Determination of starch crystallinity with the Fourier-transform terahertz spectrometer

Quantification of resistant starch content in rice after hydrothermal treatments using terahertz spectroscopy

Since hydrothermal treatments can enhance resistant starch (RS) content in rice and provide health benefits when consumed, a less laborious and non-destructive method to determine RS content is needed. Terahertz (THz) spectroscopy is hypothesized as a suitable method to quantify RS content in rice after hydrothermal treatment with its sensitivity for the intermolecular forces increase in the formation of RS. In this study, we first used the traditional in vitro hydrolysis method to determine the content of RS in rice. Then, the potential of starch absorbance peaks to quantify RS content after three commonly used hydrothermal methods, soaking, mild heat-moisture treatment, and parboiling, was investigated. The second derivative intensities of the peak at 9.0, 10.5, 12.1, and 13.1 THz were confirmed as being correlated with RS content and showed the high accuracy to predict RS content in samples (R2 > 0.96). Our results indicate the RS content of hydrothermally treated rice can be accurately quantified using these peaks.

Gamma Irradiation Effect on Polymeric Chains of Epoxy Adhesive

The study of materials for space exploration is one of the most interesting targets of international space agencies. An essential tool for realizing light junctions is epoxy adhesive (EA), which provides an elastic and robust material with a complex mesh of polymeric chains and crosslinks. In this work, a study of the structural and chemical modification of a commercial two-part flexible EA (3M™ Scotch-Weld™ EC-2216 B/A Gray), induced by 60Co gamma radiation, is presented. Combining different spectroscopic techniques, such as the spectroscopic Fourier transform infrared spectroscopy (FTIR), the THz time-domain spectroscopy (TDS), and the electron paramagnetic resonance (EPR), a characterization of the EA response in different regions of the electromagnetic spectrum is performed, providing valuable information about the structural and chemical properties of the polymers before and after irradiation. A simultaneous dissociation of polymeric chain and crosslinking formation is observed.The polymer is not subject to structural modification at an absorbed dose of 10 kGy, in which only transient free radicals are observed. Differently, between 100 and 500 kGy, a gradual chemical degradation of the samples is observed together with a broad and long-living EPR signal appearance. This study also provides a microscopic characterization of the material useful for the mechanism evaluation of system degradation.

Terahertz Spectroscopic Identification of Roast Degree and Variety of Coffee Beans

In this study, terahertz time-domain spectroscopy (THz-TDS) was proposed to identify coffee of three different varieties and three different roasting degrees of one variety. Principal component analysis (PCA) was applied to extract features from frequency-domain spectral data, and the extracted features were used for classification prediction through linear discrimination (LD), support vector machine (SVM), naive Bayes (NB), and k-nearest neighbors (KNN). The classification effect and misclassification of the model were analyzed via confusion matrix. The coffee varieties, namely Catimor, Typica 1, and Typica 2, under the condition of shallow drying were used for comparative tests. The LD classification model combined with PCA had the best effect of dimension reduction classification, while the speed and accuracy reached 20 ms and 100%, respectively. The LD model was found with the highest speed (25 ms) and accuracy (100%) by comparing the classification results of Typica 1 for three different roasting degrees. The coffee bean quality detection method based on THz-TDS combined with a modeling analysis method had a higher accuracy, faster speed, and simpler operation, and it is expected to become an effective detection method in coffee identification.

Starch/polyvinyl alcohol with ionic liquid/graphene oxide enabled highly tough, conductive and freezing-resistance hydrogels for multimodal wearable sensors

With ever-growing demand for eco-friendly materials for wearable electronics, biopolymer-based hydrogels have drawn significant attention. As one of the most abundant and biodegradable biopolymers, starch-based hydrogels have a great potential for wearable electronics. However, mechanical fragility, low conductivity and subzero freeze restrict their applications. Here, a multifunctional hydrogel was facilely fabricated by integrating ionic liquid and graphene oxide into potato starch/polyvinyl alcohol skeleton via a green physical-crosslinking method. The abundant hydrogen-bond and electrostatic interactions endowed the hydrogel with excellent stretchability (657.5 %), strength (0.64 MPa), high conductivity (1.98 S·m-1) and good anti-freezing property (< -20 °C). Multiple characterizations and theoretical simulation (DFT) were combined to understand and confirm the interactions among different components. Taking advantage of these properties, multimodal wearable sensors were constructed for sensing tension (gauge factor: 6.04), compression (gauge factor: 3.27) and temperature (sensitivity: 0.71 %/°C), which are applied for monitoring human motion, daily-life pressure and body temperature. The sensor had a good anti-fatigue property with stable signals during 2000 cycles. Moreover, the sensor can effectively recognize handwriting and perform human-computer interaction. This work provides a promising route to develop sustainable and multifunctional biopolymer hydrogels for wearable sensors with versatile applications in human health, exercise monitors and soft robots.

