Infrared spectroscopy with heated attenuated total internal reflectance enabling precise measurement of thermally induced transitions in complex biological polymers

Two-dimensional correlation infrared spectroscopy elucidated the volatilization process of the microemulsion composed of peppermint essential oil and composite herbal extract

Microemulsion is usually a transparent and isotropic liquid mixture composed of oil phase, water phase, surfactant and cosurfactant. The surfactant-framed nanoscale droplets in the microemulsion can penetrate into the skin surface to reduce its barrier function. This makes microemulsion an ideal preparation for the transdermal drug delivery. The permeability of microemulsion may be further enhanced when botanical essential oils that can dissolve the stratum corneum are used as the oil phase. However, the volatility of essential oils is possible to shorten the retention time of the microemulsion on the skin surface. Therefore, analytical methods are required to understand the volatilization process of the microemulsion composed of essential oils to develop the reasonable topical drug carrier system. In this research, Fourier transform infrared (FTIR) spectroscopy with an attenuated total reflection (ATR) accessory cooperated with two-dimensional correlation spectroscopy (2DCOS) to elucidate the volatilization processes of some microemulsions composed of peppermint essential oil. Principal component analysis (PCA) and moving-window two-dimensional correlation spectroscopy (MW2DCOS) revealed the multiple stages of the volatilization processes of the microemulsions. Synchronous 2D correlation infrared spectra indicated the compositional changes during each stage. It was found that the successive volatilizations of ethanol, water and menthone were the major events during the volatilization process of the microemulsion composed of peppermint essential oil. Ethanol can accelerate the volatilization of water, while the composite herbal extract seemed to not influence the volatilization of the other ingredients. After a 20-min-long volatilization process, the remaining microemulsion still contained considerable peppermint essential oil to affect the skin. The above results showed the feasibility of developing the microemulsion composed of peppermint essential oil for the transdermal drug delivery of composite herbal extract. This research also proved that the combination of ATR-FTIR spectroscopy and 2DCOS was valuable to study the volatilization process of the microemulsion.

Insight into multi-scale structural evolution during gelatinization process of normal and waxy maize starch

By using a mimicked heating with ex-situ liquid nitrogen flash freezing method, multi-scale structural evolution behaviors of normal maize starch (NMS) and waxy maize starch (WMS) during gelatinization process were studied. The results from SEM, X-ray diffraction (XRD), FTIR/solid state NMR spectroscopy and small angle X-ray scattering (SAXS) showed that NMS and WMS exhibited differently structural evolution behavior during gelatinization process. As the temperature increase, the proportion of the NMS granules with cavity gradually increased, while after heating beyond (peak gelatinization temperature (Tp) + conclusion gelatinization temperature (Tc))/2 the disappearance of starch granule integrity occurred for WMS. The relative crystallinity of NMS declined from 32.8 to 15.26% gradually, as that of WMS declined from 42.43 to 13.09% with a sharply descent when heated beyond (Tp + Tc)/2. The loss of short-range order structure of NMS and WMS showed same trends according to FTIR and NMR. Semicrystalline lamellae of NMS became thinner gradually while that of WMS showed an apparently narrowing after heating beyond (Tp + Tc)/2. These results suggest that the destruction of double helix in amylopectin structure had greatly influence on the larger scale structure of starch samples. This strategy is important for thorough understanding and profiting starch-based food processing.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-022-05520-2.

Characterization and application of a coating of starch extracted from avocado (Persea americana L. cv. Hass) seeds as an alternative to reduce acrylamide content in French fries

The starch extracted from avocado (Persea americana L. cv. Hass) seeds was characterized and used in the preparation of an edible coating to reduce the oil uptake and acrylamide content in French fries. Starch characterization was carried out using Differential Scanning Calorimetry, Fourier transform infrared spectrophotometry, gelatinization, and scanning electron microscopy. Uncoated (UFF) and coated (CFF) French fries were compared and evaluated for moisture, water activity (Aw), fat, color, firmness, acrylamide content, and sensorial analysis. The extracted starch presented a high crystalline structure and good stability to mechanical work and heat treatments. The CFF French fries showed significantly higher Aw, color parameter a*, but lower luminosity and acrylamide content than UFF samples. Similarly, the CFF samples tended to decrease the fat content, although without statistical differences. Avocado seed starch can be an economical and technically feasible alternative to the food industry as an effective coating to reduce acrylamide content in French fries.

