Function Of Water Activity Research Articles

Changes in the Moisture Permeability of Grain at the Critical Water Activity from Dynamic Dewpoint Isotherms

<abstract> <b><sc>Abstract.</sc></b> Moisture is an important external factor that impacts the stability and viability of grains. Movement of moisture through grain has been investigated, but not specifically as a function of water activity, and previous work did not use recently developed moisture sorption instrumentation. Moisture sorption isotherms can provide the information needed to determine moisture penetration rates into grain over different water activity ranges and can be generated automatically using recently developed instrumentation. The purpose of this study was to investigate moisture movement into grain using moisture sorption isotherms. Two methods for generating isotherms were used: static and dynamic. The information provided by each method was unique and, when combined, provided information about changes in moisture penetration into grain that occur as the water activity changes. Static isotherm data were used to calculate permeance values for the grain at different water activities, while dynamic isotherm data were used to determine a critical water activity (RHc) at which the permeance of the grain underwent significant changes, causing an inflection in the dynamic isotherm. Comparing the permeance values generated from static isotherm data and the RHc from dynamic isotherm data confirmed that permeance changes significantly when the water activity is above the RHc. Generating dynamic dewpoint isotherm (DDI) curves and finding the RHc for coated materials using automatic isotherm generators has potential to provide a simple approach to finding the water activity level at which the moisture barrier resistance of the coating is reduced.

Acid-Doped ABPBI Membranes Prepared by Low-Temperature Casting: Proton Conductivity and Water Uptake Properties Compared with Other Polybenzimidazole-Based Membranes

Phosphoric acid doped ABPBI (poly [2,5-benzimidazole]) membranes were prepared with a new low temperature casting procedure (ABPBI-ET), and their water uptake and proton conductivity were measured. The results were compared with those of ABPBI casted at high temperature (ABPBI-MSA), poly [2-2′-(m-phenylene)-5-5′ bibenzimidazole] (PBI), and commercial cross-linked Fumatech ABPBI (ABPBI-C) membranes. The water uptake of ultra thin ABPBI-ET membranes in the range 7–30 nm supported over gold substrate, was also measured and compared with PBI ones. The in-plane proton conductivities of all the membranes were measured in the temperature range from 20° to 120°C at different water activities. The ABPBI-ET doped in 10.6 M H3PO4 and ABPBI-C doped in 14.9 M H3PO4 showed the highest conductivities, even higher than those reported for Nafion membranes. ABPBI-ET membranes showed a maximum as a function of water activity at aw ≈ 0.55, a behavior that can be rationalized in terms of the dissociation constant of the ABPBI-H3PO4 complexes calculated using the Scatchard method, and the H3PO4 concentration in the water inside the membrane.

Thermodynamic analysis of sol-gel transition of gelatin in terms of water activity in various solutions.

Sol-gel transition of gelatin was analyzed as a multisite stoichiometric reaction of a gelatin molecule with water and solute molecules. The equilibrium sol-gel transition temperature, Tt , was estimated from the average of gelation and melting temperature measured by differential scanning calorimetry. From Tt and the melting enthalpy, ΔHsol , the equilibrium sol-to-gel ratio was estimated by the van't Hoff equation. The reciprocal form of the Wyman-Tanford equation, which describes the sol-to-gel ratio as a function of water activity, was successfully applied to obtain a good linear relationship. From this analysis, the role of water activity on the sol-gel transition of gelatin was clearly explained and the contributions of hydration and solute binding to gelatin molecules were separately discussed in sol-gel transition. The general solution for the free energy for gel-stabilization in various solutions was obtained as a simple function of solute concentration.

Modeling the Mechanical Texture of Foxtail Millet Extrudates during Hydrosorption with a Modified Peleg-Fermi Model

