EFFECTS OF PROCESSING METHODS ON THE PHYSICO-CHEMICAL PROPERTIES OF SWEET POTATO AND SORGHUM
This study evaluated "the effects of processing methods on the physico-chemical properties of sweet potato and sorghum flour". Sweet potato (Ipomoea batatas) is an important food crop in the tropical and sub-tropical countries and belongs to the family convolvulaceae. Sweet potatoes are rich in dietary fiber, minerals, vitamins, and anti oxidants such as phenolic acids, anthocyannins,-carotenetocopherol.Theproximatecompositionand ofβ sweet potato was determined and these include moisture, lipids, ash, protein, carbohydrates and fiber. In carrying out the analysis practically, methods used vary according to the food material. The anti oxidants were also determined alongside with phenol oxidase, pasting properties, minerals and sugar contents. Sorghum is a tropical plant belonging to the family of poaceae. More than 35% of sorghum is grown for human consumption. The analyses carried out in sweet potatoes are same with sorghum with the exclusion of phenol oxidase.
TABLE OF CONTENTS
CHAPTER ONE: INTRODUCTION
CHAPTER TWO: LITERATURE REVIEW
2.1. ORIGIN AND DISTRIBUTION OF SWEET POTATO
2.1.1. DESCRIPTION OF SWEET POTATO PLANT
2.1.2. USES OF SWEET POTATO
2.1.3. NUTRITIONAL VALUE OF SWEET POTATO
2.1.4. ANTI- NUTRITIONAL FACTORS
2.1.5. NUTRIENT COMPOSITION OF SWEET POTATO
220.127.116.11. POLYPHENOLS COMPOSITION
18.104.22.168. ANTI-OXIDATIVE, ANTI-MUTAGENICITY AND ANTI-
2.1.8. ENZYME COMPOSITION OF SWEET POTATO
2.2. ORIGIN AND DISTRIBUTION OF SORGHUM PLANT
2.2.1. DISTRIBUTION OF SORGHUM PLANT
2.2.2. USES OF SORGHUM
2.2.3. ENZYME COMPOSITION OF SORGHUM
2.2.4. NUTRITIONAL COMPOSITION OF SORGHUM
2.2.5. ANTI-NUTRIENTS IN SORGHUM
CHAPTER THREE: MATERIALS AND METHODS
3.2.1. PROCESSING OF SWEET POTATO TUBER
3.2.2. PROCESSING OF SORGHUM GRAIN
3.3. SWEET POTATO AND SORGHUM ANALYSIS
3.3.1. PROXIMATE ANALYSIS
22.214.171.124. DETERMINATION OF FAT CONTENT
126.96.36.199. DETERMINATION OF ASH CONTENT
188.8.131.52. DETERMINATION OF CRUDE FIBRE
184.108.40.206. DETERMINATION OF PROTEIN
220.127.116.11. DETERMINATION OF CARBOHYDRATES
3.4. ANTI-NUTRIENTS AND PHYTOCHEMICALS
3.4.1. DETERMINATION OF TANNINS
3.4.2. DETERMINATION OF HYDROCYANIC ACID
3.4.3. DETERMINATION OF ANTHOCYANNINS
3.4.4. DETERMINATION OF PHYTATE/PHYTIC ACID
3.5. DETERMINATION OF MINERAL CONTENT
3.6. DETERMINATION OF PASTING PROPERTIES
3.7. DETERMINATION OF PHENOL OXIDASE
3.8. DETERMINATION OF REDUCING SUGARS; FRUCTOSE, GLUCOSE AND SUCROSE
4.1. TABLE 1: PROXIMATE COMPOSITION OF THE SAMPLES AND DISCUSSION
4.2. TABLE 2: MINERAL COMPOSITION OF SAMPLES AND DISCUSSION
4.3. TABLE 3: PHYTOCHEMICAL COMPOSITION OF THE SAMPLES AND DISCUSSION
4.4. TABLE 4: PHYSICO-CHEMICAL PROPERTIES OF SAMPLES AND DISCUSSION
4.4. TABLE 5: SUGAR COMPOSITION OF THE SAMPLES AND DISCUSSION
CHAPTER FIVE: CONCLUSION
Sweet potato (Ipomoea batatas) is an important food crop in the tropical and sub tropical countries and belongs to the family convolvulaceae. It is cultivated in more than 100 countries. ( Woolfe, 1992). Nigeria is the third largest producer in the world with china leading, followed by Uganda. Sweet potato ranks seventh among the world food crops, third in value of production and fifth in caloric contribution to human diet (Bouwkamp, 1985). Sweet potatoes are rich in dietary fibre, minerals, vitamins and anti oxidants such as phenolic acids, anthocyanins, tocopherol and ß- carotene. Besides acting as anti oxidants, carotenoids and phenolic compounds also provide sweet potatoes with their distinctive flesh colours ( cream, deep yellow, orange and purple). Sweet potato blends with rice, cowpea and plantain in nigerian diets. It is also becoming popular as a substitute to yam and garri. It can be reconstituted into fofoo or blended with other carbohydrate flour sources such as wheat ( Triticum aestivum) and cassava ( Manihot esculenta) for baking bread, biscuits and other confectioneries (Woolfe, 1992).
