Sensory evaluation


   
 

10 
 

Journal homepage: www.fia.usv.ro/fiajournal 
Journal of Faculty of Food Engineering,  

Ştefan cel Mare University of Suceava, Romania  
Volume XV, Issue 1-2016, pag. 10 - 20 

 

 
APPLICATION OF D-OPTIMAL MIXTURE DESIGN  

TO OPTIMIZE THE WHEAT-PUMPKIN  
COMPOSITE FLOUR FOR BREAD PRODUCTION  

 
Georgiana Gabriela CODINĂ

1, Silvia MIRONEASA*1  

 
1Faculty of Food Engineering, Stefan cel Mare University, Suceava, Romania,  

codina@fia.usv.ro; silviam@fia.usv.ro 
*Corresponding author 

Received January 4th 2016, accepted February 18th 2016 
 
 

Abstract: As compared to wheat flour, pumpkin flour is considered a high quality raw material in 
terms of nutrients and bioactive compounds essential in providing human health benefits. Due to its 
potential, pumpkin flour can be used as a functional ingredient and in bread making can be used in 
composite blends with wheat flour. In this study, the effect of wheat-pumpkin composite flour bread on 
some physical parameters of bread was investigated. For this purpose, three raw materials - pumpkin 
pulp flour, pumpkin seed flour, wheat flour were used and as statistical program the D-optimal 
mixture design (Design Expert 7.0) was used. As response variables, some physical parameters such 
as bread porosity, elasticity and H/D ratio were evaluated. The experimental data obtained were used 
to carry out the analyses of variance (ANOVA) and to develop the regression models. Special cubic 
model were used to explain all physical parameters considered, highlighting that the composite flour 
components interacted with each other and had effects on bread porosity, elasticity and H/D ratio. 
The best formulation of composite flour formula was chosen depending on the desirability function 
which showed a value of 0.94. The optimized formulation which showed desirable physical parameters 
contained 78.3% wheat flour, 15% pumpkin pulp flour and 6.70% pumpkin seed flour. 
 
Key words: wheat flour, pumpkin flour, bread quality, mixture design approach, formula 
optimization 
 

1. Introduction 
 

Bread is an important food product based 
on wheat flour which is consumed 
worldwide due to its competitiveness cost, 
ease of preparation, versatility, sensory and 
nutritional characteristics [1]. From the 
nutritional point of view, bread is a source 
of vitamins, minerals, dietary fiber and 
proteins [2 - 5]. However, by milling and 
processing, many of the nutrients from the 
wheat are destroyed, afectting from the 
nutritional point of view the quality of the 
wheat flour as raw material. Also, some 
vitamins such as A, C, D, and B12 lacked 
from the wheat flour, decreasing it 
nutritional quality [6]. The quality of raw 
materials used in bread formulation play an 

important role, influencing not only the 
nutritional value of bread but also 
functional, sensory and physicochemical 
quality of the final bread product [7]. 
Various ingredients can be added in bread 
products to improve wheat flour 
processing and/or nutritional value of 
bread. It is known that wheat flour proteins 
are of a lower nutritional quality than the 
milk, soy, pea and lupin proteins [8], e.g. 
because it is deficient in essential amino 
acids such as lysine, tryptophan and 
threonine [8 - 11]. Therefore, nowadays, 
the trend is to improved bread quality by 
incorporation of new types of raw 
materials to produce composite breads as 
functional foods [10], made from blend of 
wheat flour and non-wheat or pseudo-

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mailto:codina@fia.usv.ro;
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Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava 
Volume XV, Issue 1  – 2016 

 

 
Georgiana Gabriela CODINĂ, Silvia MIRONEASA, Application of D-Optimal Mixture Design to optimize the wheat-
pumpkin composite flour for the bread production, Volume XV, Issue 1 – 2016, pag. 10 – 20 
 

