Impact of plasma-activated water on the supramolecular structure and functionality of small and large starch granules.

Hydrothermal (HMT) and water agitation (WA) treatments using plasma-activated water (PAW) were employed as sustainable methods to modify the molecular and functional performance of small (rice) and large (potato) starch granules. HMT-PAW and WA-PAW treatments resulted in etched and damaged granular surfaces that rearranged the long and short-range crystallinity of the modified starches. Both treatments seemed to predominantly occur in the amorphous region of the rice starch and the crystalline regions of the potato starch, changing the crystallinity values from 22.9 and 14.8 % to 31.8 and 10.4 %, respectively. Thus, the level of the arrangement of chains reached after PAW treatment decreased the ability of rice starch granules to swell (16 to 9 %) and leach out starch molecules from the granules (4.5 to 1.3 %), decreasing the viscosity and pasting profiles as indicated by n and k values. Opposite behavior was observed in the modified potato starches since starch components leached out to a higher extent (1.7 to 5.4 %). The results showed that HMT and WA treatments using PAW are feasible eco-friendly methods for modifying starch granules without chemical reagents. These modified starches could be suitable as functional ingredients or biopolymeric matrices for the food and packaging industry.

Biobased sustainable materials made from starch and plasma/ultrasound modified Agave fibers: Structural and water barrier performance.

This study aims to investigate the effect of green modification methods (ultrasound and plasma treatment) on a by-product of the tequila industry (Agave fibers), which can be useful as raw material to elaborate biodegradable and hydrophobic starch films. FTIR analysis indicated a decrease of hydrophilic lignocellulosic components, since the cavitation and etching effect of ultrasound/plasma treatment reduced the large number of hydroxyl groups of the fibers. The inclusion of ultrasound/plasma modified fibers in the starch matrix limited the starch-glycerol interactions, reducing the free volume of the starch and the binding sites for water. Therefore, the solubility (%S), swelling (%W) and water vapor permeance (WVPe) of the films decreased from 27 to 16%, 57 to 50% and 0.37 to 0.21 g/day m2Pa, respectively. Furthermore, the water contact angle (WCA) and relative crystallinity values increased. The results indicated that the treatments are suitable green technologies to obtain hydrophobic fillers useful to develop sustainable materials.

Films made from plasma-modified corn starch: Chemical, mechanical and barrier properties.

In this study, the chemical, mechanical and barrier properties of films made from plasma-modified corn starch (MSF) were evaluated as a function of the amylose content (30, 50 and 70 %). SEM analysis revealed the presence of remnant starch granules (RSG) in all films, which promoted the ordering of helices as suggested by the FTIR results. Moreover, XPS analysis was used to identify the oxidation mechanism in all MSF as the atomic proportion of hydroxyl, carbonyl and carboxyl groups changed. Also, the increase of C-C proportions suggested crosslinking in MSF70. TGA analysis indicated low interaction between starch and the plasticizer as the tensile strength and elongation at break diminished in MSF50 and MSF70 due to the low plasticizing effect of glycerol, the oxidation phenomena and the depolymerization of starch chains. However, the crosslinking of MSF70 showed characteristics of rigid films with good hydrophobic performance.

HMDSO plasma treatment as alternative to modify structural properties of granular starch.

In the present study, the effect of plasma treatment on the structural properties of three granular corn starches (normal, Hylon V and Hylon VII) was investigated. Thermal (TGA/DSC), structural (XRD/FTIR) and chemical (XPS) properties were evaluated. Plasma treatment resulted in partial evaporation of water molecules changing the organization level of the double helices in the crystalline lamellae. Moreover, XRD results suggested a decrease of the long-range crystallinity and suggested changes in amylose chains after treatments. The crosslinking of modified amylose chains measured by XPS analysis resulted in variations in the gelatinization parameters as well as in its heterogeneous crystalline structure. The results indicate that the type and extent of changes in the structure of plasma-treated corn starch depends on the distribution of the water molecules inside the crystalline regions (helical water) and on the amylose content. In addition, the obtained results indicated that plasma treatment is a suitable method to modify starch without any incorporation of new elements from hexamethyldisiloxane (HMDSO), which only promotes stronger interactions between the starch main components.

Influence of gelatinization process and HMDSO plasma treatment on the chemical changes and water vapor permeability of corn starch films.

In this study, surface, chemical, physicochemical and barrier properties of films treated with hexamethyldisiloxane (HMDSO) cold plasma were investigated. Normal and high amylose starches were gelatinized at different level to obtain films with different amount of free amylopectin. The obtained films were subjected to HMDSO plasma treatment. XPS analysis indicated chemical changes including substitution and crosslinking of the starch molecule, as reflected by the CSi bond increasing and the C-OH bonds reduction on treated films. These changes modified the thermal transitions (Tm and ΔH). The highest amount of CSi bonds was more noticeable in the TF50 film, suggesting a better interaction between active species of plasma and the free amylopectin released into the continuous phase of the film. Moreover, active species of plasma increased the crystallinity in all films. These results suggested that a higher helical packaging, crosslinking and hydrophobic blocking groups (CSi) of starch molecules resulted in films with improved barrier performance against water molecules.

Hexamethyldisiloxane cold plasma treatment and amylose content determine the structural, barrier and mechanical properties of starch-based films.

In this study, the effect of amylose content and cold plasma treatment on starch films properties was investigated. Films from normal (30%) and high amylose (50 and 70%) starches were subjected to hexamethyldisiloxane (HMDSO) cold plasma treatment. Morphological, structural, mechanical and barrier properties of the films were evaluated. The amount of remnant starch granules (RSG) in the films depended on the amylose content and on the gelatinization extent of the starch. This behavior was corroborated on the films from starch with 50% amylose, where the loss of RSG resulted in poor barrier properties and high hydrophilicity. Moreover, HMDSO cold plasma treatment incorporated methyl groups improving the hydrophobic properties and favored the helix ordering of the starch components resulting in a limited water-film interaction. Furthermore, the simultaneous effect of HMDSO coating and the ordering of the structures reinforced the surface of the films, improving the mechanical properties.