Use of New Glycerol-Based Dendrimers for Essential Oils Encapsulation: Optimization of Stirring Time and Rate Using a Plackett-Burman Design and a Surface Response Methodology

Essential oils are used in an increasing number of applications including biopesticides. Their volatility minimizes the risk of residue but can also be a constraint if the release is rapid and uncontrolled. Solutions allowing the encapsulation of essential oils are therefore strongly researched. In this study, essential oils encapsulation was carried out within dendrimers to control their volatility. Indeed, a spontaneous complexation occurs in a solution of dendrimers with essential oils which maintains it longer. Six parameters (temperature, stirring rate, relative concentration, solvent volume, stirring time, and pH) of this reaction has been optimized by two steps: first a screening of the parameters that influence the encapsulation with a Plackett-Burmann design the most followed by an optimization of those ones by a surface response methodology. In this study, two essential oils with herbicide properties were used: the essential oils of Cinnamomum zeylanicum Blume and Cymbopogon winterianus Jowitt; and four biosourced dendrimers: glycerodendrimers derived from polypropylenimine and polyamidoamine, a glyceroclikdendrimer, and a glyceroladendrimer. Meta-analysis of all Plackett-Burman assays determined that rate and stirring time were effective on the retention rate thereby these parameters were used for the surface response methodology part. Each combination gives a different optimum depending on the structure of these molecules.

A specific oligosaccharide-binding site in the alternansucrase catalytic domain mediates alternan elongation

Microbial α-glucans produced by GH70 (glycoside hydrolase family 70) glucansucrases are gaining importance because of the mild conditions for their synthesis from sucrose, their biodegradability, and their current and anticipated applications that largely depend on their molar mass. Focusing on the alternansucrase (ASR) from Leuconostoc citreum NRRL B-1355, a well-known glucansucrase catalyzing the synthesis of both high- and low-molar-mass alternans, we searched for structural traits in ASR that could be involved in the control of alternan elongation. The resolution of five crystal structures of a truncated ASR version (ASRΔ2) in complex with different gluco-oligosaccharides pinpointed key residues in binding sites located in the A and V domains of ASR. Biochemical characterization of three single mutants and three double mutants targeting the sugar-binding pockets identified in domain V revealed an involvement of this domain in alternan binding and elongation. More strikingly, we found an oligosaccharide-binding site at the surface of domain A, distant from the catalytic site and not previously identified in other glucansucrases. We named this site surface-binding site (SBS) A1. Among the residues lining the SBS-A1 site, two (Gln700 and Tyr717) promoted alternan elongation. Their substitution to alanine decreased high-molar-mass alternan yield by a third, without significantly impacting enzyme stability or specificity. We propose that the SBS-A1 site is unique to alternansucrase and appears to be designed to bind alternating structures, acting as a mediator between the catalytic site and the sugar-binding pockets of domain V and contributing to a processive elongation of alternan chains.

Biosourced Disposable Trays Made of Brewer's Spent Grain and Potato Starch

Single-use plastic items made of non-biodegradable and fossil-based materials have been identified as a major environmental problem in modern society. Food packaging materials represent an important fraction of these, and replacement with biosourced, sustainable and low-cost alternatives, is a key priority. In the present work, and for the first time, trays suitable for some food packaging applications were produced by the hot-pressing of brewer’s spent grains (BSG, a low added-value byproduct of the beer industry), bound with potato starch. Expanded polystyrene (EPS) trays were used as reference, since this material has been widely used in food packaging trays. The results demonstrated that all trays produced with varying proportions of BSG and potato starch have appropriate flexural strength, with values ranging between 1.51 ± 0.32 MPa, for 80% BSG content, and 2.62 ± 0.46 MPa, for 40% BSG content, which is higher than for EPS, 0.64 ± 0.50 MPa. Regardless of BSG content, flexural strength and modulus decreased significantly after contact with water, due to starch plasticization, attaining values below EPS. Trays produced with 60% BSG, and also with the addition of chitosan and glyoxal presented the highest flexural strength, both before and after contact with water, 3.75 ± 0.52 MPa and 0.44 ± 0.11 MPa, respectively. The latter is reasonably close to the reference value obtained for EPS.

New biosourced AA and AB monomers from 1,4:3,6-dianhydrohexitols, Isosorbide, Isomannide, and Isoidide

In the present work, we propose the synthesis of a new family of sugar derived 1,4:3,6-dianhydrohexitol based AA/AB-type monomers. Unprecedented diacids based on Isomannide and Isoidide were elaborated with high yields and showed interestingly high melting point ranges (240–375 °C). Optimization of reaction conditions (temperature, time of reaction, and reactant ratios) has been investigated to synthesize the key intermediate of a set of AB monomers with acid, ester, and acid chloride functionalities. Isosorbide based ether benzoic acid AB monomer was polymerized and characterized by NMR and DSC techniques. The results show a semicrystalline behavior of the obtained polymer thanks to the controlled stereoregular arrangement of the AB starting monomer.