11 
 

cereals flours [12] since they are rich in 
nutrients such as essential amino acids, 
dietary fiber, fatty acids, minerals, 
vitamins, phenolic compounds, e.g., with 
great potential for the human health. The 
blends between wheat flour and non-wheat 
flours can be successfully used to obtain a 
composite bread with a better overall 
balance of essential amino acids [13], 
especially the lysine content, significant in 
a balances diet [14], improving its 
nutritional characteristics. In this way, the 
used in wheat flour of not just one non-
wheat flour but a mixture of legumes and 
seeds, can have as result from bread 
products an improved taste, aroma and 
nutritional quality. Some studies made in 
order to improve bread quality from the 
nutritional point of view by 
supplementation of wheat flour with non-
wheat or pulses flours have been made by 
Mohammed et al. (2012) [13]; Harinder et 
al. (1999) [15]; See et al. (2007) [16]; 
Güemes-Vera et al. (2004) [17].  Also, 
some researches [18; 19] reported that the 
application of vegetable flours as 
functional ingredients in breads have in 
addition, many beneficial effects in 
controlling and preventing various 
metabolic diseases [20 - 22]. 
Pumpkin is an economically and 
agriculturally valuable vegetable cultivated 
around the word. Pumpkin fruits are 
suitable after processing for consumption, 
making a major contribution to human 
nutrition due to their composition which 
varies from one species or cultivar to 
another.  
Pumpkin pulp provides a valuable source 
of vitamins such as vitamin A, vitamin B2, 
and vitamin C [23 - 25], carotenoids [23; 
25; 26] that have significant roles in 
human nutrition. Also, pumpkin pulp is 
rich in bioactive compounds with high 
antioxidant activity such as phenolics and 
flavonoids [23; 27], minerals, pectin, 
dietary fiber [28] and other compounds 

which are beneficial to the human health 
[29; 30]. Among the dietary fiber, pumpkin 
flour contains cellulose, hemicelulose and 
lignin [31]. Therefore, by adding in 
composite flour, the pumpkin flour leads to 
a fiber enrichment of bread-making 
products, improving its nutritional quality 
[31]. Different levels of pumpkin pulp 
flour used for wheat flour substitution was 
used in preparation of various bakery 
products such as cakes and cookies [32; 
33], biscuits [34], toast breads [35], having 
various effects on bakery products. It was 
showed that higher levels of pumpkin pulp 
caused an unpleasant aroma and taste. 
Noor and Komatchi (2009) [36] 
investigated the potential of peeled and 
unpeeled pumpkin pulp as a raw material 
for the production of flour for use in 
composite blend with wheat flour or as a 
functional ingredient in food products. 
Processed into flour which has a longer 
shelf-life, pumpkin can be use as 
functional ingredients in bakery products, 
supplementing cereal flours. The 
incorporate of pumpkin powder for 
preparation of cake lead to a increased of 
fiber content and -carotene [32]. The -
carotene content increased with the 
increasing dose of pumpkin powder 
addition, increasing the level of vitamina A 
[33]. Same effects on pumpkin blend in 
biscuits were reported by Kulkarni and 
Joshi, 2012 [34]. In addition, they reported 
an increased of minerals content in biscuits 
as compared to the sample without 
pumpkin powder. Due to its highly-
desirable flavor, sweetness and deep 
yellow-orange color, pumpkin flour can be 
use as a natural coloring agent in 
composite flour [35].  
Pumpkin seeds are an interesting raw 
material for food application, highly 
nutritious than cereals due to its high 
protein content (39.25%), oil (27.83%), 
minerals (4.59%) and dietary fibers 
16.84% [1; 37 - 39]. By the addition of 



Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava 
Volume XV, Issue 1  – 2016 

 

 
Georgiana Gabriela CODINĂ, Silvia MIRONEASA, Application of D-Optimal Mixture Design to optimize the wheat-
pumpkin composite flour for the bread production, Volume XV, Issue 1 – 2016, pag. 10 – 20 
 

