Gelatinisation of starch: a combined SAXS/WAXS/DSC and SANS study

Prevent lumping during hot-water rehydration of lotus rhizome powder by restricted swelling treatment

Lotus rhizome powder (LRP) tends to lump during hot-water rehydration, adversely affecting its edible quality. By utilizing a restricted swelling treatment (ST), where LRP was swollen at a temperature slightly below its onset gelatinization temperature (To), the lumping rate could be substantially reduced from 30.95% to 6.39%. This treatment induced an ordered-disordered structural transition of LRP without compromising its granule morphology and water dispersibility. This transition led to significant increases in thermal transition temperatures and a notable delay in peak pasting time by 86.6 s. These changes effectively delayed the formation of a gelatinous skin surrounding the dry granules, allowing them sufficient time to absorb water and paste completely, thereby preventing lumping. The prevention of lumping was beneficial for obtaining desired viscoelasticity of LRP paste. Conversely, ST treatments conducted at temperatures markedly deviating from To resulted in significantly higher lumping rates, underscoring the importance of carefully controlling the ST temperature.

Hot-water soluble fraction of starch as particle-stabilizers of oil-in-water emulsions: Effect of dry heat modification

Dry heat treatment (DHT) ranging from 130 to 190 °C was employed to modify corn starch. The hot-water soluble fraction (HWS) of the DHT-modified starch was isolated, and its capacity and mechanism for stabilizing O/W emulsions were investigated. Corn starch underwent a significant structural transformation by DHT at 190 °C, characterized by a 7.3 % reduction in relative crystallinity, a tenfold decrease in weight-average molecular weight from 95.21 to 8.11 × 106 g/mol, and a degradation of over one-third of the extra-long chains of amylopectin (DP > 36) into short chains (DP 6-12). These structural modifications resulted in a substantial formation of soluble amylopectin, leading to a sharp increase in the HWS content of corn starch from 3.16 % to 85.06 %. This augmented HWS content surpassed the critical macromolecule concentration, prompting the formation of HWS nanoaggregates. These nanoaggregates, with an average particle size of 33 nm, functioned as particle stabilizers, ensuring the stability of the O/W emulsion through the Pickering mechanism. The O/W emulsion stabilized by HWS nanoaggregates exhibited noteworthy centrifugal and storage stability, with rheological properties remaining nearly unchanged over a storage period of 180 days. Given its straightforward preparation process, the HWS of DHT-modified starch could be a promising natural emulsifier.

Probing structural features in potato starch granules at moderate hydration through the modelling of 1H->13C polarization transfer kinetics

The structural arrangement of starch polymers in presence of water is known to impact the functional properties of starchy products. In this study, the hydration of potato starch granules was investigated at the molecular level through various 1H->13C polarization transfer solid-state Nuclear Magnetic Resonance (ss-NMR) experiments. The impact of increasing the water content from 12.3 % to 45.9 % was assessed using 13C Cross Polarization Magic Angle Spinning (CPMAS), Variable Contact Time (VCT-CPMAS), Variable Spin Lock (VSL-CPMAS), and T One Rho QUEnching (TORQUE) NMR sequences. Of these, VCT-CPMAS proved to be the most promising. When applied with an optimal number of contact times, it enabled the application of several mathematical models that provided detailed insights into the structuring of protons in the hydrated potato starch granules. At low hydration (12.3 %), the models enabled various structural domains to be distinguished, which we suggest are associated with helical and amorphous structures. At moderate hydration (45.9 %), we tested two fitting models. Two pools of protons were revealed, corresponding to loosely ordered structures on the scale of tens of nanometers. These findings suggest varying water distribution during starch hydration and are likely to indicate variable hydration levels in the multilamellar amorphous structures of starch granules.

