ABSTRACT
The effects of milling (wet and dry) and coagulants (lime, Epsom salt and tamarind) on the viscoelastic properties and growth dynamics of selected food pathogens of tofu from blends of soybean and sesame were studied. The soybean and sesame blended in different ratio (100:0, 82.5:17.5, 65:35, 47.5:52.5, 30:70, and 0:100) were processed into flour by dry and wet milling method. The physicochemical properties of the flour samples were determined. The wet and dry milled flour blend in different ratio were further processed into tofu using three coagulants – lime, Epsom salt and tamarind. The physical, proximate and mineral compositions of the tofu samples were determined. The texture profile analysis, stress strain test and stress relaxation test were also carried out. Furthermore, the texture profile analysis of the samples were subjected to different mixture models using the D-optimal mixture model. The growth dynamics of selected bacteria (Escherichia coli, Salmonella enteritidis) and fungus, Aspergillus flavus were also observed in the fresh tofu samples. Finally, the best tofu sample was identified using the optimization test result. The result from the flour analysis revealed that functional properties of 100% dry milled soybean (D100:0) was the highest. The fat and ash content were highest in 100% dry milled sesame (D0:100) while the protein content was highest in 100% dry milled soybean (D100:0). The mineral composition of the flour was highest in (D0:100). The physical characteristics of the fresh tofu revealed that 100% soybean dry milled tofu coagulated with tamarind (TD100:0) had the highest initial weight and coagulation time. Wet milled tofu coagulated with lime and tamarind was fitted in linear mixture model and cubic mixture model respectively. In texture profile responses, the wet milled tofu from soybean/sesame blend coagulated with Epson salt (EW65:35) had the highest value in hardness (569.86), chewiness (154.92N) and gumminess (181.98). The stress strain test revealed that the dry milled tofu from soybean/sesame blend coagulated with Epson salt (ED82.5:17.5) had the highest stress strain yield (0.948N/mm2) while the dry milled tofu from soybean/sesame blend coagulated with Epson salt (ED47.5:52.5), had the lowest value(0.165N/mm2). The internal stress and stress modulus had the highest values (1.206N/mm2) and (3.02N/mm2) respectively in ED47.5:52.5 while the lowest values (0.032N/mm2) and (0.66N/mm2) were found in the dry milled tofu from soybean/sesame blend coagulated with lime (LW47.5:52.5), and the dry milled tofu from soybean/sesame blend coagulated with tamarind (TD47.5:52.5) respectively. The growth dynamics of Escherichia coli, Salmonella enteritidis, Aspergillus flavus revealed that the lowest growth was found in dry milled Epson salt coagulated tofu with 30% soybean and 70% sesame mixture (ED30:70) using the optical density growth reading. Finally, the optimization test revealed that dry milled tamarind coagulated tofu with 30% soybean and 70% sesame mixture (TD30:70) had the overall best among the 30 samples based on nutritional, textural and microbial constraints. This suggests that soft tofu with high protein, fats and mineral composition is preferred for all ages and can be processed by dry milling of soybean and sesame, coagulated with tamarind.
