Changes in the microstructure and enzymatic hydrolysis performance of chitin treated by steam explosion,high-pressure homogenization,and γ radiation

This research intends to reduce the crystallinity of chitin with physical methods so as to improve the enzymatic hydrolysis efficiency of chitin. Scanning electron microscopy showed that both steam explosion and high-pressure homogenization significantly enlarged the pores in shrimp shells, which are made up of chitin, but γ radiation did not. X-ray diffraction showed that the crystallinity index of chitin decreased by 23.2% in the (110) plane and 24.7% in the (020) plane after three rounds of steam explosion and decreased by 12.4% in the (110) plane and 28.7% in the (020) plane after three rounds of high-pressure homogenization. After γ radiation, however, there was no significant change. The corresponding deacetylation degrees of the chitin treated with steam explosion and high-pressure homogenization increased by 13.2 and 5.7%, respectively. The natural, steam-exploded and high-pressure homogenized chitins respectively produced 0.251, 0.145, and 0.407 mg/ml reducing sugars with the hydrolysis of Streptomyces griseus chitinase. However, when hydrolyzed by Paenibacillus sp. A1 chitinase the steam-exploded and the high-pressure homogenized chitin respectively released 40 and 300% more reducing sugars than the natural chitin. The results found that steam explosion and high-pressure homogenization can reduce the crystallinity of chitin, and make it prone to enzymatic hydrolysis.     

Comparison of chitins produced by chemical and bioprocessing methods

Lactic acid fermentation was used to extract chitin from prawn shell (Nephrops norvegicus) at two different scales of operation. The fermentation products were characterized and compared with chitin extracted from the same source by a chemical method. Chitosans produced from the obtained chitins were evaluated in terms of their intrinsic viscosity, molecular weight and degree of acetylation (DA). The fermentation removed 690 g kg^?1 and 770 g kg^?1 of inorganic matter, 490 and 440 g kg^?1 of protein and 540 and 770 g kg^?1 of lipids from the shells at laboratory and pilot plant scales, respectively. However, the functional properties such as the DA of the chitin, the molecular weight and the DA of the chitosans were similar to those obtained for the chemically‐obtained chitin and its chitosan. Despite the incomplete extraction of chitin this biological process could be useful to produce chitin and chitosan in a more environment‐friendly approach. Copyright © 2004 Society of Chemical Industry     

Adsorption of Silver Nanoparticles onto Different Surface Structures of Chitin/Chitosan and Correlations with Antimicrobial Activities

Size-controlled spherical silver nanoparticles (Ag NPs) can be simply prepared by autoclaving mixtures of glass powder containing silver with glucose. Moreover, chitins with varying degrees of deacetylation (DDAc < 30%) and chitosan powders and sheets (DDAc > 75%) with varying surface structure properties have been evaluated as Ag NP carriers. Chitin/chitosan-Ag NP composites in powder or sheet form were prepared by mixing Ag NP suspensions with each of the chitin/chitosan-based material at pH 7.3, leading to homogenous dispersion and stable adsorption of Ag NPs onto chitin carriers with nanoscale fiber-like surface structures, and chitosan carriers with nanoscale porous surface structures. Although these chitins exhibited mild antiviral, bactericidal, and antifungal activities, chitin powders with flat/smooth film-like surface structures had limited antimicrobial activities and Ag NP adsorption. The antimicrobial activities of chitin/chitosan-Ag NP composites increased with increasing amounts of adsorbed Ag NPs, suggesting that the surface structures of chitin/chitosan carriers strongly influence adsorption of Ag NPs and antimicrobial activities. These observations indicate that chitin/chitosan-Ag NPs with nanoscale surface structures have potential as antimicrobial biomaterials and anti-infectious wound dressings.     

