ORIGINAL RESEARCH
Sensory evaluation and consumer acceptance of naturally
and lactic acid bacteria-fermented pastes of soybeans and
soybean–maize blends
€ ller2, Hilde M. Østlie2 &
Tinna A. Ng’ong’ola-Manani1,2, Agnes M. Mwangwela1, Reidar B. Schu
2
Trude Wicklund
1
Department of Food Science and Technology, Lilongwe University of Agriculture and Natural Resources, Bunda College Campus, PO Box 219,
Lilongwe, Malawi
2
Department of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, PO Box 5003,
As, 1430, Norway
Keywords
Drivers of liking, lactic acid bacteria
fermentation, natural fermentation,
preference mapping, soybean pastes
Correspondence
Tinna A. Ng’ongo’la-Manani, Lilongwe
University of Agriculture and Natural
Resources, Bunda College Campus, PO Box
219, Lilongwe, Malawi. Tel: +265 1 277 260/
+265 1 277 222; Fax: +265 1 277 364;
E-mail: tinnamanani@yahoo.co.uk
Funding Information
This research was financially supported by
the Norwegian Programme for Development,
Research and Education (NUFU).
Received: 9 April 2013; Revised: 21 October
2013; Accepted: 12 November 2013
Abstract
Fermented pastes of soybeans and soybean–maize blends were evaluated to
determine sensory properties driving consumer liking. Pastes composed of
100% soybeans, 90% soybeans and 10% maize, and 75% soybeans and 25%
maize were naturally fermented (NFP), and lactic acid bacteria fermented
(LFP). Lactic acid bacteria fermentation was achieved through backslopping
using a fermented cereal gruel, thobwa. Ten trained panelists evaluated intensities of 34 descriptors, of which 27 were significantly different (P < 0.05). The
LFP were strong in brown color, sourness, umami, roasted soybean- and maizeassociated aromas, and sogginess while NFP had high intensities of yellow
color, pH, raw soybean, and rancid odors, fried egg, and fermented aromas and
softness. Although there was consumer (n = 150) heterogeneity in preference,
external preference mapping showed that most consumers preferred NFP. Drivers of liking of NFP samples were softness, pH, fermented aroma, sweetness,
fried egg aroma, fried egg-like appearance, raw soybean, and rancid odors.
Optimization of the desirable properties of the pastes would increase utilization
and acceptance of fermented soybeans.
Food Science & Nutrition 2014; 2(2): 114–
131
doi: 10.1002/fsn3.82
Introduction
Diets of most rural Malawian households are poorly
diversified and are predominantly maize-based. Maize
contributes to over 60% of energy, total iron, zinc, riboflavin, and about half of protein consumption, when animal-source foods are scarce (Ecker and Qaim 2011). Yet,
maize has low protein content (9.42%) and is limited in
micronutrients (Nuss and Tanumihardjo 2010). Such
114
maize-based diets increase the risk of various types of
malnutrition. In Malawi, the prevalence of chronic malnutrition among under-5 children is high, that is 47%
(National Statistics Office and ICF Macro 2011), and
micronutrient deficiencies were reported among under-5
children, women, and men (National Statistics Office and
Macro 2005). Malnutrition in Malawi is attributed to
insufficient energy and nutrient intake, among other factors (Maleta 2006). Animal-source foods provide good
ª 2013 The Authors. Food Science & Nutrition published by Wiley Periodicals, Inc. This is an open access article under the terms of
the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium,
provided the original work is properly cited.
T. A. Ng’ong’ola-Manani et al.
quantities of protein and other nutrients, but they are
expensive. This calls for alternative low-cost source of
nutrient-dense food that can be consumed by adults and
children.
Legumes, including soybeans (Glycine max), provide
good quantities of protein, riboflavin, calcium, and iron
(Messina 1999). Soybeans have been used in the prevention
and treatment of protein energy malnutrition in young
children, and in improving the nutritional status of
communities. Therefore, soybean is a good alternative to
expensive animal-source proteins (United Nations Industrial Development Organization 2003). In Malawi, soybean
is produced mainly as a cash crop with limited householdbased consumption (CYE Consult 2009; Tinsley 2009).
Production increased over the past 5 years and in 2010,
73,000 tonnes of soybeans were produced. Most of the
soybeans (63,000 tonnes) were used within the country.
However, the demand for production is driven by the poultry feed industry (Markets and Economic Research Centre
of the National Agricultural Marketing Council 2011) while
there is limited demand from the corn–soy blend industry
(Tinsley 2009). Unfortunately, there is no statistics indicating the percent consumption of both industries. Nevertheless, various reports show that direct human consumption
of soybeans in Malawian households is through enriched
maize flour containing up to 20% soybean flour (KatonaApte 1993; Kalimbira et al. 2004; Maleta 2006; CYE Consult 2009; Tinsley 2009). The enriched flour locally known
as Likuni Phala is used as a weaning food in children
(Kalimbira et al. 2004; Maleta 2006; CYE Consult 2009)
and is also distributed by nongovernmental organizations
for school feeding programs, for hospitals, orphanages, and
refugee camp usage (Katona-Apte 1993; Tinsley 2009).
Consumption of maize together with soybeans provide
high-quality protein diet comparable to diets containing
animal protein (Asgar et al. 2010), because limiting amino
acids in maize are complemented by those found in
soybeans (Siegel and Fawcett 1976; FAO 1992).
Despite the nutritional benefits, household soybean utilization in Malawi is still minimal due to limited knowledge in processing (Coulibaly et al. 2009). Processing is
required to eliminate antinutritional factors and the
undesirable characteristic “beany” taste. Various processing methods such as boiling, steaming, roasting, germination, fermentation, and milling improve soybean
utilization (Siegel and Fawcett 1976; Anderson and Wolf
1995; Golbitz 1995; Wang and Murphy 1996). Use of fermented soybean products in Asia is widely documented
(Sarkar et al. 1994; Kwon et al. 2010; Dajanta et al. 2012;
Park et al. 2012).
In order to increase direct household consumption of
soybeans in Malawian diets, pastes of fermented soybeans
and soybean–maize blends were developed as an alternative
ª 2013 The Authors. Food Science & Nutrition published by Wiley Periodicals, Inc.
Sensory and Consumer Studies of Fermented Soybean
low-cost source of protein. The pastes were naturally fermented or lactic acid bacteria (LAB) fermented through
backslopping using a traditional fermented cereal gruel,
thobwa. The developed pastes were to be used as side
dishes, such as in kinema (Sarkar et al. 1994) and other
similar products of the Orient. Most soybeanfermented products are naturally fermented by Bacillus
subtilis (Steinkraus 1997), a proteolytic microorganism that
produces ammonia during fermentation (Sarkar and Tamang 1995; Dakwa et al. 2005). High amounts of ammonia result in strong odor, which some people find
objectionable (Allagheny et al. 1996; Parkouda et al. 2009).
LAB fermentations, on the other hand, improve flavor of
traditional foods (Steinkraus 1997).
The developed products were new to Malawian consumers; therefore, it was important to obtain consumer feedback for improvement of the products. Preference
mapping (PREFMAP) techniques were used to find out the
potential of the developed products for future use and to
determine the sensory properties driving consumer preferences. PREFMAP techniques have been widely used in different food products (Helgesen et al. 1997; Lawlor and
Delahunty 2000; Guinard et al. 2001; Thompson et al.
2004) to understand sensory attributes that drive consumer
acceptability (Murray and Delahunty 2000; Thompson
et al. 2004; van Kleef et al. 2006; Dooley et al. 2010; Resano et al. 2010). Thus, the objectives of this study were to
describe sensory properties of the fermented pastes, to
determine consumer acceptance of the pastes, and to find
out sensory properties that drive acceptance of the pastes.