TABLE OF CONTENTS
Title Page i
Declaration ii
Certification iii
Dedication iv
Acknowledgements v
Table of Contents vi
List of Tables ix
List of Figures xiii
List of Plates xviii
Abstract
xix
CHAPTER 1 INTRODUCTION 1
1.1 Statement
of Problem 3
1.2 Objectives of the Study 4
1.3 Justification 5
CHAPTER
2: LITERATURE REVIEW 7
2.1 Origin and Production of Tofu 7
2.2 Utilization of Soybean in Nigeria 8
2.2 Utilization
of Sesame in Nigeria 10
2.4 Tofu Coagulants 14
2.4.1 Salt coagulants calcium sulfate (gypsum) 15
2.4.2 Acids
(glucono delta-lactone (GDL)) as coagulants 16
2.4.3 Enzymes as coagulants 16
2.3.4 Lime and tamarind as locally sourced coagulants 16
2.5 Texture
Profile Analysis (TPA) 18
2.6 Microbial
Spoilage of Tofu 21
2.7 Effect of Milling on Grains 23
2.7.1 Theory of milling 24
CHAPTER 3: MATERIALS AND METHODS 27
3.1 Source of Materials 27
3.2 Sample Preparation and Tofu Production 27
3.2.1 Lime and tamarind preparation 27
3.3 Tofu Formulation from
Soybean and Sesame 29
3.4 Tofu Production 30
3.5 Steps in Tofu Processing 34
3.5 Functional Properties 36
3.5.1 Bulk density 36
3.5.2: Swelling index 36
3.5.3 Water absorption capacity 36
3.5.4 Oil absorption capacity 37
3.5.5 Gelatinization temperature 37
3.6 Determination of Minerals 37
3.6.1 Determination of calcium 38
3.6.2 Determination of magnesium 39
3.6.3 Determination of potassium and sodium 39
3.6.4 Determination of phosphorus 40
3.6.5 Determination of iron (Fe) 41
3.7 Proximate Analysis 42
3.7.1 Moisture content determination 42
3.7.2 Ash content determination 42
3.7.3: Crude fibre determination 43
3.5.4 Fat determination 43
3.5.5 Protein content determination 44
3.5.6 Determination of carbohydrate 45
3.7 Texture Profile Analysis 47
3.8 Stress Relaxation Test 48
3.9 Stress Strain Test 48
3.10 Confirmation Test for the Selected
Pathogenic Organisms 50
3.10.1 Morphological test 50
3.10.2 Gram staining 51
3.10.3 Endospore staining 51
3.10.4 Biochemical confirmation test for bacterial
catalase test 51
3.10.5 Oxidase test 52
3.10.6 Carbohydrate fermentation test 52
3.10.7 Indole production test 52
3.10.8 Methyl red test 53
3.10.9 Citrate utilisation test 53
3.10.10 Hydrogen
sulphide production test 53
3.10.11 Urease
test 53
3.11 Inoculation and Incubation of Tofu 54
3.11.1 Inoculation of Escherichia coli and Salmonella
enteritidis 54
3.11.2 Inoculation of Aspergillus flavus 54
3.12 Statistical Analysis 55
3.13 Sensory Evaluation 55
CHAPTER 4: RESULTS
AND DISCUSSION 56
4.1 Results 56
CHAPTER 5: CONCLUSION AND RECOMMENDATIONS 223
5.1 Conclusion 223
5.2 Recommendations 224
References
Appendices
LIST
OF TABLES
3.1: Mixture
D optimal for two variables for Tofu production 29
4.1: Functional
properties of dry milled soybean/ sesame flour 58
4.2: Functional properties of wet milled soybean/
sesame flour 60
4.3: Proximate
composition of dry milled soybean/ sesame flour (%) 63
4.4: Proximate
composition of wet milled soybean/ sesame flour (%) 65
4.5: Mineral
composition of dry milled soybean and sesame flour (Mg/100g) 67
4.6: Mineral composition of wet milled soybean and sesame flour
(Mg/100g) 69
4.7: Physical
characteristics of fresh Tofu from dry milled soybean and sesame
blend
coagulated with lime 72
4.8: Physical
characteristics of fresh Tofu from dry milled soybean sesame
blend coagulated with Epsom salt 74
4.9: Physical
characteristics of fresh Tofu from dry milled soybean sesame
blend coagulated with tamarind 77
4.10: Physical
characteristics of fresh Tofu from wet milled soybean sesame
blend coagulated with lime 79
4.11: Physical
characteristics of fresh Tofu from wet milled soybean sesame
blend coagulated with Epsom salt 80
4.12: Physical
characteristics of fresh Tofu from wet milled soybean sesame
blend coagulated with
tamarind 81
4.13:
Proximate composition of Tofu processed from wet milled soybean/sesame
flour coagulated with
lime. 87
4.14:
