Stress relaxation and dynamic profiles of low-moisture, part-skim (LMPS) Mozzarella cheese cylinders refrigerated 14 days (control), frozen and thawed, and stored frozen and refrigerated up to 90 days were compared. Samples were frozen at -30°C and stored at -20°C. Thawing and refrigerated storage were at 5°C. Stress relaxation tests were conducted at??O"C and dynamic spectrometry at 20°C and 60°C.The frozen and thawed Mozzarella cheese tested at 20°C became harder and more elastic with storage time, while refrigerated stored samples became softer and more elasticoviscous with time. Upon melting, both go-day-frozen and go-day-refrigerated cheeses were less elastic and less viscous than 14-day-refrigerated samples.

We report the biomechanics and anatomy of fruit wall peels (before and after cellulase/pectinase treatment) from two Lycopersicon esculentum cultivars (i.e., Inbred 10 and Sweet 100 cherry tomatoes). Samples were tested before and after enzyme treatment in uniaxial tension to determine their rate of creep, plastic and instantaneous elastic strains, breaking stress (strength), and work of fracture. The fruit peels of both cultivars exhibited pronounced viscoelastic and strain-hardening behavior, but differed significantly in their rheological behavior and magnitudes of material properties, e.g., Inbred 10 peels crept less rapidly and accumulated more plastic strains (but less rapidly), were stiffer and stronger, and had a larger work of fracture than Sweet 100 peels. The cuticular membrane (CM) also differed; e.g., Sweet 100 CM strain-softened at forces that caused Inbred 10 to strain-harden. The mechanical behavior of peels and their CM correlated with anatomical differences. The Inbred 10 CM develops in subepidermal cell layers, whereas the Sweet 100 CM is poorly developed below the epidermis. Based on these and other observations, we posit that strain-hardening involves the realignment of CM fibrillar elements and that this phenomenon is less pronounced for Sweet 100 because fewer cell walls contribute to its CM compared to Inbred 10.

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Rheological characteristics of butters made from anhydrous milk fat (AMF) and supercritically fractionated high melting triglyceride (HMT) fraction were compared. An Instron Universal Testing Machine was used to compress the samples between two lubricated plates at constant deformation rate (0.5 mm/min). Stress growth coefficients, computed from the ratios of stresses and biaxial strain rates, were plotted as function of time. HMT butter had higher stress growth coefficients than AMF butter, indicating its greater degree of firmness. Stress growth coefficients were negatively correlated to temperature due to lower crystallinity of fat at higher temperatures and increased on storage due to formation of weak van der Waal forces of attraction between crystalline fat chains.

The cytoplasm of soybean seed axes is known to undergo a glass transition as moisture content decreases. In this study we have investigated whether the glass transition is reflected in the macroscopic mechanical properties of the seeds. Constant-deformation-rate compression tests and constant-deformation relaxation tests were performed with a cylindrical indenter on soybean cotyledons equilibrated to moisture contents ranging from 2% to 16% (dry basis). The apparent modulus of elasticity was found to rise sharply as moisture content declined below 10%, showing an inflection point at 9.8%, and a relatively constant elasticity below 7%. Other measures of mechanical behaviour were also constant in the drier ranges, including linear deformation, and plastic deformation. Each of these viscoelastic characteristics showed an inflection point or a departure from a linear function in the region of 7.5–9.8% moisture content, the hydration region below which the tissue is in a glassy state. It is suggested that the viscoelastic qualities of dry soybeans are principally a consequence of the tissues being in the glassy state.

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