Deep eutectic solvents for polysaccharides processing. A review

Effect of Choline-Based Deep Eutectic Solvent Pretreatment on the Structure of Cellulose and Lignin in Bagasse

Deep eutectic solvents (DESs) is a newly developed green solvent with low cost, easy preparation and regeneration. Because of its excellent solubility and swelling effect in lignocellulose, it has received widespread attention and recognition. In this study, choline-based deep eutectic solvents (DESs)—choline chloride-urea (CC-U), choline chloride-ethylene glycol (CC-EG), choline chloride-glycerol (CC-G), choline chloride-lactic acid (CC-LA), and choline chloride-oxalic acid (CC-OA)—were used to extract and separate bagasse. The effects of hydrogen bond donors on lignin separation and the fiber and lignin structure were investigated. All five DESs could dissolve lignin from bagasse; acidic DESs exhibited higher solubility than basic DESs. CC-OA effectively separated lignin and hemicellulose. CC-LA showed weaker lignin separation ability than CC-OA. CC-G, CC-EG, and CC-U were more inclined to selectively separate lignin than hemicellulose. The crystalline cellulose II structure was retained after DES pretreatment. Acidic DESs effectively improved the crystallinity of bagasse fiber; the crystallinities for CC-OA and CC-LA pretreatment were 62.26% and 61.65%, respectively. The lignin dissolved in DES was mainly syringyl lignin. The lignin dissolved in CC-U, CC-LA, and CC-OA contained a small amount of guaiacyl lignin.

Deep eutectic solvents based on urea, polyols and sugars for starch treatment

Deep eutectic solvents (DES) based on urea (U), polyols (glycerol -G, sorbitol - S) and monosugars (glucose - Glu, fructose - Fru) were obtained, thermally characterized and used for potato starch treatment: dissolution and plasticization. The polysaccharide was dissolved in U/glycerol mixtures forming transparent, non-retrograded gels. The dissolution process was confirmed by microscopic observations and DSC analysis. Plasticizing efficiency of DES in thermoplasticized starch (TPS) via compression molding was investigated using mechanical tests, DMTA, XRD, TGA and FTIR analysis. Although all studied DES were able to plasticize starch effectively, the most flexible films were with urea/glycerol mixture: the highest elongation at break exceed 200%. XRD analysis confirmed high amorphization of starch with the urea-based DES after thermocompression. Moreover, introduction of urea as DES inhibited its recrystallization in the polysaccharide matrix.

Deep Eutectic Solvents as Catalysts for Upgrading Biomass

Deep eutectic solvents (DESs) have emerged as promising green solvents, due to their versatility and properties such as high biodegradability, inexpensiveness, ease of preparation and negligible vapor pressure. Thus, DESs have been used as sustainable media and green catalysts in many chemical processes. On the other hand, lignocellulosic biomass as an abundant source of renewable carbon has received ample interest for the production of biobased chemicals. In this review, the state of the art of the catalytic use of DESs in upgrading the biomass-related substances towards biofuels and value-added chemicals is presented, and the gap in the knowledge is indicated to direct the future research.

Keratin particles generated from rapid hydrolysis of waste feathers with green DES/KOH: Efficient adsorption of fluoroquinolone antibiotic and its reuse

Fluoroquinolone antibiotics are widely used in human and veterinary medicine. However, untreated fluoroquinolone seriously threatens the ecosystem and human health. In this study, deep eutectic solvents (DESs) were applied for the hydrolysis of waste feathers, and the keratin particles (KPs) in a low-cost teabag were utilized to adsorb fluoroquinolone norfloxacin. Results showed that choline chloride/ethylene glycol DES rapidly hydrolyzed feathers within 10 min, and the undissolved particles effectively adsorbed norfloxacin. Adding KOH markedly shortened the hydrolysis time (6 min) and increased the adsorption ability of KPs. The optimum hydrolysis conditions were DES ratio of 1 g: 4.67 g, KOH of 35.68 g L^-1, and temperature of 90 °C. When KP_DES+KOH of 2 g L^-1, norfloxacin of 25 mg L^-1, and pH₀ 7 were used, 94% of norfloxacin was removed in 60 min. A low-cost teabag effectively separated the KPs from the solution after adsorption and did not decrease the adsorption ability of the KPs. The Langmuir isotherm model well described the adsorption behavior of KPs_DES+KOH (q_max = 79.36 mg g^-1, R² = 0.9972). In addition, acetone efficiently regenerated the exhausted KPs_DES+KOH. The KPs maintained >80% of its adsorption ability after seven cycles of regeneration.

