Patent Application
20060040036
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.
Hydrocolloids or food gums are water loving materials that have potential to function as thickeners and extenders in foods. In hydrocolloid, the prefix “hydro” is the Greek word for water. The word colloid is derived from the French word “col” meaning glue and “oid” meaning like (William, 1977). Colloids form viscous sols at low concentration and gels at high concentration. Most of the hydrocolloids used in the food industry are derived from plants and marine algae (William, 1977).
Hydrocolloids can be classified into five categories, namely plant exudates (e.g., arabic gum and tragacanth), seaweed extract (e.g., carageenan and alginates), seed gums (e.g., locust bean gum and guar gum), microbial synthesized products (e.g., xanthan gum) and chemically modified natural polysaccharides (e.g., carboxymethylcellulose and microcrystalline cellulose). The structure of various gums and their properties are summarized in detail by Glicksman (1969).
Recently, mixed linked (1→3) (1→4) β-glucan obtained from cereals (concentrated in walls of endosperm cell) has been reported to possess unique physicochemical properties desired in a hydrocolloid. β-glucan has been known to possess unique physiological properties and has demonstrated health benefits (Eastwood, 1992; Newman & Newman, 1992; Wood, 1993).
Barley is a major source of β-glucan and its global production ranks fourth among that of wheat, rice and corn (Nilan & Ullrich, 1993; Bansema, 2000). Oats and barley are the richest commercially viable natural sources of β-glucan with levels as high as 3 to 8%. Barley is currently used primarily for livestock feeds and the remainder is utilized in malting, brewing, and the food industry. Only 5% of barley produced in Canada is currently being utilized for direct human consumption despite the fact that barley is an excellent source of proteins, insoluble fiber and soluble fiber or hydrocolloids. Incorporation of β-glucan into beverages and other food products creates value-addition to common food products that may enable classification as a functional food.
Due to functionality and cost consideration, blends of food gums are often used in food formulations (Hernandez et al., 2001; Nnanna & Dawkins, 1996; Le Gloahec, 1951; Casas et al., 2000; Schorsch et al., 1997; Tako et al., 1998). An important parameter that determines the acceptability of gum blends in food and beverages is the stability of the blends throughout the product shelf life.
Studies directed towards the understanding of how barley β-glucan interacts with other food gums and the applicability of these interactions to foods and beverages are limited. Factors, such as the concentration of gum, temperature and pH of the medium, have a profound effect on the stability of β-glucan in solution (Bansema, 2000). Moreover, the stability of gum mixtures in aqueous medium is also governed by the thermodynamic compatibility of gums constituting the system.
Interactions between gums modify the Theological properties of gum mixtures and are important for new product development while improving the quality of the existing food products. For instance, the addition of kappa-carageenan to locust bean gum produces highly stable thermo-reversible gels with important synergistic effects (Tako et al., 1998). A mixture of gum arabic and carrageenan as an ice cream stabilizer has been patented (Le Gloahee, 1951) and it functions to retard both ice crystal formation and growth. Hence, the establishment of fundamental rheological properties of gum blends and the understanding of the interactions of barley β-glucan with other food gums are of importance.
In accordance with the invention, there is provided a solution comprising solubilized beta-glucan (BG) and an effective amount of a gum that synergistically enhances the viscosity of the solution or enhances the shear tolerance of the solution.
In various embodiments, the gum is any one of xanthan gum (XAN), carboxy methyl cellulose (CMC), lamda-carageenan (lamda-CAR), or iota-carageenan (iota-CAR) and the weight ratio of BG:gum (weight of BG/weight of gum) is greater than 1, between 99 and 4, between 9 and 4 or is 9. Preferably, the total gum concentration (TGC) is greater than 0.25% (w/w), in the range 0.25% to 0.75% (w/w) or in the range 0.5% to 0.75% (w/w).
In further embodiments, the invention provides a method of imparting shear tolerance or synergistically enhancing the viscosity of an aqueous beta glucan (BG) dispersion comprising the steps of dry blending a BG and an effective amount of a gum and mixing the dry blend with an effective amount of water to form a solution having improved shear tolerance or enhanced viscosity.
