CHAPTER ONE
1.1 INTRODUCTION
Yogurt is produced by a fermentation
process during which a weak protein gel develops due to a decrease in the pH of
milk (Oroian et al, 2011). The gel
structure contributes substantially to the overall texture and organoleptic
properties of yogurt and gives rise to shear and time development viscosity
(Odoneell and Butter, 2002). Texture is one of the most important
attributes used by consumers to assess the quality of yogurt. The most frequent
defects related to yogurt texture that may lead to consumer rejection are
apparent viscosity variations and the occurrence of Syneresis (Kroger, 1975).
As a flow property, the Knowledge of the rheological properties is important
for design and evaluation of the process, process control, consumer
acceptability of the product and the optimization of process variables (Brennan
et al,1980; Dail and Steffe, 1990, a. b, Harrison and Gunningham, 1985). It is
important to establish relationship between structure and flow and to correlate
physical parameters (Abu-jdayil, 2003; Resch 2002).
Yogurt rheological characterization
is required for product and process development and to ensure consumer
acceptability (Benezech and Mangonnat, 1994). It is also required for effective
design of process system.
Yogurt from animal milk has received
a lot of scientific attention by many authors, but studies providing
information on the rheological characterization of legume yogurt like product
is scanty.
It is noteworthy, that the dairy sub
sector in Africa is thus relegated to the category of subsistence system of
production due to minor and peripheral status accorded the sector by various
government policies allied with the above, are poor nutrition and genetic
constitution of the Africa breeds of ruminant. The above problem leads to insufficient
milk availability of 15L of milk. This dramatic decrease in the consumption of
milk products stimulated in part the processing of milk from different seeds
and nuts.
Though undervalued in the past, milk
from plant source are key ingredients in the diet of African countries.
Recently, researchers have shown strong interest in these milk sources due to
their high nutritional values and economic potentials. It is worthy repeating
that milk sources form plants are seen as a radiating hope as well an ally in
the fight against hidden hunger. All the nuts and the seeds of interest in the
present study are found on the tropical environment including Nigeria for various
purposes.
1.2 OBJECTIVE
1. The
objectives of this study, is to evaluate the rheological characteristics of
yogurt blends with tiger nut milk and coconut milk.
2. To
evaluate the physical properties of yogurt blends with tiger nut milk and
coconut milk.
3. To
determine the sensory quality of the yogurt blends with tiger nut milk and
coconut milk.
CHAPTER TWO
2.0 LITERATURE
REVIEW
Yogurt is a diary food product,
produced by lactic acid bacteria in fermentation of milk. The conversion of
lactose into lactic acid gives yogurt its characteristic gel-like texture.
(Braing dictionary, 2005; Wikipedia, 2005; Elson and Hass, 2005).
It is also described as the
bacterial curdling of milk, which is produced with the use of specific bacteria
(Lactobacillus bulgaricus and streptococcus thermophilus). For the production of
yogurt, which has a custard-like consistency (Robins 1980).
It is believed that yogurt
originated in mesopotamia now in Iraq thousands of years ago. Evidence has
shown that these people has domestic goals and sheep around 500 B.C. the milk
from these animals was stored. In gourds, and in a warm climate, where it
naturally formed a curd (Helferich and Westhoff, 1980). Yogurt whose name comes
form the Turkish word “yogurt” is the most wisely available fermented milk in
the western world today where its popularly derived more from its flavour
(Adams and Moss, 1999).
2.2 Types
of Yogurt
There are different types of yogurt,
which include:
2.2.1 Pasteurized stirred Yogurt
This type of yogurt is pasteurized
and incubates in a tank and the final coagulum is “broken” by stirring prior to
cooling and packaging. It has extended shelf-life.
2.2.2 Strained Yogurt
This is a type of yogurt which is
stained through a paper or cloth filter, traditionally made of muslin to remove
the whey. Yogurt once made is refrigerated over night. It is poured in a muslin
or cheese cloth bag and hug in the coolest place with a tub placed underneath
to collect the dripping whey.
2.2.3 Bio-Yogurt
This is made with different types of
fermentation culture (probiotic culture). Such as lacto bacillus subspcasei,
lactobacillus acidophilus, Bifido-bacteria e.t.c and it aids digestion,
improves gastrointestinal function and stimulates the immune system.
2.2.4 Organic
Yogurt
This is made with milk form
specially fed cows. This type of yogurt is claimed to be more nutrition’s than
other yogurts.
2.2.5 Frozen Yogurt
Frozen yogurts are yogurt that are
inoculated and incubated in the same manner as stirred yogurt. In frozen
yogurt, cooling is achieved by pumping through a whippier/freezer/ chiller in a
fashion similar to ice cream.
2.2.6 Concentrated
Yogurt
These are yogurt that are fermented
and inoculated in the same manner as a stirred yogurt. The concentration is
done by boiling of some of the water and it is often done under vacuum to
reduce the temperature required.
2.3 NUTRITIONAL
VALUE AND HEALTH BENEFITS
Yogurt is nutritionally rich in
protein. Calcium, riboflavin, vitamin B6, and vitamins B12.
Yogurt thought to have additional
health benefits beyond milk.
One of the suggested benefits of
yogurts is that it acts as a digestive aid. Yogurts encourage the growth of
beneficial bacteria In the intestine of the body. This organisms help to digest
food more efficiently and protect against other harmful organisms.
Yogurt is good for people that are
lactose intolerant. These people have difficulty digestive milk products, the
typically can tolerate yogurt because much of the lactose in the milk is
converted to lactic aid by the bacteria culture (Kolars et al; 1984)
Yogurt that contain live cultures is
sometimes used in an attempt to prevent antibiotic associated diarrhea
(Beniwal, et al; 2003).
Table
I nutritional value per 100 g of yogurt (full fat)
|
|
|
ZEnergy
|
257kg
(6 kcal)
|
|
Carbohydrate
|
4.7g
|
|
Fat
|
3.3g
|
|
Protein
|
3.5
|
|
Vitamin
A equivi
|
27ug
(3%)
|
|
Riboflavin
(vit. Biz)
|
0.14
mg (9%)
|
|
Calcium
|
121mg
(12g)
|
Lactose
content diminishes during storage. Percentages are relative to US
recommendation for adults.
Source: USDA Nutrition database.
