Physico-chemical characteristics, sensory profile and shelf stability of bread incorporating shelf-storable orange fleshed sweetpotato puree

Author: Ombaka, Joshua

Supervisors: George Ooko; Michael W. and Tawanda M.

Orange fleshed sweet potato (OFSP) puree has been promoted as a functional ingredient in bread with the overall aim of alleviating vitamin A deficiency (VAD). OFSP puree 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 OFSP puree as an alternative to the fresh OFSP puree in bread production. The study employed an experimental study design with factorial arrangement where two factors including different treatments of shelf-storable OFSP puree and periods of storage. OFSP puree 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 OFSP purees were sampled monthly for analysis and incorporation into bread at 30% and 40%. Bread in which fresh OFSP puree 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 OFSP purees respectively by the fourth month (p<0.05). Bread samples made by incorporating 40% shelf-storable OFSP puree provided significant (p<0.05) levels of β-carotene to consumers up to three months of storage; treatment 2 shelf-storable OFSP bread provided up to 121.30 ±8.05 RAE. The crude ash and moisture contents of shelf-storable OFSP puree 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 fresh OFSP purees as well as wheat bread were not significantly different (p>0.05). The most acceptable breads was one in which 40% fresh OFSP puree 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 OFSP puree 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 OFSP puree, whether fresh or shelf-storable, into bread resulted into lower yeast and mold counts (p<0.05). Aerobic counts in shelf-storable OFSP puree bread increased with the period of storage of the OFSP puree (p<0.05). Shelf-storable OFSP puree bread could be stored for seven days with no visible yeast and mould spoilage. The current study found that shelf-storable OFSP puree, notwithstanding the level of preservatives, can be an alternative to fresh puree in the substitution of wheat flour with OFSP puree in bread production. Shelf-storable OFSP puree can therefore be promoted as an alternative to fresh OFSP puree in bread production.