ), low methoxy pectin ( lmp ), high methoxy pectin ( hmp ), gum arabic ( gar ), carageenan ( car ) ( kappa , lamda , and iota ), sodium alginate ( alg ), microcrystalline cellulose ( mcc ) and carboxymethyl cellulose ( cmc ), ( 2 ) to investigate the compatibility and aqueous phase stability of barley β - glucan and binary gum blends in terms of phase separation or precipitation observed visually over a period of 12 weeks at ambient temperature , and ( 3 ) to establish the most suitable gum blend containing beta - glucan in terms of the product stability of a beverage system . overall , the study was designed to provide insight into physical properties and functional properties of β - glucan in aqueous systems . within this description , bg refers to β - glucan derived from known sources such as barley and oats , whereas bbg specifically refers to β - glucan derived from barley . barley viscofiber ®, a concentrated form of bbg (˜ 60 - 65 %, w / w , β - glucan ) ( described in applicant &# 39 ; s copending patent applications incorporated herein by reference ), was obtained from cevena bioproducts inc ., edmonton , ab . beta - glucan ( bg ) in barley viscofiber ® was further purified at laboratory scale . xan was provided by adm inc ., il , whereas hmp , lmp , gug , lbg , cmc and gar were from tic gums , md . kog , mcc , car , and alg were procured from fmc biopolymer , pa , while the crystallized beverage , kool - aid , was from kraft canada , on . sodium carbonate , citric acid and hydrochloric acid were procured from bdh inc ., toronto , on and fisher scientific co ., nepean , on , respectively . ethanol and termamyl 120 ln , a thermostable α - amylase ( e . c . 3 . 2 . 1 . 1 ) of bacillus licheniformis , were procured from commercial alcohols inc ., brampton , on and novo nordisk biochem inc ., toronto , on , respectively . the purification of bbg from viscofiber ™ was based on a traditional aqueous technology as shown in fig1 . the method involved alkali extraction followed by enzymatic treatments . in brief , the steps involved were the solubilization of bbg in deionized milli - q water , treatment with thermostable α - amylase ( added at a rate of 1 %, w / w , of available starch in the sample ), followed by the protein precipitation and subsequent alcohol - assisted precipitation of bbg . content of moisture , bbg , starch , and protein of dried samples was determined in duplicate according to the methods of mcclearly and glennie - holmes ( 1985 ), megazyme assay kit ( megazyme international ireland ltd ., ireland ), holm et al . ( 1986 ) and hashimoto et al . ( 1987 ) and fp - 428 nitrogen determinator ( leco corp ., st . joseph , mich . ), respectively . dispersions of bbg alone and its blends with common food gums were prepared at a “ total gum concentration ” of 0 . 5 % and 0 . 75 % ( w / w ) in the ratios of 80 / 20 and 90 / 10 ( w / w ). for all binary blends , bbg was the major gum ingredient used . all gum solutions were prepared separately , heated at 90 ° c . for 1 h and were allowed to cool down to room temperature . the gum blend dispersions were prepared by weighing and mixing at 80 / 20 and 90 / 10 ( w / w ) ratios of gum solutions prepared individually . the samples were then mixed for 20 min at room temperature to ensure uniform mixing . viscosity tests were performed for bbg and bbg binary blend dispersions . viscosity was determined at consecutive fixed shear rates of 1 . 29 - 129 s − 1 using a parr physica uds 200 rheometer ( glenn , va .). the viscometer was equipped with a peltier heating system that controlled the sample temperature . all viscosity tests were performed at 20 ° c . using dg 27 cup and bob geometry with a 7 ± 0 . 005 g sample . shear rate was reported in s − 1 after multiplying rpm by a conversion factor of 1 . 29 s − 1 as specified by the manufacturer . thixotropy tests were also performed on both bbg and bbg binary blend dispersions using dg 27 cup and bob geometry with a 7 ± 0 . 005 g sample at 20 ° c . these tests were performed at a series of fixed shear rates that consecutively increased from 1 . 29 to 3870 s − 1 and then immediately decreased to the original shear rate of 1 . 