Dynamic viscoelastic properties of sweet potato studied by dynamic mechanical analyzer

Thermomechanical transitions of meat-analog based fried foods batter coating

This study aimed to characterize the thermomechanical transitions of meat-analog (MA) based coated fried foods. Wheat and rice flour-based batters were used to coat the MA and fried at 180 °C in canola oil for 2, 4 and 6 min. Glass-transition-temperature (Tg) of the coatings were assessed by differential scanning calorimetry, directly after frying or after post-fry holding. Mechanical texture analyzer and X-ray microtomography were employed to assess textural attributes and internal microstructure, respectively. Batter-formulation substantially impacted the Tg of fried foods coating i.e., crust. Tg of fried foods crust were ranged between -20 °C to -24 °C. Tg was positively correlated with frying time and internal microporosity (%), whereas negatively correlated with moisture content. Internal microstructure greatly influenced the textural attributes (hardness, brittleness, crispiness). Post-fry textural stability considerably impacted by Tg. Negative Tg value explains post-fry textural changes (hard-to-soft, brittle-to-ductile, crispy-to-soggy) of MA-based coated products at room-temperature (25 °C) and under IR-heating (65 °C).

Dynamic Viscoelastic Behavior of Maize Kernel: Application of Frequency-Temperature Superposition

Maize kernels were treated using two varieties of drying methodologies, namely combined hot air- and vacuum-drying (HAVD) and natural drying (ND). We performed frequency sweep tests, modified Cole-Cole (MCC) analysis, and frequency-temperature superposition (FTS) on these kernels. The kernels' elastic and viscous properties for ND were higher than those for HAVD. The heterogeneous nature of maize kernel may account for the curvature in MCC plot for the kernel treated by HAVD 75 °C and the failure of FTS. MCC analysis was more sensitive than FTS. The kernel treated by HAVD 75 °C demonstrated thermorheologically simple behavior across the entire temperature range (30-45 °C) in both MCC analysis and FTS. The frequency scale for the kernel treated using HAVD 75 °C was broadened by up to 70,000 Hz. The relaxation processes in the kernel treated by HAVD 75 °C were determined to be mainly associated with subunits of molecules or molecular strands. The data herein could be utilized for maize storage and processing.

A Systematical Rheological Study of Maize Kernel

In this study, the rheological behavior of maize kernel was systematically investigated using a dynamic mechanical analyzer. The loss in toughness caused by drying resulted in a downward shift in the relaxation curve and an upward shift in the creep curve. The long relaxation behavior became obvious when the temperature was above 45 °C, resulting from the weakening of hydrogen bonds with temperature. The maize kernel relaxed more rapidly at high temperatures, caused by a reduction in the cell wall viscosity and polysaccharide tangles. The Deborah numbers were all much smaller than one, suggesting that the Maxwell elements showed viscous behavior. Maize kernel, as a viscoelastic material, showed a dominant viscous property at high temperatures. The decline in β with increasing drying temperature indicated an increase in the width of the relaxation spectrum. A Hookean spring elastic portion made up the majority of the maize kernel creep strain. The order-disorder transformation zone of maize kernel was about 50-60 °C. Due to the complexity of maize kernel, the William-Landel-Ferry constants differed from the universal values; these constants should be ascertained through experiments. Time-temperature superposition was successfully used to describe the rheological behavior. The results show that maize kernel is a thermorheologically simple material. The data acquired in this study can be used for maize processing and storage.

Viscoelastic analysis of oat grain within linear viscoelastic region by using dynamic mechanical analyzer

The stress relaxation, creep-recovery, temperature, and frequency sweep tests were performed within the linear viscoelastic region by using a dynamic mechanical analyzer to investigate the viscoelastic characteristic of oat grain. The result showed that 5-element Maxwell and Burgers model were able to describe viscoelastic behaviors better. The relaxation stress decreased with the increasing moisture content from 6.79 to 23.35%, while the creep strain increased as well as the final percentage recovery decreased from 58.61 to 32.50%. In frequency sweep, storage modulus increased with the increasing frequency. In temperature sweep, there was a clear turning point in storage modulus, loss modulus, and tan delta curves with increasing temperature. The turning value of 167.47, 147.44, 134.27, 132.41, 110.28, and 92.62 °C detected in the tan delta were regarded as the best glass transition temperatures. This temperature was found to be lower than gelatinization heating temperature and decrease with the increase of moisture content. The crystalline structure of oat exhibited a typical A-type pattern and corresponding crystallinity increased from 22.03 to 31.86% with increasing moisture content. The scanning electron microscopy (SEM) micrograph of oat section was found that the size and adhesive effect of starch granules increased due to hydration.

