Mechanical properties and microstructural changes during soaking of individual corn and quinoa breakfast flakes

摘要

The importance of breakfast cereal flakes (BCF) in Western diets deserves an understanding of changes in their mechanical properties and microstructure that occur during soaking in a liquid (i.e., milk or water) prior to consumption. The maximum rupture force (RF) of two individual types of breakfast flaked products (BFP) - corn flakes (CF) and quinoa flakes (QF) - were measured directly while immersed in milk with 2% of fat content (milk 2%) or distilled water for different periods of time between 5 and 300 s. Under similar soaking conditions QF presented higher RF values than CF. Microstructural analysis of flakes involved freeze-drying of individual flakes and observation of their cross-section and surface via scanning electron microscopy. Three consecutive periods (fast, gradual, and slow reduction of RF) were associated with changes in the microstructure of flakes. These changes were more pronounced in distilled water than in milk 2% for both BFP, probably because liquid infiltration is hindered when fat and other solids in milk become deposited on the flakes’ surface. Structural and textural modifications were primarily ascribable to the plasticizing effect of water which softened the carbohydrate/protein matrix, inducing partial collapse of the porous structure and eventually disintegration of the whole piece through deep cracks.