Mobility characterization of waxy corn starch using wide-line (1)H nuclear magnetic resonance

Biodegradable Nanocomposites Based on Blends of Poly(Butylene Adipate-Co-Terephthalate) (PBAT) and Thermoplastic Starch Filled with Montmorillonite (MMT): Physico-Mechanical Properties

Poly(butylene adipate-co-terephthalate) (PBAT) is widely used for production of biodegradable films due to its high elongation, excellent flexibility, and good processability properties. An effective way to develop more accessible PBAT-based bioplastics for wide application in packaging is blending of PBAT with thermoplastic starch (TPS) since PBAT is costly with prices approximately double or even triple the prices of traditional plastics like polyethylene. This study is focused on investigating the influence of TPS/PBAT blend ratio and montmorillonite (MMT) content on the physical and mechanical properties and molecular mobility of TPS-MMT/PBAT nanocomposites. Obtained TPS-MMT/PBAT nanocomposites through the melt blending process were characterized using tensile testing, dynamic mechanical thermal analysis (DMTA), and X-ray diffraction (XRD), as well as solid-state 1H and 13C NMR spectroscopy. Mechanical properties demonstrated that the addition of TPS to PBAT leads to a substantial decrease in the tensile strength as well as in the elongation at break, while Young's modulus is rising substantially, while the effect of the MMT addition is almost negligible on the tensile stress of the blends. DMTA results confirmed the formation of TPS domains in the PBAT matrix. With increasing TPS content, mobility of starch-rich regions of TPS domains slightly increases. However, molecular mobility in glycerol-rich regions of TPS domains in the blends was slightly restricted. Moreover, the data obtained from 13C CP/MAS NMR spectra indicated that the presence of TPS in the sample decreases the mobility of the PBAT chains, mainly those located at the TPS/PBAT interfaces.

Molecular interactions between apigenin and starch with different amylose/amylopectin ratios revealed by X-ray diffraction, FT-IR and solid-state NMR

Starch can readily form complexes with polyphenols. However, its two components, namely amylose and amylopectin, differ significantly in their ability to complex with phenolic compounds. Given that the mechanism of their interaction is still poorly studied, this work investigated intermolecular interactions between apigenin and starch with different amylose/amylopectin ratios using ¹H NMR, FT-IR, XRD, DSC and solid-state NMR. Results showed that corn starch with high amylose/amylopectin ratios had a better complexing ability and higher complexing index with apigenin than amylopectin. Besides, solid-state NMR suggested that the molecular mechanism behind the strong intermolecular interactions between corn starch and apigenin involved hydrogen bonds. Furthermore, the detailed binding sites of hydrogen bonds, that linked by hydroxyl-starch and phenyl-apigenin were also confirmed by ¹H¹³C heteronuclear correlation (HETCOR) spectra. This study revealed the molecular mechanism on amylose/amylopectin complexing with apigenin and provides a theoretical basis for further developing polyphenols in starchy food.

3D-printing of oxidized starch-based hydrogels with superior hydration properties

High-hydration hydrogels based on carbohydrate polymers and green preparation methods have attracted intensive research focus recently. Driven by the attractive functions of starch, oxidized maize starch (OMS) was chosen and the related hydrogel (3D-OMS) was constructed by hot-extrusion 3D printing (HE-3DP). Meanwhile, the effect of different OMS concentrations (11 %-19 %) on its printability, structure and hydration properties were systematically investigated. The results showed that the formation of porous structure during HE-3DP environment contributed to rapid water absorption and well water holding capacity of 3D-OMS. Interestingly, as the OMS concentration increased from 11 % to 19 %, the 3D-OMS presented great hydration properties, with its maximum water absorption capacity and water holding capacity reaching 3013.43 % (11-OMS) and 93.53 % (19-OMS), respectively. Among them, 13 % was the best concentration for HE-3DP. Besides, 3D-OMS also exhibited good biodegradability and cytocompatibility. These results demonstrated potential for developing new starch-based biomedical hydrogel with great hydration properties through HE-3DP technology.