In a still further embodiment, the invention provides a method of preventing precipitation of beta-glucan (BG) molecules within an aqueous solution comprising the steps of dry blending BG and an effective amount of a xanthan gum and mixing the dry blend with a beverage.
In yet another embodiment, the invention provides a capsule containing a dry blend of beta-glucan and an effective amount of a gum whereupon hydration, the dry blend forms an aqueous solution within a digestive system, the solution having enhanced shear tolerance or improved viscosity. In further embodiments, the capsule contains a gel or a solution of beta-glucan and gum.
The invention is described by the following description and drawings in which:
A study was initiated having the main objectives of:
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.
Materials and Methods
Barley Viscofiber®, a concentrated form of BBG (˜60-65%, w/w, β-glucan) (described in Applicant'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.
Extraction and Purification of BBG from Barley Viscofiber™
The purification of BBG from Viscofiber™ was based on a traditional aqueous technology as shown in
Chemical Analyses
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.
Determination of Viscosity and Thixotropy
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.
Determination of Viscoelastic Properties of Gum Blends
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.
Stability Tests
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.
Beverage Formulation and Evaluation of Stability
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.
Results and Discussions
Recovery and Composition of Purified BBG
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
Viscosity of Gum Blends
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:
S=c Rn (1)
where, S is the shear stress (N/m2), 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>0.99 have been shown to be “Newtonian” whereas gums forming highly viscous solutions (n<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.
Values are means of replicate determinations.
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.
Values are means of replicate determinations.
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.
Values are means of replicate determinations.
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 & Dawkins 1996). There are several definitions for synergistic and antagonistic interactions (Howell, 1994; Kalectunc-Gencer & Peleg, 1986; Plutchok & 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”, Iv, that is defined as:
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., ci=cj=ci+j (Hernandez et al., 2001). According to the equation, Iv is always a positive value. If 0<Iv<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 Iv=0.5 and both gums are of equal viscosity (when considered separately and at identical concentrations), so that ηi+j=ηi=ηj then the situation is termed as no interaction. On the other hand, if 0.5<Iv<1, synergism occurs, provided ηi+j is more than ηi and ηj individually. If Iv>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., ηi+j>ηi+ηj, then synergism has also occurred (Pellicer et al., 2000 & 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, ηi or ηj, is >ηi+j at identical gum concentrations (Hernandez et al., 2001).
Tables 4 and 5 shows the “Viscous synergism index”, Iv 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.
Values are means of replicate determinations. All viscosity measurements [η (i), (η (j) and η (i + j)] were performed at identical total gum concentration (0.5%, w/w).
Values are means of replicate determinations. All viscosity measurements [η (i), (η (j) and η (i + j)] were performed at identical total gum concentration (0.75%, w/w).
**Marginally antagonistic
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 Iv=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.
Thixotropy of Gum Blends
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.
Elastic Modulus of Gum Blends
Elastic modulus (G′) and loss modulus (G″) define the viscoelastic properties of gum solutions (Mandala & 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 & Palogou, 2003; Dickinson & 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″>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′>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.
Stability of Gum Blends
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.
a1 - 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
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.
Stability of Beverage Formulation
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.
Values are means of replicate determinations.
aPercentage loss = (loss of viscosity/original viscosity) × 100
bViscosity was determined at two different temperatures, 5° C. and 25° C., and at a shear rate of 64.6 s−1
cnot determined - because most beverages are acidic in nature
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).
Values are means of replicate determinations.
aPercentage loss = (loss of absorbance/original absorbance) × 100
bDetermined at a wavelength of 660 nm at the room temperature.
Table 9 shows the relative stability (as determined subjectively/visually) of pure gum solutions and gum incorporated beverage samples during 12 weeks of storage at 4° C.
Values are means of replicate determinations.
a1 - 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.
Conclusions
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.
| Number | Date | Country | |
|---|---|---|---|
| 60584624 | Jul 2004 | US |