2.4 Utilization
of Yogurt
Yogurt is an excellent this by
itself. It is also valuable in its many other uses. Yogurt can be used as part
of the liquid in cakes, waffles, pancakes and muffins and would help cut down
on the amount of baking powder. The thickness of yogurt helps to hold up the
baking balter (David, 2003).
Yogurt is also used as a starter for
cheese production and also a starter for yogurt batch processing technique
(Rosenthal, 1978: Coyle. 1982).
Ernest (1996), reported that in the
developed countries, yogurt is used as a dessert, between meal, snack, complete
lunch, and diet food. Yogurt is useful in the diet for: energy-reduced diets,
warring babies on to solid foods, convalescents and alternative to puddings
(Tull, 1996).
2.5 PRODUCTION
OF YOGURT
Production of yogurt from milk starts
with pasteurization and homogenization of the milk. Before pasteurization,
stabilizer (such as gelatin or modified food starches) may also be added to
improve the body and texture by increasing firmness, mouth feel and also help
to keep the flavour uniformly mixed in the yogurt. The milk is then cooled to
430c and inclulated with 1.25% each of lactobacillus bulgaricus and
streptococcus thermophilus (Kosikiwski, 1982). During incubation (12 hours),
the pH will decreased due to lactic acid production. Yogurt is then stored in
the refrigerator at low temperature. The consistency and the flavour of the
final product depend on the type of milk used (Namsum, 2008).
During yogurt production, the micro
organism, used help in:
Production
of lactic acid which lowers the pH,
makes the yogurt sour in taste, causes the milk protein to thicken and
also acts as a preservative.
THE FLOWCHAR FOR YOGURT PRODUCTION
Milk Mix
Heat treatment (850c for 15 mins)
Homogenize
Cool to incubation
temperature (430c)
Inoculate with starter
culture
Incubation (430c),
12 hrs)
Cooling (50c)
Storage
Fig 1 flowchart for yogurt production
Source:
Adam’s and moss (1999).
2.1 Fermentation
Fermented foods are those foods which have been
subjected to the action of micro-organisms of enzymes so that desirable
biochemical changes cause. Significant modification to the food yogurt is perhaps
the oldest fermented milk product known and consumed by large segments of our
population either as a part of diet or as a refreshing beverage drink. Many fermented
milk products which are eaten as they contains living micro-organisms.
Traditionally, lactic acid bacteria
are the most commonly used micro-organism for preservation of food (Anu et. al., 2010).
2.6.1 History
of Tiger-nut
Tigernut (cyperus esculentus L.) is an underutilized crop which belongs to
the division magnoliophyta,classliopsida, order–cryerte and family-cyperaceous
(family) and was found to be a cosmopolitan perennial crops of the same genus
as the papyrus plant. Other names of the plant are earth almond as well as
yellow nut grass (Odoemlan, 2003; Belewn and Belewu, 2007). Tiger-nut also
known as Chufe as though to have originated in the Mediterranean area and
western Asia but has spread (mainly as a weed) to many parts of the world. It
will grow in a very wide range or climatic conditions, and occurs in the
tropics subtropics and warm temperate regions and is cultivated in several
countries (Kay, 1987).
2.6.2 Varieties of Tiggernut
Three varieties (yellow, brown and
black) are cultivated in Nigeria but only two varieties (yellow and brown) are
readily available in the market (Oledele and Aina, 2007). The yellow variety is
preferred to all other varieties because of it’s inherent properties like its
bigger size attractive colour and fresh body (Belewn and Belewu, 2007), Belewu
and Abodunrin, 2008, Umerie et al,
1997). The yellow variety (large and small) also yields more milk upon
extraction, contains lower fat and more protein and possesses less
anti-nutritional factors especially polyphenoil (Okafor et al, 2003).
2.6.3 Utilization
of Tiger nut
The tiger-nut has small tuberous rhizomes
which are eaten raw, baked or roasted, grated to make refreshing beverages and
ice creams. (Key 1987; Belewu and Belweay 2007; Oladele and Aina, 2007). Kay,
(1987) reported that tiger-nut one used as subsidiary in animal feeding,
confectionary, coffee and cocoa adulterant while the secondary products are
oil, start, flour, alcohol and leaves.
2.6.4 Chemical
Composition of Tiger-Nut
The high crude lipid and
carbohydrate content and its fairly good essential amino acid composition make
it a valuable source of food for man. Tiger-nut is rich in energy content,
(starch, fat, sugar and protein), mineral (sodium, magnesium, calcium,
phosphorous, potassium sine- and traces of copper) and vitamins E and C (Belewu,
2007; Belewu and Abodunrin, 2008).
Nwaoguikpe. (2010), reported that
the proximate composition of two varieties of the best (yellows, large and
small size) species of cyperus esculentus
on the wet and dry samples showed a higher protein, crude fiber, and lipid in
the dried samples.
Adeyuyitan et al, (2009), reported that tiger nut contain higher essential
amino acids than those proposed in the protein standard for satisfying adult
needs.
According to Belewu and Abodurin (2008)
and Adejuyitan et al (2009),
tiger-nut produces high quality oil, about 25.5% of its contents and the oil was
implicated as lauric acid grade oil, non acidic stable and very low instauration.
2.6.5 Health
and Nutritional Properties of Tiger-Nut
According to Masson (2008),
tier-nuts have long been recognized for its health benefits as they are high in
fiber, protein and natural sugars. They have a high content of soluble glucose
and Oleic acid, along with high energy content (Starch, fats, sugar, and
proteins) they are rich in minerals such as phosphorus and potassium and in
vitamins E and C (Belewu and Elewu, 2007; Belewu and Abodunkin, 2008).
Tiger-nut flour has been demonstrated to be a rich source of quality oil and
contains moderate amount of protein. The extract from tiger-nut is a product of
plant origin with high nutritional and health properties which can be used as a
milk substitute (Nwokolo, 1985). The nuts were found to be ideal for children,
the elderly and for sports men and women (Martinezi, 2003)
Tiger-nut (Cyperus esculentus), an under utilized crop was reported to be
high in dietary fiber content, which could be effective in the treatment and
prevention of many diabetics including colon cancer, coronary diseases,
Obesity, diabetics and gastrointestinal (Anderson et al; 1994).