Proximate composition of Tofu processed from wet milled soybean/ sesame
flour coagulated with
Epsom salt 88
4.15:
Proximate composition of Tofu processed from wet milled soybean/ sesame
flour
coagulated with tamarind 89
4.16: Proximate
composition of Tofu processed from dry milled soybean and
sesame
flour coagulated with lime 91
4.17: Proximate
composition of Tofu processed from dry milled soybean and
sesame
flour coagulated with Epsom salt 92
4.18: Proximate
composition of Tofu processed from dry milled soybean and
sesame
coagulated with tamarind 93
4.19: Mineral
composition of Tofu processed from wet milled of soybean and
sesame
coagulated with lime. 104
4.20: Mineral
composition of Tofu processed from wet milled soybean/
sesame
coagulated with Epsom salt. 105
4.21: Mineral
composition of Tofu processed from wet milled soybean/
sesame/coagulated with
tamarind. 106
4.22: Mineral
composition of Tofu processed from dry milled soybean/ sesame
flour coagulated with
lime 108
4.23: Mineral
composition of Tofu processed from dry milled soybean/ sesame
flour coagulated with
Epsom salt 109
4.24: Mineral
composition of Tofu processed from dry milled soybean/ sesame
flour coagulated with
tamarind 110
4.25: Experimental
layout and responses of the texture profile analysis of wet
milled
Tofu coagulated with lime 112
4.26: P
values of model, R square regression analysis of the model and mean
score of the
texture profile analysis of wet milled Tofu coagulated with
lime 112
4.27: Experimental
layout and responses of the texture profile analysis
of
wet milled Tofu coagulated with Epsom salt 121
4.28: P
values of model, R square regression analysis of model and the mean
square of the texture profile
analysis (TPA) of wet milled Tofu
coagulant
with Epsom Salt 121
4.29: Experimental
layout and responses of the texture profile analysis (TPA)
of
wet milled Tofu coagulated with tamarind 128
4.30: P
values of model, R2 regression analysis of model and the mean score
of the Texture profile analysis
(TPA) of wet milled Tofu coagulant with
tamarind
128
4.31: Experimental
layout and responses of the texture profile analysis (TPA)
of
dry milled Tofu coagulated with lime 135
4.32: P
values of model, R2 regression analysis of modes and the mean
score of the texture profile
analysis (TPA) of dry milled Tofu
coagulated
with lime 135
4.33: Experimental
layout and responses of the texture profile analysis (TPA)
of
dry milled Tofu coagulated with Epsom salt 142
4.34: P
values of model, R2 regression analysis of modes and the mean score
of the texture profile analysis
(TPA) of dry milled Tofu coagulated with
Epsom
salt 142
4.35: Experimental
layout and responses of the texture profile analysis of dry
milled
Tofu coagulated with tamarind 148
4.36: P
values of model, R2 regression analysis of models and the mean score
of the texture profile analysis
(TPA) of dry milled tofu coagulated
with
tamarind 148
4.37: Biochemical
test of E. coli and Salmonella 182
4.38: Escherichia
coli total viable count on wet milled Tofu from soy sesame
blend coagulated with lime, Epsom
salt and tamarind stored at
ambient
temperature for 7 days. 204
4.39: Escherichia coli total viable count on
dry milled Tofu from soy sesame
blend coagulated with lime, Epsom salt and
tamarind stored at ambient
temperature
for 7 days. 205
4.40: Salmonella enteritidis total viable
count on wet milled Tofu from soy
sesame blend coagulated with lime,
Epsom salt and tamarind stored at
ambient
temperature for 7 days. 206
4.41: Salmonella enteritidis total viable
count on dry milled Tofu from soy sesame
blend coagulated
with lime, Epsom salt and tamarind stored at ambient
temperature
for 7 days. 207
4.42 Aspergillus flavus total viable count on
wet milled Tofu from soy sesame
blend coagulated
with lime, Epsom salt and tamarind stored at ambient
temperature
for 7 days. 208
4.43: Aspergillus flavus total viable count on