The study and application of biomolecules in deep eutectic solvents

Deep eutectic solvents offer stimulating possibilities for biomolecular stabilization and manipulation, biocatalysis, bioextraction, biomass processing, and drug delivery and therapy.

Biobased poly(ester-co-glycoside) from reactive natural Brønsted acidic deep eutectic solvent analogue

{glucose : malic acid : water} [(1 : 1 : x), x ≤ 9] mixtures are Brønsted Acidic Natural Low Transition Temperature (NaLTTM) that react in solvent/catalyst free conditions to prepare all-natural poly(ester-co-glycoside) branched and crosslinked polymers.

Deep eutectic solvent-assisted phase separation in chitosan solutions for the production of 3D monoliths and films with tailored porosities

A facile and greener methodology to obtain pure chitosan-based 3D porous structures in the form of monoliths and films is proposed. It is based on a modified evaporation-induced phase separation process in a chitosan solution precursor. In this approach, a deep eutectic solvent (DES) is used as the nonsolvent system and an ecofriendly, cost effective, simple and versatile alternative for the production of highly structured chitosan materials. The porous heterogeneous structure can be fine-tuned by varying the chitosan content in the precursor solution and chitosan/DES ratio, and enabled the structured polymer to absorb large amounts of water to form hydrogels. This is a versatile and unexplored approach to design porous chitosan with tailored morphology in the absence of crosslinkers, which, based on preliminary studies on V. cholerae biofilm formation, is expected to open new avenues for various applications in biomedical, catalysis, water purification, filtration and other areas where the control of bacterial biofilm formation is critical.

Novel betaine-amino acid based natural deep eutectic solvents for enhancing the enzymatic hydrolysis of corncob

A novel natural deep eutectic solvent (NDES) with water content ranging from 65 to 93 wt%, in which betaine (Bet) acts as the cation and amino acids (AAs) as the anions, was prepared by a simple and green chemical route. [Bet][AA] NDES showed excellent xylan and lignin solubility, however, scare cellulose solubility. A mild and facile pretreatment process with [Bet][AA] NDES was carried out at 60 °C for 5 h. The enzymatic hydrolysis efficiency of cellulose and corncob was significantly improved. Detailed characterization showed that the enhancement of cellulose digestibility derived mainly from xylan and lignin removal. Xylan and lignin removal for [Bet][Lys]-W87 was 47.68 and 49.06%, while it was 42.20% and 57.01% for [Bet][Arg]-W82, respectively. FT-IR, SEM, XRD, and HSQC NMR studies confirmed the effectiveness and mechanism of [Bet][Lys]-W87 and [Bet][Arg]-W82 on biomass pretreatment.

Deep Eutectic Solvents Based Ultrasonic Extraction of Polysaccharides from Edible Brown Seaweed Sargassum horneri

In this work, a method for ultrasonic extraction of polysaccharides from Sargassum horneri using deep eutectic solvents was proposed. The studied deep eutectic solvents were composed of choline chloride, 1,2-propanediol and water. Based on the single-factor experiment results, four experimental factors were systematically evaluated, giving the optimal extraction conditions as follows: molar ratio of choline chloride to 1,2-propanediol of 1:2, water content of 30% (v/v), solid-liquid ratio of 1:30 (g/mL), and the extraction temperature of 70 °C. Fourier transform infrared spectroscopy and X-ray diffraction were utilized to investigate changes in the chemical characteristic of extracted polysaccharides. The results indicated that deep eutectic solvents had stronger protein and calcium carbonate removal ability than that of a conventional hot water extraction method. Moreover, in vitro antioxidant activity tests exhibited that the obtained polysaccharides had significant inhibition effects on DPPH and ABTS radicals. The proposed deep eutectic solvents assisted ultrasonic extraction protocol was considered to be a green, fast and effective protocol for extracting polysaccharides from Sargassum horneri.

