ABSTRACT
This study was carried out to determine the effect of different processing methods on the nutrient and anti-nutrient content of Dioscorea bulbifera. The Dioscorea bulbifera was purchased from local female farmers in Aguata local Government Area of Anambra State. A questionnaire was used to obtain information on the demographic characteristics of the women, as well as their methods of preparing Dioscorea bulbifera. Two processing methods (roasting and boiling) were identified and used in processing of D. bulbifera. The Dioscorea bulbifera tubers were divided into three portions, the first portion was boiled, the second portion was roasted and the third portion was left untreated. All samples were analysed for proximate, minerals, vitamins and antinutrients. Means were separated using ANOVA. From the result, moisture content (51.87%), crude protein (6.96%), crude fibre (2.82%), and crude lipid (1.28%) were significantly lowered in the boiled and roasted samples (p<0.05). The roasted sample had the highest ash content (2.98%), carbohydrate (83.49%) and energy (364.02 kcal) content (p<0.05). Higher calcium (104.18mg/100g), sodium (122.81mg/100g), potassium (1201.13mg/100g), and iron (4.91mg/100g) content were obtained from the raw sample, while higher content of magnesium (83.12mg/100g), manganese (6.88mg/100g) and zinc (6.51mg/100g) were recorded in the roasted sample (p<0.05). The raw sample had the highest content of beta-carotene and vitamin C (301.12 and 2.42mg/100g respectively). The antinutritional levels of the boiled and roasted samples were reduced, but were generally lower in the boiled samples. This study showed that boiling and roasting had both positive and negative effect on Dioscorea bulbifera. The positive effect was derived from the reduction of the anti-nutritional factors, while the negative effect was a reduction in some nutrients found in Dioscorea bulbifera. However, the nutrient content of the yam can be further enhanced by combining with other foods like legumes and pulses in other to improve the nutritional value.
TABLE OF CONTENT
TITLE PAGE I
CERTIFICATION II
DEDICATION III
ACKNOWLEDGEMENT IV
TABLE OF CONTENT V
LIST OF TABLES X
LIST OF FIGUREES XI
ABSTRACT XII
CHAPTER 1
INTRODUCTION 1
1.1 BACKGROUND OF THE STUDY 1
1.2 STATEMENT OF PROBLEM 5
1.3 OBJECTIVE OF THE STUDY 7
1.3.1 The general objective of the study 7
1.3.2 The specific objectives of the study include to 7
1.4 SIGNIFICANCE OF THE STUDY 8
CHAPTER 2
LITERATURE REVIEW 9
2.1 ROOTS AND TUBERS 11
2.2 YAM 12
2.2.1 Botanical characteristics of yam 15
2.2.2 Nutritive value of yams 16
2.2.3 Anti nutritional composition of yam 20
2.3 DIOSCOREA BULBIFERA (ARDU) 22
2.3.1 Taxonomy and morphology of Dioscorea bulbifera 23
2.3.2 Reproductive biology, phenology and growth of Dioscorea
bulbifera 25
2.3.3 Chemical/ nutritional composition of Dioscorea bulbifera 26
2.3.4 Uses of Dioscorea bulbifera 32
2.3.5 Medicinal uses of Dioscorea bulbifera 33
2.4 FOOD PROCESSING AND PREPARATION 35
2.4.1 Different processing techniques of yam 36
CHAPTER 3
Materials and Methods 38
Study Design 38
3.1 Study Area 38
3.2 Population of Study 39
3.3 Sampling Procedure 39
3.4 Preliminary Visit 39
3.5 Data Collection 40
3.6 Collection of Samples 40
3.7 SAMPLE PREPARATION 41
3.7.1 Preparation of boiled sample 41
3.7.2 Preparation of roasted sample 43
3.7.3 Preparation of untreated sample 44
3.8 Preparation of Sample for Chemical Analysis 44
3.9 Chemical Analysis 44
3.9.1 Proximate Composition 44
3.9.1.1 Determination of moisture content 44
3.9.1.2 Determination of ash content 45
3.9.1.3 Determination of crude fibre content 46
3.9.1.4 Determination of protein content 47
3.9.1.5 Determination of fat content 49
3.9.1.6 Determination of carbohydrates content 50
3.9.1.7 Determination of energy 50
3.4.2 Mineral Analysis 50
3.9.2.1 Determination of calcium and magnesium content 50
3.9.2.2 Determination of potassium and sodium content 52
3.9.2.3 Determination of zinc, iron, manganese 53
3.9.2.4 Determination of phosphorous 54
3.9.3. VITAMIN ANALYSIS 55
3.9.3.1 Determination of carotenoids 55
3.9.3.6 Vitamin C Determination 57
3.9.4 Determination of antinutritional factors 59
3.9.4.1 Alkaloid determination 59
3.9.4.2 Determination of tannin 60
3.9.4.4 Flavonoid determination 61
3.9.4.5 Oxalate determination 63
3.9.4.6 Determination of phenol 64
3.9.4.7 Determination of saponnin 65
3.10 STATISTICAL ANALYSIS 66
CHAPTER 4
RESULTS AND DISCUSSION 67
CHAPTER 5
CONCLUSION AND RECOMMENDATION 93
5.1 CONCLUSION 93
5.2 RECOMMENDATIONS 94
REFERENCES
Appendix I
Appendix II
Appendix III
LIST OF TABLES
Table 2.1: Nutritional content of yam species (Dioscorea spp.)