29 s − 1 . all analyses on gum blends were performed at least in duplicate . all gum dispersions and gum blends were prepared using a similar procedure as described in sample preparation for viscosity and thixotropy analyses . since the viscoelastic properties are strongly dependent on time and temperature , all systems were allowed to equilibrate for 15 min at ambient temperature . storage modulus ( g ′) and loss modulus ( g ″) were obtained at 20 ° c . using a 7 ± 0 . 005 g sample placed in a dg 27 cup and bob geometry of a parr physica uds 200 rheometer . the rheometer was set in amplitude sweep controlled shear displacement ( csd ) mode with a constant frequency of 1 hz and controlled strain of 0 . 25 - 20 % and 0 . 75 - 120 % for 0 . 5 % and 0 . 75 % total gum concentration , respectively . the stability of bbg gum blends ( at total gum concentrations of 0 . 5 and 0 . 75 %, w / w , and gum ratios of 80 / 20 and 90 / 10 , w / w ) were compared with that of bbg dispersions alone . sodium azide was added at 0 . 002 % ( w / w ) to all samples to prevent microbial spoilage . phase separation / precipitation was monitored subjectively by visual observation . the solutions were termed “ phase separated ” when two distinct phases were visible . stability was assessed subjectively by observing the gum blends for visible precipitation and phase separation over a period of 12 weeks at ambient temperature . gum blends were evaluated on a scale of 1 - 4 , where a score of 1 was assigned to solutions with extreme clarity with no visible precipitation while the extremely turbid solutions with extensive precipitation or phase separation were given a score of 4 . all other situations were given either a scores of 2 or 3 , depending upon their visual characteristics . the highly potent gum combinations for the beverage formulation were selected based on the observations made in the stability trials . two total gum concentrations selected were 0 . 23 and 0 . 46 %, w / w . these concentrations were selected to represent the feasible inclusion levels that have been reported in the literature . xan was added at a rate of 10 % ( w / w ) of the amount of bbg present in order to achieve a final total gum concentration of 0 . 23 % or 0 . 46 % ( w / w ) and gum ratio of 90 : 10 ( w / w ). eight grams of a crystallized commercial beverage were used for the preparation of 100 g of aqueous beverage containing gums at desired ratios . the final ph of the beverage was maintained at 3 . 25 . control beverage samples devoid of beverage crystals were prepared using gums and deionized milli - q water only . two sets of control samples at ph 3 . 25 and 7 were prepared . citric acid was used for adjusting the ph of control samples . all samples were stored at 4 ° c . for 12 weeks . the stability of beverage samples was assessed subjectively by observing any precipitation and changes in the viscosity over a storage period of 12 weeks at 4 ° c . viscosity measurements were recorded using a parr physica uds 200 rheometer ( glenn , va .). all timed viscosity measurements were taken at 5 ° c . and 25 ° c . (± 0 . 02 ° c .) using dg 27 cup and bob geometry with a sample size of 7 ± 0 . 005 g . development of turbidity in the beverage was monitored spectrophotometrically at 660 nm ( hp 8452a , hewlett packard , boise , id .) ( bansema , 2000 ). to prevent the microbial spoilage over the storage period , sodium azide was added at 0 . 002 % ( w / w ) to all beverage and control samples . recovery is defined as the ratio between the amount of bbg in purified sample and the amount of bbg present in viscofiber ™. the yield and purity of purified bbg , obtained using the method given in fig1 , were 82 and 94 . 7 % ( w / w , dry weight ), respectively . moisture , starch , and protein content were 3 . 8 %, 0 . 9 % and 1 . 7 % ( w / w ), respectively . lipid content was 0 . 0 % ( w / w ) in the barley viscofiber ™ used and hence it was assumed that the purified barley β - glucan contains no lipids . in fluid flow behavior studies , the power law model describes the pseudoplastic behavior of gums ( marcotte et al ., 2001 ). the following formula represents the power law model : where , s is the shear stress ( n / m 2 ), r is the shear rate ( s − 1 ), c is the consistency coefficient and n is the flow behavior index or power law index . gum dispersions with a value of n & gt ; 0 . 