Glass Transition-Associated Structural Relaxations and Applications of Relaxation Times in Amorphous Food Solids: a Review

Identification and adulteration detection of Heterotrigona itama and Apis dorsata honey using differential scanning calorimetry and convolutional neural networks with data augmentation

This study presents a simple approach for detecting honey adulteration by integrating calorimetric data from differential scanning calorimetry (DSC) with machine learning classification (MLC) techniques, specifically using convolutional neural network (CNN) model alongside the Synthetic Minority Over-sampling TEchnique (SMOTE) for data augmentation. The thermal profiles of different honey varieties, sugar adulterants, and adulterated samples were acquired using DSC. Shifts in glass transition temperatures were observed in adulterated honey. The DSC data were analyzed using principal component analysis and MLC workflow. CNN model applied to original dataset reported accuracy of 24-67 %. However, integrating CNN model with SMOTE algorithm resulted in a significant accuracy improvement to 60-91 %. The integration of DSC with MLC provides a rapid and accurate method for detecting honey adulteration, demonstrating strong generalization capability. The proposed approach could facilitate the development of a framework to detect fraudulent practices, safeguarding honey industry and consumers from sugar-based adulterations.

Quantitative Analysis of Molecular Mobility in Amorphous Lactose Above Tg: A Novel Insight from Molecular Dynamic Simulation to Strength Parameter

Measuring molecular mobility (Mm) in solid food is challenging due to the rigid and heterogeneous nature of these matrices. The thermodynamic parameter Strength (S) fails to account for molecular displacement distances. This study emphasizes the role of molecular dynamic (MD) simulation in quantifying Mm on amorphous lactose at mimic water activities (aw) at temperatures above the glass transition temperature (Tg), incorporating the S. The results show that coordinating root mean square displacement (RMSD) effectively quantifies Mm across different aw and temperature conditions. Both increased aw and higher temperatures facilitate Mm by expanding free volume and reducing energy barriers for molecular rearrangement, as indicated by the mobility coefficient calculations. This study also emphasizes the importance of system size in interpreting Mm, as larger systems exhibit emergent behaviors that smaller systems cannot capture. The calculated MD relaxation time for 10,000-molecule lactose/water cells at a specific S value was successfully translated to a real timescale of 1.8 × 106 s, consistent with experimental data (1.2 × 106 s). Moreover, water can shift from a plasticizing role to a more stabilizing one, slowing molecular motion and leading to equilibrium clustering. These findings have important implications for understanding the behavior of amorphous lactose in food and pharmaceutical formulations.

Mechanical Characterization of a Novel Cyclic Olefin-Based Hot-Melt Adhesive

A novel hot-melt cyclic olefin-based adhesive was designed as a transparent, non-tacky film of amorphous thermoplastic with a unique polymer micro-structure. The aim of the present paper is to assess the mechanical properties of the 0.1 mm thick COP hot-melt adhesive film through adhesive characterizations tests. The glass transition temperature was determined using dynamic mechanical analysis (DMA). For mechanical characterization, bulk and thick adherend shear specimens were manufactured and tested at a quasi-static rate, where at least three specimens were used to calculate the average and standard deviation values. Tensile tests revealed the effects of molecular chain drawing and reorientation before the onset of strain hardening. Thick adherend shear specimens were used to retrieve shear properties. Fracture behaviour was assessed with the double cantilever beam (DCB) test and end-notched flexure (ENF) test, for characterization under modes I and II, respectively. To study the in-joint behaviour, single lap joints (SLJs) of aluminium and carbon fibre-reinforced polymer (CFRP) were manufactured and tested under different temperatures. Results showed a progressive interfacial failure following adhesive plasticization, allowing deformation prior to failure at 8 MPa. An adhesive failure mode was confirmed through scanning electron microscopy (SEM) analysis of aluminium SLJ. The adhesive exhibits tensile properties comparable to existing adhesives, while demonstrating enhanced lap shear strength and a distinctive failure mechanism. These characteristics suggest potential advantages in applications involving heat and pressure across automotive, electronics and structural bonding sectors.