Determining changes in crystallinity of rice starch after heat-moisture treatment using terahertz spectroscopy

To investigate the potential of Fourier-transform terahertz (FT-THz) spectroscopy to follow crystalline structure changes in rice starch after heat-moisture treatment (HMT), we measured the crystallinity by X-ray diffraction (XRD) spectra and found its correlation with THz spectra. According to A-type crystal structure and Vh-type crystalline structure of amylose-lipid complex (ALC) in rice starch, crystallinity is divided into A-type and Vh-type. The intensity of second derivative spectra peak at 9.0 THz was highly correlated with both A-type and Vh-type crystallinity. Additionally, other three peaks at 10.5 THz, 12.2 THz, and 13.1 THz were also sensitive to Vh-type crystalline structure. These results indicate that after HMT, the crystallinity of ALC (Vh-type) and A-type starch can be quantified using THz peaks.

Study on the crystallization behavior and conformation adjustment scale of poly(lactic acid) in the terahertz frequency range

The observed properties of crystalline polymers are determined by their internal structure, which in turn is the result of their different crystallization behaviors. Here, we investigate the crystallization behavior of poly(lactic acid) (PLA) by terahertz time-domain spectroscopy (THz-TDS) at varied temperatures. We find that the changes in the chain packing and conformation of PLA are characterized by THz spectroscopy. Combining X-ray diffraction (XRD) and infrared spectroscopy (IR), we attributed the blue-shift of the THz peak to the tightness of the chain packing, while its absorption enhancement is caused by the conformation transition. The effects of chain packing and chain conformation on the characteristic peak are phased. Furthermore, absorption discontinuities of the characteristic peaks of PLA crystallized at different temperatures are observed, which originated from differences in the degree of conformational transition caused by different thermal energies. We find that the crystallization temperature at which the absorption mutation of PLA occurs corresponds to the temperature at which the motion of the segment and molecular chain is excited, respectively. At these two temperatures, PLA exhibits different scales of conformational transitions leading to stronger absorption and larger absorption changes at higher crystallization temperatures. The results demonstrate that the driving force of PLA crystallization is indeed from changes in chain packing and chain conformation, and the molecular motion scale can also be characterized by THz spectroscopy.

Correlation analysis on physicochemical and structural properties of sorghum starch

This manuscript analyzed physicochemical and structural properties of 30 different types of sorghum starches based on their apparent amylose content (AAC). Current results confirmed that sorghum starch exhibited irregular spherical or polygonal granule shape with 14.5 μm average particle size. The AAC of sorghum starch ranged from 7.42 to 36.44% corresponding to relative crystallinities of 20.5 to 32.4%. The properties of enthalpy of gelatinization (ΔH), peak viscosity (PV), relative crystallinity (RC), degree of double helix (DD), degree of order (DO), and swelling power (SP) were negatively correlated with AAC, while the cool paste viscosity (CPV) and setback (SB) were positively correlated with AAC. Correlations analyzed was conducted on various physicochemical parameters. Using principal component analysis (PCA) with 20 variables, the difference between 30 different types of sorghum starch was displayed. Results of current study can be used to guide the selection and breeding of sorghum varieties and its application in food and non-food industries.

Starch-lauric acid complex-stabilised Pickering emulsion gels enhance the thermo-oxidative resistance of flaxseed oil

Hydrophobic-modified starch complexes have the potential to form Pickering emulsions and improve the oxidative stability of flaxseed oil. Here, V-type starch-lauric acid complexes (SLACs) were fabricated via solid encapsulation within 0.5-12 h and applied in flaxseed oil Pickering emulsions. Complexing index, X-ray diffraction and differential scanning calorimetry analyses confirmed that the degree of complexation increased with the reaction time. Pickering emulsion gels stabilised by SLACs generated with reaction times of 6 h and 12 h exhibited good storage stability and high yield stress, G' values and apparent viscosity. Confocal laser scanning microscopy and cryo-scanning electron microscopy revealed a gelation mechanism involving increased interface roughness and enhanced droplet-droplet interaction. In comparison to pure flaxseed oil, higher thermo-oxidative resistance was observed at 130 °C, with a markedly longer oxidation induction for emulsions and emulsion gels stabilised by SLACs. Our findings could assist in the design of hydrophobic-modified starch and provide a new paradigm for delaying oil oxidation.