Efficient Hydrolysis of Chitin in a Deep Eutectic Solvent Synergism for Production of Chitin Nanocrystals

A deep eutectic solvent (DES) derived from ferric chloride hexahydrate and betaine chloride (molar ratio of 1:1) was used as hydrolytic media for production of chitin nanocrystals (ChNCs) with a high yield (up to 88.5%). The synergistic effect of Lewis acid and released Brønsted acid from betaine hydrochloride enabled the efficient hydrolysis of chitin for production of ChNCs coupled with ultrasonication with low energy consumption. The obtained ChNCs were with an average diameter of 10 nm and length of 268 nm, and a crystallinity of 89.2% with optimal synthesis conditions (at 100 °C for 1 h with chitin-to-DES mass ratio of 1:20). The ChNCs were further investigated as efficient emulsion stabilizers, and they resulted in stable o/w emulsions even at a high oil content of 50% with a low ChNC dosage of 1 mg/g. Therefore, a potential approach based on a DES on the production of chitin-based nanoparticles as emulsifiers is introduced.

From waste/residual marine biomass to active biopolymer-based packaging film materials for food industry applications – a review

Waste/residual marine biomass represents a vast and potentially underexplored source of biopolymers chitin/chitosan and alginate. Their isolation and potential application in the development and production of bio-based food packaging are gaining in attractiveness due to a recent increment in plastic pollution awareness. Accordingly, a review of the latest research work was given to cover the pathway from biomass sources to biopolymers isolation and application in the development of active (antimicrobial/antioxidant) film materials intended for food packaging. Screening of the novel eco-friendly isolation processes was followed by an extensive overview of the most recent publications covering the chitosan- and alginate-based films with incorporated active agents.

Comparison of Deep Eutectic Solvents on Pretreatment of Raw Ramie Fibers for Cellulose Nanofibril Production

Deep eutectic solvents (DESs), featured as promising green solvents, were applied to examine their effectiveness in pretreating raw ramie fibers (RFs) for cellulose nanofibril (CNF) production. The pretreatment performance of three DESs, i.e., choline chloride-urea (CU), choline chloride-oxalic acid dihydrate (CO), and choline chloride-glycerol (CG), was evaluated based on chemical composition analysis and structural and morphological changes. CO attained the most dramatic morphological changes of RFs, followed by CG and CU. Its high structural disruption of RFs during the pretreatment process, shown in the results from scanning electron microscopy and atomic force microscopy, could be due to an outstanding ability to remove amorphous cellulose and noncellulosic components from raw RFs, confirmed by the results of chemical composition analysis, Fourier transform infrared spectroscopy, and X-ray diffractometry. Overall, this study provided an innovative and effective pretreatment process for fractionating raw cellulosic fibers, so as to promote the subsequent preparation of CNFs.

Recent trends on seaweed fractionation for liquid biofuels production

Concerns about fossil fuels depletion has led to seek for new sources of energy. The use of marine biomass (seaweed) to produce biofuels presents widely recognized advantages over terrestrial biomasses such as higher production ratio, higher photosynthetic efficiency or carbon-neutral emissions. In here, interesting seaweed sources as a whole or as a residue from seaweed processing industries for biofuel production were identified and their diverse composition and availability compiled. In addition, the pretreatments used for seaweed fractionation were thoroughly revised as this step is pivotal in a seaweed biorefinery for integral biomass valorization and for enabling biomass-to-biofuel economic feasibility processes. Traditional and emerging technologies were revised, with particular emphasis on green technologies, relating pretreatment not only with the type of biomass but also with the final target product(s) and yields. Current hurdles of marine biomass-to-biofuel processes were pinpointed and discussed and future perspectives on the development of these processes given.

Enhanced Conversion of Xylan into Furfural using Acidic Deep Eutectic Solvents with Dual Solvent and Catalyst Behavior

An efficient process for the production of furfural from xylan by using acidic deep eutectic solvents (DESs), which act both as solvents and catalysts, is developed. DESs composed of cholinium chloride ([Ch]Cl) and malic acid or glycolic acid at different molar ratios, and the effects of water and γ-valerolactone (GVL) contents, solid/liquid (S/L) ratio, and microwave heating are investigated. The best furfural yields are obtained with the DES [Ch]Cl:malic acid (1:3 molar ratio)+5 wt % water, under microwave heating for 2.5 min at 150 °C, a S/L ratio of 0.050, and GVL at a weight ratio of 2:1. Under these conditions, a remarkable furfural yield (75 %) is obtained. Direct distillation of furfural from the DES/GVL solvent and distillation from 2-methyltetrahydrofuran (2-MeTHF) after a back-extraction step enable 89 % furfural recovery from 2-MeTHF. This strategy allows recycling of the DES/GVL for at least three times with only small losses in furfural yield (>69 %). This is the fastest and highest-yielding process reported for furfural production using bio-based DESs as solvents and catalysts, paving the way for scale-up of the process.