99 have been shown to be “ newtonian ” whereas gums forming highly viscous solutions ( n & lt ; 1 ) are termed pseudoplastic liquids ( marcotte et al ., 2001 ). the flow behaviour index and consistency coefficient of 0 . 5 and 0 . 75 % ( w / w ) pure gum dispersions are shown in table 1 . at 0 . 5 % ( w / w ) concentration , hmp , lmp , alg , iota - car , and gar were almost newtonian . however , at 0 . 75 % ( w / w ) gum concentration , hmp and lmp continued to behave almost like newtonian with n ˜ 0 . 99 at a shear rate of 1 . 29 s − 1 . bbg was highly pseudoplastic with a flow behavior index of 0 . 74 and 0 . 59 at 0 . 5 and 0 . 75 % ( w / w ) concentrations , respectively . in comparison to other gums at 0 . 5 % ( w / w ) concentration , xan demonstrated high pseuodoplasticity with n = 0 . 2 , followed by gug with n = 0 . 38 . in terms of flow behavior index , bbg at 0 . 5 % ( w / w ) was comparable to cmc , lbg and kog . the viscosity of 0 . 5 and 0 . 75 % ( w / w ) pure gums at 20 ° c . determined at shear rates of 1 . 29 - 129 s − 1 , is presented in table 2 . lmp , hmp , gar , and mcc showed lower viscosity at both concentrations of 0 . 5 and 0 . 75 % ( w / w ). the viscosity of all gum dispersions increased non - linearly when the concentration was increased from 0 . 5 to 0 . 75 % ( w / w ). the flow curves of individual gums and blends showed a shear thinning behavior , while yield stress was observed only in dispersions containing xan , car and alg . the yield value or yield stress that must be exceeded before the flow can begin was observed at lower shear stress . the concentration and shear rate effects on rheological properties were dependent upon the type of food gum used . the effect of concentration ( 0 . 5 and 0 . 75 %, w / w ) on viscosity enhancement was more pronounced in bbg , iota - car , and kappa - car dispersions as shown in table 2 . for xan dispersions , however , the viscosity increased from 368 to 481 mpas at shear rate of 12 . 9 s − 1 on increasing the gum concentration from 0 . 5 to 0 . 75 % ( w / w ). this may be attributed to the near saturation of xan dispersions at the concentrations tested . gug , lbg and kog dispersions demonstrated a better shear tolerance than other pure gum dispersions as evident by the viscosity data presented in table 2 . however , xan demonstrated low shear rate tolerance at both gum concentrations tested in this study . blending of gums resulted in changes in certain rheological properties such as the viscosity , compared to the corresponding values for single components . the viscosities of gum blends having total gum concentration of 0 . 5 and 0 . 75 % ( w / w ), determined at shear rates of 1 . 29 - 129 s − 1 at 20 ° c ., are presented in table 3 . at 0 . 5 % ( w / w ) total gum concentration , bbg blend with xan , cmc and lambda - car showed marked enhancement in viscosity determined at shear rates of 1 . 29 - 129 s − 1 , while bbg blend with kog , hmp , lmp , alg , mcc and gar showed marked lowering of viscosity determined at the same shear rates . at 0 . 75 % ( w / w ) total gum concentration , bbg blend with xan , iota - car , and cmc showed marked viscosity enhancement . however , bbg blend with lambda - car , kog , hmp , lmp , mcc , alg , and gar gum showed marked lowering of the viscosity . as shown in table 2 , at a shear rate of 64 . 6 s − 1 , 0 . 5 % ( w / w ) bbg and xan individually exhibited viscosities of 118 and 101 ( mpas ), respectively , whereas in table 3 , 0 . 5 % ( w / w ) bbg / xan blended in 80 / 20 and 90 / 10 ( w / w ) ratios demonstrated viscosities of 158 and 174 mpas , respectively . thus , the bbg / xan blend was more shear tolerant than bbg or xan alone . similar trends were also observed with bbg / cmc and bbg / lambda - car at low concentrations ( i . e . 0 . 5 %, w / w ) and also with bbg / cmc and bbg / iota - car at higher concentrations ( i . e . 0 . 