The objective of this study was to monitor and model the texture changes of foxtail millet extrudates with different structural properties as a function of water activity (<em>a</em>_w). Four extrudates, after equilibrated at <em>a</em>_w of 0.113-0.97, were compressed using a TA.XT2 Texture Analyzer. Two force-related texture parameters, Peak Force (PF) and Total Work (TW) and two jaggedness-related, Number of Spatial Ruptures (NSR) and Specific Ling Length (SLL), were extracted from their force-displacement curves. Water sorption led to loss of jaggedness of their force-displacement curves. All the four texture parameters decreased when a <em>a</em>_w increased to a certain value. Before the decrease occurring, <em>TW</em> and <em>PF</em> increased for all the extrudates with a <em>a</em>_<em>w</em> increase, while <em>SLL</em> increase was observed only for two extrudates and no <em>NSR</em> increase was observed for all extrudates. The critical water activity (<em>a</em>_wc) where texture parameters decreased rapidly ranged between 0.42 and 0.83 depending mainly on the kinds of the extrudates and to some extent on the texture parameters studied. The extrudates with coarse structure exhibited lower force-related values, while the extrudates with fine structure exhibited lower jaggedness-related values. Crispness index, a combination of force- and jaggedness-related texture criteria, decreased almost linearly as a <em>a</em>_w increase up to 0.61~0.66 for all the extrudtes. The Peleg-Fermi equation can satisfactorily model the changes in jaggedness-related texture parameters as a function of <em>a</em>_w. A modified form of the Peleg-Fermi equation, proposed in this study, was needed to model the changes of force-related parameters better.

Water permeability and competitive permeation with CO2 and CH4 in perfluorinated polymeric membranes

The permeability of water through polymeric membranes is of particular interest in gas separation, because of the high water vapor content found in many industrial applications. Polymeric membranes that are resistant to competitive sorption and plasticization by water are especially attractive, since they can reduce the need for gas pretreatment in many membrane applications. The perfluorinated polymers Teflon AF1600 and Hyflon AD60 are studied here for this purpose because of their strong hydrophobicity and unusual solvent properties. It was observed that water permeability through both perfluorinated polymers was of the same magnitude as CO2. Indeed, under the conditions studied, Teflon AF1600 was selective for CO2 over water. Such reverse selectivity for the CO2 – H2O gas pair has not been reported before for glassy polymeric membranes and reflects the very low solubility of water in the polymer. The water permeability through Hyflon AD60 was greater than that for CO2 with a minimum at 55°C. The change in both CO2 and CH4 permeability through Teflon AF1600 and Hyflon AD60 was investigated as a function of water activity in the feed gas to investigate the effects of competitive permeation. It was observed that CO2 and CH4 permeability in both membranes reduced with water activity. For both Teflon AF1600 and Hyflon AD60, the decrease in permeability of both gases with water activity was interpreted as water clusters blocking the diffusion of both CO2 and CH4 through the membrane.

Experimental determination of penetration depths of various spice commodities (black pepper seeds, paprika powder and oregano leaves) under infrared radiation

During infrared processing, transmitted energy is attenuated exponentially with penetration distance, and its intensity is gradually lost while passing through absorbing or scattering media. Penetration depth is a complex function of chemical composition of a food product, its physico-chemical state and physical properties and wavelength spectrum of energy source. Knowing penetration depth leads to better designing commercial sterilization processes for food products like spices. Therefore, the objective of this study was to determine penetration depth of various spices (paprika powder, black pepper and oregano) as a function of water activity under infrared processing conditions. For this purpose, spice samples were prepared at various water activity (aw) levels, and heat flux measurements were carried out to determine the penetration depth. Penetration depth was determined to increase with increasing aw for black pepper seeds and paprika powder while there was no significant change for oregano leaves as a function of aw. Knowing penetration depth is important to design an effective infra-red processing system and an important issue for surface pasteurization processes since infrared radiation effects on microbial inactivation decrease with sample thickness.

Water sorption isotherms and air drying kinetics modelling of the brown seaweed Bifurcaria bifurcata

Air drying kinetics at 35, 50, 60 and 75 °C and water adsorption and desorption isotherms at 5, 25, 40 and 55 °C of the brown seaweed Bifurcaria bifurcata were obtained. Water sorption isotherms were modelled by means of the two-parameter Halsey model. A model to estimate equilibrium moisture content of adsorption and desorption processes as function of water activity and temperature simultaneously was obtained by means of linear correlations of Halsey model parameters with temperature. Water sorption isotherms were analysed by a thermodynamic approach to obtain properties such as net isosteric heat of sorption, net equilibrium heat, differential and integral entropy. Monolayer moisture content evaluated by BET model corresponded to the moisture content at which local minimum integral entropy value was observed for sorption processes. Air drying kinetics at different temperatures were modelled using the Page model. The two parameters of the Page model were linearly correlated with temperature. The goodness of the fits was evaluated by evaluation of the coefficients of determination and root mean square errors.