dry milled Tofu from soy sesame
blend coagulated
with lime, Epsom salt and tamarind stored at ambient
temperature
for 7 days. 209
4.44:
Optimization result for proximate
composition of Tofu from soybean-
sesame
blends treated with different coagulants 211
4.45:
Optimization result for mineral
composition of Tofu from soybean-sesame
blends
treated with different coagulants 215
4.46:
Optimization result for texture profile
of Tofu from soybean-sesame blends
treated
with different coagulants 218
4.47: Optimization
result for stress and strain properties of Tofu from soybean-
sesame blends treated with different coagulants 220
4.48: Sensory
evaluation of Tofu from dry milled soybean sesame blend
treated
with different coagulant 221
4.49: Sensory
evaluation of Tofu from wet milled soybean sesame blend
treated
with different coagulant 222
LIST OF FIGURES
1: Stress
strain of milled grain, Loncin and Merson (1979) 25
2: Flow chart for dry milled Tofu produced
with blends of soybean and
sesame 32
3: Flow chart for wet milled Tofu produced
with blends of soybean and
sesame 33
4: pH
of wet and dry milled soybean and sesame milk blend coagulated with
lime,
Epsom salt and tamarind 82
5: Coagulation time (mins) of wet and dry
milled soybean and sesame milk
blend coagulated with lime, Epsom salt and
tamarind. 83
6: Weight of Tofu samples (kg) from wet and
dry milled soybean and sesame
milk
blend coagulated with lime, Epsom salt and tamarind. 83
7: Weight of dry matter (kg) from wet and
dry milled soybean and sesame
Tofu blend coagulated with lime, Epsom
salt and tamarind . 84
8: Protein content of wet and dry milled
Tofu from soybean and sesame
blend
coagulated with lime, Epsom salt and tamarind 94
9: Protein content of Tofu from dry milled
soybean sesame blend
coagulated
with lime at 20% moisture content stored for six (6) days 97
10: Protein content of Tofu from dry milled
soybean sesame blend
coagulated
with Epsom salt at 20% moisture content stored for six (6)
days 98
11: Protein content of Tofu from dry milled
soybean sesame blend
coagulated
with tamarind at 20% moisture content stored for six (6) days 99
12: Protein content of Tofu from wet milled
soybean sesame blend
coagulated
with lime at 20% moisture content stored for six (6) days 100
13: Protein content of Tofu from wet milled
soybean sesame blend coagulated
with Epsom salt at 20% moisture content
stored for six (6) days 101
14: Protein content of Tofu from wet milled
soybean sesame blend
coagulated with tamarind at 20%
moisture content stored for six (6) days 102
15 : Effect of component mixture on the hardness of wet-milled Tofu
coagulated with lime 113
16: Effect of component mixture on the cohesiveness of wet-milled
Tofu
coagulated with lime 116
17: Effect of component mixture on the chewiness of wet-milled
Tofu
coagulated with lime 118
18: Effect of component mixture on the gumminess of wet-milled
Tofu
coagulated with lime 119
19: Effect of component mixture on the hardness of
wet-milled Tofu
coagulated with epsom salts 122
20: Effect of component mixture on the cohesiveness of
wet-milled Tofu
coagulated with Epsom salts 124
21: Effect of component mixture on the chewiness of
wet-milled Tofu
coagulated with Epsom salts 125
22: Effect of component mixture on the gumminess of
wet-milled Tofu
coagulated with Epsom salts 126
23 Effect of component mixture on the hardness of
wet-milled Tofu
coagulated with tamarind 130
24 Effect of component mixture on the cohesiveness of
wet-milled Tofu
coagulated with tamarind 131
25: Effect of component mixture on the chewiness of
wet-milled Tofu
coagulated with tamarind 132
26: Effect of component mixture on the gumminess of
wet-milled Tofu
coagulated with tamarind 133
27: Effect
of component mixture on the hardness of dry-milled Tofu
coagulated with
lime 137
28: Effect
of component mixture on the cohesiveness of dry-milled Tofu
coagulated with
lime 138