Effect of deacetylation on sorption of dyes and chromium on chitin

Deacetylated chitins (10.7–67.2%) were prepared by alkaline hydrolysis to determine an optimal degree of deacetylation (DD) which can effectively remove four dyes and chromium ions from textile effluent. Sorption isotherms were carried by varying the treatment time, pH, and initial concentration of dyes or chromium ions. Experimental results were analyzed in three ways: (1) equilibrium sorption capacity and sorption rate constant, (2) Langmuir isotherms, and (3) separation factor. Results indicated that except for the chitin with a 67.2% DD, rate and capacity of the dye sorption on the chitin increased with the increase of the DD in chitin for each pH but decreased with the increase of pH for each deacetylated chitin. This was mainly due to the increase of—NH⁺₃ groups in chitin with a high DD and the low pH of the system. On the contrary, dye desorption from the deacetylated chitin was highly effective at 80° and pH ≥ 10, which could facilitate the reduction of—NH⁺₃ ions and the increase of electrostatic repulsion. The number of chromium ions sorbed on the chitin also increased with the increase of the DD at a specific time. Therefore, by controlling the DD of the deacetylated chitin maximum efficiency can be achieved in the removal of dyes and metal ions from textile effluent.     

Relationship between molecular structure and moisture‐retention ability of carboxymethyl chitin and chitosan

Carboxymethyl chitins and chitosans (CM‐chitins, CM‐chitosans) of different substitution sites were prepared under different reaction conditions, and partially depolymerized carboxymethyl chitins of various molecular weights from 24.8 × 10⁴ to 0.26 × 10⁴ were obtained by degrading with chemical reagents. Degree of substitution (DS) was estimated by potentiometric titration. Substitution site was confirmed by infrared and ¹³C‐NMR spectra. Molecular weights were determined with gel permeation chromatography and gel permeation chromatography combined with laser light scattering (GPC‐LLS). Moisture‐absorption and retention abilities of these compounds were tested in comparison with those of hyaluronic acid (HA). The results reveal that 6‐carboxymethyl group in the molecular structure of chitin and chitosan is a main active site responsible for moisture retention. Although carboxymethylation at OH‐3 and N position is not essential, they contribute to the ability. Moisture‐retention ability is also related to molecular weight; that is, higher molecular weight helps to improve moisture‐retention ability. 6‐O‐CM‐chitin (chitosan) with a DS above 0.8 and molecular weight higher than 24.8 × 10⁴ has the potential to substitute for HA for use in cosmetics and clinical medicine. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1233–1241, 2002     

Deacetylation of β‐chitin. I. Influence of the deacetylation conditions

The influences of the deacetylation temperature, deacetylation time, and NaOH concentration on the degree of deacetylation (DD) of deacetylated products prepared from β‐chitin are discussed. The DD values of deacetylated products are related to the ratio of the signal intensities of methyl on acetyl groups and the first anomeric carbon, which are obtained from ¹³C‐NMR spectra. The results show that the DD values of deacetylated product increase as the NaOH concentration, deacetylation time, or deacetylation temperature increases. The thermal properties, chemical structures, and crystalline characteristic of deacetylated products are significantly related to their DD values. Differential scanning calorimetry shows that the peak temperature is slightly increased as the DD values of deacetylated products of β‐chitin increase. Thermogravimetric analysis shows that the thermal degradation onset temperature of deacetylated products decreases as the DD values increase. Fourier transform infrared spectra show that the intensity of a specific absorption peak of ? NH₂ in deacetylated products significantly increases as DD increases. X‐ray diffraction patterns of deacetylated products with DD values of 17.5 and 44.7% have three significant diffraction peaks. However, there are only two diffraction peaks found in products with higher DD values of 76.5 and 94.7%. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2416–2422, 2004     