75 %, w / w ). many of the functional properties of the hydrocolloids have been reported to be governed by hydrogen bonding ( bresolin et al ., 1998 ). it was postulated that hydrogen bond formation between unsubstituted segments (— oh of glucopyranosyl units ) of bbg and hemiacetal oxygen atom of the inner mannose located on the side chains of xan molecules could occur . such a mechanism of interaction for synergistic associations between galactomannan / xan mixtures has been elucidated and termed “ lock and key effect ” ( bresolin et al ., 1998 ). the total gum concentration and ratio of gums in a blend affect the rate and the type of interaction ( synergistic or antagonistic ) as demonstrated by the viscosity measurements . one of the major benefits of viscosity measurements is the detection of synergistic and antagonistic interactions in aqueous dispersions consisting of binary gum blends ( pellicer et al ., 2000 ; hernandez et al ., 2001 ; nnanna & amp ; dawkins 1996 ). there are several definitions for synergistic and antagonistic interactions ( howell , 1994 ; kalectunc - gencer & amp ; peleg , 1986 ; plutchok & amp ; kokini , 1986 ; pellicer et al ., 2000 ), and in the present study , when the gum blend exhibits greater viscosity than the sum of the viscosities of the gum dispersions considered separately , the situation was considered synergism . these interactions were quantified using “ viscous synergism index ”, i v , that is defined as : i v = η i + j η i + η j ( 2 ) where i and j represent the two gums forming the mixed system , i + j . the aqueous dispersions of the systems i , j and i + j must be prepared at the same total gum concentrations , i . e ., c i = c j = c i + j ( hernandez et al ., 2001 ). according to the equation , i v is always a positive value . if 0 & lt ; i v & lt ; 0 . 5 , the viscosity of the mixed system will be less than the sum of the viscosities of its two component gums and also less than both of them individually , the situation is termed as antagonistic interaction . however , if i v = 0 . 5 and both gums are of equal viscosity ( when considered separately and at identical concentrations ), so that η i + j = η i = η j then the situation is termed as no interaction . on the other hand , if 0 . 5 & lt ; i v & lt ; 1 , synergism occurs , provided η i + j is more than η i and η j individually . if i v & gt ; 1 , and if the viscosity of the mixed system is greater than the sum of the viscosities of the two simple / individual systems i . e ., η i + j & gt ; η i + η j , then synergism has also occurred ( pellicer et al ., 2000 & amp ; hernandez et al ., 2001 ). for economical and practical reasons , blending of two pure gums together to increase the viscosity is not necessary when the viscosity of one of the pure gum , η i or η j , is & gt ; η i + j at identical gum concentrations ( hernandez et al ., 2001 ). tables 4 and 5 shows the “ viscous synergism index ”, i v calculated for 0 . 5 and 0 . 75 % ( w / w ) bbg / other gum blends , respectively , using the viscosity data determined at a shear rate of 6 . 46 s − 1 ( to mimic the approximate shear that exists in human mouth ) at 20 ° c . for gum blends such as bbg / cmc , bbg / lambda - car and iota - car at 0 . 5 % ( w / w ) total concentration , at both 80 / 20 and 90 / 10 ( w / w ) blending ratios , synergistic interactions were observed . however , other gum blends at 0 . 5 % ( w / w ) total concentration such as bbg / xan , bbg / gug , bbg / lbg , bbg / hmp , bbg / lmp , bbg / kappa - car , bbg / alg , bbg / gar , bbg / mcc , and bbg / kog demonstrated antagonistic interactions at both 80 / 20 and 90 / 10 ( w / w ) blending ratios . for gum blends at 0 . 75 % ( w / w ) total concentration , synergistic interactions were observed in the blends of bbg with xan , cmc and iota - car at both 80 / 20 and 90 / 10 ( w / w ) blending ratios . however , blending of bbg with lbg at 0 . 75 % ( w / w ) total gum concentration at both 80 / 20 and 90 / 10 ( w / w ) blending ratios was termed as “ no interaction ” as the viscosities of the resulting blends were almost similar to the viscosity of the individual gums . furthermore , an antagonistic effect was observed for the gum blends at 0 . 75 % ( w / w ) total concentration at both 80 / 20 and 90 / 10 ( w / w ) blending ratios when bbg was blended with gug , hmp , lmp , alg , kog , mcc , lambda - car and gar . lambda - car behaved synergistically when mixed with bbg to achieve total concentration of 0 . 5 % ( w / w ), whereas at 0 . 