ABSTRACT
Orange-fleshed sweet potato flour was processed from UMUSPO1, a well-known orange- fleshed sweet potato varieties from National root crop research institute Umudike. The effect of processing pretreatments and storage on total carotenoid content, proximate composition, functional properties and microbial quality of the flour samples were investigated. Three pretreatment methods; blanching, boiling and treating with 0.5% metabisulphite solution for 10mins were employed and the flour samples were either sun dried or oven dried. Significant percentage decreases (P<0.05) were observed in the total carotenoid content of the samples after storage which ranged from 5.47% - 27.3%, however blanched oven dried flour samples retained higher percentage total carotenoid content of53.83% while the untreated sun dried sample had 15% retention which is the lowest after 3months of storage. There were significant differences (P<0.05) in the proximate composition of the samples during storage and this varied among pretreatment methods. Moisture content of the flour samples ranged from 8.23% - 12.01% which is within the acceptable limit. There were significant differences (P<0.05) in carbohydrate (75.36%-83.62%), crude fiber (1.7% -2.65%), protein (6.50% - 8.00%), fat (0.47% -1.7%) and ash (1.63% - 1.89) content of the flour samples. The functional properties of the flour samples showed significant differences (P<0.05) in their values with Swelling power ranging from 13.12% - 15.54ml/g, OAC 1.45-3.55g/ml, WAC 2.40-3.05%, Gelatinization temperature 76.500C-830C and Bulk density 0.61g/ml – 0.70g/ml. There were significant increases (P<0.05) in the bacterial load of the samples during storage with boiled sundried sample having the highest increase from 10.00 - 14.00 × 104CFU/g while metabisulphite treated oven dried maintained the lowest values from 5.50-8.50 × 104CFU/g from 0 month to 3rd month. However, there was no significant difference (P>0.05) in the fungal load of the flour samples.
TABLE
OF CONTENTS
Title Page i
Declaration ii
Certification iii
Dedication iv
Acknowledgement v
Table of Content vi
List of Tables vii
List of Figure viii
Abstract ix
CHAPTER 1:
INTRODUCTION
1.0 Background of the Study 1
1.1 Statement
of the Problem 2
1.2 Objective
of the Study 3
1.2.1 The Main Objectives of the
Study 3
1.2.2 Specific
Objectives of the Study 4
1.3 Justification
of the Study 4
CHAPTER 2: LITERATURE
REVIEW
2.1 Varieties
of Sweet Potato 5
2.2 Nutritional
Composition of Sweet Potato 5
2.3 Provitamin A and Antioxidant Activities of Orange
Fleshed Sweet Potato 6
2.4 Carotenoids
7
2.5 Retinol
Equivalent 8
2.6 Effect
of Processing on the Beta Carotene Content of Orange Fleshed
Sweet
Potato 8
2.7 Degradation of Carotenoids in Sweet Potato during
Processing 9
2.8 Carotene
Retention 10
CHAPTER 3: MATERIALS AND METHODS
3.1 Sources
of Materials/Sample Collection 11
3.2 Sample
Preparation for Orange Fleshed Sweet Potato Flour 11
3.2.1 Blanched
samples (treatment I) 11
3.2.2 Boiled
sample (treatment 2) 12
3.2.3 Pretreatment
with sodium metabisulphite (treatment 3) 12
3.2.4 Preparation
of the control sample (untreated sample) 12
3.2.5 Preparation
of the fresh sample for proximate composition and
carotenoid content
analysis
12
3.3 Physiochemical
Composition Analyses 14
3.3.1 Determination
of moisture content 14
3.3.2 Determination
of crude fiber content 14
3.3.3 Determination
of fat content 15
3.3.4 Determination
of protein content
16
3.3.5