Intensifying chitin hydrolysis by adjunct treatments – an overview

Chitin is, after cellulose, the most abundant organic natural polysaccharide on Earth, being synthesized as a dominant component in the exoskeletons of crustaceans, among other sources. In the processing of seafood for human consumption, between 40 and 50% of the total raw material mass is wasted, causing a significant problem for the environment owing to its slow degradation. Efforts to find uses for chitin derivatives, particularly their oligomers, have intensified since these chemicals are highly functional and offer a wide range of applications, especially as antimicrobial agent. As a consequence, some adjunct treatments, either chemical or physical in nature, have been employed to assist acid and enzymatic hydrolysis. This work provides a detailed review of the methods employed to intensify the formation of chitin oligomers, particularly focusing on the adjunct treatments used (microwave, ultrasonication, steam explosion and gamma irradiation), and an evaluation of the yield and characteristics of the oligomers formed. Adjunct treatments are more suitable for enzymatic hydrolysis since these treatments modify the chitin structure, and enhance the hydrolysis rate and yield of the oligomers, under milder reaction conditions. For future research, it would be worth trying pre‐treatments like the application of high‐pressure to chitin in order to lower its crystallinity. © 2017 Society of Chemical Industry     

Optimum parameters for production of chitin and chitosan from squilla (S. empusa)

Chitin and chitosan of high quality were produced from squilla, a by‐catch of Indian Ocean fisheries, by demineralization, deproteination, and deacetylation. Optimum conditions for the production of chitin and chitosan were determined. The quality of chitin was assessed from its ash and protein content. Ash content was below 1% after treatment with 4% HCl for 12 h at 50°C. A protein content of less than 1% could be achieved by treatment with 4% NaOH in 12 h but only at a temperature of 70°C or higher. Production of chitin was also tested by a three‐stage treatment with altering sequence of sodium hydroxide and hydrochloric acid (HCl–NaOH–HCl or NaOH–HCl–NaOH). This three‐step treatment appeared to be successful to achieve a mineral content and protein content below 1% within 30 h and at a temperature not exceeding 50°C. The chitin obtained under optimum conditions was tested for deacetylation using NaOH concentrations of 40 and 50% for 12–44 h at 30, 50 and 70°C. The chitosan obtained had a degree of deacetylation of 77–86%, a viscosity of 8.2–16.2 × 10² cps, solubility of 98%, and molecular weight of ? 1 × 10⁶ dalton. The data show that processing of squilla waste can lead to a high quality chitosan, useful for a broad range of applications. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 103: 3694–3700, 2007     

Chitin/polyurethane blends: a thermal and morphological study

Chitin is an abundant natural polymer having important properties such as biocompatibility and biodegradability combined with healing capability. Its use in biomedical applications has been hindered by its poor processing properties such as low solubility and stiffness in the solid state. In an attempt to obtain flexible and more processable chitin‐based materials, we prepared blends of the polymer with a polyurethane containing a soft segment based on biodegradable polycaprolactone. A certain degree of miscibility was found between chitin and the polyurethane, as demonstrated by a shift in the glass transition of the polyurethane observed in dynamical mechanical analyses, with a simultaneous decrease in crystallinity of chitin observed in X‐ray diffraction analyses. A phase inversion of the blends took place for a 50/50 (w/w) composition ratio as demonstrated from thermal, dynamic mechanical, tensile and X‐ray diffraction measurements. Blends of chitin with the polycaprolactone‐based polyurethane can be effectively used to produce tough materials useful in biomedical applications. The mechanical strength of the blends demonstrated that they are able to support tensions above those required for bone replacement, making them good candidates for that purpose. Copyright © 2010 Society of Chemical Industry     

甲壳素脱乙酰化动力学模型研究

研究了甲壳素脱乙酰化反应,推导出了扩散动力学模型,经最小二乘方拟合验证后,模型能很好预测甲壳素脱乙酰化反应。对模型中的扩散系数D进行了分析,得出了反应活化能。     

The influence of processing terms of chitosan membranes made of differently deacetylated chitin on the crystalline structure of membranes

The crystalline structure of chitosan membranes made of a high degree of (90%) and low degree of (60%) deacetylated chitin by various regeneration processes was studied. The results of X-ray and IR spectroscopy investigations testify that the type of crystalline structre, the degree of crystallinity, and the average lateral crystallite size depend basically on the deacetylation degree of the chitin utilized in preparing the membranes. © 1994 John Wiley & Sons, Inc.     