75 % ( w / w ) total concentration , these gums demonstrated strong antagonism . in bbg / xan blends ( 80 / 20 and 90 / 10 , w / w ), an antagonistic effect was observed at 0 . 5 % ( w / w ) total gum concentration . the effect transformed into strong synergism with i v = 0 . 8 when total gum concentration was increased to 0 . 75 % ( w / w ). unlike the blends having 0 . 5 % ( w / w ) total gum concentration , the blends of bbg / lbg at 0 . 75 % ( w / w ) total concentration showed no interaction at both ratios tested . the phenomenon of thixotropy was originally introduced to define an isothermal sol ⇄ gel transformation ( freundlich , 1935 ; sherman , 1970 ). thixotropy can be defined as a decrease in viscosity due to destruction of 3 - d network under a constant shear rate or a consecutively increasing shear rate that is fixed for a period of time at selected shear rates followed by the structural network redevelopment when shear is withdrawn ( muller , 1973 ; schramm , 1994 ). the viscosity of non - thixotropic systems does not decrease under fixed shear rates . under consecutively increasing shear rates the viscosity decreases , but regains over time when shear is withdrawn . in the present study , the thixotropy was examined , using consecutive increasing shear rates of 1 . 29 - 3870 s − 1 for fixed intervals of time and then decreasing it immediately to the original shear rate of 1 . 29 s − 1 . fig2 shows non - thixotropic behaviour observed for 0 . 5 and 0 . 75 % ( w / w ) bbg dispersions . autio et al . ( 1987 ) also reported a similar behavior for β - glucan dispersions . fig3 and fig4 depict the thixotropy curves at 20 ° c . of 0 . 5 and 0 . 75 % ( w / w ) bbg / other gum blends , respectively . none of the gum blends used in the study demonstrated thixotropy . for pure bbg dispersions , the time required for the network disrupted at 3870 s − 1 to redevelop at 1 . 29 s − 1 exceeded 4 - 6 min . however , 0 . 5 % ( w / w ) bbg / mcc blend showed network disruption due to the high shear ( 3870 s − 1 ). bbg / xan blended at a ratio of 80 / 20 ( w / w ) at 0 . 5 and 0 . 75 % ( w / w ) total gum concentrations recovered its original viscosity in 10 - 15 sec . interestingly , during the thixotropy testing , 80 / 20 and 90 / 10 ( w / w ) bbg / xan blends demonstrated unusual increase in viscosity upon immediately decreasing the shear rate from 3870 s − 1 to 1 . 29 s − 1 compared to the original viscosity at the starting shear rate of 1 . 29 s − 1 . this shear - induced thickening of the blend dispersion suggested a change in polymer conformation . change in xan conformations in aqueous medium has been reported elsewhere , but the change occurred due to heating ( kovacs & amp ; kang , 1977 ; bresolin et al ., 1998 ). in the present study , the shear rate of 3870 s − 1 employed during thixotropy testing might have resulted in unwinding of the ordered helical conformation of xan into disordered random coil conformation , a cellulose - like conformation , and thus increasing the hydrodynamic volume and hence the increased viscosity . elastic modulus ( g ′) and loss modulus ( g ″) define the viscoelastic properties of gum solutions ( mandala & amp ; palogou , 2003 ; skendi , et al ., 2003 ). g ′ and g ″ at controlled strain and constant frequency ( 1 hz ) were recorded in order to locate the linear viscoelastic region ( mandala & amp ; palogou , 2003 ; dickinson & amp ; merino , 2002 ). fig5 shows a typical curve of g ′ and g ″ values versus strain defining a linear viscoleastic region ( mandala & amp ; palogou , 2003 ). deviations from linearity occur when the gel is strained to a point at which certain weak physical bonds of the aggregated network structure are destroyed . formation of new bonds will also influence the linear viscoelastic region . in general , gels have much shorter linear regions than cross - linked polymer gels ( dickinson & amp ; merino , 2002 ). in the present study , an amplitude sweep is applied where stress and strain is increased linearly at a constant frequency of 1 hz . dependence of g ′ and g ″ on frequency sweep was not performed in the present study because it was beyond the scope of the present study . frequency sweep is important to determine the time required for polymer entanglements to form or break within the variable periods of