12 
 

pumpkin seed powder in bread the protein 
content of the product increases [1]. 
Pumpkin seed flour is recognized as a 
good source of lysine [40] improving 
nutritional value of products by 
incorporated them in bakery products, 
especially bread [41]. The addition of 
pumpkin seed flour to this product, 
conducted to an increased of the total 
essential amino acids, protein, fat and 
mineral content, showing that the pumpkin 
seed flour is a good source of protein and 
nutrients for bread fortification [40]. The 
level effects of pumpkin seed flour added 
in wheat flour on the bread quality were 
also studied [16], showing that the level of 
5% is a feasible level to produce bread 
with good nutritional value and sensory 
characteristics.  
Taking into account it nutritionally value, 
the pumpkin pulp and seeds flours can be a 
good supplement to wheat flour which can 
be used in formulation of the composite 
flours in order to improve quality of bread. 
By using in wheat flour not just one non-
wheat flour but a mixture of vegetables 
and seeds oils we can obtain a better result 
regarding the quality of bread products. 
Although pumpkin pulp flour or pumpkin 
seed flour had been used in composite 
flour formulation, after our knowledge the 
addition of both pumpkin pulp and 
pumpkin seed flours in wheat flour in 
various ratio had not been studied before. 
The used of statistically designed 
experiments in the bread-making  
processes to develop the new products or 
to improve the existing one is one of the 
priorities of the baking industry and not 
only that can lead to a lower general 
manufacturing costs. Mixture design is a 
statistical technique that can be used for 
evaluating the quality of final product 
based on the relative proportions of the 
components in the mixture. This technique 
uses an equation that describes how the 
independent variables in a mixture 

experiment affect the response variables 
[42]. D-optimal mixture design was 
applied to find the optimal response for 
any mixture of the components of 
composite flour, and to obtain the 
influence on the response of each 
component singly and in combination with 
other components. 
The objective of this work was to 
investigate the effect of varying ratios of 
pumpkin pulp flour, pumpkin seed flour 
and wheat flour and their interaction on 
some physical parameters of bread by 
using a D-optimal mixture design approach 
and to determine the optimal mixture of 
wheat-pumpkin composite flour. 
Also, the main objective of this study was 
to optimize the mixture of the three 
ingredients used, wheat flour, pumpkin 
pulp flour and pumpkin seed flour in the 
composite flour recipe, with the purpose of 
achieving the optimum physical 
parameters of produced composite breads. 
D-optimal criteria were applied to 
determine the optimal blend for the best 
physical parameters of composite bread 
obtained. 

 
2. Materials and Methods 
 
2.1. Materials 
2.1.1. Wheat flour 
 
The research study has been carried on 650 
flour type (harvest 2015) obtained from 
S.C. MOPAN S.A. (Suceava, Romania). 
The flour used in this study presents the 
following characteristics: moisture content 
14.5%, ash content 0.65%, protein content 
12.6%, wet gluten content 34%, gluten 
deformation index 8 mm, falling number 
380 s. The flour chemical composition was 
determined according to Romanian 
standard methods: moisture (SR EN ISO 
712:2010), wet gluten content (SR 
90:2007), gluten deformation index (SR 
90:2007), ash content (SR EN ISO 



Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava 
Volume XV, Issue 1  – 2016 

 

 
Georgiana Gabriela CODINĂ, Silvia MIRONEASA, Application of D-Optimal Mixture Design to optimize the wheat-
pumpkin composite flour for the bread production, Volume XV, Issue 1 – 2016, pag. 10 – 20 
 

13 
 

2171:2010) and falling number index (SR 
EN ISO 3093:2010). 
 
2.1.2. Pumpkin flour 
Fresh pumpkins fruits (Cucurbita 
moschata) and commercial wheat flour 
were obtained from the local supermarket. 
In order to obtain the pumpkin pulp and 
seed flours, the unpeeled pulp and seeds of 
fresh pumpkins was manually separately 
and then washed under running tap water. 
The pumpkin pieces cut into slices of 2-3 
mm thickness and the seeds were dried in 
hot air oven to a moisture content of 10 -
12% at 50oC for 24 hours. The shelled 
seeds and the dried pumpkin slices was 
grounded using a mechanical mill, and 
then sieved through a 150 m mesh sieve 
in order to obtain fine flour. 
 
2.2. Methods 
2.2.1. Experimental design 
D-optimal mixture design with three 
components was used to optimize the 
composite pumpkin - wheat flour bread 
formula. The wheat flour (WF or X1) as a 
bread composite flour base, pumpkin pulp 
flour (PPF or X2) used as a source of fiber, 
and pumpkin seed flour (PSF or X3) used 
as a source of proteins and minerals are the 
mixture components which was taken as 
independent variables. 
The components proportions from 
composite flour formula, established from 
preliminary studies, are subject to 
multiple-components constraints [Cornell, 
2002], as follows: X1 + X2 + X3 = 1; 0.71 
X1  0.92; 0.05 X2  0.20; 0.03 X3  
0.09, yielding a polyhedral constrained 
region. The dependent variables selected as 
the responses were some physical 
parameters of composite pumpkin - wheat 
flour bread such as porosity, elasticity and 
D/H ratio.  
The Stat-Ease Design Expert 7.0.0 
software package (trial version) was used 

to achieve as well as to analyze the 
experimental design.  