Material and Methods
Preparation of pastes of soybeans and
soybean–maize blends
Pastes of soybeans and soybean–maize blends were prepared in the laboratory. Soybeans (Nasoko, variety code
427/6/7) were sorted, washed, and boiled for 30 min and
dehulled by rubbing between palms in cold water, washed
again, and then boiled for 1 h (Dakwa et al. 2005). Maize
(DK8071) was boiled for 2 h (to make it soft) before
being ground together with soybeans into a paste. Grinding was done for 10–15 min in a Waring Commercial
blender (800ES; Waring, Torrington, CT), which was sterilized by boiling for 5 min. Sterile water (100 mL) was
added during the grinding to make the pastes. LAB fermentation was facilitated by the addition of fermented
maize and finger millet (Eleusine coracana) gruel (thobwa). The preparation of thobwa was according to Kitabatake et al. (2003). Pastes for LAB fermentation (LFP)
were backslopped (BS) using 10% (v/w) thobwa. The pH
of the thobwa was around 4.5 with a LAB population of
115
Sensory and Consumer Studies of Fermented Soybean
108 cfu/mL. Naturally fermented pastes (NFP) were made
by similar treatments but without adding the fermented
gruel. Paste composition was determined based on preliminary laboratory trials whereby pastes containing 100%,
75%, and 50% soybeans (the remaining proportions being
maize) were studied. The preliminary study showed no
significant differences in pH reduction and microbial
loads (total aerobic count and LAB count) in pastes containing 75% and 50% soybeans. Thus for the study, pastes
were prepared according to the following compositions:
pastes of soybeans only; pastes of soybean and maize
blends containing 90% and 75% soybeans. NFP were designated as 100S, 90S, and 75S according to 100%, 90%,
and 75% soybean composition in the pastes, the remaining proportions being maize. Similarly, BS LAB-fermented
pastes were designated 100SBS, 90SBS, and 75SBS. Portions of 500 g for all treatments were fermented at 30°C
for 72 h in glass jars.
Analyses of chemical and physical
properties
Titratable acidity (g lactic acid/100 g sample) and pH
were determined according to AOAC (1990). The pH was
measured using a pH meter (WTW pH 525; D. Jurgens
and Co., Bremen, Germany) fitted with a glass electrode
(WTW SenTix 97T). Amino acids were extracted from
freeze-dried homogenized samples and were determined
using High-performance liquid chromatography according
to B€
utikofer and Ard€
o (1999). Salt content was determined using a Sherwood MK II Chloride Analyzer
(Model 926; Sherwood Scientific Ltd., Cambridge, U.K.)
according to the manufacturer’s operating instructions.
Freeze-dried samples (1.00 g) were mixed with 20 mL of
distilled water. The mixtures were heated to 55°C for
30 min and were filtered before chloride analysis. Viscoelastic properties of the samples were analyzed using a
Physica MCR301 rheometer (Paar Physica, Antony Paar,
Germany) fitted with a 50-mm plate/plate geometry,
PP50. The temperature was kept at 20°C by the Peltier
control of the bottom plate. The sample was placed on
the bottom plate and gently compressed. The gap was
~3 mm, and a constant normal force of 5 N was applied
to the sample while testing took place. Amplitude sweeps
were then done in oscillation at a frequency of 1 Hz varying the amplitude from 0.01% to 110% strain.
Descriptive sensory analysis
Panel selection and training
Ten people interested in sensory evaluation of the fermented pastes were recruited among Nutrition and
116
T. A. Ng’ong’ola-Manani et al.
Food Science students in the Department of Home
Economics and Human Nutrition; and staff members at
Lilongwe University of Agriculture and Natural
Resources, Bunda College campus. Panelists with ability
to discriminate five tastes (salty, sweet, sour, umami,
and bitter) in a solution system were selected by conducting five sets of directional paired comparison tests.
Four men and six women in the age range of 20–
32 years were selected as panelists. Consensus training
as explained by Lawless and Heymann (1998) was conducted. Panelists were exposed to soybean-fermented
pastes to be tested in the descriptive analysis sessions.
Through consensus, panelists generated terms (descriptors) and definitions to describe the sensory differences
among the samples. Panelists also decided on words to
anchor the descriptive terms and some reference standards to be used. Trial evaluations were performed to
enable decision on panelists’ reproducibility. Thirty-four
descriptors/attributes describing appearance, aroma/odor,
taste, and texture were generated. The descriptors, their
meanings, and the reference standards used are presented in Table 1. Four training sessions per week were
held for 1.5 months and each session lasted ~1 h
30 min.
Sample preparation and presentation
Maize starch (1%, w/w) was added to the fermented
pastes to prevent crumbling during frying. The pastes
were molded into rounds ca. 5 g each, and were fried in
heated (180–195°C) soybean oil for 3–5 min. Fresh oil
was used for each sample. One hour before sensory evaluation, four pieces of 5 g of each fried sample were transferred to a separate glass serving container before
covering with aluminum foil. Each sample was coded
with a three-digit random number and the samples were
presented in random order to the panelists for evaluation.
The temperature of the samples at the time of evaluation
was room temperature (around 25°C).
Descriptive analysis procedure
Ten panelists were trained to rate attribute intensities of
the six products using a 15-point unstructured line scale
labeled with either “none, weak, or least” as point 1 and
“very strong” as point 15. Each panelist evaluated the
products individually. Products were evaluated in three
sessions and all products were served at each session,
hence the sessions acted as replicates. Tap water was provided to panelists to rinse their palate before and between
tasting. The evaluation was conducted in a well-ventilated
laboratory fitted with fluorescent lights. The temperature
in the evaluation room was between 23°C and 25°C.
ª 2013 The Authors. Food Science & Nutrition published by Wiley Periodicals, Inc.
T. A. Ng’ong’ola-Manani et al.
Sensory and Consumer Studies of Fermented Soybean
Table 1. Descriptors and definitions used to explain sensory characteristics of the fermented pastes.
Descriptors
Abbreviations
Meanings of the descriptors
Appearance
Brown
Brown
Yellow
Yellow
Fried egg-like
EggL
Chitumbuwa-like
ChituL
Mandazi-like
MandL
Intensity of brown color of the fried
pastes
Intensity of the yellow color of the
fried pastes
Appearance associated with fried
egg
Appearance associated with a local
snack, chitumbuwa, made from
deep frying maize flour batter
Appearance associated with local
fritters, mandazi, made from deep
frying wheat flour batter
Aroma/odors
Raw soybean odor
RawS
Characteristic soybean odor strong
in soymilk made from raw
soybeans hydrated in cold water
Aroma associated with roasted
soybean
Odor associated with burnt roasted
soybean
Aroma associated with roasted dried
maize
Odor associated with burnt roasted
dried maize
Odor associated with soaked burnt
roasted dried maize
Aroma associated with a local snack,
chitumbuwa, made from deep
frying maize flour batter
Aroma associated with local fritters,
mandazi, made from deep frying
bread flour batter
Aroma associated with a local snack,
chigumuyoyo, made from baking
maize flour batter
Aroma associated with fried egg
Aroma associated with fermented
cereals
Roasted soybean aroma
RoastS
Burnt roasted soybean
odor
Roasted maize aroma
BRoastS
Burnt roasted maize odor
BRoastM
Soaked burnt roasted
maize odor
Chitumbuwa aroma
SBRoastM
ChituA
Mandazi aroma
MandA
Chigumuyoyo aroma
Chigumu
Fried egg aroma
Fermented aroma
EggA
FermA
Matsukwa odor
Matsukwa
Odor associated with water for
soaking degermed maize
Kondoole aroma
Kondoole
Thobwa aroma
Thobwa
Aroma associated with fermented
cassava, kondoole
Aroma associated with a local
fermented beverage “thobwa”
Aroma associated with fermented
milk, chambiko
Chambiko aroma
RoastM
Chambiko
Fermented beans aroma
FBeans
Mafuta a chiwisi odor
Chiwisi
ª 2013 The Authors. Food Science & Nutrition published by Wiley Periodicals, Inc.
Aroma associated with fermented
kidney beans
Odor associated with partially
heated cooking oil
Reference/standards
used
Color wheel
Color wheel
Fried egg
Chitumbuwa
Mandazi
Raw soymilk
Crushed roasted
soybean
Crushed burnt
roasted soybean
Crushed roasted
maize
Crushed burnt
roasted maize
Soaked burnt roasted
maize
Chitumbuwa
Mandazi
Chigumuyoyo
Fried egg
Sugar solution (20%)
fermented for 24 h
by 1.5 g yeast.
Water from
degermed maize
soaked for 2 days
Fermented cassava
Thobwa
Commercially
available
Chambiko’
Cooked beans
fermented for 24 h
Soybean cooking oil
heated at 100°C
for 2 min
117
Sensory and Consumer Studies of Fermented Soybean
T. A. Ng’ong’ola-Manani et al.
Table 1. Continued.