The leaves are rich in protein and the orange flesh varieties contain high beta carotene and are very important in combating vitamin A deficiency especially in children.
Sorghum (sorghum bicolor (S. bicolor) is a tropical plant belonging to the family of poaceae, is one of the most important crops in Africa, Asia and Latin America. More than 35% of sorghum is grown directly for human consumption. The rest is used primarily for animal feed, alcohol production and industrial products ( FAO, 1995). The current annual production of 60 million tons is increasing due to the introduction of improved varieties and breeding conditions. Several improved sorghum varieties adapted to semi-arid tropic environments are released every year by sorghum breeders. Selection of varieties meeting specific local food and industrial requirements from this great biodiversity is of high importance for food security. In developing countries in general and particularly in West Africa demand for sorghum is increasing. This is due to not only the growing population but also to the countries policy to enhance its processing and industrial utilization.
More than 7000 sorghum varieties have been identified, therefore there is a need of their further characterization to the molecular level with respect to food quality. The acquisition of good quality grain is fundamental to produce acceptable food products from sorghum. Sorghum while playing a crucial role in food security in Africa, it is also a source of income of household . In West Africa, ungerminated sorghum grains are generally used for the preparation of "to", porridge and couscous. Malted sorghum is used in the process of local beer "dolo" (reddish, cloudy or opaque), infant porridge and non fermented beverages. Sorghum grains like all cereals are comprised primarily of starch.
The aim and objective of this work is to obtain diet low in sugars, with enriched nutrients intended for diabetics.
2.1. ORIGIN AND DISTRIBUTION OF SWEET POTATO
Sweet potato (Ipomoea batatas) is a member of the convolvulaceae family (purseglove, 1972). Approximately 900 different species of convolvulaceae in 400 genera have been identified around the world. Yen, (1974) and Austin (1978,1988) recognized 11 species in the batatas, which includes sweet potato. The closest relatives of the sweet potato appears to be ipomoea trifida that is found wild in maxico, and ipomoeto tabascana. Sweet potato has a chromosomes number for the genus ipomoea is 15, sweet potato is considered to be a hexaploid. Most sweet potato cultivars are self-incompatible, which means that when self pollinated, the cannot produce viable seed. It is accepted that cultivated sweet potato originated in central America or tropical south America. Sweet potatoes are cultivated where ever there is enough water to support their growth: optimal annual rainfall for growth range between 750-2000mm. sweet potato is a warm season annual, requiring 20-25°C average temperatures and full sunlight for optimal development. Sweet potato thrives in well drained loamy soils with high humus content that provides warm and moist environment to the roots.
2.1.1. DESCRIPTION OF SWEET POTATO A. THE ROOT SYSTEM
When sweet potato is planted from stem cuttings, adventitious roots arise from the cutting in a day or two. These roots grow rapidly and form the root system of the plant. Research has shown the roots of sweet potato can penetrate the soil to a depth of over 2m, the exact depth attained being dependent on the soil condition (Onwueme, 1978 and Kays, 1985). Based on its origin, the root system of sweet potato is divided into the adventitious roots arising from subterranean nodes of a vine cutting and lateral roots arising from existing roots. Kays (1985) subdivided the adventitious roots into storage, fibrous and pencil roots. The lateral roots are subdivided into primary, secondary and tertiary roots.