The variations of wheat-pumpkin 
composite flour formulations and their 
replications including a total of 12 
formulations are shown in Table 1 and for 
each treatment combination the sum of the 
component proportions was equal to one. 
 

Table 1. 
A D-optimal mixture design for the 

composite flour formulated with wheat flour 
(WF), pumpkin pulp flour (PPF) and pumpkin 

seed flour (PSF) in various proportion 
 

Formulation 
number 

Formulation variables 
X1 (WF) X2 (PPF) X3 (PSF) 

1 0.920 0.050 0.030 
2 0.855 0.055 0.090 
3 0.831 0.108 0.061 
4 0.766 0.200 0.034 
5 0.842 0.128 0.030 
6 0.710 0.200 0.090 
7 0.766 0.144 0.090 
8 0.876 0.083 0.041 
9 0.799 0.138 0.063 
10 0.855 0.055 0.090 
11 0.766 0.200 0.034 
12 0.710 0.200 0.090 

 
According to the D-optimal approach 
effect of proportions of wheat flour (WF), 
pumpkin pulp flour (PPF) and pumpkin 
seed flour (PSF) on some physical 
parameters of composite pumpkin - wheat 
flour bread as response variables was 
evaluated and optimum combination was 
determined. The combination of 
independent variables in optimal 
proportions that lead to the best responses 
from bread physical parameters in terms of 
porosity, elasticity and height/diameter 
(D/H) ratio was determined.  
 
2.2.3. Preparation of composite pumpkin-
wheat flour bread 
The pumpkin-wheat composite flour 
including pumpkin pulp flour, pumpkin 
seed flour and wheat flour at different 



Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava 
Volume XV, Issue 1  – 2016 

 

 
Georgiana Gabriela CODINĂ, Silvia MIRONEASA, Application of D-Optimal Mixture Design to optimize the wheat-
pumpkin composite flour for the bread production, Volume XV, Issue 1 – 2016, pag. 10 – 20 
 

14 
 

proportions (Table 1) were used for the 
bread production. The 1.8 g compressed 
baker’s yeast, 1% sodium chloride and 
67% water (on 100% weight of mixed 
flour) were the other ingredients used for 
prepared the bread. All the ingredients 
were kneading in a mixer for 7 min at 28oC 
and then the modeled samples was proofed 
for 90 min at 30oC, 85% relative humidity 
and baked for approximately 30 min at 
250oC. A 30 min after removal from the 
oven, the baked bread samples were 
evaluated.  
 
2.2.4. Physical parameters of bread 
The bread elasticity, porosity and H/D 
ratio are the physical parameters 
determined for assessed the effects of 
pumpkin-wheat composite flours 
formulation on bread quality. Loaf height, 
diameter, elasticity and porosity were 
determined according to SR 91:2007 and 
H/D ratio was calculated. 
 
2.2.5. Statistical analysis and optimization 
In this study, fitting response values was 
made using the linear, quadratic and cubic 
models (Eqs. (1) – (3)). Analysis of 
variance (ANOVA) at p-value of the 
model  0.05, p-value of lack of fit  0.05 
and coefficient of determination, R2  0.85 
are the criteria’s used for the selection of 
predictive model for each response. 
 