The effect of mechanical glass transition temperature on the oxidation rates of omega fatty acids in condensed biopolymer matrices

The concept of glass transition has been used in food products to study their stability, extending shelf life and enhancing organoleptic desirability. This investigation evaluates the effect of three-dimensional structure as a barrier to oxidation of omega fatty acids in condensed hydrocolloid-based matrices. Two high-solid preparations were employed: κ-carrageenan with glucose syrup and genipin-crosslinked gelatin with polydextrose. They supported discontinuous microscopic inclusions of linoleic and linolenic acids within the rubber-to-glass transition region of the condensed mixtures. Glass transition temperatures (Tg) were estimated using differential scanning calorimetry and in-shear dynamic oscillation. The rate of lipid oxidation was monitored by analysing hydroperoxide (ROOH) production during each oxidation phase. The structural transformation of the supporting matrices as a function of temperature significantly affects the oxidation processes. The mechanical or network Tg exhibited higher values than the calorimetric Tg, supporting reduced lipid oxidation rates by suppressing ROOH accumulation in the densified glassy matrices.

Predictive model for the surface melting and puffing of freeze-dried amorphous materials

It is thought that surface melting and puffing of freeze-dried amorphous materials are related to the difference between the surface temperature (Tsur) and freeze-concentrated glass transition temperature (Tg') of the materials. Although Tg' is a material-specific parameter, Tsur is affected by the type and amount of solute and freeze-drying conditions. Therefore, it will be practically useful for preventing surface melting and puffing if Tsur can be calculated using only the minimum necessary parameters. This study aimed to establish a predictive model for the surface melting and puffing of freeze-dried amorphous materials according to the calculated Tsur. First, a Tsur-predictive model was proposed under the thermodynamic equilibrium assumptions. Second, solutions with various solute mass fractions of sucrose, maltodextrin, and sucrose-maltodextrin mixture were prepared, and three material-specific parameters (Tg', unfrozen water content, and true density) were experimentally determined. According to the proposed model with the parameters, the Tsur of the samples was calculated at chamber pressures of 13, 38, and 103 Pa. The samples were freeze-dried at the chamber pressures, and their appearance was observed. As expected, surface melting and puffing occurred at calculated Tsur > Tg' with some exceptions. The water activity (aw) of the freeze-dried samples increased as the Tsur - Tg' increased. This will have resulted from surface melting and puffing, which created a covering film, thereby preventing subsequent dehydration. The observations suggest that the proposed model is also useful for predetermining the drying efficiency and storage stability of freeze-dried amorphous materials.

On the universality of viscosity in supersaturated binary aqueous sugar solutions: Cryopreservation by vitrification

Nowadays, the physical nature of supersaturated binary aqueous sugar solutions in the vicinity of the glass transition represents a very important issue due to their biological applications in cryopreservation of cells and tissues, food science and stabilization and storage of nano genetic drugs. We present the construction of the Supplemented Phase Diagram and the non-equilibrium nature of the undersaturated-supersaturated kinetic transition. The description of its thermodynamic nature is achieved through the study of behavior of their viscosity as temperature is lowered and concentration increased. In this work, we find a universal character for the viscosities of several sugar water solutions.

The effect of Maillard reaction on the lactose crystallization and flavor release in lactose/WPI/inulin encapsulation

The crystallization of lactose usually causes the structural collapse and core material escape of flavor encapsulations. The objective of this study was to investigate the effects of different grafting degrees of WPI-inulin Maillard reaction products on the lactose crystallization and the subsequent release behaviors. Ethyl acetate was chosen as the model volatile flavor and the encapsulations were prepared by freeze-drying. The results found that the encapsulation efficiency was significantly increased from 30% to over 80% by using MRPs as wall materials. Those microparticles showed the greater flavor retention and lower moisture adsorption. In addition, the encapsulations produced by the proper Maillard reaction times (e.g., 48 h and 72 h) could effectively delay the lactose crystallization and thus improve the structural stability of the matrix. This innovation finding aims to use the Maillard reaction to control the crystallization behaviors and enhance the usefulness of high-lactose containing products in encapsulation systems.