2.7 History
of coconut
The coconut palm is botanically referred
to as the “Cocos nucifera”. It is a
member of the Arecaceae or palm family. In fact, it is the only member of the
genus cocoIs. The palm thrives in the
tropical regions and is a major trade component due to its various decorative,
Culinary and other non-culinary uses. The palm bears fruits that is light and
buoyant and hence, does not rule out the possibility of finding its own course
a cross the globe with the help of marine currents (www.buzzle.com)
It is a large and tall palm that
exhibits a height of approximately 30m. The tree has pinnate leaves, each growing
to a size of around 6m with pinnate approximately 90cm long (www.buzzle.com.)
2.7.1 Nutritional
value of coconut milk
Coconut milk is the liquid extracted
from grounding coconut meat and water. It is the milky white sweet liquid which
is obtained by squeezing granted coconut and warm water. It is used to prepare
yummy mouth watering descents, sauces, soups and curries. It is packed with
vitamins, Minerals, potassium, folate and other vital nutrients. It is included
in the list of healthy super foods. One cup of canned coconut milk Contain 445
Calories, where as frozen milk Contains
the maximum number of calories, which are approximately 552.
Table
2: nutritional value per serving
nutritional values present in 100 grams of fresh coconut milk
|
Serving
size
|
100g
|
|
Energy
|
824kj
(197kcal)
|
|
Carbohydrates
|
2.8lg
|
|
Fat
|
21.33g
|
|
-Saturated
|
18.915g
|
|
Protein
|
2.02g
|
|
Vitamin
c
|
1mg(1%)
|
|
Calcium
|
18mg(2%)
|
|
Iron
|
3.30mg(25%)
|
|
Magnesium
|
46mg(13%)
|
|
Phosphorus
|
196mg(14%)
|
|
Potassium
|
220mg(5)
|
|
Sodium
|
13mg(1%)
|
Percentage
are relative to US recommendation for adults.
Sources:
USDA Nutrient databases.
Fresh coconut milk has a consistency
and mildly sweet taste similar to cow’s milk, and it properly prepared should
have no coconut odour or at most is very faint odour. It may be consumed raw or
use as milk substitute in tea, coffees, and even baking by vegans or people allergic
to animals milk. It can also be mixed with fruits to make a yogurt. Substitute
(ww.en.wikipedia. org).
2.7.2 Health Benefit of Coconut Milk
Coconut milk contain a large
proportion of lauric acid, as actuated fat that raises blood cholesterol levels
by increasing the amount of high density lipoprotein. Cholesterol that is also
found in significant amount in breast milk and sebaceous gland secretion (www.drgranny.com)
The coconut milk helps to maintain
blood sugar. Glucose intolerance may cause manganese deficiency in the body and
it is a rich source of –manganese. Also it keeps the skin and the blood vessels
flexible and elastic.
Coconut milk helps in building
strong bones, and contains phosphorus which is an essential nutrient that the
body needs for strengthening bones. It also aids to the preventing of anemia in
the body which does not allow the body to develop enough hemoglobin for keeping
sufficient oxygen levels in red blood cells (www. Drgranny.com).
It is rich in magnesium and help in
relieving muscle cramps or muscles soreness. It also helps in controlling
weight and contains high concentration of dietary fiber (www.digranny.com.)
2. 8. Rheology
By definition, rheology is the study of the deformation and flow of
matter. It is applicable to many industrial fields such as mining, geology,
cosmetics, and polymers. Rheology of fluid foods provides good opportunities of
study due to the biological nature of foods. Optimization of product
development efforts, processing methodology and quality of food product
requires careful investigation of the rheological properties (Rao, 1999;
Steffe, 1996).
2.8.1. Significance in Food Industry
Rheological
data are essential for several areas in food industry.
• Design of process equipments including heat exchangers,
• Design of process equipments including heat exchangers,
pipelines, mixers, extruders and pumps;
• Determining the functions of ingredients during product
• Determining the functions of ingredients during product
development;
• Intermediate or final product quality control;
• Shelf life testing;
• Evaluation of food texture and sensory assessment (Pelegrine
• Intermediate or final product quality control;
• Shelf life testing;
• Evaluation of food texture and sensory assessment (Pelegrine
et al., 2002;
Rao, 1999; Manohar et al., 1998; Steffe, 1996).
2.9 Flow
Models for Rheological Properties of Fluids
A flow model is considered to be a mathematical
equation that describes rheological data such as shear rate and shear stress in
a convenient manner. It is important to quantify how model parameters are
affected by state variables such as temperature and concentration (Rao, 1999).
A fluid is distinguished from a solid by its behavior when
subjected to a stress (force per unit area of application) or applied force.
While an elastic solid deforms by an amount proportional to the applied stress,
a fluid continues to deform under the similar applied stress. Shear stress, i, is the stress component applied tangentially to the
fluid with units expressed in Pa (N/rn2). Under the applied shear stress, a
fluid flows at a velocity which increases with increasing stress. Shear rate, g, is the velocity gradient (rate of deformation)
established in a fluid as a result of the applied shear stress. It is expressed
in units of reciprocal seconds (s-1). Viscosity is the resistance of
the fluid to this stress. It is the property of a fluid which gives rise to
forces that resist the relative movement of adjacent layers in the fluid. These
viscous forces are caused by the forces existing between the molecules of the
fluid (Rao, 1999; Geankoplis, 1993; Bourne, 1982).
For an ideal Newtonian fluid, the shear stress is
linear function of the shear rate and the proportionality constant for the
relationship, μ, is
called the dynamic (or Newtonian) viscosity of the fluid. The relation is given
by Newton’s law of viscosity when the flow is laminar (Geankoplis, 1993; Barnes
et al., 1989; Van Wazer and Lyons, 1966).
i = μ.g where, i is tangential shear stress, μ is the Newtonian viscosity and g is the shear rate.
i = μ.g where, i is tangential shear stress, μ is the Newtonian viscosity and g is the shear rate.
2.9.1.
Newtonian Fluids
Fluids that obey Newton’s law of viscosity (Eq. 1) are
called Newtonian fluids. For such a fluid, there is a linear relationship
between shear stress (i) and the shear rate (g) (Figure 1). This suggests that the viscosity, μ, is constant and it is independent of the rate of shear
(Geankoplis, 1993). When shear rate is plotted against shear stress, the slope
of the curve, μ, is
constant and the plot begins at the origin. Using the units of N for force, m2
for area, m for length, and finally m/s for velocity, gives viscosity as Pa s
which is 1000 centipoise (1 Pa s = 1000 cP).