Determination of carbohydrate content 17
3.3.6
Determination of ash content 17
3.3.7
Energy value 18
3.4 Determination
of the Total Carotenoid Content 18
3.4.1 Measurement
of absorbance 19
3.5 Functional Properties 20
3.5.1 Bulk
density 20
3.5.2 Gelatinization
temperature 20
3.5.3 Determination
of swelling power 20
3.5.4 Determination
of water/oil absorption capacity 21
3.6 Determination
of Microbial Load 22
3.7 Statistical
Analysis 23
CHAPTER FOUR: RESULTS
AND DISCUSSION
4.1 Proximate
Composition 24
4.2 Total
Carotenoid Content Composition 27
4.3 Functional
Properties 29
4.4 Microbial
Content
32
4.5 Effect
of Storage on Proximate Composition of OFSP flour 33
4.6 Effect
of Storage on Functional Properties of OFSP flour 44
CHAPTER 5: CONCLUSION AND RECOMMENDATION
5.1 Conclusion 54
5.2 Recommendations 55
REFERENCES 56
LIST OF
TABLES
PAGES
4.1
Effect of pretreatment on the
proximate composition (%) of the
flour samples 24
4.2 Effect
of pretreatment on the total carotenoid content of the
flour
samples 27
4.3 Effect of pretreatment on the functional
properties of OFSP flour 29
4.4 Effect of pretreatment on the microbial
load of OFSP flour 32
4.5 Effect of storage on the moisture content
(%) of flour 33
4.6 Effect of storage on carbohydrate
composition (%) of OFSP flour 35
4.7 Effect of storage on the fiber content
(%) fiber of OFSP flour 36
4.8 Effect of storage on the protein content
(%) of OFSP flour 37
4.9 Effect of storage on the fat content (%)
of OFSP flour 39
4.10 Effect of storage on the Ash content (%) of
OFSP flour 40
4. 11 Effect
of storage period (Months) in total carotenoid content
(µg/100g) of flour
samples. 42
4.12 Effect of storage on the swelling power
(g/ml) of the OFSP flour 44
4.13 Effect of storage on the oil absorption
capacity (ml/g) of OFSP flour 45
4.14 Effect of storage on water absorption of
capacity (%) of OFSP flour 47
4.15 Effect of storage on gelation temperature
(°C) of OFSP flour 48
4.16 Effect of storage on Bulk Density (g/ml) of
OFSP flour 49
4.17 Effect of storage on bacterial load (x 102CFU/g)
of OFSP flour 51
4.18 Effect of storage on fungi load of (x 104CFU/g)
OFSP flour 52
LIST OF FIGURES
PAGES
1:
Processing flow chart for orange fleshed sweet potato flour 13
2: Sketch for dilution of orange-fleshed
sweet potato flour for microbial
content estimation.
22
LIST OF APPENDICES
PAGES
1:
Peeled orange fleshed sweet potato sample 65
2: Flour samples of processed OFSP 66
CHAPTER 1
INTRODUCTION
1.0 BACKGROUND OF THE STUDY
Sweet
potato (Ipomea batatas) is a very
important and unique staple crop in southern and eastern part of the African
continent (Tumwegamire et al., 2007) grown
for its economic importance (Woolfe, 1992). According to FAOSTAT (2019), China is the
leading producer of sweet potato, followed by Nigeria, Tanzania, Indonesia and
Uganda with an average production rate of 112.8million tons from these five
countries. Sweet
potato is one of the staple root crops abundantly grown in Africa and according
to International Potato
Center (2017) is the third most vital food crop in eastern and seven other
central Africa being the 4th most important crop in about six
southern African nations and 8th priority in four Western African
countries. It is usually cultivated and propagated by
vegetative method and they are drought resistant. The tuberous root and the
leaves are also eaten (Bovell-Benjamin, 2007).These characteristics and
qualities make Orange fleshed sweet potato a dependable crop for food security.