Novel Thermoplastic Composites Strengthened with Carbon Fiber-Reinforced Epoxy Composite Waste Rods: Development and Characterization

The increasing use of carbon fiber and epoxy resin composite materials yields an increase in the amount of waste. Therefore, we present a solution consisting of composites manufactured by hot pressing, employing polyamides (either PA11 or PA12) and a mechanically recycled carbon fiber-reinforced polymer (CFRP) as reinforcement. The main objectives are to study the manufacturing of those composites, to evaluate the fiber distribution, and to perform a mechanical, dynamical, and thermomechanical characterizations. The X-ray micro-computed tomography (μCT) shows that the fibers are well-distributed, maintaining a homogeneous fiber volume fraction across the material. The variability in the results is typical of discontinuous fiber composites in which the fibers, although oriented, are not as homogeneously distributed as in a continuous fiber composite. The mechanical and dynamic properties barely differ between the two sets of composites. A dynamic-mechanical analysis revealed that the glass transition temperature (Tg) increases slightly for both composites, compared to the polymers. These results illustrate the viability of the recycling and reuse route for preventing the deterioration of carbon fibers and promoting the subsequent reduction in the environmental impact by employing a thermoplastic matrix.

Complementarity of mDSC, DMA, and DRS Techniques in the Study of Tg and Sub-Tg Transitions in Amorphous Solids: PVPVA, Indomethacin, and Amorphous Solid Dispersions Based on Indomethacin/PVPVA

Recently, glasses, a subset of amorphous solids, have gained attention in various fields, such as polymer chemistry, optical fibers, and pharmaceuticals. One of their characteristic features, the glass transition temperature (T_g) which is absent in 100% crystalline materials, influences several material properties, such as free volume, enthalpy, viscosity, thermodynamic transitions, molecular motions, physical stability, mechanical properties, etc. In addition to T_g, there may be several other temperature-dependent transitions known as sub-T_g transitions (or β-, γ-, and δ-relaxations) which are identified by specific analytical techniques. The study of T_g and sub-T_g transitions occurring in amorphous solids has gained much attention because of its importance in understanding molecular kinetics, and it requires the combination of conventional and novel characterization techniques. In the present study, three different analytical techniques [modulated differential scanning calorimetry (mDSC), dynamic mechanical analysis (DMA), and dielectric relaxation spectroscopy (DRS)] were used to perform comprehensive qualitative/quantitative characterization of molecular relaxations, miscibility, and molecular interactions present in an amorphous polymer (PVPVA), a model drug (indomethacin, IND), and IND/PVPVA-based amorphous solid dispersions (ASDs). This is the first ever reported DMA study on PVPVA in its powder form, which avoids the contribution of solvent to the mechanical properties when a self-standing polymer film is used. A good correlation between the techniques in determining the T_g value of PVPVA, IND, and IND/PVPVA-based ASDs is established, and the negligible difference (within 10 °C) is attributed to the different material properties assessed in each technique. However, the overall T_g behavior, the decrease in T_g with increase in drug loading in ASDs, is universally observed in all the above-mentioned techniques, which reveals their complementarity. DMA and DRS techniques are used to study the different sub-T_g transitions present in PVPVA, amorphous IND, and IND/PVPVA-based ASDs because these transitions are normally too weak or too broad for mDSC to detect. For IND/PVPVA-based ASDs, both techniques show a shift of sub-T_g transitions (or secondary relaxation peaks) toward the high-temperature region from -140 to -45 °C. Thus, this paper outlines the usage of different solid-state characterization techniques in understanding the different molecular dynamics present in the polymer, drug, and their interactions in ASDs with the integrated information obtained from individual techniques.

Analysis of molecular mobility in corn and quinoa flours through 1H NMR and its relationship with water distribution, glass transition and enthalpy relaxation

Solids-water interactions of corn and quinoa flours were evaluated through ¹H NMR, DSC, and water sorption isotherms. Glass transition temperature (T_g), observed by DSC, was better distinguished through FID signals, and correlated to water content through the Gordon and Taylor model. Enthalpy relaxations, identified by thermal analysis at 50-70 °C were studied through transverse relaxation times (T₂) measured after Hahn spin-echo sequence, which revealed a rearrangement of the biopolymers structures that cause immobilization of polymer chains and reduced mobility of water molecules with weak interactions with solids (lower T₂₂). The higher lipid content of quinoa flour was manifested after the CPMG sequence (T₂ ≈ 100 ms) and caused reduced hygroscopicity and T_g values compared with corn flour systems. ¹H NMR resulted efficient for assigning proton populations and understanding the changes in their distribution with temperature, analyzing glass transition and interpreting the implications of enthalpy relaxations processes in corn and quinoa flours.