A global set of barley varieties shows a high diversity in starch structural properties and related gelatinisation characteristics

The gelatinisation temperature and bimodal granule size distribution of barley starch are important characteristics regarding resource efficiency and product quality in the brewing industry. In this work, the diversity in starch amylose content and granule proportions in a set of modern barley varieties (N = 23) was investigated and correlated with their starch gelatinisation behaviour. Milled barley samples had peak starch gelatinisation temperatures ranging from 60.1 to 66.5 °C. Upon separating the barley starch from the non-starch compounds, sample-dependent decreases in starch gelatinisation temperatures were observed, indicating the importance of differences in barley composition. The peak gelatinisation temperatures of milled barley and isolated barley starches were strongly correlated (r = 0.96), indicating that the behaviour of the starch population is strongly reflected in the measurements performed on milled barley. Therefore, we investigated whether amylose content or starch granule size distribution could predict the gelatinisation behaviour of the starches. Broad ranges in the small starch granule volumes (13.9-32.0 v/v%) and amylose contents (18.2-30.7 w/w%) of the barley starches were observed. For the barley samples collected in the north of the USA (N = 8), the small starch granule volumes correlated positively with the peak gelatinisation temperatures of barley starches (r = 0.90, p < 0.01). The considerable variation in starch properties described in this work highlights that, besides starch content, starch gelatinisation temperature or granule size distribution might provide brewers with useful information to optimise resource efficiency.

A preparation of debranched waxy maize starch derivatives: Effect of drying temperatures on crystallization and digestibility

The impact of recrystallization conditions and drying temperatures on the crystallization and digestibility of native waxy maize (Zea mays L.) starch (NWMS) was explored. This study involved subjecting NWMS to concurrent debranching and crystallization at 50 °C for up to 7 days. Samples were collected by oven-drying at 40, 60, and 80 °C for 24 h. This simultaneous debranching and crystallization process increased the resistant starch (RS) content by approximately 48 % compared to the native starch. The drying temperatures significantly influenced the RS content, with samples dried at 60 °C exhibiting the lowest digestibility. X-ray diffraction (XRD) analysis revealed that most crystals demonstrated a characteristic A-type arrangement. Debranching and crystallization processes enhanced the crystallinity of the samples. The specific crystal arrangement (A- or B-type) depended on the crystallization conditions. A 15 min heating of NWMS in a boiling water bath increased the digestible fraction to over 90 %, while the samples subjected to debranching and crystallization showed an increase to only about 45 %. A linear correlation between starch fractions and enthalpy was also observed.

Effect of different screw speeds on the structure and properties of starch straws

To illustrate the action mechanism of screw speed on the performance of starch-based straws during the extrusion process, starch-based straws at different screw speeds were prepared using a twin-screw extruder and the structures and characteristics were compared. The results indicated that as screw speeds improved from 3 Hz to 13 Hz, the A chain of amylopectin increased from 25.47 % to 28.87 %, and the B3 chain decreased from 6.34 % to 3.47 %. The absorption peak of hydroxyl group shifted from 3296 cm-1 to 3280 cm-1. The relative crystallinity reduced from 13.49 % to 9.89 % and the gelatinization enthalpy decreased from 3.5 J/g to 0.2 J/g. The performance of starch straws did not increase linearly with increasing screw speeds. The starch straw produced at screw speed of 7 Hz had the largest amylose content, the highest gelatinization temperature, the minimum bending strength, and the lowest water absorption rate in hot water (80 °C). Screw speed had a remarkable impact on the mechanical strength, toughness and hydrophobicity of starch-based straws. This study revealed the mechanism of screw speed on the mechanical strength and water resistance of starch straws in the thermoplastic extrusion process and created the theoretical basis for the industrial production of starch-based straws.

Influence of instant rice characteristics and processing conditions on starch digestibility-A review

Instant rice is increasingly popular around the world due to its convenience, but it commonly has a high glycemic index, and a frequent consumption might contribute to the occurrence of many chronic diseases. In this review, the main factors determining starch digestibility of instant rice were comprehensively evaluated, aiming to help the rice industry develop instant rice with slow starch digestibility. Starch digestibility in instant rice can be reduced by manipulating its intrinsic and extrinsic nutrients. Processing conditions, including pre-gelatinization, storage, and reheating are also important for the starch digestibility of instant rice. Individual differences in terms of glycemic response to the same carbohydrate-based diet should be considered when knowledge is transformed from in vitro method to human conditions. This review contains important information that has the potential to reduce the starch digestibility of instant rice and improve public health.