Typical Newtonian fluids contain low molecular weight
compounds (e.g. sugars) and that do not include large concentrations of either
dissolved polymers (e.g. protein, starch) or insoluble solids. Some examples of
Newtonian foods are water, sugar syrups, edible oils, filtered juices, and milk
(Rao, 1999). The following examples represent typical Newtonian viscosities at
room temperature:
water, lcP; coffee cream 10 cP; vegetable oil, 100 cP; and honey 10000 cP (Steffe, 1996).
water, lcP; coffee cream 10 cP; vegetable oil, 100 cP; and honey 10000 cP (Steffe, 1996).
2.9.2. Non-Newtonian fluids
For non-Newtonian fluids, the relation between the
shear stress (i) and shear rate (g) is not linear and/or shear stress-shear rate plot
does not begin at the origin. The fluid might exhibit time-dependent
rheological behavior as a result of structural changes. Typical non-Newtonian
materials are dispersions, emulsions, and polymer solutions. The viscosity is
not constant but is a function of shear rate and may exhibit one of the two
cases. Flow behavior may depend only on shear rate and not duration of shear
(time-independent) or may depend on the duration of shear (time-dependent).
Thus, non-Newtonian fluids can be divided into two broad categories as time-
independent and time-dependent fluids. Various types of time independent
behavior have been described in the literature (Rao, 1999; Barnes et al., 1989).
2.10 Time-Independent Fluids
2.10.1 Bingham Plastic Fluids
This category is the simplest since the only
difference from Newtonian behavior is that the linear relationship between
shear stress and shear rate does not go through the origin (Steffe, 1996).
i = μp1 g+i0 (2)
i = μp1 g+i0 (2)
Where, i0 is the yield stress and μpl is the plastic
viscosity.
A finite stress so called yield stress (i0) is required to achieve flow. Below the yield
stress, no flow occurs and the material exhibits solid like characteristics due
to the stored energy (Steffe, 1996).
Toothpaste, tomato paste, margarine and chocolate
mixtures are some examples of Bingham plastic fluids (Rao, 1999; Worlow, 1992).
2.10.2. Power-law Fluids
2.10.2. Power-law Fluids
This type of non-Newtonian behavior can be explained
by a power-law equation also called Osiwald-de Waele equation. This
model has been used extensively to describe the non-Newtonian flow behavior
both in theoretical analysis and in practical engineering calculations (Worlow,
1992; Bourne, 1982).
i = K . gn (3)
where, K is the consistency coefficient (Pa. sn)
and n is the flow behavior index, (dimensionless). The consistency coefficient
is an indicator of the viscous nature of a fluid.
Apparent viscosity: μa, is the ratio of shear stress to shear rate at a
given rate of shear for shear dependent fluids. It represents the viscosity of
a Newtonian fluid exhibiting the same resistance to flow at the chosen shear
stress or shear rate (Van Wazer and Lyons, 1966).
The apparent viscosity, ia, for power-law fluids (Steffe, 1996) is,
The apparent viscosity, ia, for power-law fluids (Steffe, 1996) is,
Μ = f (g) = K.gn = K.gn-1 (4a)
g
of which the logarithmic form is used to determine the
model parameters when experimental data are available as,
lnμa=lnK+(n—1) ln g (4b)
According to the magnitude of the flow behavior index,
n, power-law fluids are divided into two categories as shear thinning and shear
thickening fluids.
2.10.2.1. Shear thinning Fluids
The majority of non-Newtonian fluids are covered in
this category. With shear thinning (or pseudoplastic) fluids, the shear stress
vs. shear rate curve begins at the origin but is concave upward. An increasing
shear rate gives a less than a proportional increase in the shear stress.
Applesauce, banana puree, orange juice concentrate, and many salad dressings
are considered as shear thinning foods. While apparent viscosity is constant
with Newtonian materials, it decreases with increasing shear rate in shear
thinning fluids. Eq.3 applies to this type of behavior where, the flow behavior
index is less than unity (n<1) (Rao, 1999; Steffe, 1996; Bourne, 1982).
2.10.2.2 Shear
thickening Fluids
In shear thickening behavior, the shear stress vs.
shear rate curve also go through the origin and it is concave downward; that
is, an increasing shear stress gives a less proportional increase in shear
rate. Apparent viscosity, the slope of the associated curve, increases with
increasing shear rate. This type of flow is observed with gelatinized starch
dispersions and corn flour-sugar solutions (Rao, 1999). Power-law model
equation (Eq.3) is often applicable with the flow behavior index greater than
unity (n> 1).
2.10.2.3. Herschel-Bulkley Fluids
Herschel-Bulkley model is a general relationship to
describe the behavior of non-Newtonian fluids (Figure 1).
i = Kγn + io (5)
It is a very convenient model since it reduces to
Newtonian (n = 1) and to power-law behavior (n =1) as special cases (i0 = 0). In addition, the model describes the Bingham
Plastic Model where the yield stress is required (Steffe, 1996).
2.11. Time-Dependent Fluids
In some fluids, the apparent viscosity can either
increase or decrease with time of shearing at a constant shear rate. Such
changes can be reversible or irreversible. Time dependent fluids can be
categorized into two classes as thixotropic and rheopectic fluids.
2.11.1
Thixotropic Fluids
Foods that exhibit time-dependent shear thinning
behavior are said to be thixotropic fluids. Most of these fluids possess a
heterogeneous system containing a fine dispersed phase. When at rest, particles
and molecules in the food are linked together by weak forces. During shear the
hydrodynamic forces are sufficiently high to break the interparticle linkages,
resulting in a reduction in the size of structural units. Thus, a lower
resistance to flow is detected during shear. This type of flow behavior is
likely to occur with foods such as salad dressing and soft cheeses where the
structural adjustments take place in the food until equilibrium is reached
(Rao, 1999). The occurrence of thixotropy implies that the flow history must be
taken into account when making predictions about the fluid behavior (Barnes et
al., 1989).
2.11.2 Rheopectic
Fluids
Rheopexy (or antithixotropy) is associated with time
dependent shear thickening behavior. These fluids are quite rare in occurrence.
Viscosity of these fluids increases with time at a constant shear rate (Steffe
1996).
2.12. Variables
Affecting Viscosity and Flow Behavior Parameters
It is critical to emphasize the way viscosity depends
on variables like shear rate, temperature, pressure, time of shearing, and
concentration. Fluids are subjected to high sensitivity due to changes in these
variables. Time of shearing and variable shear rates affect viscosity due to
the resulting structural changes in the fluid. However, for most practical
purposes, the pressure effect is ignored. Temperature and concentration on the
other hand, considerably affect rheological parameters (Barnes et al., 1989).
