Flexible starch-polyurethane films: Physiochemical characteristics and hydrophobicity

Starch-polyurethane (PU) composite films with improved mechanical and hydrophobic properties were developed in this work. A simple and effective microwave-aided starch gelatinisation instrument was used to prepare glycerol plasticized high amylose starch (HAGS) material. Polyethylene glycol-isocyanate (PEG-iso) linker was prepared by reacting PEG 1000 with hexamethylene diisocyanate (HMDI). PEG-iso linker was then grafted into HAGS forming three dimensional urethane networks (PEG-PU). HAGS-PEG-PU composite blends were prepared and dried at ambient temperature to obtain HAGS-PEG-PU films. The mechanical properties and hydrophobicity (as contact angle, CA) of the HAGS-PEG-PU films were measured and analysed. Fourier transform infrared spectroscopy showed good grafting of PEG-iso into starch structure. Increase of PEG-iso concentration up to 20% (w/w) improved the molecular mixing and interpenetration between the starch and PEG-PU. The HAGS-PEG-PU films had improved hydrophobicity as indicated by CA values ranging from 51 to 110°and very high flexibility as evidenced from elongation at break (ε_B) values from 17 to 1000%. The HAGS-PEG-PU film formulation containing 20% (w/w) PEG-iso provided the best flexibility (ε_B>1000%) and hydrophobicity (CA>110°).

Halochromic smart packaging film based on montmorillonite/polyvinyl alcohol-high amylose starch nanocomposite for monitoring chicken meat freshness

Polyvinyl alcohol (PVA) was blended with high amylose starch (HAS) at a ratio of 3:1, and reinforced with montmorillonite (MMT K10) at different concentrations (1, 2, 5, and 7 % w/w of polymers) and anthocyanins (ANT) to develop an active and smart packaging film. MMT addition enhanced the film's mechanical, barrier, thermal, and water resistance properties. Incorporating ANT extracted from roselle calyx into the optimal nanocomposite film (MMT/PVA-HAS II) increased the films' antioxidant, pH-response, and antibacterial properties. FTIR, XRD, and SEM confirmed the intermolecular interactions and even distribution of ANT and MMT in the film matrix. Release rate of ANT was dependent on type of simulant, with higher rate in aqueous solutions compared to alcoholic/fatty food simulants, and cytotoxicity evaluation proved safety of films for food packaging applications. Storage experiments confirmed the potential applicability of the novel halochromic smart film as a promising candidate for monitoring chicken spoilage under abusive storage conditions.

Effect of natural deep eutectic solvents on thermal stability, syneresis, and viscoelastic properties of high amylose starch

This work aimed to use natural deep eutectic solvents to modify the thermal, textural, freeze-thaw, and rheological properties of high amylose rice starch. Three different natural deep eutectic solvents (NADES) composed of sugar and organic acids were applied to modify the properties of starch dispersion. In presence of NADES, the onset temperature of starch was decreased, in comparison with starch in aqueous and glycerol medium. During thermal decomposition, starch with the aqueous and glycerol systems showed two-step weight losses whereas with NADES starch showed single-stage weight losses or decomposition. Moreover, negligible syneresis was observed for starch-NADES dispersion after 3rd cycle of the freeze-thaw process. The flow behavior of starch-NADES dispersion follows Herschel-Bulkley models as R² (0.996 ≤ R² ≤ 0.999) are higher than the Mizrahi-Berk model. The flow behavior index (n) of starch-NADES dispersion was closer to 1, indicated a nearly Newtonian fluid. The loss modulus (G″) value of starch-NADES dispersions was markedly higher than the corresponding storage modulus (G') value and thus materials behaved like viscoelastic liquid. The present study manifested a green way to modify the properties of the high amylose starch to improve the processing stability.

Effect of high amylose starch on the incorporation of thymol into electrospun pullulan nanofibers

High amylose starch (HAMS) was employed as an effective carrier to incorporate thymol within pullulan nanofibers. Aqueous solutions with HAMS concentrations of 0 % - 5 % were investigated to study their effect on the incorporation of thymol during electrospinning. As a result, the loading capacity was significantly improved by the addition of HAMS, increasing from 2.38 % to 6.15 %. Thymol-starch mixture with an irregular structure was embedded within pullulan nanofiber according to SEM and TEM results. The HAMS-1, HAMS-3 and HAMS-5 were endowed with good anti-microbial inhibition against Escherichia coli and Bacillus cereus. Additionally, HAMS-5 exhibited sustained release of thymol, while the addition of HAMS improved the mechanical properties of HAMS-1. Further investigation into the interaction between HAMS, pullulan, and thymol in the nanofibers was conducted. HAMS proved effective in enhancing the bioavailability of thymol and provides a promising material for developing edible, sustainable polysaccharide antimicrobial nanofibrous films for the food industry.

Physical modification of high amylose starch using electron beam irradiation and heat moisture treatment: The effect on multi-scale structure and in vitro digestibility

This study explores a new strategy for manipulating the digestibility of high-amylose maize starch (HAMS) through combinative modifications, namely depolymerization via electron beam irradiation (EBI) followed by reorganizing glucan chains via heat moisture treatment (HMT). The results show that semi-crystalline structure, morphological features and thermal properties of HAMS remained similar. However, EBI increased branching degree of the starch at high irradiation dosage (20 kGy), resulting in more readily leached amylose during heating. HMT increased the relative crystallinity (3.9-5.4% increase) and V-type fraction (0.6-1.9% increase), without significant changes (p > 0.05) in gelatinization onset temperature, peak temperature and enthalpy. Under simulated gastrointestinal conditions, the combination of EBI and HMT either had no effect or negative effect on starch enzymatic resistance, depending on the irradiation dosage. These results suggest that the depolymerization by EBI predominantly affects the changes in enzyme resistance, rather than the growth and perfection of crystallites induced by HMT.

High-pressure pasting performance and multilevel structures of short-term microwave-treated high-amylose maize starch

Microwave treatment is an environmentally friendly method for modification of high-amylose maize starch (HAMS). Here, the effects of short-time (≤120 s) microwave treatment on the structure and pasting of two types of HAMSs, Gelose 50 (HAMSI) and Gelose 80 (HAMSII), with apparent amylose content (AAC) of 45 % and 58 %, respectively, was studied using a multiscale approach including X-ray scattering, surface structures, particle size distribution, molecular size distributions and high temperature/pressure Rapid Visco Analysis (RVA)-4800 pasting. As compared to starch with no amylose (waxy maize starch, WMS) and 25 % amylose content (normal maize starch, NMS), HAMSI underwent similar structural and pasting changes as WMS and NMS upon microwave treatment, and it might primarily be attributed to the amylopectin fraction that was affected by cleavage of the connector chains between double helices and backbone chains, which decreased the crystallinity and thickness of the crystalline lamellae. However, the multi-scale structure of HAMSII was almost unaffected by this treatment. The pasting properties of fully gelatinized HAMSI starch showed a decrease in RVA-4800 peak and final viscosities after microwave treatment. In contrast, for HAMSII starch, the microwave treatment led to an increase in these viscosities. The combined results highlight the influence of varying AAC on the effects of microwave-mediated modification, leading to diverse alterations in the structure and functionality of starches.