Investigating the influence of inulin as a fat substitute in comminuted products using rheology, calorimetric and microscopy techniques

• Fat substitution with inulin in sausages was evaluated.
• NMR data showed decreases in free water population with increasing inulin.
• Rheological analyses indicated structural modification with increasing inulin.
• Structural changes were visualized with confocal and scanning electron microscopy.

The present manuscript studied the effects of fat substitution with two commercial inulins on the magnetic resonance, rheological, calorimetric and microscopic properties of breakfast sausages. Sausage formulations were evaluated using mixture design (D-optimal). A total of 17 experimental treatments were employed, with each representing a different substitution level for fat. Sausage batters were formulated to contain lean pork shoulder, pork back fat/inulin, water, rusk and seasoning (44.3, 18.7, 27.5, 7 and 2.5% w/w, respectively). The resultant products’ water mobility, deformation and thermal behaviors were analyzed for each treatment group using nuclear magnetic resonance (NMR), rheology, differential scanning calorimetry (DSC), while their ultra-structural properties were analyzed using light, confocal and scanning electron microscopy for selected extremes. Significant models were produced for water mobility with inulin inclusions in sausages increasing the relative proton populations of bound water (T2b) values (p < 0.0001) and decreasing free water (T22) population (p < 0.0001). Inulin inclusions significantly altered the rheological characteristics with increases in both the gel strength (G′0−G″0G′0−G″0) and unit interaction strength (An) (p < 0.0001, respectively). Complementary temperature-dependent behavior was observed using rheology and DSC which showed increased elastic behavior (G′) circa 40 °C that corresponded to the endothermic peaks for the onset of protein denaturation. Cryo-scanning electron and confocal laser microscopy techniques permitted visualization of the aggregation of inulin micro-crystals and distribution of fat within the cooked sausage matrix. Overall, the work presented has improved our understanding of the fundamental properties of sausage products and will enable a more scientific-based approach to future product development.

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