Sky Journal of Food Science Vol. 5(7), pp. 050 - 054, December, 2016
Available online http://www.skyjournals.org/SJFS
©2016 Sky Journals
Full Length Research Paper
Response surface modeling and optimization of effects
of process variables combinations on sensory
properties of roasted African breadfruits
Umezuruike A. C. and Nwabueze T. U.
Department of Food Science and Technology, College of Applied Food Sciences and Tourism, Michael Okpara
University of Agriculture, Umudike, Nigeria.
Accepted 25 November, 2016
African breadfruits (Treculia africana) were roasted at different designed roasting temperatures, roasting time
and feed quantity, process variable combinations using response surface methodology complemented with
Central Composite Rotable Design (CCRD), delulled and evaluated for appearance, crispness, taste, aroma
and overall acceptability using a nine point hedonic scale. Results were modeled using second order
regression and optimization of values calculated with Minitab statistical software. Different process variable
conditions influenced the sensory indices of roasted seeds at all regressional models adequately described the
data. There were significant (P < 0.05) differences in the effect of treatment variables on sensory properties of
roasted samples. Roasting temperature and roasting time were identified as critical variables with significant (P
< 0.05) linear and squared effects on sensory attributes of African breadfruit seed snacks. All regressional
models adequately described the data. The optimum setting of 166.45°C roasting temperature 42.12min,
roasting time and 549.27 g feed quantity was identified for peak sensory properties whose mean values were
higher than minimum acceptable score of 5. The optimum locum of process setting can be easily and
successfully applied by local processors with its attendant benefits.
Key words: African breadfruits, process variables, optimization, response surface and sensory properties.
INTRODUCTION
Roasted African breadfruit seed is a snack is widely
consumed in many tropical and sub-tropical regions of
the world. The snack is eaten with coconut, Palm kernel
or roasted peanuts. The consumption of roasted African
breadfruits is fast gaining popularity because of its rich
nutrients and the quest for exploitation of lesser known
legumes for alleviation of malnutrition in developing
nations (Nwabueze, 2006). The protein (22%),
carbohydrate (63%), fat (11%) and rich mineral contents
of African breadfruit compare favourably with other
legumes such as cowpeas, soybean, peanuts, African
yam bean (Balogun and Fetuga, 1986). In addition
roasted African breadfruit seed snack is an article of
trade for urban dwellers and an important source of
income for households which derive their income from
*Corresponding author. E-mail: [email protected].
sales of seed snack to travelers (Okaka and Okaka,
2005). Two major varieties of African breadfruit (Treculia
Africana) seeds are common with local processors
(Nwabueze, 2010). Those varieties have seed diameter
dimensions ranging from 2.5 mm (small) to 4.0 mm
(large). These seed dimensions have important
implications for heat penetration and chemical changes
which occur in the roasted seeds leading to intermediate
compounds which may impact desirable and undesirable
properties such in appearance taste, aroma, etc. on the
finished products. Pre-dehulling roasting treatments are
important since consumer acceptability of African
breadfruit seed snacks is influenced by appearance,
crispness taste and aroma characteristics (Siegal and
Faweth, 1976). Roasting temperature, roasting time and
feed quantity are important process variables during the
roasting of seeds snack. These process factors exert
liner, squared or cross product effects and are
responsible for heat transfer and chemical changes in
Umezuruike and Nwabueze
51
Table 1. Experimental layout of process variable combination.
X1
+1
1.682
0
0
0
X2
+1
0
1.682
0
0
X3
+1
0
0
1.682
0
Combination
8
2
2
2
1
Replication
1
1
1
1
6
Experiments
8
2
2
2
6
Range and levels of the experimental variables used in the coded and un-coded
forms are summarized in Table 2.
Table 2. Experimental range of process variables.
Code
Variables
RT (ºC)
RM (min)
FQ (g)
X1
X2
X3
-1.682
126.36
Coded
-1
Level
0
1
1.682
31.59
331.80
140
35
400
160
40
500
180
45
600
193.64
48.41
668.20
RT: Roasting Temperature
RM: Roasting Time
FQ: Feed quantity
processed products (Nwabueze, 2009). Local heat
processing of African breadfruit seeds usually employ
temperatures above 100°C (Nwabueze, 2009) which
poses important challenges to African breadfruit seed
processing.
Inappropriate heat processing of legumes at
temperature above 177°C has been reported to result to
darker colours, burnt taste and poor acceptability of
product (Griffith and Castel – Perez, 1998). Though
roasting could be described as a simple operation, local
processors who dominate the roasted African breadfruit
seed trade do not grade their seeds and lack the
knowledge and skill needed manipulate heat treatment
needed to produced seeds snacks of very high grade
through process variable combinations. Often times, poor
processing/roasting lead to poor product acceptability,
loss of income and frustration. This study aimed to
identify for the benefits of processors, consumers and
researchers using response surface, the process
variables combinations that optimize process conditions
and the sensory properties of roasted mixed varieties of
African breadfruit seeds. Response surface methodology
complemented with central composite rotable design has
been successfully used to optimize process variable
combination leading to peak quality product in a product
class (Khuri and Cornell, 1987; Chen and Lin, 2002).