2.12.1. Effect of Temperature
There is usually an inverse relationship between
viscosity and temperature. A wide range of temperatures are encountered during
processing and storage of fluid foods, so the effect of temperature on
rheological parameters is needed to be determined. While the flow behavior
index, n, is assumed to be
relatively constant with temperature, the effect of temperature on both
apparent viscosity, μa and consistency coefficient, K of the power-law model is
explained by an Arrhenius type relationship (Rao, 1999) as,
K = K0
exp [- Ea/RT] (Equation
4)
Where K0 is reaction frequency
factor, Ea is activation energy of gelatinization (J/mole), R is gas constant
(8.314 J/mol K) and T is absolute temperature (K).
The quantity Ea, is the energy barrier that must be
overcome before the elementary flow process can occur (Rao, 1999).
2.12.2. Effect of Concentration
Hydrocolloids are polymeric materials that are soluble
or dispersible in water; for example: They are usually added to food
formulations to increase their viscosity or to obtain a gelled consistency
(Lewis, 1987) Kinsella (1976) reported that viscosity is influenced by
solubility and swelling properties. Snyder and kwon (1987) reported that the
more material there is in solution the higher the viscosity. King (2005)
reported that the viscosity of starch granules in suspension increased
depending on starch concentration. Lewis (1987) states that viscosity rapidly
increases due to concentration increase and there is often a transition from
Newtonian to non-Newtonian behavior and the extent of the concentration is
governed by the viscosity characteristics of the concentrate.
There is usually a direct nonlinear relationship
between concentration of a solute and viscosity at a constant temperature
(Bourne, 1982). In most foods, it is often possible to identify the components
that play an important role on the rheological properties.
2.12.3 Effect of other Ingredients
Food products are complex mixtures of different
ingredients where individual ingredients are mixed together to produce a
finished product. In many cases, the individual ingredients consist of mixtures
of solid as well as fluid components. Must times, they are not homogeneous, and
the properties vary throughout the sample. A change in one of the raw
ingredients can also have a dramatic effect on the final product (Herh, et
al, 2000).
2.13. Measurement of Flow
The study of the Newtonian and non-Newtonian flow
behavior necessitates considerable care and instrumentation. Data from poorly
designed instruments can be misleading. A viscometer must be capable of
providing readings that are convertible to shear rate (y) and shear stress (i).
Further a well designed instrument
should provide recording of data in order to study time dependent behavior
(Rao, 1999).
For viscometric measurements, the flow in the selected
geometry should be steady, laminar, and fully developed. The temperature of the
test fluid should be maintained uniform and constant for reliable measurement
(Rao, 1999). Viscosity of fluids is highly temperature dependent. For instance,
the viscosity of water at 20°C changes 2.5% per 1°C temperature change.
Therefore, in all viscosity measurements it is essential that the temperature
is closely controlled (Boume, 1982). For Newtonian fluids, viscometers that
operate at a single shear rate (eg. glass capillary) are acceptable. For
non-Newtonian fluids, data should be obtained at several shear rates. Common
viscometric flow geometries for rheological studies on foods are (1) concentric
cylinder, (2) cone-plate, (3) parallel plate, (4) capillary/tube/pipe, and (5)
slit flow (Rao, 1999). For viscosity measurements laminar flow conditions
are desired. Under conditions of turbulent flow of Newtonian fluids, the
measured viscosity was higher. However, since non-Newtonian fluids are
generally viscous, usually laminar flows are encountered (Rao, 1999).
2.14. Rotational
Viscometers
Traditional rotational viscometers comprise of cone
and plate, parallel plate and concentric cylinder units operated under steady
shear conditions (Steffe, 1996). The shear rate is derived from the rotational
speed of a cylinder or a cone. If the properties of flow behavior are required
for the design of processes, it is recommended to use shear rates that cover
the range that is expected to be used in the process (Rao, 1999).
2.14.1. Concentric Cylinder Viscometer
The concentric cylinder viscometer is a very common
instrument that would operate in a moderate shear rate range. This function
makes it a good choice for gathering data used in several engineering
calculations (Steffe, 1996). It permits continuous measurements to be made
under a given set of conditions and allows time-dependent effects to be
studied. This is the most common type of viscometer that is used in the food
industry (Boume, 1982). In concentric cylinder geometry, a cylinder (bob) is
placed coaxially inside a cup containing the selected volume of the test fluid
(Rao, 1999). In Searle system concentric viscometer (Figure 1.4), the bob
rotates and the cup is stationary. Couette-type systems are also available
where the cup rotates and the bob is stationary (Rao, 1999). In Searle systems,
the bob is rotated at a constant speed and the drag of the fluid on the bob is
measured by means of a torque sensor. The measured figure is the torque (M)
required to maintain a constant velocity of the bob (Q). By changing the rotational
speed, thus the shear rate and measuring the resulting shear stress, it is
possible to obtain viscosity data over a wide range of shearing conditions
(Steffe, 1996).
The following assumptions should be made in order to
derive the mathematical relationships for the instrument performance (Steffe,
1996):
• Flow is laminar and steady,
• End effects are negligible,
• Test fluid is incompressible,
• Properties are not a function of pressure,
• Temperature is constant,
• There is no slip at the wall,
• Radial and axial velocity components are zero (Steffe, 1996).
• End effects are negligible,
• Test fluid is incompressible,
• Properties are not a function of pressure,
• Temperature is constant,
• There is no slip at the wall,
• Radial and axial velocity components are zero (Steffe, 1996).
CHAPTER THREE
3.0
MATERIALS AND METHOD
3.1
SOURCES OF SAMPLES
Coconut, yellow variety of fresh
tiger nut and packaged whole milk powder was purchased from a local market
(meat market) in Abakaliki metropolis, Ebonyi state, Nigeria. While the starter culture was also purchased
from a supermarket in Abakaliki metropolis, Ebonyi, state Nigeria. The lactose and sucrose was purchased from Ogbete
main market at Enugu, Enugu State, Nigeria:
3.2 SAMPLE
PREPARATION
3.2.1 PREPARATION
OF MILK
3.2.1.1 PREPARATION
OF COCONUT MILK
The coconut was broken by using small
club while the meaty part was removed using a dull stainless stell knife. The brown skin was removed with a sharp knife
and the meaty part without the brown skin were thoroughly wash and grated using
a grater. The grated coconut meaty part were mixed with warm portable water in
a bowl allow to stand for 10mins to extract the oil, aromatic compounds and the
milk. The extract were filtered through
a muslin cloth to separate the milk from the insoluble chaff to obtain a milk –
white emuslsion with a sweet coconut flavour (Belewu, M. A., Belewu, K.Y and
Bamidele, R.A, 2010). The milk was stored
at 5oC Inside the
refrigerator before use.
