Simultaneous Extraction of Carboxylated Celulose Nanocrystals and Nanofibrils via Citric Acid Hydrolysis——A Sustainable Route

In this study, cellulose nanocrystals(CNC) with surface carboxylic groups were prepared from bleached softwood pulp by hydrolysis with concentrated citric acid at concentrations of 60 wt%~80 wt%. The solid residues from acid hydrolysis were collected for producing cellulose nanofibrils(CNF) via post high-pressure homogenization. Citric acid could be easily recovered after hydrolysis reactions through crystallization due to its low water solubility or through precipitation as a calcium salt followed by acidification. Several important properties of CNC and CNF, such as dimension, crystallinity, surface chemistry, thermal stability, were evaluated. Results showed that the obtained CNC and CNF surfaces contained carboxylic acid groups that facilitated functionalization and dispersion in aqueous processing. The recyclability of citric acid and the carboxylated CNC/CNF give the renewable cellulose nanomaterial huge potential for a wide range of industrial applications. Furthermore, the resultant CNC and CNF were used as reinforcing agents to make sodium carboxymethyl cellulose(CMC) films. Both CNC and CNF showed reinforcing effects in CMC composite films. The tensile strength of CMC films increased by 54.3% and 85.7% with 10 wt% inclusion of CNC and CNF, respectively. This study provides detailed information on carboxylated nanocellulose prepared by critic acid hydrolysis; a sustainable approach for the preparation of CNC/CNF is of significant importance for their various uses.     

Cassava Starch Coating and Citric Acid to Preserve Quality Parameters of Fresh-Cut “Tommy Atkins” Mango

Abstract: Combination of citric acid dipping (5 g/L) and cassava starch coating (10 g/L), with and without glycerol (10 g/L), was studied to verify the effectiveness of these treatments to inhibit enzymatic browning, to reduce respiration rate, and to preserve quality parameters of “Tommy Atkins” fresh-cut mangoes during storage at 5 °C. Color characteristics (L* and C*), mechanical properties (stress at failure), weight loss, β-carotene content, sensory acceptance, and microbial growth of fruits were evaluated during 15 d. The respiration rate of fruit subjected to the treatments was also analyzed. Nontreated fresh-cut mango was used as a control sample. Cassava starch edible coatings and citric acid dipping promoted a decrease in respiration rate of mango slices, with values up to 41% lower than the control fruit. This treatment also promoted better preservation of texture and color characteristics of mangoes and delayed carotenoid formation and browning reactions during storage. Moreover, the treated fruit showed great sensory acceptance by consumers throughout the whole storage period. However, the use of glycerol in the coating formulation was not efficient in the maintenance of quality parameters of fresh-cut mangoes, promoting a higher weight loss of samples, impairing fruit texture characteristics, increasing carotenogenesis, and favoring microbial growth during storage. Practical Application: Consumer demand for tropical fresh-cut products is increasing rapidly in the world market. Fresh-cut mangoes are appreciated world-wide for its exotic flavor. However, its shelf life is limited by changes in color, texture, appearance, off-flavors and microbial growth. The edible coatings act as gas and water vapor barrier, extending the storage time of fresh-cut fruit and vegetables. Thus, cassava starch is an alternative to preserve minimally processed mangoes and the quality parameters of fresh fruit. The information of this work is useful for the fresh-cut produce industry to increase shelf life of fresh-cut mangoes, which can be considered an alternative to fast food and other ready-to-eat products, attending the demand for healthy and convenient foodstuffs.     

Formation and Collapse of Cellulose Nanocrystals and Hydrophobic Association-induced Dual Cross-linked Nanocomposite Hydrogels: A Rheological Study

The rheological characteristics of a physical gelation system, in which cellulose nanocrystals (CNCs) induced the entanglement of poly(acrylic acid) (PAA) chains and partial hydrophobic association of octylphenol polyoxyethylene acrylate (OP-10-AC) branches in a micellar solution of sodium dodecyl sulfate (SDS), were investigated. The gelation time of the physical gels decreased as the CNC content and number of hydrophobic branch units increased. At the gel point, the storage modulus (G'') and loss modulus (G") followed the same frequency dependence (G'' ≈ G" ≈ ωⁿ), where the hydrophobic moieties attached to the side chains had a significant impact on the values of viscoelastic exponent (n). Beyond the gel point, the initial polymer solution was transformed to a solid-like gel, and the strength of the gel network was governed by associations between both the CNCs and hydrophobic groups. The evolution of the viscoelasticity during the gel-sol transition was monitored, demonstrating that due to a reversible arrangement of the hydrophobic units, a large proportion of physical cross-links dissociated under a thermal trigger and were reversibly reformed when the solution was cooled, while no such partial recovery was observed in the case of the single CNC-induced network systems (with no hydrophobic branches).     