Influence of the drying route on the depolymerization and properties of chitosan

In this work, a chitosan sample with a high degree of deacetylation (DD >95%) obtained from freshwater shrimp shells was subjected to drying processes in an electric oven and by supercritical CO₂. The results indicated that drying chitosan particles with supercritical CO₂ resulted in a very significant increase in specific surface area and pore volume, and also increased the material's crystallinity index. This drying route led to a more than 10‐fold reduction in viscosimetric molecular weight (from 35.3 to 3.0 kDa), indicating that the physical drying process caused the chitosan to depolymerize, which usually occurs by enzymatic and chemical methods, according to the literature. Low molecular weight chitosan is essential for some applications in the field of biomedicine (drug delivery for example); hence, drying via the CO₂ route can be considered a promising technique for the production of high value‐added materials with applications in this area. POLYM. ENG. SCI., 55:1969–1976, 2015. © 2014 Society of Plastics Engineers     

Insight on Solution Plasma in Aqueous Solution and Their Application in Modification of Chitin and Chitosan

Sustainability and environmental concerns have persuaded researchers to explore renewable materials, such as nature-derived polysaccharides, and add value by changing chemical structures with the aim to possess specific properties, like biological properties. Meanwhile, finding methods and strategies that can lower hazardous chemicals, simplify production steps, reduce time consumption, and acquire high-purified products is an important task that requires attention. To break through these issues, electrical discharging in aqueous solutions at atmospheric pressure and room temperature, referred to as the “solution plasma process”, has been introduced as a novel process for modification of nature-derived polysaccharides like chitin and chitosan. This review reveals insight into the electrical discharge in aqueous solutions and scientific progress on their application in a modification of chitin and chitosan, including degradation and deacetylation. The influencing parameters in the plasma process are intensively explained in order to provide a guideline for the modification of not only chitin and chitosan but also other nature-derived polysaccharides, aiming to address economic aspects and environmental concerns.     

On the sonication of chitin: effects on its structure and morphology and influence on its deacetylation

Summary The pre-sonication provoked noticeable changes in the chitin morphology but its overall crystallinity was unaffected. The sonication of chitin seemed to improve its homogeneity and to increase the particles surface, enhancing the accessibility of reagents. Pre-sonicated chitin was more efficiently deacetylated (up to 95%) than commercial chitin (up to 88%) probably due to the mechanical action of ultra-sound since the previous stirring of solid chitin while suspended in hot or cold water for 1 hour also enhanced the deacetylation efficiency. Received: 9 April 2001/Revised version: 21 August 2001/Accepted: 22 August 2001     

超声辐射下非均相甲壳素脱乙酰化反应动力学

在超声辐射条件下进行了甲壳素非均相脱乙酰化反应动力学研究。结果表明,超声辐射条件下,甲壳素的脱乙酰度明显提高,反应过程符合准一级动力学关系,反应控制为扩散控制,其表观活化能为3.45 kJ/mol。     

Chitosan from Muga silkworms (Antheraea assamensis) and its influence on thermal degradation behavior of poly(lactic acid) based biocomposite films

The research work is focused on extraction of chitin from Muga silkworms (MS) and its conversion into chitosan by chemical treatment process. The extracted amount of chitin and chitosan from MS were obtained ～8 wt % and ～7 wt %, respectively. Potentiometric titrations, conductometric titrations, elemental analysis, ¹H‐NMR and FTIR analyses were employed to calculate the degree of deacetylation of chitosan (extracted at 80 ºC after 10 h) and found as 77% ± 2, 81% ± 1.8, 82% ± 2.4, 97.77% ± 0.3, and 82% ± 1.8, respectively. The deacetylation process of chitin showed pseudo‐first order reaction kinetics and activation energy was estimated as ～15.5 kJ/mole. The extracted chitosan (at 80 ºC after 10 h) showed higher crystallinity and improved thermal stability with respect to chitosan extracted from other marine sources. Subsequently, poly(lactic acid) (PLA) and extracted chitosan dispersed biocomposite films were prepared by solution casting method. Significant dispersion of chitosan (extracted at 80 ºC after 10 h) micro‐particles were observed in biocomposite films using FESEM analysis. Due to chitosan interaction with PLA, significant reduction in thermal degradation and activation energy was observed during nonisothermal degradation scan of such films using Flynn‐Wall‐Ozawa and Kissinger‐Akahira‐Sunose models. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43710.     