3.2.1.1
PREPARATION OF TIGER- NUT MILK
The method of Belewu and Abodunin
(2007) was adoptd. The preparation of
the tiger-nut milk was done by picking out those foreign and bad nuts that
could affect the taste and keeping quality of the milk. The tiger-nut was washed and rinsed with
portable water. One kg of tiger nut was
conditioned over night in laities of portable water to soften the fiber. The total content was blend several times with
a blender. The mash was filtered through
a mush in cloth to separate the milk from the insoluble chaff. It was further stain to obtain a fine
consistency and was stored at 180c until use.
3.2.1.1.1
YOGURT PREPARATION
EXPERIMENTAL TREATMENTS
Various yogurt samples was prepared by combining
two of the different milk source together.
The
experimental treatment was shown in table (3)
Table (3)
T1
= 100% whole milk powder (control)
T2
=100% tiger nut milk yogurt
T3
= 100% coconut milk yogurt
T4
=30% tiger nut milk yogurt + 70% coconut milk yogurt
T5
=50% tiger nut milk yogurt+ 50% coconut milk yogurt
T6
=70% tiger nut milk yogurt + 30% coconut milk yogurt
T7
= 40% tigernut milk yogurt + 40% coconut
milk yogurt + 20% whole milk yogurt
3.2.1.2
PREPARATION OF VARIOUS BLENDS YOGURT
The method of Belewu et al; (2005) was used. The
various milk sample mixture in table3 was heated separately to a temperature of
850c for 15mins, then cool rapidly to a temperature of 430c. Each of the treatment was inoculated at this
temperature with 2% of thou this starter culture (streptococcus thermophillus
and lactobacillus bulgaricus). After
complete fermentation, 5g of sugar was added to each of the treatment. The stored yogurt was stored in the
refrigerator until for analysis.
3.3 ANALYSIS
OF SAMPLE
3.3.1
PHYSICO- CHEMICAL ANALYSIS
3.3.1.1
pH
The pH value of the yogurt sample was
measured in a 50ml beaker at a temperature of 2o.c using a Digital
flt meter (model 152k).
3.3.1.2 TOTAL
TITRATABLE ACIDITY (TTA)
The total titratable acidity of the
yogurt sample was determined as described by Morris (1999). 10ml of yogurt
sample was transferred to a proclaim dish with the aid of 10ml pipettle. The
pipettle was rinsed with 10ml of water and the rinse was added to the dish 1ml
of Phenolphthalein indicator solution was added to the dish and titrated with
0.IN sodium hydroxide (NaOH) solution until a pink colour was obtained.
The
titretable acidity (% lactic acid)= titer value x molarityx 0.09 x 100
Volume of sample (ml) 1
3.3.1.3 TOTAL
SOLIDS (TS)
The total solids was determined by
(AOAC,1995) method. 4g of the sample was
weighed into a metal dish and keep in a water bath for 30mins and thereafter
heated in an over at 1000c for 21/2
hours. The sample was cooled in a
desicator for 30mins and weighed. The
sample was reheated in the over for another one hour, cooled and
reweighed. This was repeated until
weight loss between successive weighing become.
Negligible (<0.5g). the percent
total solids was calculated from the formular:
Ts%
= Final weight of yogurt sample- weight of dish x 100
Weight of sample 1
3.2.1.3
TOTAL SOLUBILITY (oBRIX)
The total sugar (oBrix) was determined
using Refractometer method. The
refractive index of the yogurt was determined at 200c
3.4 Viscosity measurement
The
viscosity readings of each yogurt was measured using a digital display
viscometer (model NDJ-85) taken at constant time intervals with progressively
increasing shear rate 96-60/mins). Viscosity values was obtained by multiplying
viscosity readings with appropriate factor.
FLOW
CHARACTERISTICS
Flow curves
was plotted with the values obtained. From equation3, log log plot of Uapp against
y, a straight line of slope (n-1) 3.5 SENSORY ANALYSIS
A
twenty-member, semi-trained panel was used to evaluate the various sensory
parameters (flavour, appearance/colour, taste/sourness, texture/consistency and
overall acceptability). The score was base on a hedonic scale range from 9
representing “like extremely” to1 representing “dislike extremely” (Iwe, 2002).
3.6 STATISTICAL ANALYSIS
All data was
subjected to analysis of variance (ANOVA) to determine any significant
difference at 5% level (LSD) using Iwe, (2002) method.
CHAPTER FOUR
4.0 RESULT AND DISCUSSION
4.1 PHYSICAL PROPERTIES
Table 1: Physical properties of yogurt and yogurt-like product
produced from whole milk, coconut, tigernut and their composites.
|
Samples
|
pH
|
Acidity(%)
|
Total solid(%)
|
Brix(%)
|
|
100%T
|
4.53c
|
0.11a
|
13.55e
|
2.00f
|
|
100%C
|
4.49d
|
0.39a
|
26.95a
|
6.00d
|
|
30T:70C
|
4.54c
|
0.43a
|
16.68cd
|
6.50c
|
|
50T:50C
|
4.62a
|
0.35a
|
16.10d
|
6.50c
|
|
70T:30C
|
4.58b
|
0.95a
|
18.15c
|
5.00e
|
|
40T:40C:20M
|
4.54c
|
0.96a
|
22.05b
|
11.80a
|
|
100%Milk
|
4.26e
|
0.05a
|
20.85b
|
10.00b
|
Men values in the same column having the same
superscripts are not significant different (p>0.05).
100% Tigernut milk yogurt
100% Coconut milk yogurt
50% Tigernut milk yogurt + 50%cocnut milk yogurt
70% Tigernut milk yogurt + 30% coconut milk yogurt
30% tigernut milk yogurt + 70%cocunut milk yogurt
40% tigernut milk yogurt + 40% coconut milk yogurt +
20% whole milk yogurt
100% whole milk yogurt (control)
4.1.1 pH
The pH of
coconut tigernut yogurt blend sample is shown in Table 1. The pH of the samples
ranged from 4.26(100%whole milk) to 4.62(50% tigernut milk yogurt + 50% coconut
milk yogurt), this is within the range reported in literature by Belewu,(2007).
