| Puffed, quick-bread-type, high fiber snacks were prepared using a Wenger TX-52 twin-screw extruder. Four sets of processing conditions ranging from mild to intense energy inputs were used for each type of snack. Soft white wheat and rice flours were the main ingredients to which soy cotyledon fiber, corn bran, or oat bran were added as fiber sources. A no-fiber-added snack was extruded under similar conditions and used as the control. An analysis of the physicochemical properties showed that extrusion processing altered the microscopic structure of the fiber in the snacks. The extruded products had higher cold paste viscosities, in vitro diet viscosities, and water holding capacities than the corresponding raw mixes. Significant increases in resistant starch content occurred, and evidence indicated formation of starch-lipid complexes in the extruded products.; An animal study was conducted in which hypercholesterolemic hamsters were fed raw, fiber-containing snack mixes, as well as snacks extruded using four levels of energy input. After six weeks of feeding, their serum and liver cholesterol levels were inversely related to the total energy input into the extruder during the manufacture of the snacks. The total cecal short chain fatty acid levels and fecal neutral sterol and bile acid concentrations were negatively correlated to serum and liver cholesterol levels for animals fed control, soy, corn, and oat fiber snacks; the relationships were less strong for oat bran. The apparent fat digestibility and fecal fiber were lowest in animals fed oat bran snacks. The results indicated that the cholesterol lowering activity of the fiber sources studied was caused by a combination of different factors; and that those factors varied with the source of fiber. In general, one or more of the following mechanisms appeared to be responsible for the enhanced cholesterol lowering activity of extruded snacks: increased diet viscosity; formation of starch-lipid complexes leading to decreased absorption of dietary lipids; enhanced fermentability of the extruded products that could decrease cholesterol biosynthesis; and increased excretion of fecal neutral sterols and bile acids that could result in increased breakdown of dietary and blood cholesterol. |