Multi-scale NMR and MRI approaches to characterize starchy products

This review deals with the use of Nuclear Magnetic Resonance techniques to monitor the behavior of starch as well as the migration and distribution of water during the processing or storage of starchy matrices. The aim is to emphasize the potentials of NMR techniques for the quantitative characterization of water transfers in starch-water systems on different length scales. Relaxation and self-diffusion experiments using low-field NMR spectrometry provided important information on the relationship between water dynamics and the microscopic organization of starch granules at various temperatures and water contents. Some works dealt with the botanical origin of starch but also the impact of possible additives. Indeed, the investigation on model starch-based systems was recently expanded to more complex real systems, including dough, bread, cakes, spaghetti and lasagna. Two-dimensional (2D) cross correlation methods have also been developed to elucidate chemical and diffusional proton exchange phenomena, and to improve the interpretation of results obtained in 1D. Finally, magnetic resonance micro-imaging methods were developed to study or to quantify water intake into starch-based matrices.

Modeling the influence of temperature, water activity and water mobility on the persistence of Salmonella in low-moisture foods

Salmonella can survive in low-moisture foods for long periods of time. Reduced microbial inactivation during heating is believed to be due to the interaction of cells and water, and is thought to be related to water activity (a(w)). Little is known about the role of water mobility in influencing the survival of Salmonella in low-moisture foods. The aim of this study was to determine how the physical state of water in low-moisture foods influences the survival of Salmonella and to use this information to develop mathematical models that predict the behavior of Salmonella in these foods. Whey protein powder of differing water mobilities was produced by pH adjustment and heat denaturation, and then equilibrated to aw levels between 0.19±0.03 and 0.54±0.02. Water mobility was determined by wide-line proton-NMR. Powders were inoculated with a four-strain cocktail of Salmonella, vacuum-sealed and stored at 21, 36, 50, 60, 70 and 80°C. Survival data was fitted to the log-linear, the Geeraerd-tail, the Weibull, the biphasic-linear and the Baranyi models. The model with the best ability to describe the data over all temperatures, water activities and water mobilities (f(test)<F(table)) was selected for secondary modeling. The Weibull model provided the best description of survival kinetics for Salmonella. The influence of temperature, aw and water mobility on the survival of Salmonella was evaluated using multiple linear regression. Secondary models were developed and then validated in dry non-fat dairy and grain, and low-fat peanut and cocoa products within the range of the modeled data. Water activity significantly influenced the survival of Salmonella at all temperatures, survival increasing with decreasing a(w). Water mobility did not significantly influence survival independent of a(w). Secondary models were useful in predicting the survival of Salmonella in various low-moisture foods providing a correlation of R=0.94 and an acceptable prediction performance of 81%. The % bias and % discrepancy results showed that the models were more accurate in predicting survival in non-fat food systems as compared to foods containing low-fat levels (12% fat). The models developed in this study represent the first predictive models for survival of Salmonella in low-moisture foods. These models provide baseline information to be used for research on risk mitigation strategies for low-moisture foods.

Hydrolytic and oxidative stability of L-(+)-ascorbic acid supported in pectin films: influence of the macromolecular structure and calcium presence

The hydrolytic and oxidative stability of L-(+)-ascorbic acid (AA) into plasticized pectin films were separately studied in view of preserving vitamin C activity and/or to achieve localized antioxidant activity at pharmaceutical and food interfaces. Films were made with each one of the enzymatically tailored pectins (50%, 70%, and 80% DM; Cameron et al. Carbohydr. Polym.2008, 71, 287-299) or commercial high methoxyl pectin (HMP; 72% DM). Since AA stability was dependent on water availability in the network, pectin nanostructure affected the AA kinetics. Higher AA retention and lower browning rates were achieved in HMP films, and calcium presence in them stabilized AA because of higher water immobilization. Air storage did not change AA decay and browning rates in HMP films, but they significantly increased in Ca-HMP films. It was concluded that the ability of the polymeric network to immobilize water seems to be the main factor to consider in order to succeed in retaining AA into film materials.

State diagrams for improving processing and storage of foods, biological materials, and pharmaceuticals (IUPAC Technical Report)

Supplemented temperature/composition phase diagrams include the non-equilibrium glass-transition temperature (Tg) curve and equilibrium ice-melting and solubility curves. The inclusion of the non-equilibrium curve allows one to establish relationships with the time coordinate and, thus, with the dynamic behavior of systems, provided that the thermal history of such systems is known. The objective of this report is to contribute to the potential applications of supplemented state diagrams for aqueous glass-formers, in order to describe the influence of water content, nature of vitrifying agents, and temperature on the physico-chemical properties of foods and biological and pharmaceutical products. These data are helpful to develop formulations, processing strategies, or storage procedures in order to optimize the stability of food ingredients and pharmaceutical formulations. Reported experimental data on phase and state transitions for several food and pharmaceutical systems were analyzed. Some methodological aspects and the effect of phase and state transitions on the main potential chemical reactions that can alter those systems during processing and/or storage are discussed.

