Chitosan/poly-γ-glutamic acid crosslinked hydrogels: Characterization and application as bio-glues.

Ecofriendly hydrogels were prepared using chitosan (CH, 285 kDa) and two fractions of low molecular weight microbial poly-γ-glutamic acid (γ-PGA) (R1 and R2 of 59 kDa and 20 kDa, respectively). The hydrogels were synthesized through sustainable physical blending, employing three CH/γ-PGA mass ratios (1/9, 2/8, and 3/7), resulting in the formation of physically crosslinked materials. The six resulting CH/R1 and CH/R2 hydrogels were physico-chemically characterized and the ones with the highest yields (CH/R1 and CH/R2 ratio of 3/7), analyzed for rheological and morphological properties, showed to act as bio-glues on wood and aluminum compared to commercial vinyl- (V1) and acetovinyl (V2) glues. Lap shear analyses of CH/R1 and CH/R2 blends exhibited adhesive strength on wood, as well as adhesive/cohesive failure like that of V1 and V2. Conversely, CH/R2 had higher adhesive strength and adhesive/cohesive failure on aluminum, while CH/R1 showed an adhesion strength with adhesive failure on the metal similar to that of V1 and V2. Scanning electron microscopy revealed the formation of strong physical bonds between the hydrogels and both substrates. Beyond their use as bio-adhesives, the unique properties of the resulting crosslinked materials make them potentially suitable for various applications in paint, coatings, heritage preservation, and medical sector.

The fate of post-use biodegradable PBAT-based mulch films buried in agricultural soil.

The fate of black biodegradable mulch film (MF) based on starch and poly(butylene-adipate-co-terephthalate) (PBAT) in agricultural soil is investigated herein. Pristine (BIO-0) and UV-aged film samples (BIO-A192) were buried for 16 months at an experimental field in southern Italy. Visual, physical, chemical, morphological, and mechanical analyses were carried out before and after samples burial. Film residues in the form of macro- and microplastics in soil were analyzed at the end of the trial. Progressive deterioration of both pristine and UV-aged samples, with surface loss and alterations in mechanical properties, occurred from 42 days of burial. After 478 days, the apparent surface of BIO-0 and BIO-A192 films decreased by 57 % and 66 %, respectively. Burial determined a rapid depletion of starch from the polymeric blend, especially for the BIO-A192, while the degradation of the polyester phase was slower. Upon burial, an enrichment of aromatic moieties of PBAT in the film residues was observed, as well as microplastics release to soil. The analysis of the MF degradation products extracted from soil (0.006-0.008 % by mass in the soil samples) revealed the predominant presence of adipate moieties. After 478 days of burial, about 23 % and 17 % of the initial amount of BIO-0 and BIO-A192, respectively, were extracted from the soil. This comprehensive study underscores the complexity of biodegradation phenomena that involve the new generation of mulch films in the field. The different biodegradability of the polymeric components, the climate, and the soil conditions that did not strictly meet the parameters required for the standard test method devised for MFs, have significantly influenced their degradation rate. This finding further emphasizes the importance of implementing field experiments to accurately assess the real effects of biodegradable MFs on soil health and overall agroecosystem sustainability.

Physicochemical Characterization of Chitosan/Poly-γ-Glutamic Acid Glass-like Materials.

This paper sets up a new route for producing non-covalently crosslinked bio-composites by blending poly-γ-glutamic acid (γ-PGA) of microbial origin and chitosan (CH) through poly-electrolyte complexation under specific experimental conditions. CH and two different molecular weight γ-PGA fractions have been blended at different mass ratios (1/9, 2/8 and 3/7) under acidic pH. The developed materials seemed to behave like moldable hydrogels with a soft rubbery consistency. However, after dehydration, they became exceedingly hard, glass-like materials completely insoluble in water and organic solvents. The native biopolymers and their blends underwent comprehensive structural, physicochemical, and thermal analyses. The study confirmed strong physical interactions between polysaccharide and polyamide chains, facilitated by electrostatic attraction and hydrogen bonding. The materials exhibited both crystalline and amorphous structures and demonstrated good thermal stability and degradability. Described as thermoplastic and saloplastic, these bio-composites offer vast opportunities in the realm of polyelectrolyte complexes (PECs). This unique combination of properties allowed the bio-composites to function as glass-like materials, making them highly versatile for potential applications in various fields. They hold potential for use in regenerative medicine, biomedical devices, food packaging, and 3D printing. Their environmentally friendly properties make them attractive candidates for sustainable material development in various industries.

Host-Guest Complexes HP-ß-CD/Citrus Antioxidants: Exploratory Evaluations of Enhanced Properties in Biodegradable Film Packaging.