Descriptors
Rancid odor
Texture
Softness
Meanings of the descriptors
Rancid
Odor associated with rancid oil
Soybean cooking oil
reused more than
three times
Soft
Amount of force necessary to
compress the sample when
pressed between fingers
How easy it was to break the
sample (brittle)
Irregularities on the surface or not a
smooth surface
Size of the grains seen inside the
sample when broken
No standard
Easiness to break
Brittle
Surface roughness
Rough
Graininess
Grainy
Sogginess
Soggy
Tendency of the sample to absorb
oil as observed by pressing the
sample between white paper
Sour
Taste sensation typical of organic
acids
Sweetness
Sweet
Taste sensation typical of sucrose
solution
Saltiness
Salty
Taste sensation typical of sodium
chloride
Bitterness
Bitter
Umami
Umami
Taste sensation typical of caffeine
and quinine
Taste sensation typical of
monosodium glutamate (MSG)
Aftertaste
AfterT
Taste
Sourness
Consumer acceptability test
A total of 150 consumers interested in participating in
the study were recruited from three villages that participated in a nutrition, health, and agriculture project in
Lungwena extension planning area, Mangochi, Malawi.
Products were prepared and presented in the same
way as in the descriptive analysis except that 1% (w/w)
of salt was added prior to frying. Salt was added
based on consumer recommendations during a questionnaire pretesting. Products were presented one at a
118
Reference/standards
used
Abbreviations
Taste lingering on tongue after
sample is removed
Toasted bread,
intensity = 15
Custard pudding = 1
intensity
Maize and soy grains;
whole = 15 and
half = 7 intensity
Comparison of
amount of oil
absorbed on white
paper
Citric acid;
0.05% = 2
intensity,
0.2% = 15
intensity
Sucrose solution;
2% = 2 intensity
and 16% = 15
intensity
Sodium chloride;
0.2% = 2 intensity
and 1.5% = 15
intensity
0.01% quinine sulfate
solution
MSG solution;
0.3% = 3 intensity,
0.7% = 7 intensity
Similar to unripe
banana taste
time in a random order. The samples were coded with
three-digit random numbers and served in a central
location.
Consumers evaluated acceptance on taste, smell, color,
smoothness, and overall acceptance of the six products
using a 7-point facial hedonic scale. On the scale, point 1
referred to dislike extremely and 7 referred to like extremely, 4 was neither like nor dislike and was in the middle. Consumers were instructed on how to use the scale.
Consumers were instructed to sniff and taste a sample.
They were also allowed to re-taste and change their
ª 2013 The Authors. Food Science & Nutrition published by Wiley Periodicals, Inc.
T. A. Ng’ong’ola-Manani et al.
previous scores, if needed. Tap water was provided to
consumers to rinse their palate before and between
tasting.
Sensory and Consumer Studies of Fermented Soybean
IL) while PCA and PLSR were performed in UnscramblerX 10.2 (CAMO Software, AS, Norway).
Results and Discussion
Statistical analysis
During training, panelists’ reproducibility was determined
using analysis of variance (ANOVA) at P = 0.05. Scores
of each panelist were compared with the rest of the panelists for each sample. When significant differences were
found, Duncan’s test was performed to identify panelists
that differed and the specific descriptors they scored differently. Panelists who were not reproducible were
assisted to improve performance. Panel consensus was
checked using profile plots generated from PanelCheck.
At the end of the descriptive analysis, PanelCheck was
used to assess panelists’ consensus and discrimination
ability of the attributes (Tomic et al. 2010). Mean intensity scores of the descriptors were compared using threeway ANOVA and least square difference test (P = 0.05) as
post hoc, with panelists, replicates, and products as factors. Correlations between sensory attributes were also
obtained.
To understand sensory attributes that characterized the
products, principal component analysis (PCA) was performed. In order to identify attributes driving consumer
liking, external PREFMAP was obtained by performing a
partial least squares regression (PLSR) analysis. Mean
intensity scores of attributes that were significantly different (P < 0.05) on product effect and mean values of
chemical and physical properties were used in PCA and
PLSR. Data in PCA and PLSR were centered, full crossvalidated, and standardized. Sensory data and data on
chemical and physical properties of the pastes were used
as explanatory variables (X matrix) while means of overall consumer acceptance data were used as response variables (Y matrix) (Helgesen et al. 1997; Resano et al.
2010).
To identify consumer subgroups sharing common
preference patterns, hierarchical cluster analysis using
complete linkage and squared Euclidian distance was
performed on consumer overall acceptance data. Means
of overall acceptance obtained for each cluster and data
on sensory, chemical, and physical properties of the
pastes were used to obtain a PREFMAP of the clusters.
The sensory, chemical, and physical properties data
provided the X matrix while means of overall acceptance of clusters provided the Y matrix. Demographic
information of the subgroups obtained through crosstabulations provided an understanding of cluster
compositions.
ANOVA, cluster analysis, cross-tabulations, and correlations were performed in SPSS 15.0 (SPSS Inc., Chicago,
ª 2013 The Authors. Food Science & Nutrition published by Wiley Periodicals, Inc.
Chemical and physical properties of the
pastes
There were significant differences (P < 0.05) in pH of the
samples between the NFP and the LFP. LAB-fermented
pastes had lower pH values ranging from 3.91 to 4.26
compared to NFP that had pH values ranging from 5.36
to 5.81 (Table 2). There was an agreement between lactic
acid content, presented as titratable acidity, and pH levels
in the pastes and the sensory perception of sourness. Lactic acid contents were higher in LFP than in NFP and so
were the perceived sourness intensities. On the contrary,
the amino acid contents did not agree with umami, bitterness, and sweetness taste perceptions. Amino acids in
their free state (as L, D, and DL) contribute to bitter,
sweet, and umami tastes in most foods. In this study,
amino acids responsible for bitterness and umami were
generally high in NFP while those responsible for sweetness were high in LFP (Table 2). However, perceived
intensities of these tastes by descriptive sensory panel
(Table 3) differed from the expectation from the chemical
analyses. Panelists rated LFP high in bitterness and umami while NFP were rated high in sweetness. Descriptive
sensory perception of bitterness was high in LFP probably
because of interactions of the bitter compounds and the
other tastants in the fermented pastes. According to
Mukai et al. (2007), mixtures of bitter and sweet tastes
resulted in variable effects at low intensity/concentration,
while mixtures at moderate and high intensity/concentrations were mutually suppressive. In LFP, mixtures of
sweet and bitter tastes were at low concentrations resulting in enhancement of bitter taste. While in NFP, the
concentrations of sweet tastes were moderate and the
overall concentrations of bitter tastes were high, resulting
in suppression of bitterness. Furthermore, bitterness in
LFP could have been enhanced due to interactions
between sour and bitter compounds at low concentrations
(Mukai et al. 2007). On the other hand, bitterness in
NFP could have been reduced by aspartic and glutamic
acids. Although there were no significant differences in
aspartic acid contents among all samples, 90S had the
highest content. Furthermore, glutamic acid content was
highest in 100S and the content was significantly different
between 100S and the rest of the pastes except 90S
(Table 2). Thus overall, the amino acids imparting umami flavor were higher in NFP. Aspartic and glutamic
acids were reported to be effective in reducing bitterness
of solutions comprising bitter amino acids in low
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Sensory and Consumer Studies of Fermented Soybean
T. A. Ng’ong’ola-Manani et al.
Table 2. Physical and chemical analyses of the fermented pastes.