oscillations ( lazaridou et al ., 2003 ). a constant frequency of 1 hz was selected to allow sufficient time for network ( polymer entanglements ) to form and break because at higher frequencies , the molecular chains cannot disentangle during the short periods of oscillation ( lazaridou et al ., 2003 ). a gel - like material shows distinct behavior that is different from liquid or concentrated solution when subjected to amplitude sweep in a rheometer at constant frequency . freshly prepared bbg dispersions have been reported to behave like a viscoelastic liquid ( g ″& gt ; g ′) where the g ′ and g ″ are reported to be highly dependent on frequency ( skendi et al ., 2003 ). formation of a elastic gel - like network ( g ′& gt ; g ″) depends on the gum concentration as well as the induction time of gelation . once the gel like viscoleastic properties are gained , the g ′ and g ″ become less dependent on frequency ( lazaridou et al ., 2003 ). comparison of g ′ and g ″ for 0 . 5 and 0 . 75 % ( w / w ) bbg dispersions was performed at linearly increasing strain of 0 . 25 - 20 % and 0 . 75 - 120 %, respectively at a constant frequency of 1 hz . for 0 . 5 % ( w / w ) gum dispersions , the ramp of strain was carefully selected to ensure that the stress used was not exceeding 1 pa . a strain range of 0 . 25 - 20 % was selected based on observations for preliminary experiments with 0 . 5 % ( w / w ) gum dispersions and blends at different levels of strain sweep in order to prevent the destruction of physical bonds that contribute to the elastic properties . however , for 0 . 75 % ( w / w ) gum dispersions and their blends , strain sweep of 0 . 075 - 120 % was selected to ensure the stress used was not exceeding 10 pa . the main reason for selecting a maximum stress of 1 pa for 0 . 5 % ( w / w ) and 10 pa for 0 . 75 % ( w / w ) gum and gum blend dispersions was to enable the comparison of linear viscoelastic regions of different bbg / other gum blends to that of pure bbg dispersions . fig6 shows comparison of g ′ and g ″ for 0 . 5 and 0 . 75 % ( w / w ) bbg dispersions determined at 20 ° c . both 0 . 5 and 0 . 75 % ( w / w ) bbg dispersions demonstrated viscoelastic behavior since g ″& gt ; g ′. this is in agreement with other viscoleastic studies of oat and barley β - glucan dispersions of different concentrations ( lazaridou et al ., 2003 ). fig7 presents comparison of g ′ and g ″ for 0 . 5 % bbg / other gum blends . both gum ratios of 80 / 20 and 90 / 10 ( w / w ) of 0 . 5 % ( w / w ) bbg / gug , bbg / lbg , bbg / cmc , bbg / car , and bbg / kog blends exhibited viscoelastic behaviour with g ″& gt ; g ′ ( fig7 ). however , 0 . 5 % ( w / w ) bbg / xan blend mixed at a ratio of 80 / 20 ( w / w ) became typical of an elastic gel network with g ′& gt ; g ″. such an elastic gel like behavior was not exhibited by 90 / 10 ( w / w ) bbg / xan blends at 0 . 5 % ( w / w ) total gum concentration . hence , bbg / xan ratio of 80 / 20 ( w / w ) mixed at 0 . 5 % ( w / w ) total gum concentration is critical for the development of a gel - like behavior . elastic network formation may be the reason for faster recovery time observed soon after the network destruction at 3870 s − 1 during thixotropy testing . g ′ and g ″ values decreased as the proportion of xan increased from 10 - 20 % ( w / w ) in 0 . 5 % ( w / w ) bbg / xan blend . blends containing bbg and hmp , lmp , iota - car , mcc , alg and gar , having a total gum concentration of 0 . 5 % ( w / w ), could not be measured for viscoelastic tests as the stress applied ( 1 pa ) during the amplitude sweep exceeded the strength of the network . fig8 shows viscoelastic behavior of 0 . 75 % ( w / w ) bbg / other gum blends determined at 20 ° c . for both gum ratios of 80 / 20 and 90 / 10 ( w / w ) of 0 . 75 % ( w / w ) bbg / xan blend , crossover of g ′ and g ″ was observed . the cross over of g ′ and g ″ is defined as a change from the viscoelastic fluid to viscoelastic solid ( lazaridou et al ., 2003 ). this indicated a soft gel formation when total gum blend concentration was increased from 0 . 5 to 0 . 