Isolation and Screening of Starch-Degrading Microorganisms from Decaying Rootcrops for the Production of Natural Sweetener from Taro(Colocasia esculenta)

Abstract

Starch-degrading microorganisms from decaying rootcrop tubers were isolated and screened as potential starter cultures in the production of natural sweetener from taro (Colocasia esculenta). A total of 43 microbial isolates were collected from the samples, 24 of which showed starch-degrading potential as exhibited by positive results for iodine test on starch-agar plates. Further test using DNS method showed that molds in general have greater starch-degrading abilities than bacteria and yeasts. The top two isolates with the highest hydrolyzing activity were molds isolated from decaying taro and cassava tubers. The fermentation of cooked taro (VG-9) substrate using the two most promising isolates yielded syrups with TSS values of 11.65 and 13◦ Brix and pH of 5.4 and 4.06. Qualitative tests for sugars showed that the syrups contain reducing sugars, particularly monosaccharides and ketoses most of which are generally referred to as good or prebiotic sugars. Results of the study imply that taro is a potential raw material for natural sweetener production. It is recommended to study combinations of microorganisms to carry out the optimum fermentation process and produce a good quality sugar alternative with maximum health benefits.