Effect of enzymatic treatments on the physiochemical properties of different corn starches.

摘要

Amylose readily reassociates to form films and crystalline structures that are resistant to digestion by amylolytic enzymes and known as resistant starch type III (RS3). This study investigated the RS3 formation and cereal coating properties from enzyme-modified corn starches with varying amylose contents, including Hylon VII (70% amylose), Hylon V (50% amylose), and common corn (25% amylose). For RS3 formation, corn starches were first gelatinized and then hydrolyzed using beta-amylase to varying degrees. The resultant hydrolyzed starch was debranched with isoamylase and then exposed to 3 times of temperature cycling at 135/133/133°C for 30 min and 95°C for 24 hr to promote RS3 formation. For cereal coating applications, corn starches were gelatinized and debranched, and then sprayed onto ready-to-eat breakfast cereal flakes. The proportions of amylose and amylopectin long and short chains were affected by the beta-amylase treatment and varied with starch type. All three corn starches had increased RS contents after moderate beta-amylolysis with Hylon V having the highest RS content at 70.7% after 4 hr of beta-amylolysis. The RS content was positively correlated with amylose and amylopectin long chains, but negatively correlated with amylopectin short chains. A starch film of 50--130 mum was observed with scanning electron microscopy on the surface of the cereals coated with Hylon VII. After soaking in milk for 3 min, the peak force of the cereals coated with corn starches were higher than those of the controls. The cereals coated with Hylon VII were found to have an increase in dietary fiber content. The results suggest that RS3 formation is affected by starch composition as well as starch structure and can be increased by moderate beta-amylolysis. Debranched amylose-containing corn starches could be used as cereal coatings to extend the bowl-life of ready-to-eat cereals.