Textural characteristics of lactic fermented sweetpotato and its performance as sausage filler
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Attempts have been made to modify textural characteristics of sweetpotato by chemical and physical treatments but no studies on the effect of lactic fermentation on its properties have been carried out. Lactic fermentation has been reported to change textural properties of several starchy substrates, including cassava. The sausages commonly available in the local market are deficient in sensory properties especially texture. This study was carried out with the aim of investigating a) the effect of lactic fermentation on the rheological characteristics of sweetpotato flour and b) the suitability of fermented sweetpotato flour as sausage filler, especially in improving sensory quality of sausages. Nonfermented sweetpotato flour (NSPF) and naturally fermented sweetpotato flour (FSPF) were prepared by drying a fresh sweetpotato roots' pulp before fermentation and after natural fermentation, respectively, followed by comminution in a disc mill. The fermentation process was characterized by taking lactic acid bacteria count, viable count, pH and titratable acidity measurements after every 12 h. Brabender amylograph pasting properties of 7% fermented sweetpotato flour (FSPF) were investigated with non-fermented swcctpotatc flour (NSPf) as acid, citric acid, orthophosphoric acid and Hel were investigated. The effects of inhibition of of 7%FSPF slurry to 6 using NaOH on the Brabender p~::;tinbproperties. Also, 30% FSpr and a boiling water bath for 30 min. Evaluation of the performance of FSPF as sausage filler was an experiment with NSPF and sausage rusks as controls. The lean beef solids of a typical fresh beef sausage formulation were substituted with a) FSPF, b) NSPF and c) rusks solids at the rates of 20, 30, 40 and 50%. The sausage batters were evaluated for pH, water holding capacity, emulsion stability and cooking loss. Penetrometer firmness and sensory attributes of the sausages after deep-flying were also determined. The results indicated that natural fermentation of sweetpotato pulp is typical of that of other starchy substrates with a marked increase in LAB count and acidity. FSPF exhibited higher viscosity than NSPF and had a peak while the latter did not show any thermopasting behaviour. Direct acidulation and inhibition of inherent amylase system of NSPF yielded typical thermopasting curves but with peak viscosities and viscosity at 86°C lower than that of FSPF. Generally, FSPF gave better results than NSPF for emulsion stability and cooking loss. The water holding capacity of FSPF batters was comparable to that of both controls. Sensory analysis indicated that 30%FSPF gave sausages that were superior to all the controls. There was a strong correlation (r = -0.99) between penetrometer firmness and filler level and between penetrometer firmness and sensory texture (r = 0.933) of cooked sausages. This study concluded that fermentation affects viscopasting properties of sweetpotato flour and that FSPF can be used to effectively substitute sausage rusks as sausage filler.