Kinetic behaviour of Staphylococcus aureus on cheese as a function of water activity and temperature.

This study developed mathematical models in order to evaluate the effect of Aw (Water activity) and growth temperature on Staphylococcus aureus kinetic behaviour. The Aw levels (0·970, 0·975, 0·983, and 0·991) of cheese were adjusted by NaCl; then, Staph. aureus was inoculated on the cheese, followed by storage at 7-30 °C for 72-720 h. Total bacterial and Staph. aureus cell counts were enumerated on tryptic soy agar and mannitol salt agar, respectively. The Baranyi model was fitted to the Staph. aureus growth data in order to calculate the maximum specific growth rate (μmax; log CFU/g/h), lag phase duration (λ; h), lower asymptote (N0; log CFU/g) and upper asymptote (Nmax; log CFU/g). The effects of storage temperature and Aw on the kinetic parameters (μmax and λ) were then further analysed with the Ratkowsky-type model and a polynomial equation, respectively. The root mean square error (RMSE) and relative error (RE) were calculated in order to estimate the model performance. No significant effect of Aw on Staph. aureus growth was observed at 7 °C; thus, the Baranyi model was fitted to the growth data from 15, 25 and 30 °C. The μmax values (0·011-0·303 log CFU/g/h) increased (P<0·05) as the storage temperature and Aw increased. In addition, λ values (2·42-63·48 h) decreased (P<0·05) as storage temperature and Aw increased; yet, the effect of Aw on λ was observed only at 15 °C. The theoretical minimum storage temperature and Aw were 10·15 °C and 0·882, respectively. RMSE (0·010-1·544) and RE values (-0·131 to 0·187) from validation indicated that model performance was appropriate. Hence, these results suggest that the developed models in this study should be useful in describing the effect of temperature and Aw on the growth kinetic behaviour of Staph. aureus in cheese along with the exposure assessment of Staph. aureus in cheese as well.

Moisture Sorption Isotherms, Isosteric Heat of Sorption and Glass Transition Temperature of Murtilla (Ugni molinaeT.) Berry

AbstractAdsorption and desorption isotherms of fresh and dried murtilla (Ugni molinaeTurcz) berries were determined at 20, 40 and 60°C using a gravimetric technique. The experimental data obtained were fitted to eight models, namely GAB, BET, Henderson, Caurie, Smith, Oswin, Halsey and Iglesias–Chirife. A non-linear least square regression analysis was used to evaluate the models. The GAB model best fitted the experimental data. Isosteric heat of sorption was determined from the equilibrium sorption data using the Clausius–Clapeyron equation and was found to decrease exponentially with increasing moisture content. The enthalpy–entropy compensation theory applied to the sorption isotherms indicated an enthalpy controlled sorption process. Glass transition temperature of murtilla was determined by differential scanning calorimetry and modelled as a function of moisture content by the Gordon–Taylor equation and as function of water activity by Roos and Khalloufi models, which proved to be excellent tools for predicting glass transition of murtilla.

Modeling growth of three bakery product spoilage molds as a function of water activity, temperature and pH

The objective of this study was to quantify the effect of water activity, pH and storage temperature on the growth of Eurotium repens, Aspergillus niger and Penicillium corylophilum, isolated from spoiled bakery products. Moreover, the behaviors of these three mold species were compared to assess whether a general modeling framework may be set and re-used in future research on bakery spoilage molds. The mold growth was modeled by building two distinct Gamma-type secondary models: one on the lag time for growth and another one on the radial growth rate. A set of 428 experimental growth curves was generated. The effect of temperature (15–35°C), water activity (0.80–0.98) and pH (3–7) was assessed. Results showed that it was not possible to apply the same set of secondary model equations to the three mold species given that the growth rate varied significantly with the factors pH and water activity. In contrast, the temperature effect on both growth rate and lag time of the three mold species was described by the same equation. The equation structure and model parameter values of the Gamma models were also compared per mold species to assess whether a relationship between lag time and growth rate existed. There was no correlation between the two growth responses for E. repens, but a slight one for A. niger and P. corylophilum. These findings will help in determining bakery product shelf-life and guiding future work in the predictive mycology field.

