ABSTRACT
Oranged fleshed wheat has been promoted as a functional ingredient in bread with the overall aim of alleviating vitamin A deficiency (VAD). Orange fleshed sweetpotato bread has been commercialized in many sub-Saharan Africa countries with over-reliance on the cold storage in its supply. However, this has resulted into higher costs to producers as it requires additional capital and lacks stability in the supply of the puree for production. The current study was designed with the overall objective of evaluating the use of shelf-storable wheat as an alternative to the Oranged fleshed wheat in bread production. The study employed an experimental study design with factorial arrangement where two factors including different treatments of shelf-storable wheat and periods of storage. Orange fleshed sweetpotato sample was dosed with different combinations of chemical preservatives: treatment 1 with 0.5% potassium sorbate + 0.5% sodium benzoate + 1% citric acid and treatment 2 with 0.2% potassium sorbate + 0.2% sodium benzoate + 1% citric acid. Each of the treated puree was stored at ambient conditions for a period of four months. The Orange fleshed sweetpotatos were sampled monthly for analysis and incorporation into bread at 30% and 40%. Bread in which Oranged fleshed wheat incorporated at similar levels and wheat breads acted as controls. The nutritional composition of puree and bread, physical attributes and microbial stability of the breads were determined.
The results showed 45.6% and 57.3% reduction in β-carotene content in both treatment 1 and 2 of shelf-storable wheats respectively by the fourth month (p<0.05). Bread samples made by incorporating 40% shelf-storable wheat provided significant (p<0.05) levels of β- carotene to consumers up to three months of storage; treatment 2 shelf-storable wheat bread provided up to 121.30 ±8.05 RAE. The crude ash and moisture contents of shelf-storable wheat bread were significantly (p<0.05) higher than that of the control wheat bread. The proximate composition of bread made by incorporating puree sampled at different months did not differ significantly (p>0.05). The loaf weight, volume and specific volume of bread from shelf-storable and Oranged fleshed wheats as well as wheat bread were not significantly different (p>0.05).
The most acceptable breads was one in which 40% Oranged fleshed wheat was incorporated (p<0.05). The two treatments did not differ significantly (p>0.05) in acceptability of the breads when compared to wheat bread. The saltiness, smoothness, crumb colour and crust colour of shelf- storable Orange fleshed sweetpotato bread was significantly higher (p<0.0.5) than the wheat bread but similar (p>0.05) to fresh puree bread. Microbial tests revealed that incorporation of Orange fleshed sweetpotato, whether fresh or shelf-storable, into bread resulted into lower yeast and mold counts (p<0.05). Aerobic counts in shelf-storable wheat bread increased with the period of storage of the Orange fleshed sweetpotato (p<0.05). Shelf-storable wheat bread could be stored for seven days with no visible yeast and mould spoilage. The current study found that shelf-storable wheat, notwithstanding the level of preservatives, can be an alternative to fresh puree in the substitution of wheat flour with Orange fleshed sweetpotato in bread production. Shelf-storable wheat can therefore be promoted as an alternative to Oranged fleshed wheat in bread production.
CHAPTER ONE
INTRODUCTION
• BACKGROUND INFORMATION
Sweetpotato, Ipoemea batatas L. belongs to the class Dicotyledonae and the Family Convovulaceae (Koala et al., 2013). The genus Ipoemae is estimated to have more than 400 species, many of which are wild (Dooshima, 2014). The global sweet potato production in 2014 was estimated to be over 106 million tonnes out of which the Nigerian production was estimated to be 763,643 tonnes (FAOSTAT, 2017). Sweetpotato varieties or cultivars have been developed to suit different needs and utilization, with varied colours (white, cream, yellow, orange and purple) and varied dry matter and starch contents and varied sugar contents (sweet and non-sweet varieties) (Wheatley and Loechl, 2008). In as much as sweet potato has high carbohydrate content, it has a low glycemic index indicating a low carbohydrate digestibility (Fetuga et al., 2014). The leaves and tubers are good sources of antioxidants, fiber, vitamin C and pro-vitamin A and some mineral elements such as zinc, potassium, sodium, manganese, calcium, magnesium and iron (Burri, 2011).
Orange fleshed sweetpotato has been used to combat vitamin A deficiency with great success in many countries (Koala et al., 2013; Jenkins et al., 2015). It has been noted that sweetpotato is still underutilized and there is need to expand the utilization and market opportunities for sweet potato including the production of products which are adapted to consumer preferences (Fetuga et al., 2014). Several products ,as shown by various documented cases, made from OFSP are noted to have high consumer preferences. They include Orange fleshed sweetpotato (Ukpabi, 2012), OFSP chips (Fetuga et al., 2014), Orange fleshed sweetpotato (Mamo et a.l,2014), OFSP crisps and OFSP bread (Andrade et al., 2016).