Y = β1X1+ β2X2+ β3X3 +    (1) 
 
Y = β1X1+ β2X2+ β3X3+ β12X1X2+ β13X1X3 + β23X2X3 
+      (2) 
 
Y = β1X1+ β2X2+ β3X3+ β12X1X2+ β13X1X3 + β23X2X3 
+ β123X1X2X3 +     (3) 
 
where Y is the predictive response (bread 
elasticity, porosity and H/D ratio);  is the 
error of estimation; β1, β2, β3, β12, β13, β23 
and β123 are the constant coefficients for 
each linear and interaction term in the 

predicted models; and X1, X2, X3 is 
proportion of pseudo-components. 
Also, the regression coefficients of 
individual linear, interactive and cubic 
terms were determined. The significances 
of all terms in the regression models were 
assessed statistically by computing the F-
value at a level of significance of 95% or 
99%.  
After evaluating the regression models that 
reveal the relationship between flours 
mixture components and response 
variables, the desirability function 
approach was used to simultaneously 
optimize bread porosity, elasticity and H/D 
ratio. The optimal levels of mixture 
components of the composite flour 
required to yield final optimized physical 
parameters of bread were obtained by 
numeric analysis based on criteria of 
maximizing porosity, elasticity and the 
value of 8 for H/D ratio.  
The State- Ease Design Expert 7.0.0 
software package (trial version) was used 
to statistical analysis, to generate the 
surface response of the fitted regression 
equations and to determine the optimum 
proportions of the components from 
composite pumpkin-wheat flour bread. 
 
3. Results and discussion 
 
3.1. Fitting for the best model 
 
The best model for predicting physical 
parameters of composite flour bread is the 
regression model that has a low standard 
deviation, a low predicted sum of squares, 
and high R-squared [42]. Therefore, the 
results of ANOVA shown that special 
cubic model was found the best fitted for 
all response variables, bread porosity, 
elasticity and H/D ratio (Table 2).   
The R2 value obtained from special cubic 
model was found to be greater than 0.85, 
indicating a great fitting model. The 
mathematical response surface models 



Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava 
Volume XV, Issue 1  – 2016 

 

 
Georgiana Gabriela CODINĂ, Silvia MIRONEASA, Application of D-Optimal Mixture Design to optimize the wheat-
pumpkin composite flour for the bread production, Volume XV, Issue 1 – 2016, pag. 10 – 20 
 

15 
 

were carried out using Design Expert software by applying pseudo components.  
 

Table 2. 
Regression coefficients of predicted special cubic models for physical parameters 

of composite flour bread formulation using data in pseudo components 
 

Component Physical parameters of bread sample  Porosity (%) Elasticity (%) H/D ratio 
β1 (WF) 80.33 82.38 0.96 
β2 (PPF) 91.02 85.06 0.96 
β3 (PSF) -303.45 -146.73 2.99 
β12 (WF x PPF) -57.58 -21.44 -0.095 
β13 (WF x PSF) 535.55* 311.73* -3.15 
β 23 (PPF x PSF) 474.63* 297.52* -3.39 
β123 (WF x PPF x PSF) 280.19 162.14 -0.64 
p-value 0.0270 0.0471 0.0133 
Lack-of-fit 0.7765ns 0.3072 ns 0.1473 ns 
R2 0.8897 0.8596 0.9184 
β1 – wheat flour (WF) value coefficient, β2 – pumpkin pulp flour (PPF) value coefficient, β3 – pumpkin seed flour (PSF) value coefficient; 
ns no significant effect at level  0.05;  
* Significant at the level of p  0.05. 

 
 

The physical parameters of bread sample 
were significantly predicted by 
independent variables pumpkin pulp flour, 
pumpkin seed flour and wheat flour. The 
values of linear and interaction terms show 
that pumpkin seed flour is the component 
which most affects the bread porosity, 
following the elasticity and H/D ratio. The 
pumpkin seed flour was again the most 
important variable in predicting all 
physical parameters of bread. 
Residual analysis was also carried out in 
order to evaluate the adequacy of the 
prediction models. The residual values for 
porosity, elasticity and H/D ratio, 
explained through the difference between 
the observed and predicted values of these 
parameters, are normally distributed 
(Figure 1a), b) and c)). The plots showed 
that the special cubic model is adequate to 
describe the each response surface. 
The predicted models were used to 
generate contour plots for response 
variables significantly predicted by 
independent variables. Figures 2-4 show 

the estimate response surface graphs for 
the porosity, elasticity and H/D ratio. 
 
3.2. Effect of component from composite 
flour on quality measurements of bread 
The bread samples produced with different 
proportion of wheat, pumpkin pulp and 
pumpkin seeds flours shows differences 
exist among the samples in porosity, 
elasticity and H/D ratio.  
 