There were significant difference (p<0.05) between the samples.
4.1.2 Total titratable acidity (TTA)
The
titratable acidity which is an expression of the percentage Lactic acid content
(Lee, 1985) showed no significant difference (p>0.05 in the yogurt sampler.
An
indication of higher acidity of the yogurt samples may confer longer keeping
quality on the products. The total titratable acidity of the yogurt ranged from
0.05 (100%whole milk yogurt) to 0.96(40%jiger nut milk yogurt + 40% coconut
milk yogurt + 20% whole milk yogurt), this it within the range reported by
(Ihekoronye and Nooody; 1985, SON, 1997; Douglas. 1985; Alakali et al, 2005).
4.1.3 Total solid(%)
The total
solid of the yogurt ranged from 13.55 (100% Tigernut milk yogurt) to 26.95
(100% coconut milk yogurt). The total solid of 100% coconut had highest value.
All the samples are significantly different from each other accept 40T; 40C:
20m and 100% whole milk, 30% tigernut + 70% coconut and 50% tigernut + 50%
coconut.
4.1.4 Total Soluble solid (Brix0).
Table I
also should the total soluble solid (Brixo) of coconut – tigernut
yogurt blend sample. The mean values of the total soluble solid of the blend of
yogurt ranged from 2.00 (100% tigernut yogurt) to 11.80 (40% tiger + 40%
coconut + 10% whole milk). There were significant differences between the
samples (p<0.05). The result are however, important as they indicate
available substrates for yeast fermentation. On the other hand, the total
soluble solid of the test samples could be due to increased activity of amylotytic
enzymes which hydrolyze starch and other complex carbohydrates to simple sugar
(Kazanes and fields, 1981).
4.2 Rheological Propertics of Coconut – Tigernut Yogurt
blends.
The values of
consistency coefficient, K, flow behaviour index(n) and Correclation
coefficient (R2) of Coconut – Tigernut yogurt blends are presented
in table 5 below
Table 5: Rheological
characteristics of coconut tigernut yogurt blends.
|
Samples
|
Consistency index(k) Ns/m2
|
Plow behaviour index(n)
|
Correlation coefficient(R)2
|
|
Control
|
2.7290
|
0.642
|
0.9469
|
|
100% T
|
2.2267
|
0.334
|
0.9452
|
|
10%C
|
2.6608
|
0.835
|
0.5030
|
|
50% T: 50%
|
2.2607
|
0.263
|
0.9552
|
|
70%T: 30%C
|
2.2028
|
0.324
|
0.9552
|
|
30%T: 70%C
|
2.1995
|
0.331
|
0.9620
|
|
40%T:40%C:20%M
|
2.2755
|
0.266
|
0.9535
|
Control = 100% whole
milk yogurt
100%T =100% Tigernut
yogurt
100%C = 100% Cocount
yogurt
50%T: 50% C =
50%Tigernut yogurt + 50% coconut yogurt
70%T: 30% C =
70%Tigernut yogurt + 30% coconut yogurt
30%T: 70% C =30%
Tigernut yogurt + 70%cocunt yogurt
40%T: 40%C: 20%M = 40% Tigernut yogurt + 40% coconut
yogurt + 20% whole milk yogurt.
Flow
Behaviour of the yogurt samples
The values of consistency (k) and flow behaviour (n)
indices of the seven yogurt blend samples were studied and are presented in
table 5. the apparent viscosity of the yogurt blend samples increased with
increase in shear rate, with control having the highest apparent viscosity,
followed by 100%C, while the 70%T: 30%C had the lowest at all the share rate
studied. This result was expected may be due to the increasing liquid matter
content of the samples.
All
the sample showed pseudoplastic behaviour, where viscosity decreased when shear
rate increased (Figure 2) and when the yogurt blend increased (table 5).
Similar trends were observed by (Awonorin, 1993; Alvarez et al; 2005, Ariahu et al; 2001;
Alakali et al; 2003; Sopode and
Kassum, 1992; Irtwange et al; 2009;
Ikegwu and Ekwu, 2009).
This pattern
is defined as shear thinning, where shear stress increased with increase in
shear rate (figure 3) and is expected because an increased in relational speed
increases molecular alignment in the direction of flow, reducing resistance to
flow and hence viscosity (Rha, 1975).
However,
the curve obtained in figure 2, is a typical of dispersions exhibiting psudoplastic
flow and indication that the milk verities had not altered the rheological
class of the yogurt dispersion. This phenomenon has been widely reported to be
common with hydrocolloid solution and food pastes with sensitive structures
(Awonorin, 1993).
The
power mode or the Ostwald de waeles mode (o-kyn) was used in this
study to fit this experimental data. All the samples presented a flow behaviour
index, n less then I, indicating pseudoplasticity. This is consistent with
other pluid food such as tomato paste (Alakali and Ijabo, 2003), palm oil
(satimehin et al; 2003) “achi” flour
(Ikegwu and Ekwu, 2009; Uzomah and Ahiligwo, 1995), (Kumu Zaki and Kunu Gyada
(Sapode and Kassum, 1993). Earle (2004) reported that when n<,I a case of
pseudoplesticity is established. Analysis of variance (ANOVA) (P<0.05)
showed that flow behaviour index, n and consistency coefficient k, are
significantly influenced by the charge of the milk variety used.
The
values of k(table 5) were significantly influenced as the percentage of yogurt
blends increased. The lower values of the flow behaviour index(n) can be
attributed to higher departure from Newtonian behaviour. Furthermore, the
consistency coefficient, increased with the yogurt blends, with very high
correlations coefficient, R2, ranging between 0.503 and 0.9552,
indicatory that the power law education adequately described the rheolegical
pattern of yogurt dispersions.
The
effect of viscosity on the yogurt sample at shear rate of 0.5s-1
as shown in figure 1, indicate that the 100% whole milk yogurt had the highest
value of apparent viscosity, followed by 100%C while the least apparent
viscosity was 70%T: 30%C.