The aim of this work was to exploit the antioxidant potential of molecules recovered during the pectin purification process of citrus lemon waste and to encapsulate them in stable pectin films, with a view to a green and circular economy process. Antioxidant molecules were recovered during the pectin purification process, further recovering matter from the waste. Seven molecules were identified and quantified, and the antioxidant power of the mixture and its stability over time was evaluated. To improve the stability of the bioactive fraction, this was complexed with 2-hydroxypropyl-ß-cyclodextrin (HP-ß-CD); indeed, this procedure increased their thermal stability from 120 °C up to 250 °C, as verified by thermogravimetry. Furthermore, the most promising complexes were studied under autoclave-like conditions (120 °C, 28 min) to simulate thermal sterilization. The antioxidants and HP-ß-CD were combined in a pectin film, showing increased stability over time (up to three times) compared to uncomplexed antioxidants. This process represents a first step towards the development of applicable devices for the delivery of antioxidant molecules.

Mechanical, Barrier and Thermal Properties of Amylose-Argan Proteins-Based Bioplastics in the Presence of Transglutaminase.

The bioeconomy aims to discover new sources for producing energy and materials and to valorize byproducts that otherwise would get wasted. In this work, we investigate the possibility of producing novel bioplastics, made up of argan seed proteins (APs), extracted from argan oilcake, and amylose (AM), obtained from barley plants through an RNA interference technique. Argan, Argania spinosa, is a plant widespread in arid regions of Northern Africa, where it plays a fundamental socio-ecological role. Argan seeds are used to obtain a biologically active and edible oil, producing a byproduct, the oilcake, that is rich in proteins, fibers, and fats, and is generally used as animal food. Recently, argan oilcakes have been attracting attention as a waste to be recovered to obtain high-added-value products. Here, APs were chosen to test the performance of blended bioplastics with AM, because they have the potential to improve the properties of the final product. High-AM-starches present attractive features for use as bioplastics, including a higher gel-forming capacity, a higher thermal stability, and reduced swelling compared to normal starch. It has already been demonstrated that pure AM-based films provide more suitable properties than normal starch-based films. Here, we report on the performance of these novel blended bioplastics in terms of their mechanical, barrier, and thermal properties; and the effect of the enzyme microbial transglutaminase (mTGase) as a reticulating agent for AP's components was also studied. These results contribute to the development of novel sustainable bioplastics with improved properties and confirm the possibility of valorizing the byproduct, APs, using them as a new raw material.

Upgrading cardoon biomass into Polyhydroxybutyrate based blends: A holistic approach for the synthesis of biopolymers and additives.

Cardoon, Cynara cardunculus L. represents a biorefinery crop with a great potential in the bioplastic field. This work investigates the valorization of different cardoon components into high added value products, finally recombined into novel upgraded bioplastics. Bioprocesses for Polyhydroxybutyrate (PHB) and medium-chain-length Polyhydroxyalkanoates (mcl-PHA) production were set up starting from root inulin and seed oil respectively, highlighting the effect of process conditions on polymer properties. The ternary blend, in which the PHB polymer matrix was added with mcl-PHA and epoxidized cardoon oil, evidenced a synergic effect of both additives in modulating PHB structural and thermal properties, promoted by the physical interaction occurring among the components. This proof-of concept frames the paper in the holistic approach of circular economy applied to bioplastic production.

Exploiting Potential Biotechnological Applications of Poly-γ-glutamic Acid Low Molecular Weight Fractions Obtained by Membrane-Based Ultra-Filtration.

Since the potentialities of applications of low molecular weight poly-γ-glutamic acid (γ-PGA) chains have been so far only partially explored, the separation of diverse molecular families of them, as well as their characterization for potential bioactivity and ability to form films, were investigated. Two different approaches based on organic solvent precipitation or on ultra- and nano-filtration membrane-based purification of inexpensive commercial material were employed to obtain size-specific γ-PGA fractions, further characterized by size exclusion chromatography equipped with a triple detector array and by ultra-high-performance liquid chromatography to assess their average molecular weight and their concentration. The γ-PGA low molecular weight fractions, purified by ultra-filtration, have been shown both to counteract the desiccation and the oxidative stress of keratinocyte monolayers. In addition, they were exploited to prepare novel hydrocolloid films by both solvent casting and thermal compression, in the presence of different concentrations of glycerol used as plasticizer. These biomaterials were characterized for their hydrophilicity, thermal and mechanical properties. The hot compression led to the attainment of less resistant but more extensible films. However, in all cases, an increase in elongation at break as a function of the glycerol content was observed. Besides, the thermal analyses of hot compressed materials demonstrated that thermal stability was increased with higher γ-PGA distribution po-lymer fractions. The obtained biomaterials might be potentially useful for applications in cosmetics and as vehicle of active molecules in the pharmaceutical field.

Polysaccharide Based Polymers Produced by Scabby Cankered Cactus Pear (Opuntia ficus-indica L.) Infected by Neofusicoccum batangarum: Composition, Structure, and Chemico-Physical Properties.