Optical Anisotropy and Dimple Formation on Films Formed after Drying of Gelatinized Starch Solution Droplets

We study the microstructures in the drying droplets of gelatinized starch solutions on a flat substrate. Cryogenic scanning electron microscopy studies on the vertical cross-section of these drying droplets for the first time reveal a relatively thinner solid elastic crust of uniform thickness at the free surface, an intermediate mesh region below the crust, and an inner core of a cellular network structure made of starch nanoparticles. We find that the deposited circular films formed after drying are birefringent and azimuthally symmetric with a dimple at their center. We propose that the dimple formation in our sample occurs due to the evaporation-induced stress on the gel network structure in the drying droplet. The polarizing optical microscopic studies show that these films are optically uniaxial at their center and increasingly biaxial away from the center.

Novel Approach for Quantitative Characterization of Short-Range Molecular Order in Gelatinized Starch by X-ray Diffraction

A novel quantitative method was developed to characterize short-range molecular order in gelatinized wheat and potato starches using X-ray diffraction (XRD). Gelatinized starches with different amounts of short-range molecular order and amorphous starches with no short-range molecular order were prepared and characterized by the intensity and area of Raman spectral bands. The degree of short-range molecular order in the gelatinized wheat and potato starches decreased with increasing water content used for gelatinization. By comparing XRD patterns of gelatinized and amorphous starch, the XRD peak at 33° (2θ) was shown to be typical of gelatinized starch. The relative peak area (RPA), intensity, and full width at half-maximum (FWHM) of the XRD peak at 33° (2θ) decreased with the increase in water content for gelatinization. We propose that the RPA of the XRD peak at 33° (2θ) can be used to quantify the amount of short-range molecular order in gelatinized starch. The method developed in this study will help to explore and understand the relationship between the structure and functionality of gelatinized starch in food and nonfood applications.

Structure of Starch-Sepiolite Bio-Nanocomposites: Effect of Processing and Matrix-Filler Interactions

Sepiolite clay is a natural filler particularly suitable to be used with polysaccharide matrices (e.g., in starch-based bio-nanocomposites), increasing their attractiveness for a wide range of applications, such as packaging. Herein, the effect of the processing (i.e., starch gelatinization, addition of glycerol as plasticizer, casting to obtain films) and of the sepiolite filler amount on the microstructure of starch-based nanocomposites was investigated by SS-NMR (solid-state nuclear magnetic resonance), XRD (X-ray diffraction) and FTIR (Fourier-transform infrared) spectroscopy. Morphology, transparency and thermal stability were then assessed by SEM (scanning electron microscope), TGA (thermogravimetric analysis) and UV-visible spectroscopy. It was demonstrated that the processing method allowed to disrupt the rigid lattice structure of semicrystalline starch and thus obtain amorphous flexible films, with high transparency and good thermal resistance. Moreover, the microstructure of the bio-nanocomposites was found to intrinsically depend on complex interactions among sepiolite, glycerol and starch chains, which are also supposed to affect the final properties of the starch-sepiolite composite materials.

The Effects of Starch Molecular Fine Structure on Thermal and Digestion Properties of Rice Starch

Whole white rice is a major staple food for human consumption, with its starch digestion rate and location in the gastrointestinal tract having a critical role for human health. Starch has a multi-scale structure, which undergoes order-disorder transitions during rice cooking, and this structure is a major determinant of its digestibility. The length distributions of amylose and amylopectin chains are important determinants of rice starch gelatinization properties. Starch chain-length and molecular-size distributions are important determinants of nucleation and crystal growth rates, as well as of intra- and intermolecular interactions during retrogradation. A number of first-order kinetics models have been developed to fit starch digestograms, producing new information on the structural basis for starch digestive characteristics of cooked whole rice. Different starch digestible fractions with distinct digestion patterns have been found for the digestion of rice starch in fully gelatinized and retrograded states, the digestion kinetics of which are largely determined by starch fine molecular structures. Current insights and future directions to better understand digestibility of starch in whole cooked rice are summarized, pointing to ways of developing whole rice into a healthier food by way of having slower starch digestibility.