Parameter1
Taste
100S
pH
Titratable acidity (TA)
Histidine (His)
Arginine (Arg)
Tyrosine (Tyr)
Valine (Val)
Methionine (Met)
Isoleucine (Iso)
Phenylalanine (Phe)
Leucine (Leu)
Aspartate (Asp)
Glutamate (Glu)
Serine (Ser)
Glycine (Gly)
Alanine (Ala)
Lysine (Lys)
Salinity
Sourness
Bitterness
Bitterness
Bitterness
Bitterness
Bitterness
Bitterness
Bitterness
Bitterness
Umami
Umami
Sweetness
Sweetness
Sweetness
Sweetness
Saltiness
5.81
0.58
0.38
0.06ab
0.07
1.00
0.03
0.55
2.19
1.66
0.79
4.84
0.63
0.47
3.63
0.95
240
100SBS
0.59a
0.31a
ab
0.05
0.31a
0.02a
0.16ac
0.81ab
0.91a
0.40a
0.39a
0.06a
0.08ac
0.38a
0.06abc
32.66a
4.26
0.56
n.d
0.07
0.06
0.53
0.04
0.13
0.96
0.38
0.78
2.55
0.18
1.07
3.84
1.49
262.5
90S
0.28c
0.13a
0.01ab
0.02ab
0.21ab
0.02a
0.06a
0.71ab
0.20b
0.10a
0.31b
0.04b
0.38b
1.25a
0.63a
23.63a
5.36
0.37
0.24
0.07
0.18
0.89
0.05a
0.65
2.59
1.61
1.23
3.71
0.29
0.57
2.63
0.92
228.75
90SBS
0.14b
0.08b
0.06ab
0.19a
0.95a
0.72c
2.85b
1.76a
0.86a
2.16ab
0.25b
0.25ac
1.90ab
0.53bc
49.39a
4.01
0.68
n.d
0.05
0.04
0.26
0.02a
0.04
0.42
0.22
0.90
3.07
0.19
1.06
3.27
1.47
241.25
75S
0.31c
0.16ac
0.01ab
0.01b
0.14b
0.03b
0.40a
0.12c
0.03a
0.26b
0.01b
0.05b
0.54a
0.21ab
33.26a
5.41
0.50
0.07
0.04
0.08
0.50
n.d
0.32
1.11
0.67
0.78
2.38
0.3
0.29
1.43
0.74
245
75SBS
0.18b
0.18a
0.05
0.02a
0.06ab
0.35ab
0.21ac
0.77ab
0.58ab
0.31a
0.59b
0.14b
0.13c
0.34b
0.24c
19.15a
3.91
0.85
n.d
0.10
0.04
0.18
0.01a
0.1
0.28
0.17
0.72
3.14
0.18
0.73
2.54
0.78
272.5
0.29c
0.24c
0.03b
0.02b
0.10b
0.07a
0.27a
0.10c
0.12a
1.06b
0.01b
0.01a
0.66a
0.19c
22.55a
Means not sharing a superscript within a row are significantly different (P < 0.05). Samples coded 100S, 90S, and 75S represent naturally fermented pastes, while samples coded 100SBS, 90SBS, and 75SBS represent lactic acid-fermented pastes. Pastes are designated according to
100%, 90%, and 75% soybean composition, the remaining proportions being maize.
1
Units of measurement: titratable acidity (g lactic acid/100 g sample), amino acids (lmol/g), salinity (mg/L).
concentrations (Lindqvist 2010). Apart from amino acids,
bitterness in soybeans is also influenced by bitter isoflavone glucosides, which are hydrolyzed during fermentation
to bitter isoflavone aglycones (Drewnowski and GomezCarneros 2000). Salt content ranged from 228 to 272 mg/
L (0.037–0.046%) and was low compared to other fermented soybean pastes, which can contain up to 14% salt
(Kim et al. 2010). Salt was mainly due to chlorides naturally present in plants. Although saltiness was rated high
in LFP, there were no significant differences (P > 0.05) in
salinity among the samples. This study agrees with the
suggestion that the interaction between tastes is not a
fixed action depending on the intensity/concentration of
each taste, but rather an enhancing or inhibitory effect,
changing with the combined pattern of intensity and concentration (Mukai et al. 2007).
All the samples behaved as viscoelastic solids. Tests in
normal rotation were not done as the samples slipped on
the rheometer surfaces before yield occurred. The reason
for the slimy sample surface was probably due to the
presence of exopolysaccharides produced by some LAB.
There were no significant differences in relative stiffness
between NFP and LFP.
Descriptive sensory analysis
Thirty-four descriptors/attributes describing appearance,
aroma/odor, taste, and texture were generated to characterize the sensory properties of the fermented pastes
120
(Table 1). There was high agreement among panelists in
rating the intensities of the attributes as observed from
the profile plots (data not shown) as most assessor lines
followed the consensus lines closely (Tomic et al. 2010).
Out of the 34 attributes, 27 were significantly different
(P < 0.05) on product effect. The attributes not significantly different were roasted maize, kondoole, chambiko,
and fermented beans aromas, mafuta a chiwisi odor, and
readiness to be broken (Table 1 presents meanings of
descriptors). Only attributes that were significantly different on product effect were used in further analyses.
Differences among samples in the following attributes:
burnt roasted soybean, chitumbuwa and mandazi aromas,
rancid odor, brown and yellow colors, chitumbuwa-like,
mandazi-like, and fried egg-like appearances, umami, and
sourness tastes and soggy texture were clearly discriminated by panelists as observed from the high F ratios
(Table 3). Overall, the panel’s ability to discriminate
between samples was good, although Tucker plots (data
not shown) showed that some assessors had low discrimination ability in a few attributes, namely graininess,
roasted soybean, soaked roasted maize and thobwa aromas. These attributes had relatively low F ratios as well
(Table 3).
Significant correlations were observed among sensory
descriptors. Attributes strong in intensities in NFP had
significant (P < 0.001) positive correlations with each
other and this trend were similar in LFP (Table 4).
Conversely, attributes strong in intensities in NFP
ª 2013 The Authors. Food Science & Nutrition published by Wiley Periodicals, Inc.
T. A. Ng’ong’ola-Manani et al.
Sensory and Consumer Studies of Fermented Soybean
Table 3. Mean intensity scores, F ratios and P-values of descriptors/attributes based on product effect.
Attribute
Raw
soybean odor
Roasted
soybean aroma
Burnt roasted
soybean odor
Roasted
maize aroma
Burnt roasted
maize odor
Soaked burnt
roasted maize
odor
Chigumuyoyo
aroma
Chitumbuwa
aroma
Mandazi
aroma
Fermented aroma
Matsukwa odor
Kondoole aroma
Thobwa aroma
Chambiko aroma
Fermented beans
aroma
Fried egg aroma
Mafuta a
chiwisi odor
Rancid odor
Brown
Yellow
Chitumbuwa-like
Mandazi-like
Fried egg-like
Sweetness
Saltiness
Umami
Sourness
Bitterness
Aftertaste
Surface
roughness
Softness
Easiness to
break
Graininess
Sogginess
100S
100SBS
90S
7.17 3.52a
4.37 1.65bc
5.07 2.35ab
3.43 1.65
4.21 1.65a
5.1 1.90b
4.67 2.31ab
4.53 2.85ab
2.55 1.15a
4.9 2.23b
3.67 2.22c
4.93 1.99b
3 1.51ac
3.2 1.63a
4.6 1.96b
4.21 2.04ab
3.33 1.45a
4.33 3.03b
2.7 1.68a
4.57 2.37b
3.43 2.25ac
4.03 1.87bc
3.07 1.99ab
3.53 2.92a
3.55 2.72a
2.13 1.36a
4.17 2.33b
1.9 1.03a
4.87 2.74b
3.4 1.48ac
3.57 2.03ab
6.93
3.2
3.8
4.10
2.73
2.57
3.66a
1.92a
2.66a
2.55a
1.57a
1.55ab
3.43 1.91a
2.57 2.27a
9.07
2.83
10.07
3.37
2.67
7.73
2.07
1.93
3.5
3
1.8
3.13
5.2
4.02a
2.10a
2.82a
2.95a
2.16ac
2.74a
1.36ac
0.91acd
1.72a
1.49a
1.49ad
2.16ac
2.55a
4.07