4.3 The result of
the sensory analysis of yogurt sample are presented in Table 2
|
Samples
|
Appearance
|
Flavour
|
Taste
|
Texture
|
General Acceptance
|
|
100%T
|
4.9b
|
4.8b
|
5.2b
|
4.6b
|
5.3b
|
|
100%C
|
5.7b
|
4.9b
|
4.3bc
|
4.2b
|
5.3b
|
|
30T:70C
|
5.2b
|
4.7b
|
4.6bc
|
3.6bc
|
4.7b
|
|
50T:50C
|
4.8b
|
5.5b
|
5.2b
|
4.8b
|
5.2b
|
|
70T:30C
|
5.1b
|
5.3b
|
5.8b
|
4.5b
|
5.1b
|
|
40T:40C:20M
|
8.0a
|
7.8a
|
8.0a
|
8.0a
|
8.0a
|
|
100% whole Milk
|
7.9a
|
7.8a
|
8.4a
|
8.3a
|
8.4a
|
Men values in the same column having the same superscripts
are not significant different (p>0.05).
100% whole milk
(control)
100% Tigernut milk yogurt
100% Coconut milk yogurt
50% Tigernut milk yogurt + 50%cocnut milk yogurt
70% Tigernut milk yogurt + 30% coconut milk yogurt
30% tigernut milk yogurt + 70%cocunut milk yogurt
40% tigernut milk yogurt + 40%cocunut milk yogurt +
20% whole milk yogurt.
4.2.1 Appearance
The
appearance of the yogurt refers to the level of visual appeal of the products
obtained by fermenting the various milk substrates. From table 2, 1005 whole
milk (control) and 40% tiger nut milk
+40% content milk + 20% whole milk are not significantly different from each
other but they are significantly different from other samples at (p<0.05).
40% tigernut milk + 40% coconut milk + 20% whole milk produced a clean natural
colour with a smooth appearance.
4.2.2 Flavour
The flavour
produced from the fermentation of the yogurt is essentially due to the
production of acetaldehyde and other volatile aromatic compounds resulting from
the breakdown of carbohydrates by the relevant microbes (Ihekoronye and Ngoody;
1985). It is seen from table 2 that 100% whole milk was most preferred interms
flavour and was significantly different
from all other samples. Flavour or yogurt depends on lactic acid, acetaldehyde,
acetic acid and diacetyle (Douglas, 1985).
4.2.3 Taste/Sourness
Sources is
a desirable characteristic of yogurt
which expresses the level of tang produced as a result of the production lactic
acid by the action of lactobascilus bulgaricus on lactose (sugar in milk) in
the substrates (Moore, 2004). From table 2 this on sources for the yogurt
samples indicate that whole milk yogurt was most preferred in terms of taste
flowered by 40% tigernut milk + 40%
coconut milk + 20% whole milk and they are significantly different form other
samples.
4.2.4 TEXTURE
Texture or
consistency is an attribute of the yogurt to flow without forming hagging
insoluble particles on the inner side of the containers (Moore, 2004). It
refers to the property of the yogurt to exhibit smoothness and good flow
behaviour or properties. From table 2, the result revealed that whole milk
yogurt was most desirable followered by 40% tigernut milk + 40% coconut milk +
20% whole milk and was significantly different from all other samples. 30%
tigernut milk + 790% coconut milk has the least desired consistency rated as
dislike when compared with the other yogurt sample blends. All other samples
containing 100% tigernut milk, 100% coconut milk or blend were not
significantly different from each other at (p>0.05).
4.2.5 GENERAL ACCEPTANCE
Generally,
it could be deduced from the results that the control (100% whole milk yogurt)
was most desirable followered by 40% tigernut milk + 40% coconut milk + 20%
whole milk and was significantly different from all other sample at
(p>0.05). All samples containing 100% tigernut milk, 100% coconut milk and
the blend of the two were not significantly different from each other. Base on
the sensory evaluation. It appeared that sample 50% tigernut milk 50% coconut
milk was the third most referred. According to sinful (2009) on the use of
tigernut (Cyperus esculantus), cow
moil and their composite as substrate for yogurt production, consumers are more
inclined to accept yogurt made form two composite substrate than one substrate.
Fig. 1. Apparent viscosity of
yogurt samples at shear rate of 0.5 s-1
Fig. 2. Apparent viscosity Vs
shear rate of yogurt samples
Fig. 3. Shear stress Vs shear
rate of yogurt samples
|
|
Rheological
parameter
|
|
||
|
Sample
|
K (Pa.s)
|
n
|
R2
|
|
|
Control
|
2.729
|
0.642
|
0.9469
|
|
|
30%T:70%C
|
2.1995
|
0.331
|
0.962
|
|
|
100%T
|
2.2267
|
0.334
|
0.9452
|
|
|
70%T:30%C
|
2.2028
|
0.324
|
0.9552
|
|
|
50%T:50%C
|
2.2607
|
0.263
|
0.9552
|
|
|
40%T:40%C:20%M
|
2.2755
|
0.266
|
0.9535
|
|
|
100%C
|
2.6608
|
0.835
|
0.503
|
|
|
|
|
|
|
|
CHAPTER FIVE
5.0 CONCLUSION AND RECOMMENDATION
5. 1 Conclusion
The
results obtained from the physical properties indicate the pontenelitity blend
of coconut milk and tigernut milk in the production of yogurt.
The results
obtained from the reheological study, shown that the apparent viscosity decreased
with increase in shear rate indicating shear thinning behaviour characteristics.
The coconut Tigernut yogurt blends studied exhibited pseudoplastic behaviour
because their “n” values were generally below I (n<1) it was evident that
shear stress also increased with increased in shear rate.
The sensory
evaluation of yogurt produced from coconut – tigernut milk studied did not show
a different trend in variation statistical (p>0.0.5) between samples
produced in terms of appearance, testes, flavour and texture. However, there
was no significant different (p> 0.05) between sample 100% tigernut yogurt,
100% coconut yogurt, 30% tigernut yogurt + 70% coconut yogurt 50% tigernut
yogurt + 50% cocnut yogurt and 70% tigerunt + 30% coconut yogurt in their
appearance, flavour, taste, texture and general acceptance. The increase in
protein demand in developing countries led to effort in finding alternative sources
of protein in plant seeds. However, data obtained from this study shows that
coconut – tigernut yogurt could be helpful in meeting a significant portion of
the daily needs of these nutrients.
5.2 Recommendation
The high
cost of imported milk and milk production in Nigeria and Africa seen to have
made consumers more ready to accept milk produced from plant source.
This
research work revealed that products from tigernut and coconut should be
encourage so as to solve the problem of protein calorie malnutrition in Africa
and improve the protein intake of the Nigeria population.