Neofusiccocum batangarum is the causal agent of scabby canker of cactus pear (Opuntia ficus-indica L.). The symptoms of this disease are characterized by crusty, perennial cankers, with a leathery, brown halo. Characteristically, a viscous polysaccharide exudate, caking on contact with air, leaks from cankers and forms strips or cerebriform masses on the surface of cactus pear cladodes. When this polysaccharide mass was partial purified, surprisingly, generated a gel. The TLC analysis and the HPLC profile of methyl 2-(polyhydroxyalkyl)-3-(o-tolylthiocarbomoyl)-thiazolidine-4R-carboxylates obtained from the mixture of monosaccharides produced by acid hydrolysis of the three EPSs examined in this research work [the polysaccharide component of the exudate (EPSC) and the EPSs extracted from asymptomatic (EPSH) and symptomatic (EPSD) cladodes] showed the presence of d-galactose, l-rhamnose, and d-glucose in a 1:1:0.5 ratio in EPSC while d-galactose, l-rhamnose, d-glucose, and d-xylose at the same ratio were observed in EPSH and EPSD. The presence of uronic acid residues in EPSC was also showed by solid state NMR and IR investigation. Furthermore, this manuscript reports the chemical-physical characterization of the gel produced by the infected cactus pear.

Ulomoides dermestoides Coleopteran action on Thermoplastic Starch/Poly(lactic acid) films biodegradation: a novel, challenging and sustainable approach for a fast mineralization process.

Ulomoides dermestoides (UL) are macroinvertebrates insects belonging to Tenebrionidae Coleopteran family. They were used to hasten, in five days, the biodegradation-mineralization of thermoplastic starch (TPS)-poly(lactic acid) (PLA) films, otherwise biodegradable under composting conditions. After the contact of TPS-PLA film with UL for five days, TPS was metabolized and PLA was hydrolysed, as evidenced by decreasing of hydroxyl and carbonyl group peaks intensity by FTIR spectra, increasing of 13% of PLA crystallinity by DSC thermograms, reduction of PLA and TPS thermal stability by TGA analysis; faecal residues evidenced two glass transition temperature Tg, at 33 °C and 57 °C, associated with depolymerized TPS and PLA, respectively. SEM micrographs highlighted consumption of TPS-PLA surface, while GPC analysis showed a decrease in PLA concentration by 20% during contact by UL. Mineralization tests evidenced UL boosted effect on TPS biodigestion-biodegradation (80%) and PLA biodisintegration (50%), envisaging a challenging perspective for end-life management of bioplastics in environmental conditions.

Nutritional and Chemical-Physical Characterization of Fresh Pasta Gnocchi Prepared with Sea Water as New Active Ingredient.

This study shows the chemical-physical and nutritional results obtained using food-grade sea water for the preparation of fresh pasta Gnocchi with respect to those prepared with tap water. Gnocchi obtained by mixing the flour with seawater (GSW) were compared with traditional Gnocchi made with tap water (GTW). The contents of sodium chloride, macro and micro elements, volatile molecules profile, thermal properties, and morphological analysis were investigated in both Gnocchi types. The analysis of chlorides showed that the samples prepared with sea water had a significantly lower NaCl content after cooking in comparison with those prepared with tap water. These results were also confirmed by the inductively coupled plasma (ICP) analysis for sodium content. The profiles of the volatile molecules acquired by gas chromatography-mass spectrometry (GC-MS) evidenced significant differences between the groups of aromatic molecules of the two typologies of samples. Morphological analysis evidenced that both raw and cooked GSW Gnocchi were structurally tightened whereas GTW Gnocchi showed a labile and weak macromolecular network. In addition, GSW Gnocchi was more thermally stable than GTW Gnocchi, as evidenced by thermogravimetric analysis (TGA).

Citrus Pomace Biomass as a Source of Pectin and Lignocellulose Fibers: From Waste to Upgraded Biocomposites for Mulching Applications.

Citrus pomace derived from the industrial processing of juice and essential oils mostly consists of pectin, cellulose, hemicellulose, and simple sugars. In this work, citrus pomace waste from an agricultural company in South Italy was used as source of pectin. The extraction conditions of the polysaccharide were optimized using a suitable combination of time and a concentration of a mild organic solvent, such as acetic acid; thus recovering high Mw pectin and bioactive molecules (flavonoids and polyphenols). The pectin was structurally (GPC, FTIR), morphologically (SEM), thermally (TGA/DTG), and mechanically characterized, while bioactive molecules were separated and the total phenolic content (TPC) and total flavonoids content (TFC) were evaluated. With the aim to develop novel biocomposite-based materials, the pectin extracted from citrus waste was reinforced with different amounts of lignocellulose fractions also recovered from citrus waste after polysaccharide extraction, according to a "zero waste" circular economy approach. The prepared biocomposites were morphologically and mechanically characterized to be used as biodegradable mulching systems for crop protection. Thus, the citrus waste biomass was recovered, fractionated into its main raw materials, and these were recombined to develop novel upgraded biocomposites for mulching applications, by means of a cost-effective and eco-sustainable approach.