75 %, w / w . in addition to the gum concentration , the gel setting or gelation time has been reported to be affected by time and temperature of storage ( lazaridou et al ., 2003 ). in the present study , critical time of g ′ and g ″ cross over for the gum blends was not detected . gum blends containing bbg and hmp , lmp , mcc , alg or gar at a total gum concentration of 0 . 75 % ( w / w ) was subjected to viscoelastic tests as the stress applied ( 10 pa ) during the amplitude sweep exceeded the strength of the network . bbg dispersions are known to undergo phase separation when stored for a long period as bbg molecules undergo associations / aggregation via linear cellulosic segments of the molecules and precipitate . the relative scores ( as determined subjectively ) for phase stability and visible precipitation for 0 . 5 and 0 . 75 % ( w / w ) bbg / other gum blends are given in table 6 . the phase stability of β - glucan molecules increased during the first two weeks upon increasing the total gum concentration from 0 . 5 - 0 . 75 % ( w / w ). this is due to the increased viscosity of the dispersions at high concentration that slowed down the aggregation process of bbg molecules inhibiting the phase separation . unique stability properties of the bbg when blended with xan were observed ( table 6 ). the blends were found to be stable with no signs of phase separation for more than 12 weeks of storage at ambient temperature . bbg / xan blends having total gum concentrations of 0 . 5 and 0 . 75 % ( w / w ) exhibited excellent phase stability against visible phase separation / precipitation due to excellent thermodynamic compatibility of gum components in aqueous medium . the mechanism behind this phenomenon may be the polysaccharide - polysaccharide complex formation . existence of such a complex formation may be the reason behind the high degree of viscous synergism observed for these blends . phase separation was observed for all other 0 . 5 and 0 . 75 % ( w / w ) bbg / other gum blends . this occurred probably due to the limited thermodynamic compatibility between bbg and other gums present in the mixture . beverage samples devoid of gum demonstrated stable viscosity throughout the entire storage period ( table 7 ). the % loss of the original viscosity for pure gum solutions and gum incorporated beverage samples measured at a shear rate of 64 . 6 s − 1 and at 5 ° c . and 25 ° c . is given in table 7 . the beverage samples were prepared at two concentrations , 0 . 23 % ( w / w ) and 0 . 46 % ( w / w ), and tested only at ph 3 . 25 . the % loss of the original viscosity of the beverage containing bbg / xan at 0 . 23 % ( w / w ) and 0 . 46 % ( w / w ) were 0 . 5 % and 7 . 5 %, respectively , as compared to 7 % and 18 . 5 %, respectively for the beverage containing bbg alone . the above data clearly indicated that the incorporation of xan is beneficial in preventing the loss of viscosity in acidic aqueous dispersions of beta - glucan . this may be attributed to the high stability of xan in acidic environments ( kovacs and kang , 1977 ) and its interaction with bg . pure gum solutions , especially with a high gum concentration ( 0 . 46 %, w / w ) exhibited higher viscosity loss than 0 . 23 % ( w / w ) control solutions during the storage period . the solution containing bbg alone ( 0 . 46 %, w / w ; ph 3 . 25 ) exhibited 28 . 5 % loss of the original viscosity as compared to 17 . 9 % loss in bbg / xan blend ( table 7 ). acidic condition accentuated the loss of viscosity of 0 . 46 % ( w / w ) bbg dispersions as the viscosity loss progressed from 8 . 4 % at ph 7 to 28 . 5 % at ph 3 . 25 . loss in viscosity may be attributed to molecular aggregation of beta - glucan via linear cellulosic segments and its precipitation ( phasing - out ) from the solution . the molecular aggregation / precipitation and consequent cloud loss in bbg dispersions has been reported to be reflected by absorbance measurement at 660 nm ( bansema , 2000 ). regardless of the ph , at both gum concentrations , the % loss of the absorbance ( cloud - loss ) for pure gum dispersions containing bbg alone was substantially higher than its counterpart containing bbg / xan blend ( table 8 ). similarly , beverage samples containing bbg alone at both gum concentrations exhibited higher cloud loss ( table 8 ) as compared to beverage containing bbg / xan . this is in agreement with bansema ( 2000 ) who reported cloud loss for bbg beverages during the first three weeks of storage . acidity negatively affected the cloud stability ( increased cloud loss ) of aqueous gum dispersions containing bbg alone at both 0 . 