Oligosaccharides elevate the gelatinization temperature of wheat starch more than sucrose, paving the way for their use in reduced sugar starch-based formulations

The gelatinization of wheat starch influences the final structure and texture of baked goods. Sucrose effectively elevates the gelatinization temperature (T_gel) of starch more than many sweeteners, and maintaining a higher T_gel has been a challenge while reducing the amount of sucrose in baked goods. The objective of this study was to quantify the effects of 14 different oligosaccharides (OS: maltose, isomaltulose, kestose, maltotriose, melezitose, raffinose, stachyose, a fructo-OS, a galacto-OS, an isomalto-OS, lactosucrose, a xylo-OS, and two glucose-based dextrins), allulose, and sucrose at different concentrations (0 to 60% w/w) on the T_gel of wheat starch using DSC, and to determine which OS physicochemical properties best explained the T_gel results. OS type and concentration significantly altered T_gel. Many OS elevated the T_gel as much as or more than sucrose at the same solution concentrations, while allulose did not. The onset T_gel in water was 60 °C, in 60% sucrose was 96 °C, in 60% allulose was 80 °C, and T_gel increased up to 107-108 °C in 60% fructo-OS and Nutriose® solutions. The effects of OS on T_gel correlated most strongly (r > 0.95) with two OS solution parameters: the solvent effective volume fraction (ϕ_w,eff, related to solute intermolecular hydrogen bond density) and solution viscosity, to a lesser extent with solution water activity, and not to the glass transition temperature of the OS. Based on T_gel elevation, many of the OS are promising sucrose replacements in baked goods, which could facilitate their use in desirable higher fiber, reduced sugar starch-based baked product formulations.

Histological Evaluation of Cassava Starch/Chicken Gelatin Membranes

The use of biopolymers for tissue engineering has recently gained attention due to the need for safer and highly compatible materials. Starch is one of the most used biopolymers for membrane preparation. However, incorporating other polymers into starch membranes introduces improvements, such as better thermal and mechanical resistance and increased water affinity, as we reported in our previous work. There are few reports in the literature on the biocompatibility of starch/chicken gelatin composites. We assessed the in vivo biocompatibility of the five composites (T1–T5) cassava starch/gelatin membranes with subdermal implantations in biomodels at 30, 60, and 90 days. The FT-IR spectroscopy analysis demonstrated the main functional groups for starch and chicken gelatin. At the same time, the thermal study exhibited an increase in thermal resistance for T3 and T4, with a remaining mass (~15 wt.%) at 800 °C. The microstructure analysis for the T2–T4 demonstrated evident roughness changes with porosity presence due to starch and gelatin mixture. The decrease in the starch content in the composites also decreased the gelatinization heats for T3 and T4 (195.67, 196.40 J/g, respectively). Finally, the implantation results demonstrated that the formulations exhibited differences in the degradation and resorption capacities according to the starch content, which is easily degraded by amylases. However, the histological results showed that the samples demonstrated almost complete reabsorption without a severe immune response, indicating a high in vivo biocompatibility. These results show that the cassava starch/chicken gelatin composites are promising membrane materials for tissue engineering applications.