MATERIALS AND METHODS
Seed samples and preparation
Freshly harvested African breadfruit seeds (T. africana)
were purchased from Umuahia main market Abia State
Nigeria. The seeds were thoroughly washed with clean
water, screened for contaminants and dried under a
shade at ambient temperature from 24 h. The air dried
seeds were roasted in Electric oven (Fishers Scientific) in
20 experimental runs.
Experimental design
Response surface methodology was used in the
experimental design and analyses (Nwabueze, 2010). A
central composite rotable design at three variables and
five levels combinations involving 8 factorials, four axials
and six replications as the center as described on Tables
1 and 2 was used.
The roasted seeds were the dehulled with locally
fabricated dehuller. The dehulled seeds were
characterized for sensory qualities on a 9 point hedonic
scale.
Evaluation and statistical modeling of sensory
properties
Nineteen trained judge evaluated the sensory properties
of the roasted and dehulled African breadfruit seed
snack. Sensory parameters such as appearance, taste,
chewiness/crispness, and aroma and over all
acceptability were assessed using a 9 point hedonic
scale according to the method described by Iwe (2007).
The data obtained from of the sensory properties
examined was statistically analyzed using Analysis of
variance (Anova), second order polynomial regression
and summarized in the Equation 1 below.
Y=
0
+∑
∑
x
2
12 +
∑
Where y = measured response,
xi xj + e
0
= intercept,
(1)
52
Sky J. Food Sci.
Table 3. Regression co-efficient of roasted seeds sensory properties.
Co-efficient
B0
B1
B2
B3
B11
B22
B33
R2
R2()Adjusted)
Lack of fit
Appearance
-30.798
0.725
-0.816
NS
NS
NS
NS
92.45
85.15
NS
Crispness
-54.204
1.885
NS
NS
0.019
NS
63.84
61.30
NS
Taste
-40.290
0.312
1.004
NS
0.001
0.011
NS
85.98
73.36
NS
Aroma
-85.604
0.858
NS
NS
0.003
0.011
NS
92.4`1
85.57
NS
Overall acceptance
-62.017
0.671
NS
NS
0.002
NS
NS
74.42
61.40
NS
NS: not significant (P < 0.05); All other co-efficient are significant (P < 0.05).
Table 4. Optimal values of process variables and sensory
attributes.
Variables
Temperature
Roasting time
Feed quality
Sensory attributes
Appearance
Crispness
Taste
Aroma
Overall acceptance
Optimum values
166.45°C
42.12min
549.27g
Predicted
7.20
8.24
7.82
7.98
7.92
= co-efficient, Xi xj = interactions and e = error term
Minitab statistical software (Minitab Inc, USA) was used
for the regression analysis and prediction of optimal
values for process variables.
RESULTS AND DISCUSSION
The estimated regression co-efficient for sensory
properties of roasted African breadfruit seeds snack are
shown on Table 3. The optimum obtainable sensory
properties values of the roasted seeds corresponding to
optimum process variables values are shown in Table 4
Appearance
Heat processing as consistent with roasting has
significant impact on the overall quality of roasted African
breadfruit seeds. The appearance of roast processed
seats of African bread fruits is the primary attribute that
influences the decision of consumer to purchase or
consume the snack (Nwabueze, 2009). Sensory scores
for appearance ranged from 4.21 to 7.88 under different
process conditions. Roasting temperature (RT) and
Roasting time (RM) were identified to be critical to
appearance (Table 3). Increased roasting temperature
and duration resulted in the darkening of the roasted
Experimental
7.88
8.30
8.01
8.00
8.10
seeds at higher temperature. These effects were
significantly (P
0.05) linear and quadratic in their
contribution to the final appearance of roasted African
breadfruit seeds snack. The coefficient of determination
2
2
R , adjusted R and lack of fit implied the adequacy of the
model to describe variability in appearance. The
regression equation for appearance with the significant
terms can be written as the Equation 2 below:
Ap = -30.793 + 0.725RT –0.816RM – 0.002RM
2
2
0.012RM (R = 0.93) …. (2)
2
+
Where Ap = appearance
RT = roasting temperature
RM = roasting time.
The optimum sensory score for appearance was
predicted at 7.20 at the optimum process variable
combinations of 166.45ºC, 42.12min and 549.27g of
African breadfruit seeds (Table 4).
A sensory score of 7.2 on a 9 point hedonic scale is
indicative of good product appearance important for
consumer acceptability.
Crispness
Texture properties especially chewiness and crispness
Umezuruike and Nwabueze
are important for the savouring of roasted African
breadfruit seeds snacks. Hardness influence chewiness
by affecting the amount of energy needed to chew the
snacks. Grain hardness is affected by moisture content,
chemical composition and heat treatment (Ahmed et al.,
1996) in direct response to roasting temperature and
time. For most grains reduction in moisture content
reduces hardness, but reduction
But reduction in
moisture content has been reported to increase the
hardness of roasted African breadfruit seeds (Nwabueze,
2009) through the compaction of starch granules of the
seeds. The peak sensory score for chewiness/crispness
was 8.30 at 166.45°C, 42.12min and 549.27 g feed
quantity (Table 4). Among the process variables only
roasting time produced significant (P
0.05) effects on
2,
2
chewiness/crispness. The models R adjusted R and
lack of fit for describing the response parameter of
texture implied the adequacy of modes to describe
variability in data and the direct relationship between
roasting time and chewiness/crispness.
