Aqueous Microbial Treatments Alter Starch and Glucomannan Composition of Konjac ( Amorphophallus oncophyllus ) Flour

ABSTRACT Konjac ( Amorphophallus oncophyllus ) is well known for its abundance in glucomannan. The study investigated the impact of aqueous microbial treatments using three different commercial microbial cultures at different incubation periods at 12, 24, 36, and 48 h. The microbial cultures used included baking yeast containing Saccharomyces cerevisiae , a mixed starter containing Amylomyces sp., Aspergillus sp., Mucor sp., Saccharomyces sp., and Candida sp., and a commercial culture containing a mixture of lactic acid bacteria (LAB). The treatments significantly ( p < 0.05) affected the composition and color properties of the resulting flour. Starch content decreased from 60.4% in untreated flour to 48%–59.6% in microbial‐treated flours, while apparent amylose increased from 9.2% to 11.9%–14.9% of total starch and amylopectin decreased from 90.9% to 85.1%–88.1%. The microbial treatments generally increase flour lightness and reduce yellowness. The lowest glucomannan content (6.7%–10.7%) was obtained with the LAB treatment, whereas aqueous incubation without microbial inoculation resulted in the highest recoverable glucomannan content (22.6%–30.3%). Treatment with S. cerevisiae resulted in glucomannan contents of 11.5%–24.9%. These findings indicate that aqueous microbial treatment modifies the carbohydrate composition, color, and microstructure of konjac flour, but microbial inoculation does not necessarily favor glucomannan recovery. Overall, aqueous incubation without microbial inoculation was more favorable for retaining or recovering glucomannan, whereas microbial cultures produced greater modification of the flour matrix. Based on these findings, aqueous incubation without microbial inoculation is recommended when maximizing recoverable glucomannan is the primary processing objective, whereas microbial treatment may be selected when greater modification of the flour matrix is desired.