29: Effect
of component mixture on the chewiness of dry-milled Tofu
coagulated with
lime 139
30: Effect
of component mixture on the gumminess of dry-milled Tofu
coagulated with
lime 140
31: Effect of component mixture on the hardness of
dry-milled Tofu
coagulated
with Epsom salts 143
32: Effect of component mixture on the cohesiveness of
dry-milled Tofu
coagulated with Epsom salts 144
33: Effect of component mixture on the chewiness of
dry-milled Tofu
coagulated with Epsom salts 145
34: Effect of component mixture on the gumminess of
dry-milled Tofu
coagulated with Epsom salts 146
35: Effect of component mixture on the hardness of
dry-milled Tofu
coagulated with tamarind 150
36: Effect of component mixture on the cohesiveness of
dry-milled Tofu
coagulated with tamarind 151
37: Effect of component mixture on the chewiness of
dry-milled Tofu
coagulated with tamarind 152
38: Effect of component mixture on the gumminess of
dry-milled Tofu
coagulated with tamarind 153
39: Texture profile analysis (hardness) of wet
and dry milled Tofu from
soybean and sesame blend coagulated
with lime, Epsom salt and tamarind. 154
40: Texture profile analysis (cohesiveness) of
wet and dry milled Tofu from
soybean and sesame blend coagulated with
lime, Epsom salt and tamarind. 155
41: Texture profile analysis (chewiness) of
wet and dry milled Tofu from
soybean and sesame blend coagulated with
lime, Epsom salt and tamarind. 156
42: Texture profile analysis (gumminness) of
wet and dry milled Tofu from
soybean and sesame blend coagulated with
lime, Epsom salt and tamarind. 157
43: Stress strain test of Tofu processed from
wet milled soybean/sesame blend
coagulated
with lime 160
44: Stress strain test of Tofu processed from
wet milled soybean and sesame
blend coagulated with Epsom salt 161
45: Stress strain test of Tofu processed from
wet milled soybean and sesame
blend coagulated with tamarind 162
46: Stress strain test
of Tofu processed from dry milled soybean and sesame
blend coagulated with lime 163
47: Stress strain test of Tofu processed from
dry milled soybean and sesame
blend coagulated with Epsom salt 164
48: Stress strain test of Tofu processed from
dry milled soybean and sesame
blend coagulated with tamarind 165
49 Stress yield of wet and dry milled Tofu
from soybean and sesame blend coagulated with lime, Epsom salt and tamarind. 166
50 Stress yield of wet and dry milled Tofu
from soybean and sesame blend coagulated with lime, Epsom salt and tamarind. 167
51:
Stress relaxation test of Tofu
processed from wet milled soybean and
sesame blend coagulated with lime 171
52: Stress relaxation test of Tofu processed
from wet milled soybean and
sesame
blend coagulated with Epsom salt 172
53: Stress relaxation
test of Tofu processed from wet milled soybean and
sesame blend coagulated with tamarind 173
54: Stress relaxation test of Tofu processed
from dry milled soybean and
sesame blend coagulated with lime 175
55: Stress relaxation test of Tofu processed
from dry milled soybean and
sesame blend coagulated with Epsom salt 176
56: Stress relaxation test of Tofu processed
from dry milled soybean and
sesame blend coagulated with tamarind 177
57: The internal stress of wet and dry milled
Tofu from soy/sesame blend coagulated with lime, Epsom salt and tamarind 178
58: Stress relaxation time of wet and dry
milled Tofu from soy/sesame blend
coagulated
with lime, Epsom salt and tamarind 179
59: Stress modulus of wet and dry milled Tofu
from soy/sesame blend
coagulated with lime, Epsom salt and
tamarind 180
60 Escherichia
coli optical density growth on wet milled Tofu from soy and
sesame
blend coagulated with lime stored at ambient temperature for
7 days. 184
61: Escherichia
coli optical density growth on wet milled Tofu from soy and
sesame
blend coagulated with Epsom salt stored at ambient temperature
for
7 days. 185
62: Escherichia