Bread porosity 
Bread porosity is an important parameter 
of bread quality which indicate it 
assimilability that can be higher or lower. 
The influence of composite flour 
components on bread porosity has been 
shown in the response surface graph in 
Figure 2. Regarding to porosity, a high 
correlation (R2 = 0.8897) was obtained. 
The formulation components, wheat flour 
(WF), pumpkin pulp flour (PPF) and 
pumpkin seed flour (PSF), independently 
not influenced significantly the porosity, 
however, the interactions between WF and 



Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava 
Volume XV, Issue 1  – 2016 

 

 
Georgiana Gabriela CODINĂ, Silvia MIRONEASA, Application of D-Optimal Mixture Design to optimize the wheat-
pumpkin composite flour for the bread production, Volume XV, Issue 1 – 2016, pag. 10 – 20 
 

16 
 

PSF, between PPF and PSF, significantly 
(p  0.05) influenced bread porosity. 
 

(a)  

(b)  

(c)  
Fig. 1. Residual plots for porosity % (a), 

elasticity % (b) and H/D ratio (c) 
 
The value of linear parameter PSF showed 
negative coefficient for porosity which 
indicated a decrease of this physical 
parameter.  
 

 
Fig. 2. The response surface plot of porosity 

 
This result is in agreement with the results 
obtained by See et al. (2007) [16] who 
concluded that addition of 5% pumpkin 
seed flour in wheat flour resulted in bread 
with high loaf volume are most acceptable. 
After this level, the specific volume 
decreased. The increased level of PSF 
addition in bread composite flour up of 5% 
leaded to a decrease of bread porosity.  
It was evident from this study that at lower 
PSF proportion the bread porosity 
increased. An increase in WF level in 
composite flours lead to an increase of 
bread porosity values. The increase in 
porosity value with increasing level of PPF 
in composite flour has also been reported 
previously [35], the bread obtained beeing 
acceptable at 10% level. 
Porosity value is proportional to the 
increase level of PPF and WF in composite 
flour. Therefore, high proportions of PPF 
and WF in composite flour may increase 
the bread porosity, by improving gas-cell 
stability according to Ptitchkina et al. 
(1998) [31] which affirm that the enhanced 
stability comes from surface activity of 
pumpkin pectin. Pectin constitutes about 
30% of the dry weight of pumpkin tissue. 
The increase in aeration is tentatively 
attributed to surface activity of the highly 
acetylated pectin present as a major 
component (about 30% of the total dry-
matter content) of pumpkin tissue. Różyło 



Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava 
Volume XV, Issue 1  – 2016 

 

 
Georgiana Gabriela CODINĂ, Silvia MIRONEASA, Application of D-Optimal Mixture Design to optimize the wheat-
pumpkin composite flour for the bread production, Volume XV, Issue 1 – 2016, pag. 10 – 20 
 

17 
 

et al. (2014) [27] showed that bread with 
pumpkin pulp had smaller and more 
compact pores. 
 
Elasticity 
The bread having high elasticity are 
considered to be having desirable features. 
Figure 3 shows response surface plot of 
elasticity as a function of wheat flour (WF) 
proportion, pumpkin pulp flour (PPF) 
proportion and pumpkin seed flour (PPS) 
proportion in composite flour.  

 
 

 
Fig. 3. The response surface plot of elasticity 

 
Elasticity was maximum at intermediate to 
higher flours proportions. Addition of PPF 
to composite flour showed a positive 
coefficient indicated that PPF had a 
synergistic effect on porosity. The WF/PSF 
and PPF/PSF combinations showed a 
positive significant influence on porosity, 
while the three component combination is 
insignificant.  
Also, in present study, interaction of 
WF/PPF showed a negative coefficient 
indicating an antagonistic effect on 
elasticity, while the interaction WF/PSF 
and PPF/PSF has a synergistic effect on 
this physical parameter. 
 