An insight into tapioca and wheat starch gelatinization mechanisms using TD-NMR and complementary techniques

To provide evidence for previously proposed assumptions concerning starch gelatinization sub-mechanisms, a more detailed investigation was carried out using multiscale analysis of a starch type selected for its marked difference. Tapioca starch was chosen due to its cohesive/springy properties and its growing use in the food industry. Time-domain nuclear magnetic resonance (TD-NMR) was used to investigate the leaching of material, water absorption and crystallite melting in hydrated tapioca starch (45%). The interpretation of T2 mass intensity evolutions, especially those of the (intra- and extra-granular) aqueous phases, was discussed drawing on complementary techniques such as microscopy, Rapid Visco Analyser (RVA), differential scanning calorimetry (DSC) and swelling factor (SF) and solubility index (SI) measurements. Results show that the T2 assignments usually proposed in the literature are dependent on starch origin. The differences in T2 evolutions (value and mass intensity) observed between wheat and tapioca starches at intermediate hydration levels could be linked to the different gelatinization behaviour of tapioca starch involving the latter's higher granule rupture level, higher gelatinization temperature and greater swelling power above its gelatinization temperature.

Starch granule size: Does it matter?

Nature has developed starch granules varying in size from less than 1 μm to more than 100 μm. The granule size is an important factor affecting the functional properties and the applicability of starch for food and non-food applications. Within the same botanical species, the range of starch granule size can be up to sevenfold. This review critically evaluated the biological and environmental factors affecting the size of starch granules, the methods for the separation of starch granules and the measurement of size distribution. Further, the structure at different length scales and properties of starch-based on the granule size is elucidated by specifying the typical applications of granules with varying sizes. An amylopectin cluster model showing the arrangement of amylopectin from inside toward the granule surface is proposed with the hypothesis that the steric hindrance for the growth of lamellar structure may limit the size of starch granules.

Wheat Biocomposite Extraction, Structure, Properties and Characterization: A Review

Biocomposite materials create a huge opportunity for a healthy and safe environment by replacing artificial plastic and materials with natural ingredients in a variety of applications. Furniture, construction materials, insulation, and packaging, as well as medical devices, can all benefit from biocomposite materials. Wheat is one of the world’s most widely cultivated crops. Due to its mechanical and physical properties, wheat starch, gluten, and fiber are vital in the biopolymer industry. Glycerol as a plasticizer considerably increased the elongation and water vapor permeability of wheat films. Wheat fiber developed mechanical and thermal properties as a result of various matrices; wheat gluten is water insoluble, elastic, non-toxic, and biodegradable, making it useful in biocomposite materials. This study looked at the feasibility of using wheat plant components such as wheat, gluten, and fiber in the biocomposite material industry.

Structural factors governing starch digestion and glycemic responses and how they can be modified by enzymatic approaches: A review and a guide

Starch is the most abundant glycemic carbohydrate in the human diet. Consumption of starch-rich food products that elicit high glycemic responses has been linked to the occurrence of noncommunicable diseases such as cardiovascular disease and diabetes mellitus type II. Understanding the structural features that govern starch digestibility is a prerequisite for developing strategies to mitigate any negative health implications it may have. Here, we review the aspects of the fine molecular structure that in native, gelatinized, and gelled/retrograded starch directly impact its digestibility and thus human health. We next provide an informed guidance for lowering its digestibility by using specific enzymes tailoring its molecular and three-dimensional supramolecular structure. We finally discuss in vivo studies of the glycemic responses to enzymatically modified starches and relevant food applications. Overall, structure-digestibility relationships provide opportunities for targeted modification of starch during food production and improving the nutritional profile of starchy foods.

Valorization and Application of Fruit and Vegetable Wastes and By-Products for Food Packaging Materials

The important roles of food packaging are food protection and preservation during processing, transportation, and storage. Food can be altered biologically, chemically, and physically if the packaging is unsuitable or mechanically damaged. Furthermore, packaging is an important marketing and communication tool to consumers. Due to the worldwide problem of environmental pollution by microplastics and the large amounts of unused food wastes and by-products from the food industry, it is important to find more environmentally friendly alternatives. Edible and functional food packaging may be a suitable alternative to reduce food waste and avoid the use of non-degradable plastics. In the present review, the production and assessment of edible food packaging from food waste as well as fruit and vegetable by-products and their applications are demonstrated. Innovative food packaging made of biopolymers and biocomposites, as well as active packaging, intelligent packaging, edible films, and coatings are covered.