Pretreatment Techniques and Green Extraction Technologies for Agar from Gracilaria lemaneiformis

Optimizing the alkali treatment process alone without tracking the changes of algae and agar quality with each pretreatment process will not achieve the optimal agar yield and final quality. In this study, we monitored the changes of the morphology and weight of algae with each treatment process, and comprehensively analyzed the effects of each pretreatment process on the quality of agar by combining the changes of the physicochemical properties of agar. In conventional alkali-extraction technology, alkali treatment (7%, w/v) alone significantly reduced the weight of algae (52%), but hindered the dissolution of algae, resulting in a lower yield (4%). Acidification could solve the problem of algal hardening after alkali treatment to improve the yield (12%). In enzymatic extraction technology, agar with high purity cannot be obtained by enzyme treatment alone, but low gel strength (405 g/cm²) and high sulfate content (3.4%) can be obtained by subsequent acidification and bleaching. In enzyme-assisted extraction technology, enzyme damage to the surface fiber of algae promoted the penetration of low-concentration alkali (3%, w/v), which ensured a high desulfurization efficiency and a low gel degradation rate, thus improving yield (24.7%) and gel strength (706 g/cm²), which has the potential to replace the traditional alkali-extraction technology.

Interaction of Squid (Dosidicus giga) Mantle Protein with a Mixtures of Potato and Corn Starch in an Extruded Snack, as Characterized by FTIR and DSC

The majority of snacks expanded by extrusion (SEE) are made with vegetable sources, to improve their nutritional content; it has been proposed to incorporate squid (Dosidicus gigas), due to its high protein content, low price and high availability. However, the interaction of proteins of animal origin with starch during extrusion causes negative effects on the sensory properties of SEE, so it is necessary to know the type of protein-carbohydrate interactions and their effect on these properties. The objective of this research was to study the interaction of proteins and carbohydrates of SEE elaborated with squid mantle, potato and corn. The nutritional composition and protein digestibility were evaluated, Fourier transform infrared (FTIR) and Differential Scanning Calorimetry (DSC) were used to study the formation of protein-starch complexes and the possible regions responsible for their interactions. The SEE had a high protein content (40-85%) and biological value (>93%). The melting temperature (Tm) was found between 145 and 225 °C; the Tm values in extruded samples are directly proportional to the squid content. The extrusion process reduced the amine groups I and II responsible for the protein-protein interaction and increased the O-glucosidic bonds, so these bonds could be responsible for the protein-carbohydrate interactions.

Crystalline morphology of thermoplastic starch/talc nanocomposites induced by thermal processing

A structural study about the changes induced by plasticization of native corn starch was carried out in this work. The influence of talc nanoparticles presence during starch thermal processing was also evaluated. Macroscopic observation of the granules appearance evolution during melt-mixing and thermo-compression was supported by a theoretical description related to these processing methods. Melt-mixing induced a polymorphic transformation from A- to V_h-type and a reduction in the degree of crystallinity. Homogenous appearance of the plasticized starch was in accordance to the disruption of granules integrity, evidenced by SEM. This observation agreed to the distinctive XRD pattern of plasticized starch from unprocessed granules. Talc incorporation did not require the adjustment of processing parameters in order to obtain a homogenous thermoplastic material, with an adequate particles distribution within the matrix. Regardless talc presence, plasticized starch presented a V_h-type crystalline structure. Thermo-compression led to particles alignment promoted by talc laminar morphology.