New guidelines for testing "Deep eutectic solvents" toxicity and their effects on the environment and living beings

Deep eutectic solvents (DESs) were described at the beginning of this century as an alternative to ionic liquids (ILs) in green chemistry. Despite their obvious sustainable advantages as reaction media, there is still controversy about their potential toxicity. Most of the ecotoxicity assays done up to now involving DESs are based on antibiograms. This is not a good approach due to the high density and viscosity of most DESs already described. Additionally, antibiograms do not allow continuous monitoring of neither cellular growth nor changes on physicochemical parameters like culture acidification due to cellular growth or DESs metabolization. This work starts by displaying advantages and disadvantages of the DESs toxicity assays already reported. Then, using a new DES recently described and Escherichia coli as a model microorganism, liquid cultures with continuous monitoring of pH, temperature, shaking and optical density have been used, for the first time, to quantify potential toxicity of the DES as well as the degree of the cellular tolerance (in preadapted and non-preadapted cells). The results obtained show that this new DES is not toxic for E. coli at concentrations up to 300 mM and cellular preadaptation was crucial for the cells to grow. At concentrations between 300 mM and 450 mM, cells can tolerate this DES. Above 600 mM, the DES is toxic causing complete inhibition of growth. This toxicity is not only due to the chemical composition of the DES, but also due to the high acidification of the media caused by the DES hydrolysis during cellular growth. The consequences of sterilization procedures on the DES stability are also analysed into detail, finding that sterilization by autoclave promotes DES hydrolysis. From these results, new guidelines are proposed for furthers studies aiming to characterize and quantify DESs toxicity.

Green and Efficient Extraction of Polysaccharides From Poria cocos F.A. Wolf by Deep Eutectic Solvent

Deep eutectic solvents (DESs) were proposed for the extraction of polysaccharides from Poria cocos (PCPs). Six types of DESs were prepared, and the DES composed of choline chloride and oxalic acid was proved to be suitable. Based on the results of single-factor test, the Box-Behnken experimental design with response surface methodology was carried out, giving the optimal extraction conditions including mole ratio of 1:2 (choline chloride:oxalic acid) and extraction 15 minutes at 100°C. Under the optimal extraction conditions, the extraction yield (46.24% ± 0.13%) was 8.6 times higher than that of hot water. The reusability of DES was demonstrated by a 6-run test, and an extraction yield of PCP was 38.40% ± 0.23% after reusing for 6 times without adding any additional chemicals. Moreover, molecular weight distributions of the resulting PCP were analyzed, and then mainly distributed in the range of 753 to 3578 g/mol. Therefore, DESs were proved to be an excellent extraction solvent alternative to the extraction of PCP.

Chitosan Composites in Packaging Industry-Current Trends and Future Challenges

Chitosan-based composites play an important role in food packaging applications and can be used either as films or as edible coatings. Due to their high costs and lower performance (i.e., lower barrier against water vapor, thermal, and mechanical properties) when compared to the traditional petroleum-based plastics, the use of such biopolymers in large-scale is still limited. Several approaches of chitosan composites in the packaging industry are emerging to overcome some of the disadvantages of pristine polymers. Thus, this work intends to present the current trends and the future challenges towards production and application of chitosan composites in the food packaging industry.