A kinetics-based decomposition approach to reveal the nature of starch asymmetric gelatinization thermograms at non-isothermal conditions

Starch gelatinization under non-isothermal conditions with limited moisture content is a common industrial process involved in the processing of many starchy foods, while the nature of its asymmetric differential scanning calorimetry thermograms is still undefinable. This study for the first time developed a kinetics-based mathematical model, which could yield a parameterization of gelatinization thermograms that are essentially the same as experimental ones. Even more, the model is capable of decomposing gelatinization thermograms into kinetics-based sub-patterns, and revealing hidden features. By applying this newly developed methodology to nine starches with different plant origins and correlated with their lamellar structures, the results indicated that distinctly arranged groups (sub-components) of semi-crystalline lamellae with different thermal stabilities are existed in the native starch granules. This gives ways to better understand starch structure-property relations, and suggests useful directions for food manufactures to produce functional foods by understanding and differentially controlling the starch gelatinization sub-components.

Active coatings of thermoplastic starch and chitosan with alpha-tocopherol/bentonite for special green coffee beans

The quality of green coffee beans (GCBs) is possibly affected by storage conditions. Edible polymer coatings for GCBs can help preserve flavors and improve shelf life of GCBs. This study aimed to incorporate α-tocopherol, a powerful antioxidant, in thermoplastic starch [TPS] and chitosan [TPC] and determined the best cavitation energy (960-3840 J·mL-1) using an ultrasonic probe. Then, we evaluated the incorporation of bentonite (0% and 2% m/m) and α-tocopherol (0% and 10% m/m) in the best energy cavitation/biopolymer combination. The TPS and TPC coatings demonstrated good adherence to the GCBs, measured by surface energy. The dispersion of α-tocopherol in TPC, with cavitation energy 960 J·mL-1, promoted greater stability (greater zeta potential), thereby increasing antioxidant activity by 28% compared to TPS, therefore, was selected for a second stage. Incorporation of 2% bentonite into the TPC, with 10% α-tocopherol, resulted in a 3.7 × 10-10 g·m-1·s-1·Pa-1 water vapor permeability, which is satisfactory for prevented of moisture gain during storage. The compressive load showed values of 375 N to the non-coated GCB and around 475 N with the insertion of coatings to the GCB. Thus, a TPC/α-tocopherol/bentonite combination, dispersed with 960 J·mL-1 energy, was highly effective in the development of biopolymeric coatings for the GCBs.

Stabilisation of betalains and phenolic compounds extracted from red cactus pear (Opuntia ficus-indica) by spray and freeze-drying using oca (Oxalis tuberosa) starch as drying aid

The objective of this work was to evaluate the stabilisation of betalains and phenolic compounds extracted from red cactus pear by spray and freeze-drying. After hydroethanolic extraction and partial solvent removal under reduced pressure, the highly coloured extracts were enriched with oca starch and maltodextrin as drying aids in different ratios (100:0, 70:30, and 50:50, oca starch: maltodextrin) prior to spray and freeze-drying. The obtained microencapsulated extract powders were characterised by moisture content, hygroscopicity, solubility and morphology. In addition, the stability of the encapsulated betalains and phenolics was evaluated during storage at room temperature for 105 days. All microcapsules showed high retentions of betacyanins (69.9-86.5% after 105 days), betaxanthins (72.2-81.9%), phenolic compounds (46.5-63.5%) and antioxidant capacity (60.1-64.9%, FRAP method; 49.7-57.5%, ABTS method). The system with 70:30 starch:maltodextrin ratio as drying aids showed the highest values of retention regarding the polyphenol content (63.5%), antioxidant capacity (64.9% to FRAP method) and betacyanin content (86.5%), as well as a low degradation rate constant of betacyanins (1.23 × 10^-3 days^-1) and a long half-life (563 days). Oca starch used alone or in combination with maltodextrin has been shown to work adequately as a microencapsulating agent and stabilizer of pigments and antioxidants derived from red cactus pear.