coli optical density growth on wet milled Tofu from soy and
sesame
blend coagulated with tamarind stored at ambient temperature
for
7 days. 186
63: Escherichia
coli optical density growth on dry milled Tofu from soy and
sesame
blend coagulated with lime stored at ambient temperature for 7
days. 187
64: Escherichia
coli optical density growth on dry milled Tofu from soy and
sesame blend
coagulated with Epsom salt stored at ambient temperature
for
7 days. 188
65: Escherichia
coli optical density growth on dry milled Tofu from soy
sesame blend
coagulated with tamarind stored at ambient temperature
for
7 days. 189
66: Salmonella
enteritidis optical density growth on wet milled Tofu from soy sesame blend
coagulated with lime stored at ambient temperature
for
7 days. 191
67: Salmonella
enteritidis optical density growth on wet milled Tofu from soy sesame blend
coagulated with Epsom salt stored at ambient temperature
for
7 days. 192
68: Salmonella
enteritidis optical density growth on wet milled Tofu from soy sesame blend
coagulated with tamarind stored at ambient temperature
for
7days 193
69: Salmonella
enteritidis optical density growth on dry milled Tofu from soy sesame blend
coagulated with lime stored at ambient temperature for
7days 194
70: Salmonella
enteritidis optical density growth on dry milled Tofu from soy sesame blend
coagulated with Epsom salt stored at ambient temperature
for
7days 195
71: Salmonella
enteritidis optical density growth on dry milled Tofu from soy sesame blend
coagulated with tamarind stored at ambient temperature
for
7days 196
72: Aspergillus
flavus optical density growth on wet milled Tofu from soy
sesame
blend coagulated with lime stored at ambient temperature for 7
days. 198
73: Aspergillus
flavus optical density growth on wet milled Tofu from soy
sesame blend coagulated with Epsom salt stored
at ambient temperature
for 7 days. 199
74:
Aspergillus flavus optical density growth on wet milled Tofu from soy
sesame blend
coagulated with tamarind stored at ambient temperature
for
7 days. 100
75: Aspergillus
flavus optical density growth on dry milled Tofu from soy
sesame blend coagulated with lime stored at
ambient temperature for 7
days. 201
76: Aspergillus
flavus optical density growth on dry milled Tofu from soy
sesame blend
coagulated with Epsom salt stored at ambient temperature
for
7 days. 202
77: Aspergillus
flavus optical density growth on dry milled Tofu from soy
sesame blend coagulated with tamarind stored
at ambient temperature
for 7 days. 203
LIST OF PLATES
1: Tofu press. 28
2: Tamarind seed used as coagulant 28
4: Thirty (30) samples of Tofu at 20%
moisture content from soybean/
sesame
blend 35
3: Thirty (30) samples of fresh Tofu from
soybean and sesame blend 35
5:
Thirty (30) samples of Tofu
subjected to calibration for uniformity of
shape. 46
6: Tofu at 20% moisture content from
soybean sesame blend under
viscoelatic test. 46
7: Aspergillus
flavus in potato dextrose agar (PDA) 50
8: Escherichia
coli and Salmonella enteritidis
in MacConkey agar (MAC)
and Shigella Salmonella agar (SSA) 50
CHAPTER 1
INTRODUCTION
In Nigeria as in other
countries of the world, the consumption of meat is an indication of social and
economic class. This is because meat is one of the nutritious foods used for
human consumption. The trend has changed from animal protein consumption to
vegetable protein consumption due to the health challenges caused by high consumption
of animal meat (Ikeme 1990).
The three-dimensional
structure of the soybean protein molecule which involves the exposure of the
–SH,S-S and the hydrophobic amino acid on the location accessible to water from
the inside of a molecule by denature. This interaction of soybean protein
molecule allows it to be used as a textured protein product (Iwe,2003). Tofu, a
meat substitute, is one of those textured protein products. Tofu, a soy food,
is a fermented soybean product.