During the early ontogeny of young adventitious roots emerging from the stem, they are often separated into (Togari, 1950). According to Wilson (1982) and Kays (1985), thin roots are typically tetrarch in the arrangement of their primary vascular tissue, i.e. four xylem and phloem poles found within the vascular cylinder. The most important functional differences between these root types are their capacity for storage root initiation in a specific region of the thick roots. Several factors such as exposure of potential storage roots to long photoperiod (Bonsi et al, 1992), water logged soil conditions (Kays, 1985), high levels of nitrogen supply (Chua & Kays, 1981), gibberellic acid application (McDavid
& Alamu, 1980), as well as exposing the plant to long days (McDavid & Alamu, 1980; Du Plooy, 1989) encourage lignification and inhibit storage root development. Alternatively high potassium supply (Isuno, 1971, Hahn
& Hozyo, 1984), the absence of light (Wilson, 1982), as well as well aerated soil conditions, low temperature and short days been demonstrated to encourage storage root formation (Du Plooy, 1989).
a. Storage Roots
Storage roots arise from pentarch or hexarch thick young roots if the cells between the protoxylem point and the central metaxylem cell do not become lignified, or if only a slight proportion of these cells are lignified (Togari, 1950). The increase in storage root size is attributed to the activity of the vascular cambium as well as the activity of the anomalous cambia (Wilson, 1982). The initial sign of storage root formation is the accumulation of photosynthetic consisting predominantly of starch (Chua & Kays, 1982). Storage root initiation is reported to occur between the periods of 35 to 60 days after planting (Agata, 1982, Wilson 1982). But the work of Du Plooy (1989) indicated that storage root initiation might occur as early as 7 days after planting. These conflicting results suggest the need for further research on the storage root formation in sweet potato.
Agata (1982) reported that storage root formation started about 30 to 35 days after planting and the roots dry weight increased linearly until harvest.
b. Pencil Roots
Pencil roots are generally between 5 and 15mm in diameter, they are the least well defined of the adventitious root emerging from the subterranean node of the culting. They develop mainly from young thick adventitious roots under conditions not conducive for the development of storage roots. In pencil roots lignification is not total, but result in uniform thickening of the entire root.
c. Fibrous Roots
According to Chua and Kays (1981), fibrous roots develop mainly from tetrarch, thin adventitious roots. The fibrous roots are generally less than 5mm in diameter and are branched with lateral roots forming a dense network throughout the root zone constituting the water and nutrient absorbing system of the plants. Fibrous roots have heavily lignified steels and very low levels of vascular cambial activity. High nitrogen and low oxygen within the root zone favors their formation (Chua & Kays, 1981).
d. Lateral roots
The lateral roots of sweet potato emerge from existing roots adventitious roots (storage, pencil and fibrous) have a profusion of lateral roots at varying
densities along their axis. The primary lateral roots emerge from adventitious roots. Lateral emerging from the primary laterals are called secondary lateral and those emerging from the secondary laterals are named tertiary laterals (Kays, 1985).
B. ABOVE GROUND PLANT ORGANS
Sweets potato has long thin stems that trail along the soil surface and can produce roots at the nodes. Sweet potato genotypes are classified as either erect, bushy, intermediate, or spreading, based on the length of their vines (Yen, 1974, Kays, 1985). Stem length varies with cultivar, and highly variable, ranging from a few centimeters up to 10cm in length. Planting density has pronounced effect on the internode length as well as on vine length (Somda & Kays, 1990a). The stem is circular or slightly angular. Stem color is predominantly green, but purplish pigmentation is often present.
Branching is cultivar dependent (Yen, 1974) and branches vary in number and length. Normally, sweet potato produces three types of branches, primary, secondary and tertiary, at different periods of growth. The total
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