Effect of morphology of nanoscale hydrated channels on proton conductivity in block copolymer electrolyte membranes.

Hydrated membranes with cocontinuous hydrophilic and hydrophobic phases are needed to transport protons in hydrogen fuel cells. Herein we study the water uptake and proton conductivity of a model fuel cell membrane comprising a triblock copolymer, polystyrenesulfonate-block-polyethylene-block-polystyrenesulfonate (S-SES), as a function of water activity in both humid air and liquid water. We demonstrate that the water uptake and proton conductivity of S-SES membranes equilibrated in liquid water are fundamentally different from values obtained when they were equilibrated in humid air. The morphological underpinnings of our observations were determined by synchrotron small-angle X-ray scattering and cryogenic scanning transmission electron microscopy. A discontinuous increase in conductivity when nearly saturated humid air is replaced with liquid water coincides with the emergence of heterogeneity in the hydrated channels: a water-rich layer is sandwiched between two polymer-rich brushes. While the possibility of obtaining heterogeneous hydrated channels in polymer electrolyte membranes has been discussed extensively, to our knowledge, this is the first time that direct evidence for the formation of water-rich subdomains is presented.

Water permeation and sorption properties of Nafion 115 at elevated temperatures

There is the potential to use membrane technology to recover high purity water from power station flue gas streams. In this work, the permeation of water, CO2 and N2 through Nafion 115 was investigated as a function of water activity at 70–150°C. It was found that all permeances increased with increasing water activity but reduced with increasing temperature. This data was supplemented by sorption analysis at lower temperature which conversely showed decreasing solubility as temperature increased. The changes in solubility and permeance with water activity were attributed to membrane swelling as water activity increased. A comparison with a thinner perfluoro-sulphonic acid polymer, from an alternate supplier, suggested that permeance did not scale linearly with membrane thickness, possibly reflecting inhomogeneity in membrane swelling. The results were used to simulate the capture of water from a brown coal power station flue gas and it was found that a permeate pH of 3.3–4.0 is achievable with Nafion 115 at 150°C. This suggests that for use as boiler feed this stream will need to undergo further treatment.

Thermodynamic analysis of osmolyte effect on thermal stability of ribonuclease A in terms of water activity

Thermal unfolding of ribonuclease A (RNase) was analyzed in various osmolyte solutions of glycine, proline, sarcosine, N,N-dimethylglycine, betaine, myo-inositol, taurine, and trimethylamine-N-oxide (TMAO). All the osmolytes tested stabilized the protein. The thermal unfolding curve was described well by the van't Hoff equation and the melting temperature and the enthalpy of protein unfolding were obtained. The Wyman–Tanford equation, which describes the unfolded-to-folded protein ratio as a function of water activity, was successfully applied to obtain a linear plot. In consideration of this experimentally obtained linearity, the Wyman–Tanford plot could be integrated to calculate the stabilization free energy of the protein (∆∆G) in the solution. The ∆∆G was proved to be described by the property of the microstructure around the protein surface, which is composed of the protein hydration, the cosolute-binding, and the preferential exclusion, and the property of the bulk solution; water activity. The m-values of osmolytes for protein unfolding were obtained from ∆∆G calculated. Among the osmolytes tested, myo-inositol showed the highest m-value.

Heat Inactivation of Polyphenol Oxidase and Peroxidase as a Function of Water Activity: A Case Study of Mango Drying

An innovative method was developed to study the specific uncoupled effect of temperature and water activity (Aw) during mango drying. Thermal treatment of reconstituted lyophilized mango powder at targeted Aw enabled evaluation of the inactivation of polyphenol oxidase and peroxidase activity in a range 0.98–0.6 Aw and a time-temperature range of 1–4 h and 50–60°C. We established that thermal treatment of the enzymatic extract was not the same as the inactivation phenomena that occurred in the mango matrix, mainly due to differences in the pH of the buffer extract (6.4) and reconstituted food matrix (3.8). Even if the inactivation of these two enzymes was directly correlated with the temperature of the treatment, this behavior was also strongly linked to the Aw. A two-step change in the fruit was observed at high Aw (i.e., at 0.98 in fresh fruit), polyphenol oxidase (PPO) was shown to be more thermostable than peroxidase (POD), whereas when evaporation reduced the Aw to around 0.6, the opposite behavior was observed. As a consequence, enzymatic inactivation during drying should be considered as the result of the coupled effects of time-temperature and water activity.