per 100g –edible tuber portion 19
Table 2.2 Antinutritional composition of yam varieties (mg/100g) 22
Table 4.1 Demographic data of women interviewed 67
Table 4.2: Different methods of preparing Dioscorea bulbifera (Ardu) 68
Table 4.3 Mean energy and proximate composition of raw, boiled
and roasted Dioscorea bulbifera 69
Table 4.4 Mineral composition of raw, boiled and roasted
Dioscorea bulbifera (mg/100g) 75
Table 4.5: Beta carotene and C content of raw, boiled and roasted
Dioscorea bulbifera 83
Table 4.6 Phytochemical and Antinutrients components of raw, boiled
and roasted Dioscorea bulbifera (mg/100g) 86
LIST OF FIGURES
Figure 3.1: Flow chart for preparation of boiled Dioscorea
bulbifera tubers 42
List Figure 3.2: Flowchart for preparation of roasted Dioscorea
bulbifera tubers 43
CHAPTER 1
INTRODUCTION
1.1 BACKGROUND OF THE STUDY
Hunger and malnutrition continue to be a serious problem for many people in developing countries (Bello, 2009). It is increasingly being recognized that an inadequate quantity of food, with an insufficiency of calorie or energy intake, and not merely protein deficiency, is the cause of widespread protein-calorie malnutrition, since, with insufficient food calories, protein is used to supply energy instead of fulfilling its body-building role (Idusogie and Olayide, 1972).
In order to have a healthy population that can promote development, the relation between food, nutrition and health should be reinforced (Bwai et al., 2014). In developing countries, one of the ways of achieving this is through the exploitation of available local resources, in order to satisfy the needs of the increasing population (Achu et al., 2005).
Yam is one of the staple foods in Nigeria and other tropical African countries. The yams are members of the genus Dioscorea in the section, Enantiophyllum. Dioscorea is the largest genus of the family Dioscoreaceae, containing between three and six hundred species (Vernier et al., 1998). Yam is grown and cultivated for its energy-rich tuber. Only a few species of yams are cultivated as food crops, the most economically important species which are grown are white yam (Dioscorea rotundata), yellow yam (Dioscorea cayensis), water yam (Dioscorea alata), Chinese yam (Dioscorea esculenta), aerial yam (Dioscorea bulbifera) and trifolate yam (Dioscorea dumentorum) (Ike and Inoni, 2006).
Calculations show that yams are all good and cheap sources of energy, and produce high amounts of food calories per acre of land (Ihekoronye and Ngoddy, 1985).
Yams make a major contribution to the nutrition of Nigerians as a source of carbohydrate, before the introduction of cassava and sweet potatoes (Princewill and Ibeji, 2015). They have been very important in times of famine (Food and Agriculture organization (FAO), 1991). Yam is a premium crop in the Nigerian food system and Nigeria is the world’s largest producer with an aggregate annual output in excess of 50% of total world production (Raw Material Research And Development Councl (RMRDC), 1990). Work on yams and other tropical root tuber crops have been generated in the last 10-15 years through the formation and subsequent activities of the International Society for Tropical Root Crops (Okonkwo, 1985).
In Nigeria, government awareness of the need to increase food production for feeding the teeming population has lent support for studies on better methods of tuber and root crops production. Unfortunately, some of these food crops have been under exploited for their food values, an example Dioscorea bulbifera (Aerial yam) and Dioscorea dumentorum (Bitter yam) (RMRDC, 1990).
D.bubifera has been sidelined over the years and is going extinct as a result of its poisonous characteristic (Princewill and Ibeji, 2015). Currently, a large number of research are being carried out on root and tuber crops in research institutes and in Universities (Princewill and Ibeji, 2015). Improvement on the processing method and utilization of this crop (D. bulbifera) will reduce food insecurity in Nigeria. While there are various methods by which this crop can be made safe for consumption, a properly scientifically researched method is yet to be known and publicized (Princewill and Ibeji, 2015).
