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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 (0.11aw to 0.76aw) 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 0.44aw 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 0.44aw. 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.

Maltose crystallization affects the processibility and stability of sugar-rich foods. This study introduced a color-based clustering algorithm (CCA) to analyze crystallinity from the images of amorphous maltose/protein models. The XRD and DSC were also implemented in maltose crystallization characterization and validated the CCA analysis. The results indicated that CCA could effectively recognize maltose crystals (R = 0.9942), and amorphous maltose mainly crystallized to anhydrate α-maltose and β-maltose monohydrate according to its morphological aspects measured by CCA, XRD, and DSC. However, protein could change the mechanism of maltose crystal formation by disturbing the mutarotation and recrystallization processes of unstable β-maltose. Besides, maltose crystal formation and crystallinity were governed by molecular mobility as the CCA-derived Avrami indexes changed with the Strength parameter. Compared to XRD and DSC, the proposed CCA can provide a rapid and quantitative measure for maltose crystallinity and has great potential applications in the online detection of sugar crystallization.

BACKGROUND Maltose is an essential derivative of starch. To understand the processability and stability of maltose-containing foods, material characterization of the phase and state transition from its amorphous state is required. Although the crystallization of amorphous maltose is well understood, few studies have reported the relationship between the crystallization and the glass transition temperature (Tg )-related molecular mobility. In this study, water sorption, crystallization, Tg -related α-relaxation, and the corresponding time factor for amorphous maltose and maltose / whey protein isolate (WPI) mixtures are measured at various water activity (aw ) levels and 25 °C. RESULTS The water-additive principle for maltose / WPI mixtures was observed at aw ≤ 0.440 at the molecular level, whereas the crystallization of amorphous maltose occurred at high aw values (≥0.534). The crystal formation and crystallization kinetics of amorphous maltose were affected by water and WPI at aw ≥ 0.534 and 25 °C, as determined by X-ray diffraction. The relationship between Tg and the water content was fitted by the Gordon-Taylor model, and its constant showed a compositional dependence for the maltose / WPI mixtures. The α-relaxation temperature of the amorphous samples decreased due to water plasticization, but increased with an increase in the WPI quantity. The Strength (S) value for amorphous maltose, which was a quantitative estimate of the compositional effects on molecular mobility, was based on the William-Landel-Ferry (WLF) equation. CONCLUSION The S concept exhibits considerable potential for application in controlling the crystallization of amorphous maltose and improving the processability and stability of maltose-containing foods. © 2020 Society of Chemical Industry.

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 aw and pre-humidified amorphous lactose (0.33 aw) 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 aw and storage temperature. Moreover, the spectral changes assigned in OH group provided useful information for determining the critical aw or temperature when Tg-related molecular mobility occurred in lactose-containing products.

The glass transition and corresponding glass transition temperature (T g ) as found for food solids have received considerable attention, and their relationships with food solid behavior in various processes and food storage have been disputed. However, understanding glass transition-associated relaxations and their coupling with physicochemical properties of food materials is still a challenging and developing area of food material science. This review shows the improved understanding of the glass transition, structural relaxations, and corresponding relaxation times (τ) as well as their relevant applications on glassy food solids. Above information contributes to understanding of physical changes, molecular mobility, and solid flow characteristics of food components around their glass transition during processing and storage. We also emphasized the limitations of “fragile” concept in food solids and introduced a “strength, S” parameter to measure and describe solid flow characteristics of amorphous food mixtures by using a William-Landel-Ferry (WLF)-based approach for the analysis of α-relaxation derived τ above T g . The use of the S concept, therefore, can provide a quantitative measure to estimate compositional effects on τ and the control of solid properties, such as stickiness, caking, collapse, and crystallization.

Freeze-dried lactose and lactose/whey protein isolate (WPI) mixtures were used as amorphous food models at various aw, and the effects of temperature and water and WPI contents on physical state were analyzed. Thermal behavior and mechanical properties were studied and Williams-Landel-Ferry (WLF) model was fitted to structural relaxation times (τ). The WLF-analysis gave a strength parameter (S) that was used to describe structural strength of the food solids. Our results showed that lactose and WPI in mixtures exhibited fractional water sorption. Thermal properties and structural strength of the solids were affected by water and WPI while Tg measured for the lactose/WPI systems followed that of the lactose component and showed phase separation of lactose and proteins. A relationship between S and water content was established, whereas the crystallization of amorphous lactose was more rapid in systems with a smaller S. Therefore, S provided a simple and convenient measure of τ controlling structure formation in food processing as well as to control lactose crystallization. Industrial relevance Sugars are common ingredients and often used as a mixture with other components, e.g., proteins, in the food and pharmaceutical industries. Thus, understanding the physical state and thermal behavior of sugar containing food materials has a great importance in the development of processing and shelf life control procedures for such ingredients and relevant products. This study provides physicochemical information about thermal and mechanical properties of freeze-dried lactose/whey protein systems used as food models at various water activities. Data on water sorption, time-dependent lactose crystallization, calorimetric glass transition and crystallization temperatures, and structural relaxation times can be used to understand and predict structural changes during processing and storage of relevant foods. Moreover, the structural strength concept, described in this study, allows of the control of crystallization behavior as a physical state and time-dependent phenomenon, and therefore, stability of food and pharmaceutical materials

