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Effect of bambara groundnut flour on the stability and rheological properties of oil-in-water emulsion
Author(s)
Adeyi, Oladayo
Date Issued
2014
Type
Thesis
Publisher
Cape Peninsula University of Technology
Abstract
The effect of bambara groundnut flour (BGNF) on the stability and rheological properties of
sunflower oil-in-water (o/w) emulsions was studied. BGNF dispersions were gelatinized and
used to stabilize sunflower o/w emulsions. The sunflower oil-in-water emulsions were prepared
by homogenizing gelatinized BGNF and sunflower oil using the Ultra Turrax T-25 homogenizer.
D-optimal response surface methodology (RSM) was used to investigate the effect of BGNF
and sunflower oil (SFO) on emulsion stability. Emulsion stability was studied using Turbiscan
MA 2000 by observing changes in the average ∆-backscattering flux (%) at 20°C. Quantification
of droplet size and droplet size distribution of emulsions was done by image analysis. Emulsion
stability parameters such as microstructure, droplet size (d3,2 and d4,3), initial backscattering
(BSAVO) and equilibrium backscattering (BSeq) values were quantified and modeled using RSM.
The time-dependent, steady shear and visco-elastic properties were studied using Rheolab MC
1 and Discovery HR-1 rheometers. The rheological behaviours were modeled using rheological
equations and predictive equations were developed using RSM. Both BGNF and SFO
concentration affected the emulsion stability and rheological properties of emulsions. Increase
in oil phase fraction and BGNF concentration improved emulsion stability. The linear and
interaction effects of BGNF and SFO were found significant (p < 0.05) on droplet size and
BSAVO. BGNF-stabilized emulsions showed multiple destabilization mechanism with
flocculation/coalescence more prevalent. Kinetics of destabilization showed that increase in
SFO and BGNF concentration has profound effect on emulsion destabilization. Increased
BGNF in the emulsion decreased particle size. A quadratic polynomial relationship was found
between the emulsion main components and droplet sizes (d3,2 and d4,3) and BSAVO. However, a
linear relationship was established between BGNF and SFO for BSeq. Emulsion formulated with
7% (w/w) BGNF and 40% (w/w) SFO possessed highest stability with equilibrium backscattering
and desirability values of -0.084% and 89.3% respectively. Regarding the rheological
properties, all emulsions were thixotropic, pseudoplastic and viscoelastic fluids. The timedependent behaviour of the emulsions was well modeled by Weltman, Figoni and Shoemaker
and Hahn’s models. Both the shear rate and emulsion main components (BGNF and SFO)
greatly influenced the time-dependent model parameters. First order stress decay with a zero
equilibrium stress value was found not suitable to predict the time-dependent rheological
properties of BGNF stabilized emulsions. The time-independent characteristics of the BGNFstabilized emulsions were well predicted by the Power law, Herschel-Bulkley, Bingham and
Casson model (high R2
and low RMSE and SE). All emulsions possessed viscous (G’) and
elastic (G”) properties. The G’, G” and recoverable strain (Q (t)%) of the emulsion were found to depend on BGNF and SFO concentrations. The linear and quadratic equations were
appropriate to describe the relationship between rheological parameters and emulsion
components as the case may be. However the emulsion formulated with 7% (w/w) BGNF and
40% (w/w) SFO which possessed maximum storage stability also recorded the highest
thixotropic area, pseudo-plasticity, G’, G” and Q (t)%. The result strongly indicated a close
relationship between emulsion stability and rheological properties for BGNF-stabilized
emulsions. Varietal differences of BGNF was insignificant (p < 0.05) on the stability parameters
such as microstructure, oil-droplet size, BS and BSeq and on rheological properties such
apparent viscosities, thixotropic area, power law parameters (K and n), Weltman parameters,
G’, G” and Q(t)%. Food additives (NaCl, vinegar and citric acid) significantly affected emulsion
stability and rheological properties of BGNF stabilized emulsions. Storage stability results
indicated that all emulsions were most stable at low temperature of 5oC and least stable at high
temperature of 45oC. Destabilization due to oil droplet aggregation was prevalent in all the
emulsions. The rheological behaviour during storage was a peculiarity of each of the studied
emulsion systems. However, most of the emulsions showed significant (p < 0.05) initial
increase in rheological parameters (such as apparent viscosity and consistency coefficient of
power law equation) in the first three days of study. There was however no general descriptive
trend as a function of storage days at all investigated temperatures. All experimental results
demonstrated that BGNF may find applications in food emulsion deliveries if appropriately
engineered. All the developed empirical models may find uses during formulation of BGNF
stabilized emulsions of predetermined stability and rheological properties. Additives may as
well be used to control the rheology and physical stability of such emulsions and the presence
of BGNF may present the structures (in terms of the matrix) necessary for rigidity during long
term storage stability, particularly if BGNF is used as a stabilizer.
sunflower oil-in-water (o/w) emulsions was studied. BGNF dispersions were gelatinized and
used to stabilize sunflower o/w emulsions. The sunflower oil-in-water emulsions were prepared
by homogenizing gelatinized BGNF and sunflower oil using the Ultra Turrax T-25 homogenizer.