Physicochemical properties and Strength analysis of vitreous encapsulated solids for the safe delivery of β-Carotene

β-Carotene (β-Car) is insoluble compounds in water and liable to degradation, which has health benefits for human beings. Although layer-by-layer (LBL) emulsions provide a better protection for β-Car towards environmental stresses, the handling and transportation of LBL emulsions still faces restrictions. In this paper, therefore, the LBL emulsions including β-Car were carefully prepared and encapsulated to obtain vitreous encapsulated solids (VES) using trehalose and maltodextrins (MD) as wall materials. Morphological results indicated that the LBL emulsions were formed a spheric shape, in where the polyelectrolyte shell was 30 nm. The MD exhibited the characteristics of not easy to absorb moisture, suitable carrier, and good stabilizer, which could improve the stability of VES systems at studied environmental stresses. Despite compositional effects from MD and environmental stresses, LBL emulsions changed the water sorption behavior of VES as oil dispersion in storage. Strength analysis indicated that LBL emulsions lubricated systems and increased the molecular mobility of wall materials. Structural collapse, rapid color changes, and β-Car loss were confirmed in VES systems at 0.56 a_w from 25 to 45 °C after 30 days of storage. Besides, a relationship between S and β-Car loss kinetics was established, where the β-Car degraded more rapidly in a sample with quicker molecular mobility of wall materials Therefore, the controlling of molecular mobility in wall materials can slow down the β -Car degradation and improve the quality and stability of lipophilic nutrients delivery systems with high total solids.

Dehumidified Air-Assisted Spray-Drying of Cloudy Beetroot Juice at Low Temperature

This paper discusses the physicochemical properties of powders obtained by spray drying of cloudy beetroot juice, using dehumidified air in variants with or without carriers. The inlet air temperature was 130 °C or 90 °C, and the addition of the carriers was at a ratio of juice to carrier solids of 3:2. In the obtained powders, the following physicochemical properties were determined: water content and water activity, apparent density, loose and tapped density, porosity, flowability, particle size and morphology, and the content and retention of betalains. It was possible to dry cloudy beetroot juice without the use of carriers at low temperatures (90 or 130 °C). The 100% beetroot powders were characterized by satisfactory physicochemical properties, often better than those with carriers (including lower hygroscopicity and higher color saturation and yield). A lower loss of betalains was found for the powders with the addition of carriers. The best process yields were obtained for the powder without carriers at 130 °C and 90 °C.

Rheology of carbohydrate blends close to the glass transition: Temperature and water content dependence of the viscosity in relation to fragility and strength

Several modifications of the Williams-Landel-Ferry (WLF) equation that incorporate the water-content dependence of the viscosity are introduced and applied to the fitting the zero-shear viscosity of a systematic series of maltopolymer-maltose blends for water contents w between 4% and 70% (M. Dupas-Langlet et al., Carbohydrate Polymers 213 (2019) 147-158). These models include a previously published model that addresses the water-content dependence of the viscosity via a Gordon-Taylor-type modification of the C₂ coefficient of the WLF equation. New models that are based on two simple assumptions are introduced: 1. The viscosity at the glass transition temperature T_g decreases exponentially with the water content and 2. The WLF coefficient C₂ depends linearly on the water content. The modified WLF models allow to extract the so-called isoviscosity lines, that connect points of varying temperature and water content that are characterized by the same viscosity. Based on data obtained between T = -15 °C and 70 °C using shear rheology (w = 30-70% w/w) and dynamic mechanical thermal analysis (w = 4-9% w/w), we conclude that the models provide a good fit of the experimental data, and that additional data, specifically very close to the glass transition line, is needed, to assess the hypotheses underlying the various modified WLF models. It is established that the viscosity at T_g is dependent on the composition and decreases with the content of maltose and water. The modified WLF models are used to determine Angell's fragility parameter m and Roos' strength parameter S. m and S are observed to increase, respectively decrease with increasing water and maltose content, signifying an increasing temperature dependence of the viscosity close to T_g with decreasing diluent content. The application of the isoviscosity concept to unit operations in the food and pharmaceutical industry is discussed. Specifically, we show how to analyze atomization, agglomeration, sintering and compaction using the isoviscosity concept.