High Purity and Low Molecular Weight Lignin Nano-Particles Extracted from Acid-Assisted MIBK Pretreatment

A simple and economical biorefinery method, organosolv methyl isobutyl ketone (MIBK) pretreatment assisted by Lewis acid ferric trichloride hydrolysis, was proposed for fractionating the lignin from extractive-free Eucalyptus powder at the nanoscale, accompanied by another product furfural, derived from hemicellulose. Under the conditions (180 °C, 1 h) optimized based on the best yield of furfural, 40.13% of the acid-insoluble lignin (AIL) could be obtained with a high purity of 100%, a low molecular weight of 767 (M_n) and improved thermostability. The extracted lignin was characterized by its chemical structure, thermostability, homogeneity, molecular weight, and morphology as compared with milled wood lignin (MWL). The results showed significant variations in chemical structures of the extracted lignin during the pretreatment. Specifically, the aryl ether linkage and phenylcoumarans were broken severely while the resinols were more resistant. The G-type lignin was more sensitive to degradation than the S-type, and after the pretreatment, H-type lignin was formed, indicating the occurrence of a demethoxylation reaction at high temperature. Moreover, the lignin nano-particles were identified visually by AFM and TEM images. The dynamic light scattering (DLS) showed that the average diameter of the measured samples was 131.8 nm, with the polydispersity index (PDI) of 0.149. The MIBK-lignin nano-particles prepared in our laboratory exhibit high potentials in producing high functional and valuable materials for the application in wide fields.

Ionic Conductivity and Structure of Chitosan Films Modified with Lactic Acid-Choline Chloride NADES

The natural deep eutectic solvent (NADES) based on choline chloride (ChCl) and lactic acid (LA) was used for the preparation of chitosan (CS) films by the solution casting method. The content of NADES in films was from 0 to 82 wt%. The impact of NADES on the morphology and crystalline structure of films was investigated using scanning electron microscopy as well as wide-angle and small-angle X-ray scattering. The experimental results allow to propose CS chains swelling in NADES. FTIR spectroscopy confirms the interactions between CS and NADES components via the formation of hydrogen and ion bonds. The thermal properties of the composite films were studied by simultaneous thermogravimetric and differential thermal analysis. Thermomechanical analysis demonstrated appearance of two transitions at temperatures between -23 and -5 °C and 54-102 °C depending on NADES content. It was found that electrical conductivity of film with 82 wt% of NADES reaches 1.7 mS/cm. The influence of the composition and structure of films on the charge carriers concentration and their mobility is discussed.

Deep eutectic solvent for lignocellulosic biomass fractionation and the subsequent conversion to bio-based products - A review

Since the introduction of deep eutectic solvent (DES) in biomass processing field, the efficiency of DES in lignocellulosic biopolymer model compounds' (cellulose, hemicellulose and lignin) solubilisation and conversion was widely recognized. Nevertheless, DES's potential for biorefinery application can be reflected more accurately through their performance in raw lignocellulosic biomass processing rather than model compound conversion. Therefore, this review examines the studies on raw lignocellulosic biomass fractionation using DES and the subsequent conversion of DES-fractionated products into bio-based products. The review stresses on three key parts: performance of varying types of DESs and pretreatment schemes for biopolymer fractionation, properties and conversion of fractionated saccharides as well as DES-extracted lignin. The prospects and challenges of DES implementation in biomass processing will also be discussed. This review provides a front-to-end view on the DES's performance, starting from pretreatment to DES-fractionated products conversion, which would be helpful in devising a comprehensive biomass utilization process.

Enzymatic Modification of Native Chitin and Conversion to Specialty Chemical Products

: Chitin is one of the most abundant biomolecules on earth, occurring in crustacean shells and cell walls of fungi. While the polysaccharide is threatening to pollute coastal ecosystems in the form of accumulating shell-waste, it has the potential to be converted into highly profitable derivatives with applications in medicine, biotechnology, and wastewater treatment, among others. Traditionally this is still mostly done by the employment of aggressive chemicals, yielding low quality while producing toxic by-products. In the last decades, the enzymatic conversion of chitin has been on the rise, albeit still not on the same level of cost-effectiveness compared to the traditional methods due to its multi-step character. Another severe drawback of the biotechnological approach is the highly ordered structure of chitin, which renders it nigh impossible for most glycosidic hydrolases to act upon. So far, only the Auxiliary Activity 10 family (AA10), including lytic polysaccharide monooxygenases (LPMOs), is known to hydrolyse native recalcitrant chitin, which spares the expensive first step of chemical or mechanical pre-treatment to enlarge the substrate surface. The main advantages of enzymatic conversion of chitin over conventional chemical methods are the biocompability and, more strikingly, the higher product specificity, product quality, and yield of the process. Products with a higher Mw due to no unspecific depolymerisation besides an exactly defined degree and pattern of acetylation can be yielded. This provides a new toolset of thousands of new chitin and chitosan derivatives, as the physio-chemical properties can be modified according to the desired application. This review aims to provide an overview of the biotechnological tools currently at hand, as well as challenges and crucial steps to achieve the long-term goal of enzymatic conversion of native chitin into specialty chemical products.

