Cellular architecture and its relationship with mechanical properties in expanded extrudates containing apple pomace

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• 作者：Elisa L. Karkle ; Sajid Alavi ; ^{salavi@ksu.edu} ; Hulya Dogan
• 关键词：Extrusion ; Fiber ; Phase transition analysis ; Microstructure ; Mechanical properties
• 刊名：Food Research International
• 出版年：2012
• 期刊代码：53_09639969
• 类别：abs
• 出版时间：April, 2012
• 卷：46
• 期：1
• 页码：10-21
• 文件大小：1428 K

摘要

Cereal-based puffed foods can deliver significant amounts of fruit and vegetable fiber, however a major hurdle is the accompanying decrease in expansion and poor textural properties. The objective of this work was to develop a comprehensive understanding of the operative rheology, processing conditions, cellular architecture, macrostructure and mechanical properties of high fiber, starch-based expanded matrices produced using extrusion. The combination of phase transition analysis and non-invasive X-ray microtomography provided a unique analytical approach for this purpose. A lab-scale twin screw extruder was used for processing directly expanded products from corn flour and apple pomace blends containing up to 22.5%total dietary fiber. Different levels of pomace (0-28%) and in-barrel processing moisture (17.5-25%) resulted in extrudates with a wide range of microstructures (average cell size 0.05-3.43 mm, wall thickness 0.12-0.34 mm and void fraction 0.53-0.76). Structural anisotropy biased towards radial expansion was observed in foams without pomace, whereas cellular isotropy, higher cell number density and greater longitudinal expansion were favored in the presence of pomace. A conceptual model for foaming and collapse was developed based on flow temperature of blends (123.7-167.6 掳C), specific mechanical energy, and anticipated changes in visco-elasticity and extensibility of the high-fiber melt. Cell size was significantly correlated to average crushing force (r = 鈭?#xA0;0.69), crispness work (r = 鈭?#xA0;0.69) and number of spatial ruptures (r = 0.74). Microstructure data in combination with standard theory for brittle foams was employed to understand mechanical properties of extrudates under compression.