Abstract

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 (CO₂₎. 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 CO₂ 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.

Key words: Sweet potato starch, fermentation, FTIR, GCMS.