Catalytic conversion of fructose into 5-HMF under eco-friendly-biphasic process

One-pot conversion of fructose into valuable 5-hydroxymethyl-2-furaldehyde (5-HMF) was investigated under a deep eutectic solvent-biphasic system.

Polysaccharides of mushroom Pleurotus spp.: New extraction techniques, biological activities and development of new technologies

The biodiversity of mushrooms Pleurotus spp. is impressive due to its complexity and diversity related to the composition of chemical structures such as polysaccharides, glycoproteins and secondary metabolites such as alkaloids, flavonoids and betalains. Recent studies of polysaccharides and their structural elucidation have helped to direct research and development of technologies related to pharmacological action, production of bioactive foods and application of new, more sophisticated extraction tools. The diversity of bioactivities related to these biopolymers, their mechanisms and routes of action are constant focus of researches. The elucidation of bioactivities has helped to formulate new vaccines and targeted drugs. In this context, in terms of polysaccharides and the diversity of mushrooms Pleurotus spp., this review seeks to revisit the genus, making an updated approach on the recent discoveries of polysaccharides, new extraction techniques and bioactivities, emphasising on their mechanisms and routes in order to update the reader on the recent technologies related to these polymers.

Deep Eutectic Solvents for Pretreatment, Extraction, and Catalysis of Biomass and Food Waste

Valorization of lignocellulosic biomass and food residues to obtain valuable chemicals is essential to the establishment of a sustainable and biobased economy in the modern world. The latest and greenest generation of ionic liquids (ILs) are deep eutectic solvents (DESs) and natural deep eutectic solvents (NADESs); these have shown great promise for various applications and have attracted considerable attention from researchers who seek versatile solvents with pretreatment, extraction, and catalysis capabilities in biomass- and biowaste-to-bioenergy conversion processes. The present work aimed to review the use of DESs and NADESs in the valorization of biomass and biowaste as pretreatment or extraction solvents or catalysis agents.

Use of Deep Eutectic Solvents in Polymer Chemistry-A Review

This review deals with two overlapping issues, namely polymer chemistry and deep eutectic solvents (DESs). With regard to polymers, specific aspects of synthetic polymers, polymerization processes producing such polymers, and natural cellulose-based nanopolymers are evaluated. As for DESs, their compliance with green chemistry requirements, their basic properties and involvement in polymer chemistry are discussed. In addition to reviewing the state-of-the-art for selected kinds of polymers, the paper reveals further possibilities in the employment of DESs in polymer chemistry. As an example, the significance of DES polarity and polymer polarity to control polymerization processes, modify polymer properties, and synthesize polymers with a specific structure and behavior, is emphasized.

Sugar Alcohol-Based Deep Eutectic Solvents as Potato Starch Plasticizers

The aim of this work was to prepare sugar alcohol-based deep eutectic solvents (DES) and test them as starch plasticizers. Thermoplastic starch (TPS) films were obtained via a simple and convenient thermocompression method. Influence of starch/DES premixtures conditioning (preheating, storage time) on TPS properties was investigated. TPS/sorbitol (S)-based DES exhibited similar tensile strength (TS) (8.6 MPa) but twice higher elongation at the break (ε) (33%) when compared with TPS plasticized only with S. Extra treatment, i.e., heating or prolonged storage time, facilitated starch/DES plasticizing. Starch with selected DES was also extruded and the influence of preconditioning and extrusion rotational speed were subsequently studied on thermocompressed films. Extrusion at 100 rpm led to films with TS up to ca. 10 MPa and ε up to 52%. Some differences in film samples morphology obtained via two processing methods were observed. X-ray diffractograms revealed that extruded samples exhibited a V-type peak at 18.2°, with intensity depending on plasticizer total molecular size. Applied techniques (mechanical tests, XRD, Dynamic Mechanical Analysis (DMA), FTIR-Attenuated Total Reflection (ATR), and moisture sorption) indicated that S-based DES forms stronger interactions with starch than glycerol (G) only used as conventional plasticizer, thus leading to better mechanical properties and inhibited tendency to starch recrystallization (studied up to one year).