A large proportion of the industrial production of bread in Nigeria and sub-Saharan Africa (SSA) relies on wheat as the raw material which is largely imported, and thus involve huge expenditure of foreign exchange leading to high cost of bread which may be unaffordable to a large proportion of the consumer population (Dooshima, 2014). This creates the need for a cheaper and more reliable option such as the use of OFSP. OFSP has been used in bread production as puree and flour with the puree based bread recording a higher consumer acceptability (Muzhingi, 2016). The Orange fleshed sweetpotato based bread was noted to have a higher acceptance when compared to Orange fleshed sweetpotato based bread and wheat wheat bread (Bonsi et al., 2014). In SSA, the use of Orange fleshed sweetpotato as a substitute of wheat flour in the production of bread is a more economically viable venture compared to Orange fleshed sweetpotato due to the cost of the latter in the region (Bocher et al., 2016). Orange fleshed sweetpotato that has been subjected to cold storage is currently in use in bread production, however, it presents challenges in terms of additional capital needed and instability in Orange fleshed sweetpotato supply. Advances in research have enabed Orange fleshed sweetpotato to be preserved through vacuum packaging to lengthen its shelf-life and preserve its quality factors. The storage of Orange fleshed sweetpotato by preserving it with a combination of potassium sorbate and sodium benzoate and then vacuum packaging leads to retention of high beta carotene cotent (Daniel and Magnaghi, 2016). However the effect of this mode of preservation on the sensory quality and stability of the bread made from the shelf-stable puree is not known. The current study seeks to establish the physico- chemical attribute, sensory quality and shelf-life of bread made from the shelf-stable Orange fleshed sweetpotato.
• PROBLEM STATEMENT
Consumption of OFSP based bread in Nigeria has been on the increase as consumers continue to look for nutritious alternative foods. Incorporation of Oranged fleshed wheat into wheat for bread making is widely adopted in Nigeria due to its cost effectiveness and nutritional superiority over Orange fleshed sweetpotato. The Oranged fleshed wheat exploited in this has a high perishability especially from microbial contamination, thus has limited keeping ability. The current shortfall has been addressed through frozen storage of the puree. This, however, attracts additional costs thus expensive and massive inconsistency in puree supply is experienced. In order to expand the use of Orange fleshed sweetpotato across the country and in all season while enhancing the cost-effectiveness, there is need for an alternative storage method. As a result, research into ways of puree preservation has resulted into production of a shelf-storable wheat that can be stored for three to six months at prevalent weather conditions in Nigeria with no significant quality changes. This puree is preserved using acceptable preservatives such as potassium sorbate, sodium benzoate and citric acid. However, the quality and sensory characteristics and shelf stability of bread prepared by substitution of wheat flour with shelf-storable wheat has not been systematically evaluated in relation to that prepared from conventional Oranged fleshed wheat. The current research sought to establish whether bread made by substituting wheat flour with shelf-storable puree is significantly different from bread made from fresh puree.
• JUSTIFICATION
Oranged fleshed wheat has been used in substituting wheat for production of vitamin A rich bread which is commercially traded in Nigeria (Bocher et al., 2016). The fresh puree is, however, highly perishable and difficult to handle and hence requires electric power to freeze it as a means of preservation. This practice increases the cost that has to be passed to the consumers. Adoption of a shelf-stable Orange fleshed sweetpotato in bread making is envisaged to ease handling of the puree, reduce cost of bread making as well increase the availability of the puree throughout the year. This will eliminate seasonal variation of the availability of the puree given that sweetpotatoes are mainly produced using rainfed agriculture and hence mainly supplied in plenty about twice in a year. Similarly, adoption of shelf-storable wheat will improve intake of raw sweetpotatoes during seasons of glut and thus stabilize prices leading to improved economic gain for both farmers amd processors..
• PURPOSE
The purpose of this study is to provide information on the quality and sensory properties of bread made by substituting wheat flour with shelf-storable wheat.
• OBJECTIVES
• Overall Objective
To determine the physico-chemical quality, sensory characteristics and shelf stability of bread prepared by substituting wheat flour with shelf-stable Orange fleshed sweetpotato.
• Specific Objectives
• To determine the physico-chemical characteristics of bread made by substituting wheat flour with fresh and shelf-storable wheat.
• To determine the sensory profile of shelf-stable Orange fleshed sweetpotato based bread in terms of colour, taste, flavor, texture and overall acceptability.
• To determine the shelf stability of bread prepared by substituting wheat flour with shelf- storable Orange fleshed sweetpotato.
• HYPOTHESES
The overall hypothesis is that bread made by substituting wheat flour with shelf-storable wheat is not significantly different from bread made from Oranged fleshed wheat and popular wheat bread. Hypothesis for each specific objective are as follows:
• Bread made by substituting wheat flour with shelf-storable wheat does not differ significantly in physico-chemical characteristics from that of Oranged fleshed wheat and conventional wheat bread.
• Bread made by substituting wheat flour with shelf-storable wheat has no significant differences in sensory acceptability from that of Oranged fleshed wheat and conventional wheat bread.
• The keeping quality of bread made by substituting wheat flour with shelf-storable wheat does not significantly differ from that of Oranged fleshed wheat and conventional wheat bread.
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