Swelling of Ultrathin Molecular Layer‐by‐Layer Polyamide Water Desalination Membranes

ABSTRACTThe water vapor swelling behavior of ultrathin crosslinked aromatic polyamide (PA) films, synthesized via molecular layer‐by‐layer deposition, is characterized via specular X‐ray reflectivity. The results show that these films expand only along the thickness direction and their maximum swelling ratio can be controlled by the specific diamine monomer chemistry. By measuring the swelling ratio as a function of water activity, the Flory interaction parameter and monomers between crosslinks of these PAs are characterized using the Flory‐Rehner and the Painter‐Shenoy thermodynamic swelling models. Comparing the monomers between crosslink calculated from the swelling theories with values obtain from chemical analysis indicate that the PS model gives a more accurate description of the PA networks. This suggests that these low functionality but highly crosslinked networks swell via a combination of chain expansion and topological rearrangement. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1647–1655

Immersion freezing of water and aqueous ammonium sulfate droplets initiated by humic-like substances as a function of water activity

Abstract. Immersion freezing of water and aqueous (NH4)2SO4 droplets containing leonardite (LEO) and Pahokee peat (PP) serving as surrogates for humic-like substances (HULIS) has been investigated. Organic aerosol containing HULIS are ubiquitous in the atmosphere; however, their potential for ice cloud formation is uncertain. Immersion freezing has been studied for temperatures as low as 215 K and solution water activity, aw, from 0.85 to 1.0. The freezing temperatures of water and aqueous solution droplets containing LEO and PP are 5–15 K warmer than homogeneous ice nucleation temperatures. Heterogeneous freezing temperatures can be represented by a horizontal shift of the ice melting curve as a function of solution aw by Δaw = 0.2703 and 0.2466, respectively. Corresponding hetrogeneous ice nucleation rate coefficients, Jhet, are (9.6 ± 2.5)×104 and (5.4 ± 1.4)×104 cm−2 s−1 for LEO and PP containing droplets, respectively, and remain constant along freezing curves characterized by Δaw. Consequently predictions of freezing temperatures and kinetics can be made without knowledge of the solute type when relative humidity and ice nuclei (IN) surface areas are known. The acquired ice nucleation data are applied to evaluate different approaches to fit and reproduce experimentally derived frozen fractions. In addition, we apply a basic formulation of classical nucleation theory (α(T)-model) to calculate contact angles and frozen fractions. Contact angles calculated for each ice nucleus as a function of temperature, α(T)-model, reproduce exactly experimentally derived frozen fractions without involving free-fit parameters. However, assigning the IN a single contact angle for the entire population (single-α model) is not suited to represent the frozen fractions. Application of α-PDF, active sites, and deterministic model approaches to measured frozen fractions yield similar good representations. Furthermore, when using a single parameterization of α-PDF or active sites distribution to fit all individual aw immersion freezing data simultaneously, frozen fraction curves are not reproduced. This implies that these fitting formulations cannot be applied to immersion freezing of aqueous solutions, and suggests that derived fit parameters do not represent independent particle properties. Thus, from fitting frozen fractions only, the underlying ice nucleation mechanism and nature of the ice nucleating sites cannot be inferred. In contrast to using fitted functions obtained to represent experimental conditions only, we suggest to use experimentally derived Jhet as a function of temperature and aw that can be applied to conditions outside of those probed in laboratory. This is because Jhet(T) is independent of time and IN surface areas in contrast to the fit parameters obtained by representation of experimentally derived frozen fractions.

Modeling Growth Rate and Assessing Aflatoxins Production by Aspergillus flavus as a Function of Water Activity and Temperature on Polished and Brown Rice

