From mango by-product to food packaging: Pectin-phenolic antioxidant films from mango peels.

The objective of the study was to prepare active films based on pectin and polyphenol-rich extracts from Tommy Atkins mango peels. Aqueous and methanolic extracts showed a variety of phenolic compounds that were identified by UPLC-MS analysis, and a high content of total phenolics that were quantified by the Folin-Ciocalteau method. The methanolic extract showed better results in antioxidant tests and was more effective in inhibiting the growth of Gram-positive and Gram-negative bacteria. The pectin extracted from mango peels showed good thermal stability and a degree of methoxylation of 58.3% by 1H NMR. The films containing the phenolic extracts showed lower water vapor permeability when compared to the control film (without any phenolic extracts). The incorporation of the extracts led to an increase in elongation (ε) and a decrease in tensile strength (σ) and modulus of elasticity (Y). The films with aqueous or methanolic extracts showed higher antioxidant activity in terms of inhibition of the DPPH radical. Therefore, the films developed in this work are presented as a promising alternative for food packaging and/or coating applications.

Antioxidant films and coatings based on starch and phenolics from Spondias purpurea L.

The objective of this study was to prepare, for the first time, active films and coatings from fruit starch (SPFS) and phenolic stem bark extract (SBPE) from Spondias purpurea L. Starch film formulations were prepared with different SBPE contents (5-20 wt% on starch), then cast and dried into films. SBPE showed higher antioxidant activity and antimicrobial activity against both Gram-negative and Gram-positive bacteria. Chemical, morphological, thermal, optical, mechanical, and barrier properties were studied for SPFS-SBPE films. In general, the phenolic extract caused significant changes in starch films (especially when in excess), such as gradual reduction of elastic modulus and tensile strength, increased elongation, opacity, and thermal properties (e.g. glass transition and melting enthalpy). On the other hand, SBPE provided the films with active properties (antioxidant and UV-absorbing). Coatings were applied to minimally processed mangoes (MPM), which were stored for 10 days at 12 °C. SBPE-containing coatings provided better protective action, reducing the total color difference (∆E⁎) and delaying the browning index (BI) during storage as well as reducing fungus attack. The active SPFS-SBPE films showed great potential as environmentally friendly active films and coatings.

ECO-FRIENDLY hybrid hydrogels for detection of phenolic RESIDUES in water using SERS.

Herein is presented a simple and sensible method to determine organic pollutants in water, based on the utilization of silver nanoparticles (AgNPs) loaded in Polyacrylamide (PAAm)/starch hybrid hydrogels combined with surface-enhanced Raman scattering (SERS) spectroscopy. The materials were characterized by swelling degree studies, UV-Visible spectroscopy (UV-Vis), X-ray diffraction (XRD) and scanning electron microscopy (SEM). PAAm/starch hydrogels showed variable swelling capacity, according to the synthetic molar composition. The most promising results were attributed to lower concentrations of starch and crosslink agent (N,N'-methylenebisacrylamide - MBA). Spectroscopic analysis confirmed the formation of AgNPs, by noticing the peak at around 420 nm, due to its surface plasmon resonance (SPR) effect. The results showed that AgNPs were stabilized by hydrogels networks. The average size of the AgNPs was smaller than 100 nm and the size and quantity of nanoparticles were influenced by the molar composition of the hydrogel matrix. The SERS substrate based on the AgNPs-PAAm/starch exhibited reproducibility, stability, and limit of detection (LOD) of phenol in water of 1 × 10-8 M. The average mass of AgNPs-PAAm/starch hydrogels used for each detection analysis was around 10 mg. The spectra with enhanced intensities were possible due to a large number of hot spots generated on the AgNPs-PAAm/starch hydrogel substrate, which leads to potential use for organic pollutant detection. In addition, there is also the possibility of reusing the hydrogel matrix substrate in other analyzes.

Bacterial cellulose nanocrystals produced under different hydrolysis conditions: Properties and morphological features.

Bacterial cellulose (BC) is a polymer with interesting physical properties owing to the regular and uniform structure of its nanofibers, which are formed by amorphous (disordered) and crystalline (ordered) regions. Through hydrolysis with strong acids, it is possible to transform BC into a stable suspension of cellulose nanocrystals, adding new functionality to the material. The aim of this work was to evaluate the effects of inorganic acids on the production of BC nanocrystals (BCNCs). Acid hydrolysis was performed using different H2SO4 concentrations and reaction times, and combined hydrolysis with H2SO4 and HCl was also investigated. The obtained cellulose nanostructures were needle-like with lengths ranging between 622 and 1322nm, and diameters ranging between 33.7 and 44.3nm. The nanocrystals had a crystallinity index higher than native BC, and all BCNC suspensions exhibited zeta potential moduli greater than 30mV, indicating good colloidal stability. The mixture of acids resulted in improved thermal stability without decreased crystallinity.

Extraction and characterization of nanocellulose structures from raw cotton linter.

This study aimed to characterize nanocellulose extracted from cotton (Gossypium hirsutum) linters. The nanocellulose was subjected to electronic microscopy, thermal analysis, X-ray diffractometry, light scattering, and contact angle. The properties of the nanocellulose are considerably different from the linter. The acidic hydrolyses applied to extract the nanocrystals increased the crystallinity index and the hydrophilicity and decreased the thermal stability. On average, the nanocrystals were 177 nm long and 12 nm wide, with an aspect ratio of 19 when measured by microscopy. The light scattering results were coherent with the crystal dimensions. Cotton linter is a potential source of nanocellulose crystals, particularly to be used in the production of hydrophilic nanocomposites. Extraction of nanocellulose from raw cotton linter does not require pulping.