Lord Liu An, a Han Dynasty
prince, invented tofu in Northern China around 164BC (Sacks et al, 2006). According to another
hypothesis, tofu was inadvertently discovered when a slurry of boiled ground
soybeans was combined with impure sea salt. The calcium and magnesium salt in
such sea salt would have allowed the soy mixture to curdle and create a
tofu-like gel (Anderson et al, 1995).
Tofu has a number of
advantages, including a lower risk of cancer, the ability to act as an
antioxidant, and an increase in the supply of nutrients such as folate, vitamin
K, calcium, magnesium, iron, and fiber (Ohr,2002). Tofu also contains a variety
of phytonutrients such as flavonoids and isoflavonoids, phenolic acids,
protein, and peptides. Obesity, type 2 diabetes, and other chronic obstructive
pulmonary conditions can all be prevented and treated with tofu (Iwe, 2003).
Sesame is an under-utilized
legume rich in oil (48 - 58% fat), protein (16.96%) and carbohydrates (26.04%).
The dietary fibre content is also high (16.9%) (Kapadia et al, 2002). Sesame seeds are exceptionally rich in iron,
magnesium, manganese, copper, calcium. It also contains thiamine and tocopherol
(Bedigian, 2003). Sesame seeds contain lignans that includes sesamin which
exerts antioxidants and anti-cancer properties. Sesame seeds contain
phytosterols that reduce the levels of blood cholesterol (Obiajunwa et al, 2005). Sesame seed is deficient
in lysine, but rich in sulphur amino acids such as methionine and cystine,
which makes it an appropriate supplement to diets that contains soybean that
tends to be deficient in sulphur amino acids (Elkafi, et al, 1991). Moreover, the use of sesame in tofu production will
also help to diversify its use being an under-utilized legume.
Milling, also known as reduction in size, is a unit process that
involves the application of grinding, compression, or impact forces to minimize
the average size of solid food bits. It influences the surface sulfhydryl
content and surface hydrophobicity of soymilk protein. This in turn affects the
rheological properties of soymilk as well as the texture of soycurd (Tofu)
(Makoto, et al, 2012). Cereals
of various kinds are processed by soaking, fermentation, milling (wet or dry)
to detoxify the anti nutritional factors, increase palalability and improve
bio-availability of nutrients (Otitoju 2009). Likewise tofu from soybean is
generally produced using wet milling method which is believed that the soaking
period leads to reduction in nutritional inhibitor and toxic substances thus
improving dietary protein digestibility (Iwe 2003).
Tofu is a very nutritious food typically containing 11.00 to 12.40%
protein (Ezeama and Dobson, 2019). Hence it is quite susceptible to microbial
growth. For this reason tofu is consumed traditionally within a day or two
after production. Therefore the evaluation of the microbiological safety of
tofu under ambient condition is necessary.
To evaluate the texture of
Tofu, both viscous and elastic properties can change the texture which is the
viscoelastic material (Kohyama and Nishinari, 1992). Therefore this work is
focused on the effect of wet and dry milling on the physico-chemical properties,
viscoelastic properties and microbiological safety of Tofu from blends of
soybean and sesame. These different blends were coagulated with Lime, Tamarind
and Epsom salt.
1.1.1
STATEMENT
OF PROBLEM
Meat is possibly the most
controversial of all food products. For some, it is such an important part of
the diet that they cannot imagine living without it. For others it provokes
revulsion to such a degree that they would never think of placing it on the
table. The impact of meat consumption today, particularly on the consumers has
created a tax as well as health challenges to the poorest of the world.
Consumers exhibit a noticeable increase in the incidence of various diseases
particularly cardiac, cardiovascular, rheumatic as well as cancer. These
diseases occur as a result of high consumption of meats from animal origin
(Brown, 1983). Meat is not the most essential in the human diet.
