Effect of lactic acid fermentation on physico-chemical properties of starch derived from cassava, sweet potato and rice

Instead of natural fermentation, the microbial starters prepared from natural fermentation of mung beans were applied to cassava, sweet potato and rice during extraction and the starch was collected without or with prolonged fermentation (lactic acid fermented starch (LAF-starch)). Their structural and physico-chemical properties of each starch types were evaluated and then compared with the natural fermented starch (NF-starch) and the control (i.e. freshly extracted starch). No great significant change in chemical composition (i.e. starch, lipid and fiber) of LAF-starch was observed, but the protein and ash content increased. When compared to the control starch, both NF-and LAF-starch had lower paste viscosity, but the latter was more pronounced due to starch depolymerization of a higher acid concentration. Prolonged fermentation did not significantly cause more change to starch properties. In addition, the lactic acid fermentation caused an alteration in the gel texture, which was starch-dependent. The endothermic peak of LAF-starch gelatinization, as analyzed by the Differential Scanning Calorimeter, was slightly shifted to a higher temperature, suggesting the modification in starch granules. This was evident by Scanning Electron Microscopy as all fermented (NF and LAF) starch granules had lost their surface smoothness. The addition of the microbial starter led to more irregular surface due to external corrosion. The results suggested a similar trend in property modification by the natural fermentation and by the application of microbial starter, which provided a greater extent of starch modification within a shorter period of time. The use of the microbial starter, therefore, can minimize the fermentation time and starch properties can be further diversified by varying the quantity of starter used.