Water sorption-induced crystallization, α-relaxations and relaxation times of freeze-dried lactose/whey protein isolate (WPI) systems were studied using dynamic dewpoint isotherms (DDI) method and dielectric analysis (DEA), respectively. The fractional water sorption behavior of lactose/WPI mixtures shown at aw ≤ 0.44 and the critical aw for water sorption-related crystallization (aw(cr)) of lactose were strongly affected by protein content based on DDI data. DEA results showed that the α-relaxation temperatures of amorphous lactose at various relaxation times were affected by the presence of water and WPI. The α-relaxation-derived strength parameter (S) of amorphous lactose decreased with aw up to 0.44 aw but the presence of WPI increased S. The linear relationship for aw(cr) and S for lactose/WPI mixtures was also established with R2 > 0.98. Therefore, DDI offers another structural investigation of water sorption-related crystallization as governed by aw(cr), and S may be used to describe real time effects of structural relaxations in noncrystalline multicomponent solids.

Water sorption, crystallization, calorimetric glass transition temperature ( T g ), structural relaxations and relaxation times ( τ ) of freeze-dried sugars (lactose and trehalose) and whey protein isolates (WPI) in mixed systems were measured at various water activities ( a w ≤ 0.76, and 25 °C). The results indicated that sugar/WPI mixtures showed fractional water sorption behavior. The crystallization and crystalline forms of lactose were affected by trehalose and WPI based on XRD analysis. DMA analysis showed that the α-relaxation temperatures ( T α ) at loss modulus peak at frequency of 0.5 Hz for sugar/protein systems were affected by the presence of water and WPI. The τ and T α −T g relationships in sugar/WPI systems were successfully modeled by using the WLF model. The WLF-type structural strength ( S ), indicating decrease of τ from 10 2 to 10 −2 s, of trehalose decreased with a w up to 0.44 (from 15.8 to 12.1 °C) but WPI increased S . Moreover, a relationship for S and water content for glass forming sugar systems at a w ≥ 0.56 was established. The S concept gave a quantitative measure to estimate compositional effects on τ and could be used to estimate crystallization of food solids components.

Structural relaxations and relaxation times, τ, of lactose in freeze-dried amorphous lactose and lactose-WPI mixture systems were studied with glass transition data. The results indicated that Tg, enthalpy relaxation and α-relaxation temperature, Tα, of amorphous lactose was affected by the presence of lactose crystals and WPI at 0.33 aw (25 °C) due to water migration. The τ and Tα−Tg relationship of the materials was successfully modeled by the WLF equation with the material-special constants (−C1 and C2). A strength parameter, S, indicating decrease of τ from 102 to 10−2 s, could be used to measure the structural stability of lactose systems above their glass transition. The strength of amorphous lactose decreased with aw increasing up to 0.44 and enhanced by α lactose crystals and WPI in storage at 0.33 aw. Hence, the strength parameter provided a simple and convenient means to measure compositional effects on structure formation in food processing.

Water sorption, time-dependent crystallization and XRD patterns of lactose and lactose–WPI mixtures were studied with glass transition data. The results indicated that the sorbed water of lactose–WPI mixtures was fractional and water content of individual amorphous components in lactose–WPI mixtures at each aw from 25 °C to 45 °C could be calculated. Crystallization occurred in pure lactose whereas partial crystallization was typical of lactose–WPI mixtures (protein content ≤ 50%) at intermediate and high aw (> 0.44 aw) from 25 °C to 45 °C. The extents of crystallization were significantly delayed by WPI. The Tg values of lactose–WPI systems showed the composition-dependent property in systems and might indicate the occurrence of phase separation phenomena during 240 h storage. XRD showed no anhydrous β-lactose and mixed α-/β-lactose with molar ratios of 4:1 crystals in crystallized lactose–WPI systems (70:30 and 50:50 solids ratios). Reduced crystallization in the presence of WPI was more pronounced possibly because of reduced nucleation and diffusion during crystal-growth. The present study showed that WPI could present an important role in preventing sugar crystallization.

Advanced treatment of a complex pharmaceutical wastewater by Desal-5 DK nanofiltration (NF) membrane was carried out. The membrane fouling and chemical cleaning in this application were investigated. It was found that at the initial stage of NF process, the deposition of sulfate and carbonate of calcium was the main cause of membrane fouling. At the later fouling stage, besides calcium salts, complex organic foulants containing carboxyl acid, amide, and alkyl halide functional groups also deposited onto membrane surface and gradually formed a densely packed fouling layer. Accordingly, in cleaning process, the efficiency of a cleaning agent depended on its ability to break down the integrity of the compact fouling layer by reacting with the foulants. The results showed that the cleaning efficiencies of the agents increased in the sequence of NaOH (pH 11)