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Fats are ubiquitous in biological membranes, foods, and many other commercial products. In these, they play essential roles in biological, nutritional, and physical functions. In this review, we focus on physical mechanical functions. The rheology of fats arises from the crystal network, which displays hierarchical structural levels from the molecular to the mesoscopic. Under linear deformations, the crystal network behaves as a viscoelastic solid with elasticity dictated by particle concentration and microstructural features as represented in fractal rheo-mechanical models. Under nonlinear deformations, the crystal network yields, showing a variety of nonlinear phenomena, i.e., softening, stiffening, thixotropy. These features largely contribute to functionality or performance as essentially all processing and end-uses of fatty materials involve large nonlinear deformations. Early work on rheology of fats gave hints of their nonlinear mechanical behavior, although in many cases the measured properties were empirical. In contrast, recent efforts from our group measured fundamental rheological functions using large amplitude oscillatory shear rheology. We demonstrate the ability of this technique to discern among the bulk functionality of bakery fats (all-purpose and lamination shortenings) based on well-defined rheological signatures that also relate to the fat structure. This technique has the potential to provide similar insights on other fatty systems and novel ideas for reformulation and design of alternative lipid-structuring materials.

Overall, roll-in shortening differed from other samples in regard to molecular makeup but not greatly in their physical parameters, suggesting that triacylglycerol composition has important implications on their functionality.

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The rheological properties of shortenings with similar physicochemical characteristics but diverse functionality were investigated under small and large oscillatory shear. Particular attention was drawn to the mechanical behavior of roll-in shortenings, characterized for resisting work softening and forming continuous fat thin films during dough lamination and sheeting. All shortenings displayed low-frequency dependence, reminiscent of viscoelastic solids where the storage modulus is higher than the loss modulus, and displayed a comparable linear envelope, encompassing relatively small shear strains, such as those encountered in other fat systems. Linear elastic moduli and yield stress, previously used to designate roll-in functionality, remained unremarkable. In contrast, nonlinear viscoelastic behavior of roll-in shortenings differed considerably from all-purpose commercial shortenings. Lissajous-Bowditch curves suggested less local intracycle strain stiffening and less average intercycle strain softening for roll-in shortenings than other shortenings. Likewise, their Fourier spectra indicated a gradual evolution of the third harmonic into the nonlinear regime characterized by higher slopes. The third and fifth harmonics grew monotonically, and the third overtone leveled off and showed no stress decays unlike other samples, suggesting a marked ability of roll-in shortenings to withstand deformation at high stresses. Conversely, the dissipative energy scaled in a similar fashion for all shortenings. Moreover, roll-in shortenings displayed enhanced thixotropic behavior supported by lower power law indexes and prompt structural rebuilding after steady shear cessation. Overall, these rheological signatures facilitated the differentiation among the utilization of shortenings and correlated well with the functionality of roll-in shortenings.

Summary The efficiency of pulsed UV light (PL) for inactivation of E. coli K12 on hard‐cooked eggs was investigated. Temperature, colour and texture were recorded to determine adverse effects on quality. Distance from the quartz window (5.5, 9.5 cm) and time (1–30 s) was set as the experimental variables. Results indicated that E. coli K12 viability decreased at closer distances and increased time (P < 0.05). Bacterial populations were reduced to 3.54 log CFU per egg and 3.23 log CFU per egg after 15 and 20 s at 5.5 cm and 9.5 cm, respectively. Scanning electron micrographs revealed the existence of photophysical mechanisms, bacterial overlapping and internalisation interfering inactivation. Treated samples experienced slight thermal increases (6–9 °C) contributing to the preservation of colour and texture, not significantly different from untreated samples (P > 0.05). Our findings support the use of PL to enhance the safety of hard‐cooked eggs although bacterial shadowing may have significant implications on treatment efficiency.

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