Structural and enzyme kinetic studies of retrograded starch: Inhibition of α-amylase and consequences for intestinal digestion of starch

Retrograded starch is known to be resistant to digestion. We used enzyme kinetic experiments to examine how retrogradation of starch affects amylolysis catalysed by porcine pancreatic amylase. Parallel studies employing differential scanning calorimetry, infra red spectroscopy, X-ray diffraction and NMR spectroscopy were performed to monitor changes in supramolecular structure of gelatinised starch as it becomes retrograded. The total digestible starch and the catalytic efficiency of amylase were both decreased with increasing evidence of retrogradation. A purified sample of retrograded high amylose starch inhibited amylase directly. These new findings demonstrate that amylase binds to retrograded starch. Therefore consumption of retrograded starch may not only be beneficial to health through depletion of total digestible starch, and therefore the metabolisable energy, but may also slow the rate of intestinal digestion through direct inhibition of α-amylase. Such physiological effects have important implications for the prevention and management of type 2 diabetes and cardiovascular disease.

In-situ micro-FTIR spectroscopic observation on the hydration process of Poria cocos

In Poria cocos, triterpene compound and polysaccharides are the main compositions. The heteropolysaccharide was identified as a linear chain of β-(1→3)-d-glucan, which has the strong water absorbing capacity. In order to investigate the effect of water on the structure of Poria cocos, which belongs to a kind of Polyporaceae, the Micro-Fourier transform infrared spectroscopy (micro-FTIR) technique has been employed with the ambient relative humidity (RH) increasing. The gained IR spectra are measured and analyzed in detail. Because of strong overlaps between some bands, the differential spectra and band decompositions have been applied to analyze the structural change. IR spectra show the transformation of hydrogen bonds with the RH. The blue shift of the CH2 bending vibration from 1417 to 1424cm(-1) with the increase in RH means that the hydrogen bonds are formed between CH2 groups and water molecules at lower RH and some transferred to weak hydrogen bonds. The further study suggests that the C1OH, C2OH, and C3OH groups from polysaccharide bond formed C1OH⋯H2O, C2OH⋯H2O, and C3OH⋯H2O steady modes, respectively, with water molecules.

Infrared microspectroscopic imaging of plant tissues: spectral visualization of Triticum aestivum kernel and Arabidopsis leaf microstructure

Infrared microspectroscopy is a tool with potential for studies of the microstructure, chemical composition and functionality of plants at a subcellular level. Here we present the use of high-resolution bench top-based infrared microspectroscopy to investigate the microstructure of Triticum aestivum L. (wheat) kernels and Arabidopsis leaves. Images of isolated wheat kernel tissues and whole wheat kernels following hydrothermal processing and simulated gastric and duodenal digestion were generated, as well as images of Arabidopsis leaves at different points during a diurnal cycle. Individual cells and cell walls were resolved, and large structures within cells, such as starch granules and protein bodies, were clearly identified. Contrast was provided by converting the hyperspectral image cubes into false-colour images using either principal component analysis (PCA) overlays or by correlation analysis. The unsupervised PCA approach provided a clear view of the sample microstructure, whereas the correlation analysis was used to confirm the identity of different anatomical structures using the spectra from isolated components. It was then demonstrated that gelatinized and native starch within cells could be distinguished, and that the loss of starch during wheat digestion could be observed, as well as the accumulation of starch in leaves during a diurnal period.

Effect of surfactant treatment on swelling behaviour of normal and waxy cereal starches

Starch swelling behaviour greatly affects its functionality in a food matrix. For some granular starches pre-treatment with the surfactant, sodium dodecyl sulphate, is known to dramatically affect swelling behaviour. The purpose of this study was to assess the effect of this surfactant treatment on the swelling behaviour of a variety of waxy and normal cereal starches. A concurrent mid-infrared spectroscopy study was carried out to investigate the chemical nature of variations in swelling behaviour. The native normal starches (amylose content 23-28%) showed significant variation in their pasting properties, which was largely eliminated by surfactant treatment. Surfactant treatment had less effect on the behaviour of the waxy starches (amylose contents 1-8%), which still exhibited some residual variation. Waxy durum appeared to be unique within the waxy starches, behaving more similarly to the normal starches. The spectroscopic data highlighted the carbohydrate fingerprint region as the main source of variation between samples.

