In vitro utilization of amylopectin and high-amylose maize (amylomaize) starch granules by human colonic bacteria

It has been well established that a certain amount of ingested starch can e scape digestion in the human small intestine and consequently enters the la rge intestine, where it may serve as a carbon source for bacterial fermenta tion. Thirty-eight types of human colonic bacteria were screened for their capacity to utilize soluble starch, gelatinized amylopectin maize starch, a nd high-amylose maize starch granules by measuring the clear zones on starc h agar plates, The six cultures which produced clear zones on amylopectin m aize starch-containing plates were selected for further studies for utiliza tion of amylopectin maize starch and high amylose maize starch granules A ( amylose; Sigma) and B (Culture Pro 958N), Sodium dodecyl sulfate-polyacryla mide gel electrophoresis (SDS-PAGE) was used to detect bacterial starch-deg rading enzymes. It was demonstrated that Bifidobacterium spp., Bacteroids s pp,, Fusobacterium spp,, and strains of Eubacterium, Clostridium, Streptoco ccus, and Propionibacterium could hydrolyze the gelatinized amylopectin mai ze starch, while only Bifidobacterium spp, and Clostridium butyricum could efficiently utilize high amylose maize starch granules. In fact, C, butyric um and Bifidobacterium spp. had higher specific growth rates in the autocla ved medium containing high-amylose maize starch granules and hydrolyzed 80 and 40% of the amylose, respectively. Starch-degrading enzymes were cell bo und on Bifidobacterium and Bacteroides cells and were extracellular for C. butyricum. Active staining for starch-degrading enzymes on SDS-PAGE gels sh owed that the Bifidobacterium cells produced several starch-degrading enzym es with high relative molecular (M-r) weights (>160,000), medium-sized rela tive molecular weights (>66,000), and low relative molecular weights (<66,0 00), It was concluded that Bifidobacterium spp. and C. butyricum degraded a nd utilized granules of amylomaize starch.