Development of a high methoxyl pectin edible film for retention of l-(+)-ascorbic acid

An edible film to carry l-(+)-ascorbic acid (AA) was formulated for natural antioxidant food protection. Considering previous works where films based on the "rigid" structure of gellan (deacylated) or on a mixture of acylated-deacylated (more "disordered") gellan were used for network development, pectin was herein chosen by considering that the alternating presence of "disordered" (hairy) regions together with ordered (homogalacturonan) ones could sufficiently immobilize water for better AA retention and lower browning. High methoxyl pectin (HMP) was first investigated. AA stability and browning were studied during film storage at 33.3, 57.7, or 75.2% relative humidity (RH) and 25 degrees C; their dependence on water mobility determined through (1)H NMR analysis as well as the correlation between browning and AA degradation were again found. Network characteristics and glycerol (plasticizer) interactions were analyzed through X-ray diffraction and Fourier transform infrared spectroscopy as well as through uniaxial tensile assay. From all results obtained, it was hypothesized that browning development in solidlike systems may be directly related to the water molecules more closely adsorbed on the hydroxyl-polymeric (active) surfaces. The HMP film microstructure produced the best immobilization of water molecules except at 75.2% RH, where it showed lower AA stability than acylated-deacylated gellan film. It is suggested that disordered regions of this pectin network may not be adequately counterbalanced by more transient junction zones of alternating hydrophilic (water) and hydrophobic (methyl ester) interactions, also disturbed by glycerol molecules, for accomplishing enough water immobilization in the whole network at 75.2% RH.

Multi-level approach for the analysis of water effects in corn flakes

The purpose of this work was to analyze the effect of water on thermal transitions, mechanical properties, and molecular mobility in corn flakes (CF), and their relationships. Commercial common (CCF) and sugar-frosted (SCF) corn flakes were studied in a water content (wc) range from 5 to 20 (% dry basis). The slope of (1)H NMR spin-spin relaxation time T 2* (determined by FID) versus temperature plot changed close to T g. Compression force showed a maximum at wc of ca. 12 and 16% (db) for SCF and CCF, respectively. (1)H NMR complemented DSC data in determining the temperature dependence of water and solid mobility, in order to assess quality of laminated corn products. The results of the present work indicate that while the compression force showed a maximum value as a function of water content, T g values determined by DSC or by spin-spin relaxation decreased progressively with increasing water content.

New approach for characterization of gelatin biopolymer films using proton behavior determined by low field 1H NMR spectrometry

The behavior of protons in biopolymer films (BFs) formed with gelatin, water, and glycerol was investigated at various relative humidities (RHs) and concentrations of glycerol using a low field 1H NMR spectrometer. At a RH of approximately 0%, the distributed spin-spin relaxation times (T2) of protons in BFs showed two components: a rapidly relaxing proton with the shortest T2 derived from protons in the rigid backbone of the gelatin polymer such as CH1-, CH2-, and CH3-, and a slowly relaxing component with longer T2 from protons of the functional groups in amino acid residues in gelatin such as -OH, -COOH, and -NH3. These two components are referred to as nonexchangeable (T2N) and exchangeable protons (T2E), respectively, indicating the different mobility of the protons. The T2E increased as RH increased indicating the increase in relative mobility of protons due to the larger free volume in the BF matrix. Above a RH of 33%, the slowest relaxing component was found in all BFs and referred to as hydration-water protons (T2W) with the highest relative mobility of all protons in the films. It suggests that the free volume in BFs can be formed above a RH of 33% in the absence of glycerol. The behaviors of T2N, T2E, and T2W reveal the formation of free volume in the BF matrix associated with the presence of plasticizers (water and glycerol). The T2 behavior in BFs is consistent with the behavior of spin-lattice relaxation (T1). Our result is the first attempt to characterize using low field 1H NMR technology how all protons in a film matrix behave and to develop correlations between proton mobility and free volume in protein-based BFs plasticized with water and glycerol.