3.97
3.43
3.71
2.97
2.73
2.08b
1.94a
1.89ab
2.53ab
1.87a
2.02b
3.2 1.83a
2.5 2.10a
4.87
7.2
5.5
6.43
5.23
4.37
1.67
2.53
5.23
7.08
2.48
4.27
6.07
2.36bcd
3.03b
2.95b
2.25b
2.43b
2.55b
0.71b
1.91ab
2.58b
3.05b
2.38ab
2.42ab
2.83a
90SBS
75S
F ratio
P-value
6.00 2.84ab
2.80 1.73d
7.51
<0.000
4.4 2.90
4.40 2.55a
2.67
0.03
5.10 2.34b
10.15
<0.000
3.87 1.78ab
2.12
0.07
3.4 2.65ac
4.43 2.16b
3.80
0.00
3.13 2.33ac
2.37 1.47bc
4.00 3.04a
2.41
0.04
3.33 1.99c
4.47 2.42b
2.83 1.84ac
5.67 2.42d
8.62
<0.000
3.53 2.37c
9.07 2.75d
2.83 1.86ac
9.44 3.19e
48.82
<0.000
3 1.58a
4.55 2.38b
3.9 2.07bc
6.73 3.05d
12.54
<0.000
5.37
0.44
1.26
2.55
0.37
1.18
0.00
0.83
0.29
0.03
0.87
0.33
4.12
0.10
0.00
0.99
4.2
3.37
2.87
2.71
2.7
2.27
2.12b
1.94a
1.63bc
1.65c
1.91a
1.51a
3.13 1.53a
2.5 1.94a
5.07
3.07
9.8
3.7
3.47
7.5
1.83
1.57
3.5
5.47
1.6
2.6
5.7
2.42c
2.09a
2.59a
2.55a
2.36c
2.70a
0.83bc
0.77c
1.81a
2.85c
1.16ac
1.59c
2.44a
5.63
3.4
2.8
3.33
2.73
2.6
cd
75SBS
2.76c
2.21a
1.81c
2.18ac
2.24a
2.04ab
2.5 1.59b
2.43 1.92a
3.4
11.03
2.5
8.35
6.97
1.69
1.4
2.63
6.07
10.07
2.9
4.6
7.5
2.16d
2.40c
1.31c
2.98c
3.30bd
0.81c
0.50b
2.55a
2.86b
3.29d
2.86b
2.96ab
3.15b
4.87
3.13
2.9
2.91
2.63
1.8
3.09bc
2.01a
2.01ac
1.81bc
1.94a
1.03a
3.67 2.43a
2.33 2.26a
5.8
2.8
10.6
2.7
2.57
7.73
2.63
1.83
3.47
4.4
1.47
2.53
7.73
2.46c
1.86a
2.40d
1.56d
1.72a
2.84a
1.97a
0.95 cd
1.80a
2.28c
0.78 cd
1.80c
2.52b
4.53
3.20
2.66
3.35
2.77
2.3
2.37bc
2.37a
1.80bc
2.35bc
2.15a
1.78ab
2.2 1.38b
2.67 2.37a
3.57
12.97
1.33
8
7.63
1.3
1.7
2.7
7
10.9
3.0
5.1
8.4
2.22bd
1.40d
0.55c
3.62c
2.79d
0.60c
0.65b
1.97ad
3.09c
3.24d
3.49b
2.68b
2.94b
13.37
101.65
74.90
23.78
19.36
42.25
4.77
3.39
17.29
32.17
3.11
5.09
6.01
<0.000
<0.000
<0.000
<0.000
<0.000
<0.000
0.001
0.007
<0.000
<0.000
0.01
0.000
<0.000
7.63 3.46a
6.47 2.97a
6.6 3.29ab
6.97 2.91a
5.93 3.26a
6.83 2.65a
5.03 3.40c
7.5 4.02a
5.17 2.89bc
6.37 3.05a
4.03 2.76c
6.77 3.38a
7.08
0.58
<0.0001
0.72
3.9 1.90a
8.5 2.55a
4.35 2.35a
7.11 3.05a
4.5 2.42a
6.31 2.52b
4.53 2.30a
8.6 2.81a
6.17 2.96b
5.31 2.42b
4.97 3.09a
11.12 2.85c
2.89
20.79
0.02
<0.000
Intensity based on a scale of 1–15 (1 = none or least or very weak, 15 = very strong intensity). Means not sharing a superscript within a row are
significantly different (P < 0.05). Samples coded 100S, 90S, and 75S represent naturally fermented pastes, while samples coded 100SBS, 90SBS,
and 75SBS represent lactic acid-fermented pastes. Pastes are designated according to 100%, 90%, and 75% soybean composition, the remaining
proportions being maize. Full names of terms and their meanings are given in Table 1.
negatively correlated with those strong in intensities in
LFP. Strong correlations were observed amongst appearance attributes (r = 0.439 to 0.844). Brown color
ª 2013 The Authors. Food Science & Nutrition published by Wiley Periodicals, Inc.
strongly positively correlated with chitumbuwa-like and
mandazi-like appearances and also negatively correlated with yellow color and fried egg-like appearance.
121
RawS
BRoastS
BRoastM
ChituL
Thobwa
Grainy
Soft
0.468
0.470
0.356
0.344
0.334
0.280
0.366
Chigumu
0.477
0.391
0.496
0.410
0.290
0.303
0.358
0.394
0.271
0.299
0.527
ChituA
0.665
0.670
0.503
0.526
0.612
0.409
0.719
0.347
0.353
0.231
0.412
0.372
RoastS
0.476
0.346
0.280
0.357
0.270
Rough
0.228
0.437
0.367
0.256
0.375
0.363
0.271
0.292
Brown
1
0.844
0.736
0.733
0.717
0.496
0.577
0.446
0.362
Yellow
1
0.617
0.563
0.757
0.441
0.643
0.351
0.383
ChituL
1
0.672
0.444
0.555
0.355
0.405
0.226
MandL
1
0.439
0.497
0.411
0.376
0.292
EggL
Umami
Thobwa
0.371
0.327
1
0.374
0.603
0.247
0.360
1
0.365
0.361
0.251
0.369
0.404
0.224
0.283
0.221
0.269
0.381
0.291
0.509
0.462
0.350
0.339
0.448
0.315
0.268
0.219
0.326
Rancid
0.491
0.297
0.277
0.296
0.248
0.362
MandA
0.287
0.261
0.274
0.259
0.224
0.336
0.262
0.267
0.283
0.262
0.238
0.256
0.252
0.298
0.261
0.294
0.296
0.284
0.237
0.268
0.360
0.573
SBRoastM
Salty
Grainy
BRoastM
0.335
0.244
0.295
Sweet
Soggy
0.280
0.263
0.266
0.381
Soft
Soggy
Sweet
Rough
Sour
0.261
0.472
0.277
0.235
0.415
EggL
MandA
Grainy
SBRoastM
AfetrT
Sweet
EggA
0.327
0.266
0.282
0.251
0.282
0.270
AfterT
Rough
SBRoastM
Salty
0.292
0.353
0.335
0.393
0.230
Grainy
0.258
0.245
0.219
Bitter
0.375
SBRoastM
0.229
0.259
0.238
1
Only attributes showing significant correlations at P = 0.001 are presented. Full names of terms and their meanings are given in Table 1.
0.553
0.337
RawS
Rancid
FermA
0.347
0.574
T. A. Ng’ong’ola-Manani et al.
ª 2013 The Authors. Food Science & Nutrition published by Wiley Periodicals, Inc.
Brown
Yellow
ChituL
MandL
EggL
Umami
Sour
AfterT
Soggy
MandA
Rancid
Sweet
Bitter
Rough
Soft
Salty
Grainy
ChituA
SBRoastM
BRoastM
BRoastdS
Sensory and Consumer Studies of Fermented Soybean
122
Table 4. Pearson correlations between descriptors/attributes characterizing the fermented pastes.
T. A. Ng’ong’ola-Manani et al.
Sensory and Consumer Studies of Fermented Soybean
fermentation by natural microflora over a long period
(Kim et al. 2010). Significant positive correlations were
also observed between textural properties, including
roughness and graininess, which were attributes influenced by composition.
Appearance attributes also strongly correlated with aroma
attributes and some tastes. For instance, brown color,
chitumbuwa-like, and mandazi-like appearances showed
significant (P < 0.001) positive correlations with chitumbuwa aroma, umami, bitterness, aftertaste, and sourness. Mandazi aroma positively correlated with thobwa
aroma, fried egg aroma, umami, and aftertaste. Egg-like
appearance positively correlated with sweetness. The
intensities of attributes with significant positive correlations with brown color were high in LFP, while the intensities of attributes with significant positive correlations
with yellow color were high in NFP. Therefore, the type
of fermentation greatly influenced the appearance of the
fermented pastes. Among aromas that strongly correlated
with each other were fermented aroma and rancidity. Fermented aroma intensity and rancidity were highest in
100S; in addition, rancidity was high in all NFP (Table 3).
High fermented aroma intensity in 100S could be due to
uneven fermentation in NFP due to spontaneous
(a)
4
75S
Sensory properties of the fermented pastes
Sensory properties characterizing the products are shown
in PCA map in Figure 1. The first two principal components (PC1 and PC2) explained 74% of the variation.