Comprehensive characterization and evaluation of the process chain and products from Euphausia superba exocuticles to chitosan

Antarctic krill (Euphausia superba) is a source for compounds of high nutritive value. Within that process of extraction, exocuticles (shells) accumulate which are currently disposed. A valorization of the compounds of the exocuticle such as chitosan would be beneficial to avoid waste and to obtain a versatile polymer at the same time. In contrast to previous investigations focusing on chitosan production from whole krill, we applied and optimized process stages of the chitosan production from the exocuticles, performing a comprehensive analytical evaluation of the whole process, the side streams and the products for the first time. Degreasing was the first step resulting in a krill oil yield of 6.2% using ethanol. The fatty acid profile exhibited high contents of phospholipids (21.2%). Citric acid offered a demineralization efficiency of 93%. Deproteinization investigation revealed 2 M NaOH and 90°C for 2.5 h to be the best parameters, resulting in a deproteinization efficiency of 99.9% and a chitin content of 92.8%. The spectroscopic investigation indicated that the chitin has a crystallinity index of 76% and an acetylation degree of 88%. The deacetylation degrees of the resulting chitosans is determined to be 74%–88%, the molecular weight ranges from 102 to 126 kDa.     

龙虾壳甲壳素的提取和壳聚糖的制备及性能研究

以淮南地区的龙虾壳为原料,经脱钙、脱蛋白、脱色工艺制备出的甲壳素经过脱乙酰化反应制得壳聚糖。对按以上工艺路线合成的壳聚糖的脱乙酰度和粘度两项主要指标进行测定,经过单因素实验分析,找到了由甲壳素生产壳聚糖的最佳工艺条件,并对最佳工艺条件合成的壳聚糖产品进行絮凝效果测试,验证了壳聚糖的絮凝效果优于阴离子聚丙烯酰胺。     

Enzymatic treatments as alternative to produce chitin fragments of low molecular weight from Alternaria alternata

Chitin and its oligosaccharides are involved in the plant defense response against fungal pathogens. In most studies, these molecules come from crustacean shell, and there are scarce studies on the use of fungal chitin. Usually the extraction of chitin is by alkaline treatments, which affect the acetylation degree (DA), and the obtaining of oligosaccharides of low molecular weight; so the use of enzymes is proposed as an alternative treatment to obtain chitin oligosaccharides from fungi. The objective of this work was to characterize the chitin fragments of Alternaria alternata extracted by alkaline and enzymatic treatments. The chitin extracted was ultrasonicated and ultrafiltrated to produce chitin fragments. Enzymatic treatments decreased the protein content to 29%, and the bands corresponding to β-glucans decreased when β-1,3-glucanase was applied. Fragments smaller than 1 kDa, DA of 76.7%, and 35.4 μg glucosamine/mg dry weight were obtained by enzymatic treatments. The enzymatic treatments show promising results to extract chitin fragments from A. alternata without severely affect the DA of the molecule. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47339.     

红螯螯虾壳制备壳聚糖的研究

以红螯螯虾壳为原料提取甲壳素,得到白色片状产品,收率为18%。甲壳素通过脱乙酰化制备壳聚糖,脱乙酰度可达83%。考察了浸酸时间、浸酸温度和NaOH浓度对产品质量的影响。结果表明,采用红螯螯虾壳制备壳聚糖是可行的。