H/D ratio 
The predictive model for H/D ratio showed 
the three variables, WF, PPF and PSF 

hadn’t significant effects, but which was 

positive. All the three flours showed not 
significant quadratic negative effects on 
H/D ratio. Comparatively with other 
components of composite flour, pumpkin 
seed flour has a high contribution on H/D 
ratio. Interactive effects between wheat 
flour and pumpkin pulp flour, pumpkin 
seeds flour and, triple interaction effect 
between wheat flour, pumpkin pulp flour 
and pumpkin seeds flour had a negative 
effect on H/D ratio of the bread. According 
to ANOVA, there was no significant effect 
of the regression model on H/D ratio 
(Table 2), but a high correlation (R2 = 
0.9184) was detected. In H/D ratio, the 
contour plot can be observed that the 
reduction of wheat flour content and 
increasing of pumpkin seed flour in 
composite flours formulation resulted in 
lower H/D ratio values (Figure 4). 
 

 
Fig. 4. Response surface plot showing effects of 

composite flour formulations on H/D ratio 
 
3.3. Optimized composite flour formulation 
Upon comprehensive evaluation of 
available Design Expert solutions, the 
optimum mixture ratio of flours with wheat 
flour, pumpkin pulp flour and pumpkin 
seed flour was determined on the basis of 
desirability function, using the 



Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava 
Volume XV, Issue 1  – 2016 

 

 
Georgiana Gabriela CODINĂ, Silvia MIRONEASA, Application of D-Optimal Mixture Design to optimize the wheat-
pumpkin composite flour for the bread production, Volume XV, Issue 1 – 2016, pag. 10 – 20 
 

18 
 

optimization process suggested by 
Derringer and Suich [43]. Simultaneous 
optimization was performed by imposing 
some constraints such as H/D ratio of 8, 
and maximum porosity and elasticity.  
The best combinations between the 
proportion of wheat flour, pumpkin pulp 
and pumpkin seeds flours used in this 
study in order to obtain optimum values 
for some physical parameters of bread 
were extracted by State-Ease Design 
Expert software that performs from the 
thousands of iterations and calculation the 
maximum desirability value and the 
conditions on which it was arrived. On the 
basis of these calculations, a total 
desirability value (D) of 94.1% was 
obtained for the optimal formulation of 
composite flour with wheat flour (WF), 
pumpkin pulp flour (PPF) and pumpkin 
seed flour (PSF) in proportion of 78.30%, 
15.00% and 6.70% (w/w). The response-
surface plot corresponding to D value is 
represented in Figure 5, and it was used to 
predict final mixture proportion.  

 

 
Fig. 5. Desirability function response surface 
 

Under these mixture proportions, the 
predicted H/D ratio of 0.81, bread porosity 
of 89.80% and elasticity of 88.53% were 
obtained. 
 

4. Conclusion 
 
This study highlights the usefulness of D-
optimal design in the assessment of the 
simultaneous influence of composite flour 
components and their interaction on bread 
physical parameters. The effects of 
composite flour components on response 
variables could be accurately predicted by 
special cubic type models. A high linearity 
was observed between predicted and actual 
value of response variables. By using 
numerical technique, the optimized 
pumpkin-wheat composite flour was 
obtained. The optimized composite flour 
formula chosen on the basis of desirability 
function revealed that the composite flour 
with 78.30% wheat flour, 15.00% pumpkin 
pulp flour and 6.70% pumpkin seed flour 
(w/w) is the best formulation which can be 
used to obtain pumpkin-wheat flour bread 
with the desirable physical parameters. 
 
Acknowledgements 
This work was supported by a grant of the 
Romanian National Authority for Scientific 
Research and Innovation, CNCS – UEFISCDI, 
project number PN-II-RU-TE-2014-4-0214. 

 
 

5. References 
 
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Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava 
Volume XV, Issue 1  – 2016 

 

 
Georgiana Gabriela CODINĂ, Silvia MIRONEASA, Application of D-Optimal Mixture Design to optimize the wheat-
pumpkin composite flour for the bread production, Volume XV, Issue 1 – 2016, pag. 10 – 20 
 

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Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava 
Volume XV, Issue 1  – 2016 

 

 
Georgiana Gabriela CODINĂ, Silvia MIRONEASA, Application of D-Optimal Mixture Design to optimize the wheat-
pumpkin composite flour for the bread production, Volume XV, Issue 1 – 2016, pag. 10 – 20 
 

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	3.3. Optimized composite flour formulation