Development of sorghum-based shortbread biscuits from "muskwari" flour

In order to produce biscuits from off-season sorghum, a local "Muskwari" sorghum was milled and sieved. This flour was used to produce shortbread biscuits with different substitutions rates of wheat flour to that of sorghum. The standard formulation of this same type of shortbread biscuits was used and biscuits were produced with incorporation rates of wheat flour to that of sorghum, from 0% to 100%, with a gap of 10 between two consecutives percentages. The technological characterization of the sorghum flour produced indicates a good water absorption capacity, and interesting solubility index and swelling rate. Technological aspect indicated that by changing speed and kneading time, resting the dough, it is possible to produce 100% sorghum flour shortbread biscuits. Shortbread biscuits made from 70% of wheat flour incorporation had the best average scores for overall preference criteria (6.97 ± 1.30), color (7.1 ± 1.45), and texture (6.62 ± 1.54). For smell and taste criteria, the 40% biscuits and the witness received the highest average scores, respectively, namely 6.77 ± 1.55 for smell and 7.12 ± 1.29 for taste. Analysis of the nutritional and energy intake of the control biscuit and the 70% substitution revealed that between the two, the latter had a significantly higher intake of total carbohydrates (58.51 g), dietary fiber (2.15 g), and total energy (454.1 kcal.

Starch-Mediated Immobilization, Photochemical Reduction, and Gas Sensitivity of Graphene Oxide Films

This work unveils the roles played by potato starch (ST) in the immobilization, photochemical reduction, and gas sensitivity of graphene oxide (GO) films. The ST/GO films are assembled layer by layer (LbL) onto quartz substrates by establishing mutual hydrogen bonds that drive a stepwise film growth, with equal amounts of materials being adsorbed in each deposition cycle. Afterward, the films are photochemically reduced with UV irradiation (254 nm), following a first-order kinetics that proceeds much faster when GO is assembled along with ST instead of a nonoxygenated polyelectrolyte, namely, poly(diallyl dimethylammonium) hydrochloride (PDAC). Finally, the gas-sensing performance of ST/reduced graphene oxide (RGO) and PDAC/RGO sensors fabricated via LbL atop of gold interdigitated microelectrodes is evaluated at different relative humidity levels and in different concentrations of ammonia, ethanol, and acetone. In comparison to the PDAC/RGO sensor, the ones containing ST are much more sensitive, especially when operating in a high-relative-humidity environment. An array comprising these chemical sensors provides unique electrical fingerprints for each of the investigated analytes and is capable of discriminating and quantifying them in a wide range of concentrations, from 10 to 1000 ppm.

Effect of Initial Conformation on the Starch Biopolymer Film Formation Studied by NMR

The formation of a rigid porous biopolymer scaffold from aqueous samples of 1% w/v (suspension) and 5% w/v (gel) corn starch was studied using optical and nuclear magnetic resonance (NMR) techniques. The drying process of these systems was observed using a single-sided NMR scanner by application of the Carr-Purcell-Meiboom-Gill pulse sequence at different layer positions. The echo decays were analyzed and spin-spin relaxation times (T₂) were obtained for each layer. From the depth dependent T₂ relaxation time study, it was found that the molecular mobility of water within the forming porous matrix of these two samples varied notably at different stages of film formation. At an intermediate stage, a gradual decrease in mobility of the emulsion sample towards the air-sample interface was observed, while the gel sample remained homogeneous all along the sample height. At a later stage of drying, heterogeneity in the molecular dynamics was observed in both samples showing low mobility at the bottom part of the sample. A wide-angle X-ray diffraction study confirmed that the structural heterogeneity persisted in the final film obtained from the 5% corn starch aqueous sample, whereas the film obtained from the 1% corn starch in water was structurally homogeneous.