Mechanical basis of shortening functionality

This thesis is an investigation on the functionality of bakery fat shortenings, with major emphasis on the mechanical function of those designed for lamination. Laminating or roll-in shortenings are fats used in the manufacture of layered doughs. Their main role is to separate sheets of dough to allow the formation of a multilayered structure responsible for pastry quality (“puff” and “flakiness”). To achieve this, laminating shortenings must “survive” processing deformations. To date, there is limited understanding on the factors underlying the functionality of these materials. There is also a major shortcoming with their utilization; their typically high content of trans and saturated (inconclusive evidence) fatty acids, implicated in cardiovascular health. These provide strong motivation to understand the structure-function relationships in laminating shortenings. Here, we differentiated physico-chemical and rheological properties of laminating shortenings, from those of shortenings designed for all-purpose, cake and icing applications. We found that laminating shortenings had contents of trisaturated and unsaturated TAGs higher than other shortenings, although their overall “hard” fat content were comparable. Physical properties, believed to be crucial to designate the laminating functionality such as polymorphism, solid fat content and melting, were comparable. Laminating shortenings hosted a range of rheological properties; some common to other fats and some unique to their mechanical functionality. While elastic material properties were comparable to those of other shortenings, their viscous properties were strikingly different. Stress responses to large amplitude oscillatory shear (LAOS) revealed that the laminating shortenings behave as viscoelastic ductile solids, in that they convert the vast majority of the released strain energy into viscous dissipative energy, associated with plastic flow. Structural investigations indicated that laminating shortenings featured smaller and smooth crystal nanoplatelets, three hierarchy levels, and crystal aggregates with layer-like arrangements. It is suggested that the hierarchy and microstructure spatial distribution play a pivotal role on high-energy dissipation (rather than on energy storage) which confers superior load-bearing ability in laminating shortenings. This research provides a good ground for advancing our understanding on the macro functionality of laminating shortenings and guide the selection and design of healthier alternative lipid structuring materials based on the displayed rheological behavior.