Effects of single and dual modifications through electron beam irradiation and hydroxypropylation on physicochemical properties of potato and corn starches

In this study, electron beam irradiation (EBI; 2, 4, 6, 8 and 10 kGy), hydroxypropylation (HP) and dual modification of EBI-HP were applied to modify corn and potato starches. The results showed that the molar substitution (MS) of EBI-HP modified corn and potato starches were in the range of 0.060-0.087 and 0.080-0.124, respectively. After modifications, amylose content of corn (30.0 %) and potato (31.2 %) starches were declined to 24.2-28.1 % and 26.1-29.5 %, respectively, and relative crystallinity was reduced from 35.5 to 30.0 % for corn and 34.1 to 20.2 % for potato. Pasting properties decreased significantly in both starch sources with increasing irradiation dose. EBI decreased springiness, enthalpy of retrograded starch (ΔHr) and percentage of retrogradation (R%) on corn starches, which were different from those effects observed on potato starches. Meanwhile, HP increased peak viscosity up to 312.6 RVU and 1359.3 RVU for corn and potato starches, respectively. Moreover, EBI-HP was highly responsible for the decreases in the textural, gelatinization and retrogradation properties and relative crystallinity in both corn and potato starches. These results enhance the understanding of starch functionality modified by using both physical and chemical methods, and provide further insights on food and non-food applications.

A high-conductive, anti-freezing, antibacterial and anti-swelling starch-based physical hydrogel for multifunctional flexible wearable sensors

Flexible wearable sensors based on conductive hydrogels are attracting increasing interest. To meet the urgent demands of sustainability and eco-friendliness, biopolymer-based physically crosslinked hydrogels have drawn great attention. Starch has a great potential due to its renewability, biocompatibility, nontoxicity and low cost. However, poor mechanical property, low conductivity and lack of versatility are seriously limiting the applications of starch-based hydrogels in wearable sensors. Moreover, the development of starch hydrogel-based wearable sensors in harsh conditions remains a challenge. Herein, multifunctional and physical crosslinking hydrogels were developed by introducing ionic liquid (1-ethyl-3-methyl imidazolium acetate) and metal salt (AlCl₃) into starch/polyvinyl alcohol double-network structure. The hydrogel exhibited excellent stretchability (567%), tensile strength (0.53 MPa), high conductivity (2.75 S·m^-1), good anti-freezing, antibacterial and anti-swelling properties. A wearable sensor assembled from the starch-based hydrogel exhibited a wide working range, high sensitivity (gauge factor: 5.93) and excellent reversibility. Due to the versatility, the sensor effectively detected human motion in normal and underwater environment, and possessed a sensitive pressure and thermal response. Overall, the present work provided a promising route to develop multifunctional and "green" biopolymer-based hydrogels for wearable sensors in human health and sporting applications.

Evaluation of formation and proportion of secondary structure in γ-polyglutamic acid by terahertz time-domain spectroscopy

The study of secondary structure is essential for understanding peptides and proteins. Here, we measured the terahertz (THz) spectra of γ-polyglutamic acid (γ-PGA) dominated by α-helix and random coil (RC) respectively. The α-helix has two absorption peaks in the THz region, but no absorption peak is observed in the RC conformation. We believe this is because the hydrogen bonding effect leads to a higher orientation in the helix-dominated γ-PGA. At lower pH, the absorption intensity of γ-PGA increases with the induction time. Similar changes were obtained in the Fourier infrared spectroscopy (FTIR). Through the correlation analysis of THz and IR spectroscopy, it is found that the characteristic peak at 1.2 THz can be used as a sensitive indicator of the intermediate conformation of the α-helical structure. In addition, the transformation of α-helix-RC conformation is related to the peak intensity at 1.99 THz (R² = 0.991), which preliminarily indicates that terahertz time-domain spectroscopy (THz-TDS) has the potential to become a new effective method for characterizing and evaluating secondary structure.