This highly explained variance in PC1 and PC2 shows
that there was high systematic variation within the data,
indicating that the panel discriminated well between the
products. The score plot (Fig. 1A) shows product distribution in multivariate space and PC1 explains differences
in the products according to type of fermentation, distinguishing NFP on the left from LFP on the right. Attributes responsible for this categorization were appearance,
90S
3
PC-2 (20%)
2
1
90SBS
75SBS
0
–1
–2
–3 100S
–4
–6
(b)
100SBS
–5
–4
–3
–2
–1
1
0
PC-1 (54%)
2
3
4
5
6
7
1
0.8
Grainy
0.6
Sweet
PC-2 (20%)
0.4
TA
Yellow
EggL
pH
EggA
RawS
Rancid
0.2
0
–0.2
–0.4
Lys
RoastS
FermA
Soft Ser
HisLeuIso
Val
–0.6
–0.8
Rough
Glu
Phe
Tyr
Ala
Gly
ChituA
Chigumu
MandA Sour
BRoastM
BRoastS
Brown
SRoastM ChituL MandL
ArgSalty Umami
Bitter
Soggy
AfterT
Thobwa
–1
–1
–0.8
–0.6
–0.4
–0.2
0
0.2
PC-1 (54%)
0.4
0.6
0.8
1
Figure 1. Principal component analysis of fermented pastes and sensory attributes. (A) Score plot showing relatedness of samples in terms of
sensory, chemical, and physical properties of the pastes. (B) Correlations loading plot showing sensory properties of the pastes. On the map,
100S, 90S, and 75S represent naturally fermented pastes (NFP) while 100SBS, 90SBS, and 75SBS represent lactic acid-fermented pastes (LFP).
Pastes are designated according to 100%, 90%, and 75% soybean composition, the remaining proportions being maize.
ª 2013 The Authors. Food Science & Nutrition published by Wiley Periodicals, Inc.
123
Sensory and Consumer Studies of Fermented Soybean
some odors/aromas, taste, and pH. The mean intensities
of yellow color, fried egg-like appearance, raw soybean
odor, fried egg aroma, and pH were high in NFP. These
attributes also loaded highly on the negative side of PC1
(Fig. 1B) and were sensory properties characterizing NFP.
On the positive side of PC1, brown color, chitumbuwaand mandazi-like appearances, burnt roasted soybean
odor, chigumuyoyo and chitumbuwa aromas, umami,
bitterness, aftertaste, and sourness loaded highly (Fig. 1B).
These attributes had high intensities in LFP, hence
characterized LFP. Most of the amino acids responsible
for bitterness (histidine, arginine, tyrosine, valine, isoleucine, phenylalanine, leucine) and glutamate responsible
for umami loaded highly on the negative side of PC1.
Due to the comparatively higher content of bitter amino
acids, it would be expected that NFP would have higher
bitterness intensity compared to LFP. On the contrary,
LFP were perceived to be more bitter than NFP, probably
because of taste interactions in which glutamate could
have suppressed bitterness in NFP and sourness could
have enhanced bitterness in LFP.
The proximity of 90S and 75S; and 90SBS and 75SBS
on the PCA map (Fig. 1A) indicates close similarity in
terms of sensory properties, unlike 100S and 100SBS,
which are clearly separated from the other NFP and LFP,
respectively. This delineation is along PC2 on which
graininess and sweetness loaded highly on the positive
dimension, while thobwa aroma, fermented aroma, and
softness loaded highly on the negative dimension
(Fig. 1B). The intensities of fermented aroma and softness
were high in 100S, while the intensities of sweetness and
graininess were high in 90S and 75S.
Yellow color of NFP originated from the color of soybeans, while brown color in LFP could be due to caramelization and Maillard reactions. Color of fermented
soybean pastes like doenjang/miso is due to the raw materials used, amino carbonyl reaction of Maillard browning,
oxidative browning, enzymatic browning, and browning
enhancers (Chung and Chung 2007). In this study, 100S,
90S, and 75S underwent natural fermentation, while
100SBS, 90SBS, and 75SBS were BS with a LAB-fermented
product; hence, type of fermentation had a major influence on color, giving the strong browning intensity in
LFP. LAB fermentations increase the amount of reducing
sugars in products (Sripriya et al. 1997) and the sugars
could be responsible for the browning intensity due to
caramelization and participation in Maillard reactions
with amino carbonyls during frying. As increasing pH
values enhance both caremelization and Maillard
reactions (Ajandouz and Puigserver 1999; Ajandouz et al.
2001), it would be expected that NFP would have
stronger browning intensities than LFP. However, all the
samples had pH values below 6.0, thus were slightly acidic
124
T. A. Ng’ong’ola-Manani et al.
and offered some stability of the amino acids that were
heated in the presence of reducing sugars (Ajandouz and
Puigserver 1999). The difference in browning intensity
was probably due to the difference in the amount of
reducing sugars, which were more in LFP than in NFP
(data not shown).
Tastes of the pastes were significantly different
(P < 0.05). NFP had low sourness intensity and their pH
values were only slightly reduced from the initial.
However, sweetness intensities were higher in NFP and
particularly in 75S, probably because of its high maize content; hence high content of sugars resulted in higher sweet
intensity. On the other hand, LFP were positively associated with sourness, umami, bitterness, saltiness, and aftertaste. The intensities of these tastes were highest in 75SBS.
Chung and Chung (2007) found that fermented soybean
products with high saltiness also had high umami (monosodium glutamate, MSG) and sour tastes. Although salt
was not added to all the samples, its perception could be
due to the presence of NaCl and KCl, which were attributed to saltiness perception in Korean-fermented soybean
pastes, doenjang (Kim and Lee 2003). Besides, salt content
alone does not sufficiently predict perceived saltiness
intensity as synergistic interactions of salt and other flavor
compounds also affect saltiness perception (Kim et al.
2010). Sourness in fermented products is due to organic
acids, which increase during LAB fermentations. Because
75SBS had the highest maize content, it provided more fermentable sugars as substrate for organic acid production
by LAB. In soybean-fermented pastes, malic, citric, succinic, and lactic acids are responsible for the sour taste (Kim
et al. 2010). In this study, sour taste could have been due
to succinic, lactic, and acetic acids, which were detected
(data not shown). Umami taste is related to glutamic and
aspartic acids (Kim and Lee 2003), which are present in
soybeans and tend to increase with fermentation (Dajanta
et al. 2011). Another study on similar products (Kim et al.
2010) reported high bitterness intensities, which were
attributed to bitter amino acids produced during fermentation. Amino acids responsible for bitter taste include leucine and isoleucine (Namgung et al. 2010). Salts, sugars,
organic acids, umami compounds, amino acids, Maillard
peptides, types of base ingredients, microorganisms, and
various aroma compounds contribute to flavors of fermented soybean products (Chung and Chung 2007).
A range of aromas and odors were described. NFP had
high intensities of raw soybean odor, rancid odor,
fermented aroma, and fried egg aroma. Raw soybean and
rancid odors are among the flavors that reduce consumer
acceptance of soy products (Torres-Penaranda et al.
1998). The two odors were highest in 100S. On the other
hand, LFP were characterized by aromas associated
with roasted soybeans and maize. In this case, LAB
ª 2013 The Authors. Food Science & Nutrition published by Wiley Periodicals, Inc.
T. A. Ng’ong’ola-Manani et al.
Sensory and Consumer Studies of Fermented Soybean
fermentation was able to mask the characteristic beany
and rancid odors of soybeans that are due to oxidation of
polyunsaturated lipids catalyzed by lipoxygenase (Ediriweera et al. 1987). Rancid odor is associated with volatile
compounds such as 3-methylbutanoic acid, 2-methylpropanoic acid, and butanoic acid, a major compound in
different fermented soybean foods (Jo et al. 2011).
Textural differences were also described. 100S was rated
softer than the rest of the samples while graininess and
roughness intensities were high in products containing
maize, particularly 75S, 75SBS, and 90SBS. Differences in
composition of the products accounted for the differences
in textural properties, resulting in rough appearance and
large particle sizes in the products containing maize.
Additionally, LFP absorbed more oil during frying than
NFP; this tendency could have been due to their slightly
higher moisture content (data not shown), which led to
more oil uptake as the water evaporated during frying
(Krokida et al. 2000).
Consumer acceptance
A total of 150 consumers participated in the consumer
acceptance study but demographic information was collected on 148. A consumer was defined as a person who
occasionally consumed soybeans and soybean-based products. At the time of the study, 32.4% of the participants
had consumed soybean-based products within the past
2 months from the date of data collection. Soybeans were
mostly consumed in porridge (69%), although some of
the consumers used texturized soy products locally known
as soya pieces as relish (side dish), roasted beans as snack,
soy flour as a condiment in vegetables and other foods, in
addition to using soybeans in porridge (Table 5). Soybean
flour is used together with maize flour in a weaning food
prepared as porridge and locally known as Likuni Phala.