The aim of this study was to model the radial growth rate and to assess aflatoxin production by Aspergillus flavus as a function of water activity (a(w) 0.82 to 0.92) and temperature (12 to 42 °C) on polished and brown rice. The growth of the fungi, expressed as colony diameter (mm) was measured daily, and the aflatoxins were analyzed using HPLC with a fluorescence detector. The growth rates were estimated using the primary model of Baranyi, which describes the change in colony radius as a function of time. Total of 2 secondary models were used to describe the combined effects of a(w) and temperature on the growth rates. The models were validated using independent experimental data. Linear Arrhenius-Davey model proved to be the best predictor of A. flavus growth rates on polished and brown rice followed by polynomial model. The estimated optimal growth temperature was around 30 °C. A. flavus growth and aflatoxins were not detected at 0.82 a(w) on polished rice while growth and aflatoxins were detected at this a(w) between 25 and 35 °C on brown rice. The highest amounts of toxins were formed at the highest a(w) values (0.90 to 0.92) at a temperature of 20 °C after 21 d of incubation on both types of rice. Nevertheless, the consistencies of toxin production within a wider range of a(w) values occurred between 25 to 30 °C. Brown rice seems to support A. flavus growth and aflatoxin production more than the polished rice. The developed models can be used to estimate to what extent the change in grain ecosystem conditions affect the storage stability and safety of grains without the need for running long-standing storage study. By monitoring the intergranular relative humidity and temperature at different locations in the storage facility and inputting these data into the models, it is directly possible to assess either the conditions are conductive for the growth of A. flavus or aflatoxin production.

Water vapor sorption and free volume in the aromatic polyamide layer of reverse osmosis membranes

Thin film composite membranes consist of an ultra thin active layer of polymer that governs the membrane's salt rejection and water permeation properties. However, the fragility of the ultrathin layer makes it challenging to select a technique capable of differentiating between the properties of this layer from the supporting layer. In this study, we isolated enough active layer material to characterise the water vapour sorption and free volume cavity size as functions of water activity. The sorption data were modelled using the Guggenheim–Anderson–De Boer (G.A.B.) isotherm and from this the number of sorption sites for water was calculated to be 189×1019 per gram for the active layer from a commercial Dow Filmtec SW30 membrane and 188×1019 per gram for an aromatic polyamide material prepared in house. The activation energy for diffusion of water through the active layer of SW30 was also evaluated and found to be 6.95kcal/mol, lower than the heat of liquefaction of water. This suggests that water does not permeate as individual molecules in the vapour state, but rather as clusters of water molecules. The free volume cavity size in the active layer as a function of moisture uptake was also investigated and the results were explained using a pore filling and pore swelling mechanism. This study sheds light on the mechanisms of water entry into the active layer, water transport through the active layer, and the corresponding response of the polymer chains, thereby giving critical insight for the development of more novel systems.

The crystalline state of methylene blue: a zoo of hydrates

A re-investigation of the crystalline state of methylene blue has led to the identification of five different hydrates with clearly distinct structures. These include the already known pentahydrate, a hydrate with 2.2-2.3 equivalents of water, two dihydrates, and a monohydrate. Contrary to older reports, no trihydrate was found. The preparation and characterization of the hydrates as well as the transformations between them are reported. The applied analytical methods include X-ray powder diffraction (XRPD), infrared spectroscopy (ATR-IR), thermogravimetry (TGA), differential scanning calorimetry (DSC), dynamic water vapor sorption (DVS) and solution calorimetry (SolCal). A phase diagram of temperature vs. composition has been established, and the stability domains of the different hydrates as a function of water activity and temperature have been determined based on data from DSC, SolCal and suspension equilibration experiments. Four out of the five hydrates are thermodynamically stable within a certain range of temperature and humidity.

Effect of different fractions of zein on the mechanical and phase properties of zein films at nano-scale

The phase behavior of zein films has been investigated at nano-scale using atomic force microscopy (AFM) and compared to the phase behavior of the bulk using a thermal characterization technique. The local surface properties of the films were evaluated as a function of water activity using AFM. The glass transition temperature (Tg) of zein films decreased with increasing water activity. Adhesion forces measured by the AFM force curves increased with increasing water activity. Topography of zein and zein fractions were evaluated both qualitatively and quantitatively by the use of AFM and dedicated software to calculate the surface roughness. It has been found that processing technologies (solvent casting, drop deposition and spin casting) has influence on the surface structures of films. The films which were formed by the alpha zein rich fraction were found to have highest roughness values. Sectional surface profiles revealed that α-zein films have mean roughness (Ra) of 1.808 nm and root mean square roughness (RMS) of 2.239 nm while β-zein films have mean roughness (Ra) of 1.745 nm and root mean square roughness (RMS) of 3.623 nm. The discussions conducted on the differences/similarities in the observations were based on the hydrophobic/hydrophilic properties and interactions of these zein fractions.