Physical and viscoelastic properties of carrots during drying

It is essential to understand the physical and mechanical properties of a product since these properties affect the structure, texture, and ultimately consumer acceptance. The effect of drying conditions on dynamic viscoelastic properties, stress relaxation function and creep compliance, and physical properties, such as moisture distribution, color parameters, and shrinkage, was studied. An increase in drying temperature and duration resulted in a decrease in moisture content and volume, which were highly correlated (R = .988). Water evaporation followed the falling rate period, demonstrating that the water transport was limited by internal resistances. The decomposition of carotenoids led to a decrease in magnitude of color parameters (L, a, and b), between 30.1% and 51.6% with 4 hr drying. It was observed that the material shrinkage and moisture content highly affected the mechanical properties; increased stress relaxation modulus and decreased creep compliance values of the sample. The creep behavior, expressed with Burger's model (R²  ≥ .986), was highly dependent on moisture content. The linear viscoelastic region of carrots was found to be at strains lower than 3%. The three-element Maxwell model well fitted to describe the viscoelastic behavior of carrots (R²  ≥ .999, RMSE ≤ 2.08 × 10^-4 ). The storage moduli (G') were higher than loss moduli (G″), indicating that samples presented solid-like behavior. The findings can be used to improve the textural attributes of carrots and carrot-based products.

Preparation and Characterization of High Amylose Corn Starch⁻Microcrystalline Cellulose Aerogel with High Absorption

Microcrystalline cellulose (MCC) aerogels were synthesized, blendingwith high amylose corn starch of different contents based on a NaOH–urea solution, and following by vacuum freeze-drying technology. The microstructure of the aerogel was observed by scanning electron microscopy (SEM) as an interconnected, porous three-dimensional structure, while X-ray diffractogram (XRD) measurements showed that the crystalline form was converted from cellulose I to cellulose II during dissolution and regeneration. Thermogravimetric analysis (TGA) showed that the content of starch had little effect on the thermal stability of the aerogel, whereas the content of starch had great influences on absorption and viscoelastic properties. When the ratio of starch was 10% and 15%, the prepared aerogels presented a low density and abundant pores, which endowed the aerogels, not only with the highest absorption ratio of pump oil and linseed oil (10.63 and 11.44 g/g, respectively), but also with better dynamic viscoelastic properties.

Mechanical Properties of Hulless Barley Stem with Different Moisture Contents

Mechanical properties of hulless barley stems with different moisture contents (10.23%–43.14%) were investigated by using temperature sweep, frequency sweep, stress relaxation and creep tests of dynamic mechanical analyzer (DMA) in this study. Results showed a significant dependence of storage modulus, loss modulus and tan delta on moisture content. The data from stress relaxation and creep was fitted by using generalized Maxwell model and Burgers model. 5-element Maxwell model was better for describing relaxation behaviors of hulless barely stem compared with the 3-element Maxwell model. The peak values of loss modulus and tan delta both occurred at a low temperature when moisture content increased. The dynamic mechanical properties can provide useful information for the harvesting and processing of huless barely stem.

The Stress-Relaxation Behavior of Rice as a Function of Time, Moisture and Temperature

Stress-relaxation behavior of single rice kernel was studied using a dynamic mechanical analyzer (DMA) in compression mode. The relaxation modulus was measured in a moisture content range of 12–30 % on dry basis (d.b.) and a temperature range of 25–80°C. A constant stain value of 1 % (within the linear viscoelastic range) was selected during the stress-relaxation tests. The relaxation modulus was found to decrease as the temperature and moisture increased. A master curve of relaxation modulus as a function of temperature and moisture content was generated using the time–moisture–temperature superposition principle. Results showed that the generalized Maxwell model satisfactorily fitted the experimental data of the stress-relaxation behavior and the master curve of relaxation modulus (R2> 0.997). By shifting the temperature curves horizontally, the activation energy of the stress relaxation was obtained which significantly decreased with increase in the moisture content.