Most consumers (88%) were aware that soybeans are
nutritious as they associated the promotion of its use in
growth-monitoring centers and in nutrition rehabilitation
programs for under-5 children.
Table 5. Ways
consumers.
of
household
soybean
consumption
by
the
Ways of consumption
Consumers (%)
n = 129
Porridge only
Porridge and soya pieces
Soya pieces only
Porridge and roasted soybeans as snack
Porridge and soy flour vegetable condiment
Porridge, roasted soybeans, and soya pieces
Used in maize flour-based snacks
89
8
11
7
8
4
2
(69)
(6.2)
(8.5)
(5.4)
(6.2)
(3.1)
(1.6)
ª 2013 The Authors. Food Science & Nutrition published by Wiley Periodicals, Inc.
External PREFMAP
To understand the attributes driving consumer liking, sensory, chemical, and physical data were regressed with consumer acceptance data using PLSR. The sensory, chemical,
and physical data were used as predictor variables, while
overall consumer acceptance data were used as response
variables. In Figure 2, PC1 and PC2 together explain 73%
of the variation in the pastes in terms of their properties
and 47% of the variation in consumer preference for the
pastes. The location of the samples on the map is based
mainly on sensory attributes and the preference pattern
shows that consumers also used the same underlying
sensory properties to make their acceptability. The high
density of consumers in the two left quadrants (Fig. 2B)
indicates that the direction of preference was toward NFP.
These samples were characterized by strong yellow color,
higher pH, fried egg-like appearance, and aroma, sweetness,
softness, rancid odor, and raw soybean odor. It appears that
the positive impact of higher pH (low sourness intensity),
sweetness, and fried egg aroma exceeded the negative
impact of rancid and raw soybean odors. These two odors
have been documented as deterring consumer acceptance
of soybeans (Gupta 1997; Torres-Penaranda et al. 1998).
Therefore, higher pH (low sourness intensity), fried egg
aroma, and sweet taste seem to be the drivers of liking of
the fermented soybean pastes, especially for NFP for most
consumers. Nevertheless, other consumers preferred LABfermented pastes, which had strong brown color, sourness,
bitterness, saltiness, umami, burnt roasted soybeans, and
maize aromas. These attributes seem to be drivers of liking
of 90SBS and 75SBS and as they load directly opposite drivers of liking of NFP, they can be considered as drivers of
disliking for consumers preferring 75S, 90S, and 100S.
Taste and pleasure are among the most important predictors of food choice (Brunsø et al. 2002). Bitterness and
strong sourness could have been the key attributes leading
to little acceptance of LFP. Bitter taste is a major problem
in the food and pharmaceutical industries due to its negative hedonic impact on ingestion (Drewnowski and
Gomez-Carneros 2000; Ley 2008). In most cases, the bitter taste is not desirable and has to be eliminated from or
masked in the product to increase a product’s acceptance.
Umami is the savory delicious taste in meat, poultry, sea
foods, and fermented beans (Yamaguchi and Ninomiya
2000). Although umami is among the drivers of dislike in
this study, it could not have been the reason for dislike
of LFP. Its inclusion among drivers of disliking in this
study is because of its significant (P < 0.001) correlation
with sourness and aftertaste (r = 0.365 and 0.361, respectively) intensities. Consumption of foods that are strong
in sourness is typically avoided (Breslin and Spector
2008).
125
Sensory and Consumer Studies of Fermented Soybean
(a)
T. A. Ng’ong’ola-Manani et al.
5
100SBS
Factor-2 (19%, 20%)
4
3
2
100S
1
75SBS
0
90SBS
–1
–2
75S
–3
–6
(b)
–5
–4
90S
–3
–2
–1
0
1
2
Factor-1 (54%, 27%)
3
4
5
6
7
1
LeuIso
Tyr
Val
Thobwa
His
C140
Phe C75
C129 C110
C31 Glu
C93 C120
C59
RoastS
0.6
C81
Soft C36 C133
C116
C115
C12
C131
C18 C76
Salty
C11C122
C10
C22
AfterT
C126
C7 Ser
C143
SRoastMBRoastM Bitter
0.4 C117 C134 C106
C150
C49
C105
C125
C87
C14
C45
C78
C55
C21 Ala
C50C70
C72
Arg
ChituL
C25
C65 C119
Rancid
C109 C100
C91
C147
C84
C73
C15 BRoastS Umami
0.2EggA C146
C82
C121
C51C127
C53
C47
Soggy
C138 FermA
Brown MandL
C28
C102 C3 C137
C29 C6
Chigumu
C66
C41
RawS
C32 C46 C57
0
C141
C48
Sour
C108
C64C23
C27
Lys
C68
C54 C85
Yellow
C74 C4 C8 MandA
C130
C148
C142 C9
C94
ChituA
C13
C61
C5
C99
C38
C111
–0.2
SweetC2
EggL C144
C43
C1 Gly C71
C39 C149 C124
pHC103
C35
C132 C80 C69C60
C63
C97
C16C20
C58
C79
C26C30 Grainy
–0.4
C136 C44 C67
C86
Rough
C62
C40
C135
–0.6
TA
C77C139
C42
C145
C96
C95
C37
C104
C128
C101
C92
C17
C52
C33C34
C24
C89
–0.8
C107
C123
Factor-2 (19%, 20%)
0.8
–1
–1
–0.8
–0.6
–0.4
–0.2
0
0.2
Factor-1 (54%, 27%)
Sensory, chemical and physical properties of
fermented pastes
0.4
0.6
0.8
1
Consumer distribution in multivariate
space (C1 - C150)
Figure 2. External preference mapping showing sensory attributes driving consumer preference of the pastes. (A) Grouping of pastes according
to sensory, chemical, and physical properties and consumer preference. (B) Consumer preference pattern as influenced by sensory, chemical, and
physical properties. On the map, 100S, 90S, and 75S represent naturally fermented pastes, while 100SBS, 90SBS, and 75SBS represent lactic acidfermented pastes. Pastes are designated according to 100%, 90%, and 75% soybean composition, the remaining proportions being maize.
In this study, mixed strains of LAB from thobwa were
used in the fermentation of LFP. To improve acceptance
of LAB-fermented soybeans, selection of strains that
results in desirable sensory properties would be recommended. This strain selection can be achieved through
identification and characterization of LAB involved in
soybean fermentation.
Consumer preferences according to clusters
A visual inspection of the PREFMAP (Fig. 2) reveals
heterogeneity in consumers’ acceptability, although more
consumers liked the NFP. Figure 2A shows four clusters
as follows: 100S; 90S and 75S; 75SBS and 90SBS; and
100SBS. These clusters are mainly based on sensory properties as the PREFMAP is based on the PCA representation of sensory attributes (Resano et al. 2010). To
126
understand this heterogeneity in consumer preference
pattern more, a cluster analysis using a 6 9 150 matrix of
pastes and overall consumer acceptance scores was performed. Cluster analysis assigned consumers with similar
preference patterns to one group resulting in four clusters
as well. A PCA of mean overall acceptance of the clusters
and the pastes was then obtained (Fig. 3). The clustering
pattern was slightly different from the pattern in Figure 2.
Clusters 1 and 3 were composed of consumers who liked
100S and 90S, cluster 2 was composed of consumers who
preferred LFP with a bias of 100SBS and 75SBS, while
cluster 4 was composed of consumers that liked 75S. As
seen in Figure 2, the direction of preference is biased
toward NFP. The composition of consumers in each cluster is shown in Table 6. Consumers in cluster 2 disliked
NFP and preferred LFP, particularly 100SBS. Consumers
in cluster 3 liked 90S and 100S and disliked all the sour
ª 2013 The Authors. Food Science & Nutrition published by Wiley Periodicals, Inc.
T. A. Ng’ong’ola-Manani et al.
Sensory and Consumer Studies of Fermented Soybean
1
Cluster4
Cluster2
PC-1 (28%)
0.5
75S
100SBS
Cluster3
90S
100S
75SBS
0
Cluster1
–0.5
90SBS
–1
–1
–0.8
–0.6
–0,4
–0.2
0
0.2
0.4
0.6
0.8
1
PC-1 (59%)
Figure 3. Principal component analysis of fermented pastes and consumer clusters. Naturally fermented pastes (100S, 90S, 75S) and lactic acid
bacteria-fermented pastes (100SBS, 90SBS, and 75SBS). Pastes are designated according to 100%, 90%, and 75% soybean composition, the
remaining proportions being maize.