23 % and 0 . 46 % ( w / w ) total concentrations ( table 8 ). table 9 relative stability ( as determined subjectively / visually ) of pure gum solutions and gum incorporated beverage samples during 12 - weeks of storage at 4 ° c . gum scores a concentration no . of weeks gum blends (%, w / w ) 0 2 4 8 12 comments pure gum solutions ph 3 . 25 bbg ( control ) 0 . 23 1 1 3 3 4 precipitate at bottom 0 . 46 1 2 3 4 4 precipitate at bottom bbg / xan 0 . 23 1 1 1 1 1 no precipitate seen 0 . 46 1 1 1 1 1 no precipitate seen ph7 bbg ( control ) 0 . 23 1 1 2 3 4 precipitate at bottom 0 . 46 1 2 3 4 4 precipitate at bottom bbg / xan 0 . 23 1 1 1 1 1 no precipitate seen 0 . 46 1 1 1 1 1 no precipitate seen gum incorporated beverage samples beverage only ( control ) 1 1 1 1 1 no precipitate seen beverage + bbg 0 . 23 1 1 3 3 4 precipitate at bottom 0 . 46 1 2 3 4 4 precipitate at bottom beverage + bbg / xan 0 . 23 1 1 1 1 1 no precipitate seen 0 . 46 1 1 1 1 1 no precipitate seen values are means of replicate determinations . a 1 - extremely clear , no phase separation and no precipitation ; 2 - clear , some phase separation and some precipitation ; 3 - extreme phase separation and extreme precipitation ; 4 - complete phase separation and precipitation those containing 0 . 23 % ( w / w ) bbg and 0 . 23 % bbg / xan remained as single - phase solutions for 12 weeks of storage at 4 ° c . this is in agreement with bansema ( 2000 ) who reported the concentration of 0 . 25 % ( w / w ) β - glucan to be lower than the phase separation threshold and therefore no phase separation . visible precipitation in dispersions containing 0 . 46 % bbg at both ph 3 . 25 and 7 was observed during the 12 week storage at 4 ° c . the bbg / xan blends at total concentrations of 0 . 23 and 0 . 46 % ( w / w ) demonstrated improved cloud stability with no signs of precipitation at both ph 3 . 25 and 7 throughout the storage period . bbg in binary systems exerted synergistic interactions with xan , iota - car , and cmc , and the interactions depended mainly on the blending ratios and the total gum concentrations . blending of xan into aqueous dispersions of bbg generates viscous synergism at the high total gum concentration of 0 . 75 % ( w / w ) and that was not observed at the concentration of 0 . 5 % ( w / w ). the high shear tolerance of bbg / xan blends may be beneficial in food applications where enhanced shear tolerance is required . a soft gel transformation ( a change from viscoelastic fluid to viscoelastic solid ) when bbg was blended with xan may provide a unique consistency needed for “ solids suspension property ” much desired in products such as salad dressings or other cloudy beverages . the unique thermodynamic compatibility of bbg and xan in binary gum blends as demonstrated by no phase separation observed during the 12 - week storage at ambient temperature suggested its potential application in aqueous food systems . the bbg / xan blends at neutral and acidic conditions demonstrated higher viscosity stability and phase stability than those of the aqueous systems containing bbg alone . incorporation of xan into bbg dispersions changed the rheological properties of bbg dispersions from viscoelastic fluid to viscoelastic solid . this demonstrated the potential of bbg / xan blends in food applications ( such as salad dressings ) where weak gel - like characteristics are desired . in particular , the addition of xan or cnc to aqueous solutions of bg improves the shear tolerance of bg solutions meaning that at particular shear rates ( eg . intestinal shear rates ), blends of bg with xan or cnc will maintain higher viscosities than bg alone . this finding will improve the satiety effect of bg within the human body and may be particularly useful in the formulation of food or beverage products targeting the satiety effect . the evidence gathered from the present study indicates the potential applications for bbg in the functional food / nutraceutical industry . autio , k ., myllymaki , o ., & amp ; malkki , y . 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