Time–temperature studies of κ-carrageenan gelation in the presence of high levels of co-solutes

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.

Recent advances and future challenges in the explanation and exploitation of the network glass transition of high sugar/biopolymer mixtures

Through the years, the concept of glassy phenomena evolved from non-science to a highly specialized subject following the appreciation that structural properties or product defects could be rationalized on the basis of this amorphous vitreous transition. Special reference will be made in this review to sugar glasses in the presence of biopolymers which, increasingly, are used to innovate (e.g., replace gelatin) in confections, ice cream, boiled down sweets, etc. Keeping in mind that the subject cuts across several conventional fields, this manuscript is written with several objectives in view. I deemed it necessary to provide a historic itinerary of the nature of the rubber-to-glass transition in association with the concepts of plasticizing and unfreezable water. That should facilitate comprehension and hopefully encourage young scientists to take an interest in the field that continues to offer considerable challenges, as well as opportunities. Second, the food scientist is exposed to the "sophisticated" synthetic polymer approach pioneered by J.D. Ferry and his colleagues via the WLF equation/free volume theoretical framework. Extension of this school of thought to biomaterials introduces the concept of mechanical or network glass transition temperature, which is contrasted to data obtained using differential scanning calorimetry. Applications of the network T(g) as a relevant indicator for evaluating the stability criteria and the quality-control aspects of foodstuffs are also discussed. All along, information available in the literature is critically presented ranging from the misuse of the WLF equation to a recent challenge to the theory mounted by the coupling model, which addresses in some detail the physics of interactions and the cooperativity of molecular mobility at the vicinity of T(g).

Time-temperature studies of gellan polysaccharide-high sugar mixtures: effect of sodium ions on structure formation

Changes to the viscoelastic storage and loss moduli were measured as a function of temperature and oscillatory frequency for 0.5% (w/w) gellan:80% (w/w) cosolute dispersions with added Na(+) (40 to 160 mM). Isothermal frequency (0.15 to 15 Hz) and thermal scans (at 0.15 Hz) were performed over a decreasing then increasing temperature range of 85 to 5 degrees C and 5 to 85 degrees C, respectively. Moduli were found to increase in magnitude with decreasing temperature and increasing levels of Na(+) during cooling, then remained relatively thermally irreversible upon heating. Isothermal frequency (ITF) data were described using the time-temperature superposition (TTS) principle and the modified Cole-Cole (MCC) analysis. Both TTS and the MCC analyses successfully described the behavior of samples containing 40 mM added Na(+) during cooling and heating, and at the 100-mM Na(+) level during cooling. TTS superposed ITF data over the entire temperature range, whereas successful superposition was restricted to lower temperatures in the MCC analysis, where the viscoelastic response was dominated by the long-range relaxation of gellan chains between junction zones. Failure of both analyses was attributed to the formation of junction zones composed of polymer-polymer associations. It is proposed that the addition of Na(+) promotes the formation of a weakly cross-linked gellan network.