Table 6. Demographic information of the clusters (numbers in parentheses are percentages).
Demography
Sex
Male
Female
Total
Age
14–29
30–49
50–80
Cluster 1
Cluster 2
Cluster 3
Cluster 4
Total
22 (14.9)
79 (53.4)
101 (68.2)
3 (2.0)
9 (6.1)
12 (6.1)
2 (1.4)
11 (7.4)
13 (8.8)
4 (2.7)
18 (12.2)
22 (14.9)
31 (20.9)
117 (79.1)
148 (100)
53 (35.8)
28 (18.9)
20 (13.5)
5 (3.4)
5 (3.4)
2 (1.4)
5 (3.4)
4 (2.7)
4 (2.7)
16 (10.8)
4 (2.7)
2 (1.4)
79 (53.4)
41 (27.7)
28 (18.9)
Table 7. Mean overall acceptance scores for consumer clusters.
Cluster
1
2
3
4
100S
6.25
2.67
5.00
6.46
100SBS
a
1.35
2.01b
2.35c
0.67a
5.20
6.25
1.31
5.36
90S
a
2.1
0.87a
0.75b
1.18a
6.23
2.75
6.15
6.32
90SBS
a
1.46
2.18b
1.68a
1.09a
6.23
3.17
2.69
2.00
75S
a
0.90
2.86b
2.39bc
1.31c
6.39
6.50
4.38
6.00
75SBS
a
1.10
0.8a
2.96b
1.35a
5.51
5.50
2.77
4.18
1.84a
2.02ac
2.49b
2.04c
Means not sharing a superscript within a column are significantly different (P < 0.05). 100S, 90S, and 75S represent naturally fermented pastes,
while 100SBS, 90SBS, and 75SBS represent lactic acid-fermented pastes. Pastes are designated according to 100%, 90%, and 75% soybean composition, the remaining proportions being maize.
LFP products and 75S, while consumers in cluster 4 liked
75S and were slightly tolerant of the sour products except
for 90SBS (Table 7).
Although 100SBS was rated lowest with an overall
acceptance score of 1.31 by consumers in cluster 3
(Table 7), the same sample was rated 6.25 by consumers
in cluster 2. Differences in overall acceptances of the same
sample by different clusters underscore consumer heterogeneity. Attributes characterizing 100SBS also characterized LFP. These attributes were also considered as drivers
ª 2013 The Authors. Food Science & Nutrition published by Wiley Periodicals, Inc.
of disliking by many consumers. Although the sensory
attributes characterizing LFP were not necessarily highest
in 100SBS, this paste stood out in terms of thobwa and
roasted soybean aromas. These aromas loaded highly on
PC2 (Fig. 2) and distinguished 100SBS from the other
LFP samples, which were mainly characterized by attributes loading highly on PC1. These findings agree with
the concept that consumer perception is complex and
multidimensional. Consumers respond not only to a
certain sensory input but also to other inputs perceived
127
Sensory and Consumer Studies of Fermented Soybean
1
Tyr
Cluster2
Thobwa
RoastS
0.8
0.6
Factor-2 (17%, 32%)
T. A. Ng’ong’ola-Manani et al.
0.4 SaltyBRoastM
AfterT BRoastS
0.2
Bitter Umami
SRoastM
ChituL
0 Chigumu
Brown
ArgSoggy
Ala
MandL
–0.2 SourMandA
Rough
Lys
–0.4 ChituA
Gly
Phe
Iso
Val
Leu
His
Glu
Grainy
Soft
Cluster4
EggA
Ser
Rancid
EggL
Sweet
RawS
Yellow
FermA
pH
Cluster3
Cluster1
–0.6
TA
–0.8
–1
–1
–0.8
–0.6
–0.4
–0.2
0
0.2
Factor-1 (52%, 42%)
0.4
0.6
0.8
1
Sensory, chemical and physical properties of fermented pastes
Consumer clusters
Figure 4. External preference mapping showing sensory attributes driving liking of the pastes by consumers in the clusters.
simultaneously and also to physical perceptual interactions among inputs (Costell et al. 2010).
To understand attributes driving preference of consumers in these clusters, PLSR was performed with sensory,
chemical, and physical data as X matrix and means for
overall consumer acceptance of the clusters as Y matrix.
Figure 4 shows sensory properties driving consumer liking in the clusters. Consumers in clusters 1, 3, and 4 had
similar drivers of liking, with some drivers having a
greater influence in some clusters than in others. For
instance, clusters 1 (n = 101) and 3 (n = 13) were characterized by consumers who liked 100S and 90S. Drivers of
liking of these products were yellow color, higher pH,
raw soybean odor, and fermented aroma. In this case
fermented aroma was the main driver. In addition to
attributes driving liking in clusters 1 and 3, sweet taste,
fried egg aroma, fried egg-like appearance, rancid odor,
and soft texture were drivers of consumer liking in cluster
4 (n = 22). In cluster 2, the main driver of liking of consumers (n = 12) was roasted soybean aroma and thobwa
aroma. Attributes that loaded highly on the opposite
direction of attributes driving liking of the majority of
the consumers can be considered as drivers of dislike of
these products. Therefore, burnt roasted soybean odor,
chigumuyoyo aroma, soaked burnt roasted maize aroma,
mandazi aroma, chitumbuwa aroma, mandazi- and chitumbuwa-like appearances, sourness, bitterness, saltiness,
aftertaste, and brown color were drivers of dislike for
most consumers.
Cluster 1 was the largest in terms of consumer
composition followed by cluster 4 (Table 6). There were
no significant differences in overall acceptance of the
products by consumers of cluster 1 (Table 7), even
128
though liking was biased toward NFP. This indicates that
both naturally fermented and LAB-fermented pastes have
the potential of being used by the consumers. However,
to increase utilization and acceptance of the fermented
pastes, it would be necessary to optimize drivers of liking
influencing acceptance of NFP. Thus, optimizing pH,
softness, raw soybean odor, rancid odor, fermented
aroma, sweet taste, fried egg aroma, and appearance, and
yellow color by increasing the desirable properties while
decreasing intensities of undesirable properties would
increase acceptability and utilization of fermented pastes.
Conclusions
The study concluded that the trained panel discriminated
the products based on their type of fermentation; and
consumers used similar discrimination in determining
their preference patterns. Most consumers preferred NFP
to LAB-fermented pastes. Strong intensities of yellow
color, pH, sweet taste, raw soybean odor, rancid odor,
fermented aroma, and soft texture in NFP were considered as positive. On the contrary, strong intensities of
burnt roasted soybean odor, chigumuyoyo aroma, soaked
burnt roasted maize odor, mandazi aroma, chitumbuwa
aroma, mandazi and chitumbuwa-like appearances, sourness, bitterness, saltiness, aftertaste, and brown color,
which characterized LFP were considered negative.
Consumer segmentation in liking of the products was
identified, with direction of preference toward NFP. Consumers were assigned to four clusters, with the largest cluster composed of consumers who accepted all products
almost similarly. This indicates that there is potential of
utilization of both naturally and LAB-fermented soybean
ª 2013 The Authors. Food Science & Nutrition published by Wiley Periodicals, Inc.
T. A. Ng’ong’ola-Manani et al.
pastes. However, optimization either by increasing or
reducing intensities of drivers of liking or disliking would
be recommended to increase utilization of the fermented
pastes. Because of heterogeneity, optimization of attributes
which were the main drivers of liking in different clusters
such as pH, raw soybean odor, rancid odor, soft texture,
sweet taste, egg aroma, yellow color, egg-like appearance,
fermented aroma, and roasted soybean aroma would be
recommended. However, as pH values of NFP were relatively high, a food safety challenge is recognized for NFP.
Being the first study on fermented soybean and
soybean/maize blend pastes in Malawi, the information
provided could be used in future developments of similar
products for wide acceptance and utilization of soybeans.
Acknowledgments
We acknowledge financial support from the Norwegian
Programme for Development, Research and Education
(NUFU) and Norwegian State Education Fund (L
anekassen). We are also grateful to Nutrition and Food Science
students and staff at Bunda College who participated in
the descriptive sensory analysis. We also acknowledge
Ellen Skuterud for rheometer measurements. Last but not
least, we also acknowledge Margrethe Hersleth at NOFIMA,
As, Norway, for guidance during data analysis.
Conflict of Interest
None declared.
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