It requires less labour to maintain once it is established and can be stored
over a broad range of time in the soil without considerable loss if not
harvested immediately at maturity (Woolfe, 1992). Harvest Plus was the very
first to release conventionally bred Vitamin A bio-fortified sweet potato varieties
(Andrade et al., 2013). Sweet potato has
become a sustainable low-input/low-out crop to a significantly important cash
crop, reliable revenue and food source to low income farmers as it can be
gradually harvested on demand (Tairo et
al., 2005). It has helped to improve the health of poor families in
Sub-Saharan Africa due to its high pro-vitamin A content (Ganiyat et al., 2013). Efforts have been made to
preserve these crops after harvest in order to make them more available through
the process of moisture removal using different methods of drying and
pretreatments. Processing sweet potato into dry form helps to reduce the moisture content and
converts the roots into a product that is more stable and transportable (FAO,
1990). Despite its versatility, it is still among
the world’s most underutilized crop in many underdeveloped and developing
countries after rice, wheat, maize and cassava (Owori et al., 2007; Ezeano, 2010). Sweet potato and its products have
different roles they play. They act as supplement in the human diets and also
luxury food besides being a staple crop. Due to the improved drying techniques
and technology that have evolved in recent times, different kinds of dried
sweet potato chips and flour are popular in the market shelves. Flours
processed from these sweet potatoes dried chips are used to produce end
products such as ready to eat foods like noodles and snacks.
1.1 STATEMENT OF THE PROBLEM
Orange-fleshed
sweet potato (OFSP) is a very good source of provitamin A used in many
developing countries to combat blindness and vitamin A deficiency because of
its rich beta-carotene content. Sweet potato is considered a secondary staple
food in Sub-Saharan Africa where it plays an important role in controlling
malnutrition (Jaarsveld et al., 2005).
It is usually planted as an intervention crop after disasters because it
matures early and gives bountiful amount of food supply to the populace (Katz
and Weaver, 2003). However, the short life due to its
perishability is a great challenge in developing countries. Sweet potatoes are
generally in abundance during harvesting period, but due to their very high
water content, they are faced with the challenges of storage owing to their
high perishability. They are therefore consumed as boiled, steamed or fried
potato for only a limited period after harvest. Hence processing it into
products such as flour which are then, packaged and stored would help to
increase the shelf life of sweet potato. This can be used to develop composite
flour with wheat to produce several confectionaries like bread, cake etc.
Functional properties of flours have been shown to be
affected by different processing methods e.g taro flour being affected by heat
process (Tagodoe and Nip, 1994) and gelatinization profiles of cassava flour
being affected by drying temperature, milling procedure and particle size (Fernmandez et al., 1996). Factors such as variety,
processing step, processing method (parboiling and blanching) have been
reported to influence the beta carotene quality of sweet potato flour
(Osundahunse et al., 2003; Van Hal,
2000; Jangchud et al., 2003).
Beta-carotene content of sweet potato is also affected as a result of the
drying technique, drying temperatures, peeling, and the pretreatment method
applied (Yadav et al., 2006; Maruf et al.,2010).
1.2 OBJECTIVE OF THE STUDY
1.2.1 The main objectives of the study
The main objective of this study was to evaluate the
changes in the proximate, functional properties, microbial quality and the
extent of losses on the total carotenoid content of flour processed from UMUSPO
1 orange fleshed sweet potato variety as a result of pretreatment, drying
methods applied storage period.
1.2.2 Specific objectives of the study
The specific objectives of this study are;
i.
To determine the total
carotenoid content of orange fleshed sweet potato roots
ii. To
determine the nutrient composition/total carotenoid content of Orange fleshed
sweet potato flour during and after storage.
iii. To determine the functional properties of the
flour samples during and after storage.
iv. To determine the microbial quality of the
flour samples during and after storage
1.3 JUSTIFICATION OF THE STUDY
Due to high moisture content of sweet potatoes, they
do not store for a long time. They are usually processed into more shelf stable
products like flour which are used in making composite flour used in baking
products like cake, bread and chin chin. Orange-fleshed sweet potatoes are
known for their high beta-carotene content. However, losses of beta carotene
are observed during the processing of sweet potato tubers into flour and more
is lost during storage. This is usually observed especially if kept for a long
period of time, hence it is expedient to determine the actual quantity of the
total carotenoid/nutrients lost during processing of these orange fleshed sweet
potato roots into flour and how much is retained after storage for a period of
3months, and hence this research study. The results obtained from the study
will guide processors as to the better processing methods that will reduce
losses of these nutrients and carotenoids.
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