Bioavailability of starch in bread rich in amylose: metabolic responses inhealthy subjects and starch structure

Objective: This study investigated whether postprandial metabolic responses to bread could be lowered by substituting high amylose maize starch for a part of the flour. Design and subjects: Eight healthy subjects consumed test meals of equivale nt nutritional composition based on white wheat bread, bread rich in amylos e (HAWB) and spaghetti as a breakfast meal. Blood samples were collected to measure insulin and glucose concentration during two hours after consumpti on. The degree of starch crystallinity was investigated by X-ray diffractio n and DSC analysis. Results: HAWB produced low glycaemic (60 +/- 18) and insulinaemic (57 +/- 2 0) indexes similar to those of spaghetti (83 +/- 46, 61 +/- 16). In vitro a mylase hydrolysis of the three foods showed that high amylose content in HA WB significantly lowered starch degradation in bread without affecting hydr olysis kinetics. Addition of amylose in dough increased the resistant starc h content of HAWB (14% of dry matter). The resistant starch fraction was ma inly composed of crystalline amylose (B-type X-ray diffraction pattern, mel ting temperature 105 degrees C) attributable to native high amylose maize s tarch incompletely gelatinised during bread-cooking. Conclusions: Bread produced by the substitution of high amylose maize starc h for a part of wheat flour showed a low glycaemic index. Resistant starch in HAWB corresponded to native crystalline amylose not gelatinised during: normal bread-processing conditions.