The regression equation with only significant terms is
Cp = -54.204 + 1.885RM –
0.64)……………… (3)
Where Cp = Chewiness/crispness
RM = Roasting time
0.019RM
2
(R2
=
53
temperatures above 160°C will yield seed snack of poor
taste.
Aroma
The Aroma score for the processed African breadfruit
seeds peaked at 8.00 Roasting temperature, roasting
time showed significant (P
0.05) linear and squared
effects on Aroma (Table 4). The roast odour has been
shown to influence taste perception (Iwe, 2007). Aroma is
an important quality attribute of roasted African breadfruit
seeds snacks as it is the first stimulus that reaches the
olfactory system of the consumer. In the presence of
moisture, protein, carbohydrate, fat and other chemical
components of food, heat acts as catalyst for chemical
reactions that produce desirable and undesirable odour
products (Wilcox, 2006). African breadfruits seeds
contain averagely 22% protein, 63% carbohydrates, 11%
fat, and 36% moisture which readily provide the condition
for odorous products generation (Okaka and Okaka,
2005). The co-efficient of determination predicting the
mean score for aroma explained up to 92.41% (Table 3)
variability in data. The regression equation (5) predicting
the relationship between Aroma and process variables
showed the significant (P < 0.5) linear effect of Roasting
Temperature and the quadratic effect of roasting time on
aroma of roasted seeds.
Taste
The equation can be written as:Taste is an important sensory attribute for the
consumption of roast processed African breadfruit seeds
snack. These results are in agreement with reports of
Srivaster et al. (1994) and Nwabueze (2009), which
stated the important influence of roasting temperature
and time on taste of roasted products such Soybean,
Maize, and African breadfruit seeds.
Roasting temperature and roasting time showed
significant (P
0.05) linear and quadratic effects on
taste. The mean sensory scores for taste ranged from
6.04 to 8.01. The peak value of 8.01 was reported at
optimum setting of 166.45°C 42.12min, and 549.27 g
feed quantity (Table 4). The model predicted up to
85.98% of data variability. The regression equation
without non-significant terms can be written as:
Ts = -40.290 + 0.312RT + 1.004RM – 1.001RT
2
0.011RM (R2 = 0.86)….. (4)
2
–
Where Ts = taste
RT = roasting temperature
RM = roasting time
Increasing roasting temperature and roasting time above
160ºC and 40min leads to poor taste of product. Optimum
control of roasting conditions is important in order to
prevent burnt flavor of roasted seeds.
Result showed that roasting African Bread fruit seeds at
2
2
Ar = -85.604 + 0.858RT – 0.003RT – 0.011RM – (0.92)
………………. (5)
Where Ar = Aroma
RT = roasting temperature
RM = Roasting Time
The preference score (8.00) for aroma is similar to the
hedonic score (8.01) for taste. As flavor components
aroma and taste scores depict high flavor acceptability of
the roasted seeds.
Overall acceptability
The overall acceptability score of the roasted seeds was
8.10 for experimental model which showed that roasting
was responsible for producing seed snack of superior
quality. Roasting temperature showed significant linear
and quadratic effects on overall acceptability of roasted
2
African breadfruit seeds (Table 3). The models R ,
2
adjusted R and lack of fit implied adequacy of model to
describe variability as well as underscoring the influence
of roasting temperature on overall acceptability. The
regression equation which explains the relationship
between overall acceptability and roasting temperature
was described by
54
Sky J. Food Sci.
2
OA = -62.017 + 0.671RT – 0.002RT (0.74)
(6)
Where OA = overall acceptability
RT = roasting temperature
The overall acceptability score (8.10) reflects the high
quality attributes for appearance, chewiness/crispness
taste and aroma.
Conclusion
This study identified and characterized the unified
optimum condition for peak sensory qualities of roasted
African breadfruit seeds eaten snack.
Roasting of African breadfruit seeds for snacks at
different temperature and time combinations affected the
sensory properties and overall acceptability of the
product. Roasting temperature and roasting time are the
two most important processing variables. Which impacted
both significant (P 0.05) linear and quadratic effects on
appearance, crispness, aroma, taste and overall
acceptability. Moderate roasting at temperature of 160 –
166°C, roasting time 40 - 42.12 min, feed and quantity of
549.29 g produced product of higher sensory values.
Response surface methodology was effective in
identifying the optimum variable combinations for
maximum sensory attributes of the processed seeds.
Optimum sensory quality parameters were shown to
reside at 166.45°C roasting temperature; 42.12 min
roasting time and 549.27 g feed quality. Roasting of
African breadfruit seeds for snacking at the optimum
process condition is important for enhanced consumer
product appeal, purchase for consumption, and boast
income from African breadfruit industry.
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