Vibrational spectra analysis of amorphous lactose in structural transformation: Water/temperature plasticization, crystal formation, and molecular mobility

Lactose is a common component found in many foods and dairy products. In this study, the vibrational signatures in the crystalline structure of α-, β-, and α-lactose monohydrate were calculated based on quantum chemistry calculation (QCC), whilst the vibrational spectra in freeze-dried lactose equilibrated at various a_w and pre-humidified amorphous lactose (0.33 a_w) stored from 25 to 95 °C were determined by using Raman and FT-IR spectroscopies. The vibrational signatures of crystalline lactose were affected by the presence of water according to QCC results. Water plasticization, involving water insertion, exposure of H-bonding sites, and structure disruption, was accelerated by storage temperature based on Raman and FT-IR spectra analysis. Raman spectra indicated that the crystal formation of lactose was affected by a_w and storage temperature. Moreover, the spectral changes assigned in OH group provided useful information for determining the critical a_w or temperature when T_g-related molecular mobility occurred in lactose-containing products.

Encapsulation of black pepper seed oil using maltodextrin and pea protein

The goal of this research was to determine the physicochemical and emulsifying properties of pea protein, gum arabic, and maltodextrin and to investigate their potential for stabilizing black pepper seed oil emulsions and acting as carrier materials for spray dried microcapsules. The moisture content and water activity of pea protein and maltodextrin (∼5.5 g/100 g and ∼0.22) were found to be significantly lower than that of gum arabic (11.5 g/100 g and 0.46) whereas the glass transition temperatures of pea protein and maltodextrin (∼99.4 ℃) was significantly higher than that of gum arabic (72 ℃). Pea protein showed the highest viscosity (53.8 mPa s), the lowest surface tension (42.5 mN/m), and interfacial tension (10.5 mN/m) among the biopolymer materials studied. A mixture design was employed to investigate the effect of biopolymer formulation on droplet size and creaming stability of black pepper seed oil emulsions. Stable emulsions with relatively smaller droplet size were spray dried to produce microcapsules. Spray dried black pepper seed oil microcapsules produced with 1% pea protein and 39% maltodextrin had low surface oil (∼0.8%) and high encapsulation efficiency (95%). The results of this study suggest that pea protein in combination with maltodextrin can be used as carrier materials in encapsulation of black pepper seed oil.

Physicochemical properties, structural transformation, and relaxation time in strength analysis for honey powder models

Present study developed a strength analysis for relaxation time (τ) in characterizing physicochemical properties and structural transformation of freeze-dried honey/whey protein isolate (H/WPI) and honey/maltodextrin (H/MD) models based on water sorption, time-dependent crystallization, glass transition, and α-relaxation at various water activities (0.11a_w to 0.76a_w) and 25 °C. Water sorption data of two models explained WPI was a more effectiveness drying stabilizer than MD as H/WPI model owned higher monolayer water content. Crystallization was observed in prepared models with drying-aids content below 50% of mass ratios at water activity above 0.44a_w and 25 °C, whereas the extent of crystallization and structural collapse were inhibited by WPI and MD addition based on sorption isotherms. Glass transition temperature, α-relaxation temperature, and τ for two models were composition-dependent and altered by water, WPI, and MD at water activity below 0.44a_w. According to strength analysis of τ, the S for H/WPI and H/MD models was affected by drying-aids and could give a quantitative measure to estimate compositional effects on τ. Moreover, a S-involved state diagram was established to determine the critical parameters (water content and S) for controlling structural transformation of honey powder models during production and storage, i.e., collapse and stickiness.