Food processing is an important aspect of agricultural production and marketing; it adds value, removes anti-nutritional components, increases the nutritional value of foods thereby converting them into a form that is more acceptable (Princewill and Ibeji, 2015). Root crops are not easily digested in their natural state and should be cooked before they are eaten. Cooking improves their digestibility, promotes palatability and improves their keeping quality as well as making the roots safer to eat. However, cooking may affect the nutritional composition and phytoconstituents in food (Ezeocha and Ojimelukwe, 2012). Two principal traditional methods used for preparing yams for consumption in coastal West Africa, especially Nigeria, are boiling tuber pieces and pounding into a dough after boiling (Omonigho and Ikenebomeh, 2000). Several traditional household food-processing methods can affect the bioavailability of nutrients in plant-based diets. These include thermal processing, mechanical processing, soaking, fermentation and germination (Hotz and Gibson, 2007). The study therefore focuses on identifying the different processing methods of Dioscorea bulbifera (Aerial yam) and the effect of these processing methods on the nutrient and anti-nutrient content of Dioscorea bulbifera (Aerial yam).
1.2 STATEMENT OF PROBLEM
The utilization of Aerial yam can be limited by the presence of toxic anti-nutrients. Yams has been suggested to have nutritional superiority when compared with other tropical root crops (Shajeela et al., 2011). They are reported as good sources of essential dietary nutrients (Baquar and Oke, 1976; Bhandari et al., 2003; Shanthakumari et al., 2008; Maneenoon et al., 2008; Arinathan et al., 2009). The tubers were found with a high amount of protein, a good proportion of essential amino acids and appeared as a fairly good source of many dietary minerals (Shajeela et al., 2011). However, their wider utilization is limited due to the presence of some toxic and antinutritional factors (Shajeela et al., 2011). Earlier reports have also pointed out that a few yam species contain some toxic compounds and can impact serious health complications (Anthony, 2004). Yam tubers are known to contain different toxic substances that affect both humans and animals when they are consumed, despite their high nutritional values (Shajeela et al., 2011). Some species of wild yams, particularly wild forms, are toxic and / or unpalatable, taste bitter and cause vomiting and diarrhoea when large amount are ingested without proper processing or if eaten raw (Webster et al., 1984). Anti-nutritional factors, which consists of polyphenols, oligosaccharides (α-galactosides), lectins, proteases and amylase inhibitors, are widely distributed in most yams (Medoua et al., 2007). Yang and Lin (2008) reported that the age, the cultivar, the geographic locality of a plant or the storage condition after harvest could significantly affect its anti-nutritional content. The presence of enzyme inhibitors in yams, for example could impair digestion of starch and protein thereby limiting their utilization as food (Polycarp et al., 2012). Commercial development of Dioscorea bulbifera (Aerial yam) is virtually nil, probably because the plant is only known in remote, normally poverty-stricken areas (Mbaya et al., 2013). Studies of nutritional value of wild plant food are of considerable significance since it may help to identify long forgotten food resources. In this study, an attempt was made to identify the common methods of processing Dioscorea bulbifera (Aerial yam) as well as determining the chemical composition and antinutritional factors of Dioscorea bulbifera (Aerial yam), and suggest ways and means to remove the antinutrients/toxins to make the edible tubers safe food sources for mass consumption.
1.3 OBJECTIVE OF THE STUDY
1.3.1 The general objective of the study:
The general objective of the study is to determine the effect of different processing methods on the nutrient and antinutrient content of Dioscorea bulbifera (ardu)
1.3.2 The specific objectives of the study include to:
i. identify the common methods of processing Dioscorea bulbifera using a questionnaire. .
ii. process the Dioscorea bulbifera tubers using two of the identified methods (boiling and roasting).
iii. determine the proximate composition of the processed Dioscorea bulbifera tubers.
iv. determine the mineral and vitamin composition of the processed Dioscorea bulbifera tubers.
v. determine the antinutrient composition of the yams (Dioscorea bulbifera tubers).
vi. determine differences in the nutrient and antinutrient compositions of the Dioscorea bulbifera tubers processed using the two methods(boiling and roasting).
1.4 SIGNIFICANCE OF THE STUDY:
1. This study will provide information on the nutrient content of aerial yam which will enlighten consumers to consume more of it if found to be safe.
2. This study could provide an insight into increasing the production of aerial yam in a bid to improve national food security.
3. It is expected that information from this study will enlighten people on methods of processing that can help increase nutrient content and subdue the antinutrient found in aerial yam
4. Information from this study will increase people’s acceptability and utilization of aerial yam.
5. This study will provide information on the nutrient and antinutrient content of aerial yam for use by nutritionists, dieticians and other health professionals.
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