The present study develop various microorganisms for starter culture purpose from fermented sweet potato and used the developed starters in the fermentation of sweet potato and products for consistent quality product with improved hygiene. Sweet potato was purchased from different markets and microorganisms were isolated and developed as starters. Comparative studies on different starters for the fermentation of sweet potato for 48 h were investigated. The microbial count of the starter cultures increased as fermentation period increased from 6.06 to 9.14 cfu/ml, the pH reduced from 5.49 to 3.28 while the total titrable acid increased from 0.001 to 0.04. Amongst the various starters used, the use of the mixed cultures (combination of lactic acid bacteria L201 and yeast 601A) as starter cultures in the fermentation of sweet potato for 48 h had the best attributes in terms of texture, flavour, rate of fermentation and consistency when prepared as meal (bolus). The mineral analysis showed that most of the mineral content in the sample increased after fermentation for calcium (Ca) 2043.9 to 2177.5 ppm and Mn 6.29 to 26.32 ppm. The functional properties of the fermented sweet potato flour produced showed moisture content of 10.42%, water absorption capacity of 1.77 g/g and swelling capacity of 86.67%.

Starch is the major component of cereal grains and starchy foods, and changes in its biophysical and biochemical properties (such as, amylose, amylopectin, pasting, gelatinization, viscosity) will have a direct effect on its end use properties (such as, bread, malt, polymers). Lactobacillus brevis and Debaromyces polymorphous earlier obtained from fermented sweet poatao broth were used to ferment sweet potato and these starter cultures broke down the carbohydrate (starch) to produce alcohol, organic acid and carbon dioixde (CO 2). The study identified that starter cultures L. brevis and D. polymorphous fermented the sweet potato thereby breaking down the carbohydrate (starch) to produce alcohol, organic acid and CO 2 hence lactic acid fermentation occurred. Fourier Transform Infrared Spectroscopy (FTIR) and Gas Chromatography Mass Specrometry (GCMS) were used to identify the chemical properties of starter culture fermented sweet potato flour. The FTIR spectra showed peaks at 3322.15, 3298.87, 3292.59, 3279.59 and 3274.59 cm-1 for the raw sweet potato, starter culture fermented sweet potato flour at various periods (24, 48 and 72 h) and spontaneous fermented sweet potato (control) respectively. The peaks at 2930, 2928.10, 2930.33, 2929.48, 2929.31 and 2927.29 cm-1 are attributed to C-H bond stretching. Functional groups such as hydroxyl, aldehydes, alcohol and carboxyl were detected in the fermented samples. The GCMS analysis detected the presence of alcohol such as ethanol, butanol etc., and carboxylic acid such as hexadecanoic acid, octadecadienoic acid etc. They were produced in situ from the fermentation process and this can serve as antioxidants, help inhibit spoilage organisms and serve as preservatives, thereby increasing shelf life of the product.

No abstract

In this study, sweet potato was purchased and processed using different methods to obtain 4 different sweet potato flour samples. Sample A was unfermented sweet potato flour, sample B was fermented spontaneously, while sample C and D were produced by fermentation using indigenous starter cultures of lactic acid bacteria and yeast for 48 h and 72 h respectively. Colour profile, Pasting and Sensory evaluation was conducted. The whiteness (L* value) obtained in this study is within the range of value (87.29-89.52), Also, the redness value (a*) and yellowness value (b*) of the sweet potato flour samples also showed a significant difference (p<0.05). Sample a had a higher value when compared with samples B,C and D. Pasting properties such as peak viscosity, trough viscosity, breakdown viscosity, setback, pasting temperature were determined. It was noticed that fermentation process and increase in fermentation time significantly (p<0.05) decrease the peak viscosity in this research work and all samples had a higher cooled paste viscosity than their corresponding hot paste viscosity. Nevertheless, sensory evaluation was carried out using thet 9-point hedonic scale, samples A,B,C,D are significantly different (P < 0.05).