By understanding the nutritional value of the available
alternatives to meat, it can be very useful and healthful. Meat Analogues such
as ''Tofu'' are prepared from soybean. They are useful for those seeking a
transitional diet from meat to one based on plant foods (Ezeama and Dobson,
2019). Tofu as nutritious as it has been is known to be produced from soybean
using a popular method of wet milling. Though wet milling in tofu production
gives a high quality tofu both nutritionally and texturally but it takes a
longer time in processing due to the fermentation time (Otitoju
2009).
Furthermore, there should be an alternative plant to be used for tofu
production other than soybean. This will give a wider variety for vegetarians
and others who do not take meat due to health reasons. Therefore, it is
necessary to process tofu using both wet milling and dry milling method to
determine the nutritional and textural properties of tofu using blends of
soybean and sesame. This will ensure continuity in tofu production even when
there is scarcity of soybean.
Tofu is also prone to microbial attack because of its proteinous
nature and vigorous handling processes. It is also deemed necessary to
determine the ability of food borne pathogens to grow in tofu held at ambient
temperature.
1.2 OBJECTIVES
OF THE STUDY
The main objective of the
study is to determine the viscoelastic properties (shear-strain behavior and
stress relaxation) and growth dynamics of selected food pathogens of tofu
produced from blends of soybean and sesame coagulated with lime, tamarind and epsom
salt using wet and dry milling methods.
Other specific objectives are
to.
1.
Determine the physico-chemical properties of
both wet milled and dry milled flour from blends of soybean and sesame used in
the production of tofu
2.
Produce tofu from wet milled and dry milled
flour from blends of soybean and sesame using three coagulants (lime, tamarind
and epsom salt).
3.
Determine the viscoelastic properties (texture
profile analysis, shear-strain and stress relaxation) of the produced tofu from
the soybean and sesame blend.
4.
Determine the proximate and mineral composition
of tofu made from soybean and sesame blends using Wet and dry milling methods
5.
Evaluate the shelf life of tofu made from
soybean and sesame blends.
6.
Analyze the microbial growth dynamics of
selected food pathogens on the produced tofu.
7.
Find out the optimization result of tofu from
blends of soybean and sesame using the various nutritional and textural
analysed results.
1.3 JUSTIFICATION
Soybean proteins no doubt provide a source of low cost protein with
good nutritional value. Soybean is used in the production of meat Analogue
known as “Tofu” with some many health benefits such as cholesterol lowering
effect of tofu caused by the ability to moderate low density lipoproteins (LDL)
receptor levels in the liver. Anti cancer effects are obtained from constant
consumption of tofu (Iwe,2003). This is as a result of the several
phytochemical some of which appears to protect against hormones dependent
cancer. The high content of isoflavones concentrations present can inhibit
prostate cancer cell growth to different extent (Ohr, 2002). Tofu as a product
of soybean must be processed by fermentation to liberate the minerals for
adsorption into the body system (Eiman et al, 2008).
Soybean must be milled (wet or dry milled) before it is converted
to tofu. Wet milling of soybean before tofu production takes a longer time of
soaking (fermentation of 12hrs) while dry milling takes 2 - 4 hrs of soaking
due to increased surface area. Assessing both wet milling method and drying
method on the nutritional and textural qualities will help the producer and
consumer to get the best processing method as well as the sensory attributes.
The blends of soybean to sesame at different ratios (100:0% and 30: 70%) ratio will
serve as a way of either using both or each in the production of tofu to ensure
continuity in cases of scarcity of each crop. It will also ensure more variety
in taste and texture for consumer's selection.
The use of different coagulants ensures versatility in production
depending on their availability and affordability. The use of different
coagulants impact different taste, texture, colour and nutrient particular to
the type of coagulant used. In addition, the shelflife stability is determined
by the type of coagulant used in tofu production (Ezeama and Dobson,2019).
The evaluation of the microbiological safety of tofu under
different storage conditions will allow tofu to be processed hygienically and
be stored for a longer period of time. Therefore, this research on the effects
of milling and coagulants on the viscoelastic properties and the growth
dynamics of selected food pathogens of tofu from blends of soybean and sesame
is justified.
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