In situ study of water uptake by the seeds, endosperm and husk of barley using infrared spectroscopy

Variations in the amount and rates of water uptake influence the seed hydration as well as the modification of the endosperm for industrial uses (e.g., malting). The aim of this study was to investigate and interpret absorption frequencies in the mid infrared (MIR) region associated with water uptake in whole seeds, husk and endosperm of barley seeds during the initial period of soaking in water. Partial least squares (PLS) regression models for the prediction of water uptake in the set of samples yield a coefficient of determination (R(2)) and a standard error in cross validation of 0.75 and 2.57 (% w/w), respectively. The biological implications of this study are that the first stages of germination can be monitored using the information derived from the MIR spectra. These results also demonstrated that whole seeds, endosperm and husk derived from the same variety or genotype have different patterns in the MIR region.

A novel approach to monitor the hydrolysis of barley (Hordeum vulgare L) malt: a chemometrics approach

Malting barley is a process that has been profusely studied and is known to be influenced by several physical and biochemical properties of the grain. In particular, the amount of material that can be extracted from the malt (malt extract) is an important measure of brewing performance and end quality. The objectives of this study were (a) to compare the time course of hydrolysis of different malting barley (Hordeum vulgare L) varieties and (b) to evaluate the usefulness of mid-infrared (MIR) spectroscopy as high-throughput method to monitor malt hydrolysis. Differences in the pattern of hydrolysis were observed between the malt samples analyzed where samples from the same variety that have similar hot water extract (HWE) values tend to have the same pattern of hydrolysis. Principal component score plots based on the MIR spectra showed similar results. Partial least-squares discriminate analysis (PLS-DA) was used to classify malt samples according to their corresponding variety and time course of hydrolysis. The coefficient of determination (R(2)) and the standard error of cross validation (SECV) obtained for the prediction of variety and time course of hydrolysis were 0.67 (1.01) and 0.38 (19.90), respectively. These differences might be the result of the different composition in sugars between the barley varieties analyzed after malting, measured as wort density and not observed when only the HWE value at the end point is reported. This method offers the possibility to measure several parameters in malt simultaneously, reducing the time of analysis as well as requiring minimal sample preparation.

Vibrational microspectroscopic identification of powdered traditional medicines: chemical micromorphology of Poria observed by infrared and Raman microspectroscopy

Microscopic identification using optical microscopes is a simple and effective method to identify powdered traditional medicines made from plants, animals and fungi. Sometimes, the criteria based on physical properties of the microscopic characteristics of drug powder may be ambiguous, which makes the microscopic identification method subjective and empirical to some extent. In this research, the vibrational microspectroscopic identification method is proposed for more explicit discrimination of powdered traditional medicines. The chemical micromorphology, i.e., chemical compositions and related physical morphologies, of the drug powder can be profiled objectively and quantitatively by infrared and Raman microspectroscopy, leading to better understanding about the formation mechanisms of microscopic characteristics and more accurate identification criteria. As an example, the powder of Poria, which is one of the most used traditional Chinese medicines, is studied in this research. Three types of hyphae are classified according to their infrared spectral features in the region from 1200 to 900 cm(-1). Different kinds of polysaccharides indicate that these hyphae may be in different stages of the growth. The granular and branched clumps observed by the optical microscope may be formed from the aggregation of the mature hyphae with β-D-glucan reserves. The newfound spherical particles may originate from the exuded droplets in the fresh Poria because they are both composed of α-D-glucan. The results are helpful to understand the development of the hyphae and the formation of active polysaccharides in Poria and to establish accurate microspectroscopic identification criteria.

Characterization Methods for Starch-Based Materials: State of the Art and Perspectives

Improving starch-containing materials, whether food, animal feed, high-tech biomaterials, or engineering plastics, is best done by understanding how biosynthetic processes and any subsequent processing control starch structure, and how this structure controls functional properties. Starch structural characterization is central to this. This review examines how information on the three basic levels of the complex multi-scale structure of starch – individual chains, the branching structure of isolated molecules, and the way these molecules form various crystalline and amorphous arrangements – can be obtained from experiment. The techniques include fluorophore-assisted carbohydrate electrophoresis, multiple-detector size-exclusion chromatography, and various scattering techniques (light, X-ray, and neutron). Some examples are also given to show how these data provide mechanistic insight into how biosynthetic processes control the structure and how the various structural levels control functional properties.