D-optimal response surface methodology (RSM) was used to investigate the effect of BGNF
and sunflower oil (SFO) on emulsion stability. Emulsion stability was studied using Turbiscan
MA 2000 by observing changes in the average ∆-backscattering flux (%) at 20°C. Quantification
of droplet size and droplet size distribution of emulsions was done by image analysis. Emulsion
stability parameters such as microstructure, droplet size (d3,2 and d4,3), initial backscattering
(BSAVO) and equilibrium backscattering (BSeq) values were quantified and modeled using RSM.
The time-dependent, steady shear and visco-elastic properties were studied using Rheolab MC
1 and Discovery HR-1 rheometers. The rheological behaviours were modeled using rheological
equations and predictive equations were developed using RSM. Both BGNF and SFO
concentration affected the emulsion stability and rheological properties of emulsions. Increase
in oil phase fraction and BGNF concentration improved emulsion stability. The linear and
interaction effects of BGNF and SFO were found significant (p < 0.05) on droplet size and
BSAVO. BGNF-stabilized emulsions showed multiple destabilization mechanism with
flocculation/coalescence more prevalent. Kinetics of destabilization showed that increase in
SFO and BGNF concentration has profound effect on emulsion destabilization. Increased
BGNF in the emulsion decreased particle size. A quadratic polynomial relationship was found
between the emulsion main components and droplet sizes (d3,2 and d4,3) and BSAVO. However, a
linear relationship was established between BGNF and SFO for BSeq. Emulsion formulated with
7% (w/w) BGNF and 40% (w/w) SFO possessed highest stability with equilibrium backscattering
and desirability values of -0.084% and 89.3% respectively. Regarding the rheological
properties, all emulsions were thixotropic, pseudoplastic and viscoelastic fluids. The timedependent behaviour of the emulsions was well modeled by Weltman, Figoni and Shoemaker
and Hahn’s models. Both the shear rate and emulsion main components (BGNF and SFO)
greatly influenced the time-dependent model parameters. First order stress decay with a zero
equilibrium stress value was found not suitable to predict the time-dependent rheological
properties of BGNF stabilized emulsions. The time-independent characteristics of the BGNFstabilized emulsions were well predicted by the Power law, Herschel-Bulkley, Bingham and
Casson model (high R2
and low RMSE and SE). All emulsions possessed viscous (G’) and
elastic (G”) properties. The G’, G” and recoverable strain (Q (t)%) of the emulsion were found to depend on BGNF and SFO concentrations. The linear and quadratic equations were
appropriate to describe the relationship between rheological parameters and emulsion
components as the case may be. However the emulsion formulated with 7% (w/w) BGNF and
40% (w/w) SFO which possessed maximum storage stability also recorded the highest
thixotropic area, pseudo-plasticity, G’, G” and Q (t)%. The result strongly indicated a close
relationship between emulsion stability and rheological properties for BGNF-stabilized
emulsions. Varietal differences of BGNF was insignificant (p < 0.05) on the stability parameters
such as microstructure, oil-droplet size, BS and BSeq and on rheological properties such
apparent viscosities, thixotropic area, power law parameters (K and n), Weltman parameters,
G’, G” and Q(t)%. Food additives (NaCl, vinegar and citric acid) significantly affected emulsion
stability and rheological properties of BGNF stabilized emulsions. Storage stability results
indicated that all emulsions were most stable at low temperature of 5oC and least stable at high
temperature of 45oC. Destabilization due to oil droplet aggregation was prevalent in all the
emulsions. The rheological behaviour during storage was a peculiarity of each of the studied
emulsion systems. However, most of the emulsions showed significant (p < 0.05) initial
increase in rheological parameters (such as apparent viscosity and consistency coefficient of
power law equation) in the first three days of study. There was however no general descriptive
trend as a function of storage days at all investigated temperatures. All experimental results
demonstrated that BGNF may find applications in food emulsion deliveries if appropriately
engineered. All the developed empirical models may find uses during formulation of BGNF
stabilized emulsions of predetermined stability and rheological properties. Additives may as
well be used to control the rheology and physical stability of such emulsions and the presence
of BGNF may present the structures (in terms of the matrix) necessary for rigidity during long
term storage stability, particularly if BGNF is used as a stabilizer.
Additional information
Thesis (DTech (Chemical Engineering))--Cape Peninsula University of Technology, 2014
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