Extraction of Polyphenolics from Plant Material for Functional Foods—Engineering and Technology

Polyphenolic substances or polyphenols include many classes of compounds ranging from phenolic acids, colored anthocyanins, simple flavonoids, and complex flavonoids. Polyphenolics contribute to the bitterness and astringency of fruits and fruit juices due to the interaction between polyphenolics, mainly procyanidins, and the glycoproteins in saliva. Polyphenols contribute largely to cellular processes within the body. In terms of pharmacological activity, they act against the oxidation of high-density lipoproteins (HDLs). Hence, they help the body retain important HDL while helping it get rid of problematic low-density lipoproteins (LDLs). In addition, polyphenols have also been found to have antiulcer, anticarcinogenic, and antimutagenic activities. The reason behind these activities is polyphenol's strong antioxidant power because they are able to quench free radicals. Green tea and grape seed extracts provide a superior source of monomers that are relatively inexpensive to extract. Comparatively, pine bark and other fruits extracts have low levels of monomers. Therefore, the nutraceutical industry has focused on optimizing extraction processes for green tea leaves and grape pomace, skins, and seeds. During extraction, a solvent is mixed with the plant material (grape seeds, grape skins, pine bark, or tea leaves). Extraction can be either completed by the addition of a solvent to the sample in a container and then removed by drying, or the solvent can be removed by concentration by ultrafiltration (UF). After any one of these processes, the extract must be dried to obtain a powder form. Alternatively, supercritical fluid extraction (SFE) can also be used, which produces the final product as a powder without any use of final drying. Organic solvent extraction is efficient and simple, yet costly. Large amounts of organic solvents are needed. This, in turn, is also detrimental to human use because traces of the organic solvent are present in the polyphenol extract. Polyphenol separation and concentration by membrane separation is even more efficient than organic solvent extraction. Organic solvents are still used but in lower quantities, and UF ensures the purity of the polyphenol extract. The drawback is membrane fouling, which can disrupt the process, and the time it takes to complete the process. The separation process has to be repeated several times. Supercritical fluid extraction is the extraction process of the future. CO₂ is low cost, nontoxic, nonflammable, and noncorrosive, making it the perfect solvent for natural products. In the U.S. market, where $141 million was spent on grape seed products in 1999, it is imperative that safe and efficient extraction procedures are delivered that guarantee a pure polyphenol product.     

Physiological Effects of Eicosapentaenoic Acid (EPA) and Docosahexaenoic Acid (DHA)—A Review

Marine lipids have long been documented to be the major source of polyunsaturated fatty acids (PUFAs), especially n-3 fatty acids such as eicosapentaenoic acid (EPA; 20:5 n-3) and docosahexaenoic acid (DHA; 22:6 n-3). Both EPA and DHA have been documented to have significant influence on biochemical and physiological changes in the body. Although these long chain PUFA exert positive influences on human nutrition and health, there are also some controversies pertaining to the functioning of these n-3 PUFAs including the extent of their requirement by the body. As marine lipids have been thoroughly reviewed often, the present review mainly focuses on works related to physiological effects of EPA and DHA.     

Simultaneous separation and determination of sugars,ascorbic acid and furanic compounds by HPLC—dual detection

An HPLC method was developed for the simultaneous separation and determination of sugars, ascorbic acid, 5-HMF (5-hydroxymethylfurfural), furfural and four other furanic compounds as the possible degradation products of sugars and ascorbic acid on heating and by Maillard reaction. Sucrose, glucose, fructose, ascorbic acid, dehydroascorbic acid, 5-HMF, furfural, DMHF (2,5-dimethyl-4-hydroxy-3(2H)-furanone), 2-furoic acid, 2-acetylfuran and furfuryl alcohol were separated on an Aminex HPX-87H column (300×7.8 mm). The mobile phase consisted of acetonitrile and 0.005 mol l⁻¹ sulfuric acid aqueous solution (16:84, v/v). Two detectors, a refractive index detector and a photodiode array detector, were used to detect these compounds. Several fruit juice and drink samples were analyzed using this HPLC method. For alcoholic beverages, the content of alcohol was also simultaneously determined by refractive index detector.     

National Development and Reform Commission, Ministry of Environmental Protection of People＇s Republic of China-- Notice about Sifting Out the Backward Enterprises of Papermaking, Alcohol, Monosodium Glutamate and Citric Acid

National Development and Reform Commission together with Ministry of Environmental Protection of People＇s Republic of China announced ＂The Notice about Sifting Out the Backward enterprises of Papermaking, Alcohol, Monosodium Glutamate and Citric Acid＂.     

Hydrolysis of porcine β-casein by bovine plasmin and bovine chymosin

 The action of bovine chymosin and bovine plasmin on porcine β-casein was studied and compared with their effect on bovine β-casein in an attempt to elucidate the similarities in specificity of these enzymes on porcine and bovine β-caseins. Bovine plasmin rapidly hydrolysed porcine β-casein at Lys₁₀₆-Arg₁₀₇, Lys₄₉-Ile₅₀ and Lys₁₆₈-Val₁₆₉ to yield γ-caseins. Several peptides that had the same N-terminal amino acid sequence as porcine β-casein were also produced. Plasmin hydrolysis sites determined by separating the pH 4.6-soluble peptides formed on hydrolysis were Lys₃₃-Leu_34, Lys₄₉-Ile₅₀, Lys₉₅-Asp₉₆, Lys₉₈-Ala₉₉, Lys₁₀₆-Arg₁₀₇, Lys₁₀₈-Gly₁₀₉ and Lys₁₆₈-Val₁₆₉. Porcine β-casein, like bovine β-casein, was hydrolysed by bovine chymosin into three distinct electrophoretic bands designated porcine β-I-, β-II- and β-III-casein, all of which had the N-terminal sequence of porcine β-casein. Two initial pH 4.6-soluble peptides formed on hydrolysis of porcine β-casein by chymosin had N-terminal amino acid sequences commencing at porcine β-casein amino acid 197, suggesting that porcine β-I-casein corresponds to fragment 1–196, while the sequences of two other small peptides commenced at amino acids 1 and 207. The C-terminal cleavage site(s) leading to formation of porcine β-II and β-III casein were not determined. Received: 9 February 1998 / Revised version: 2 June 1998     

纳米纤维素及其在水性涂料中的应用研究进展

纳米纤维素具有高长径比、高结晶度、高杨氏模量、高强度等优点,加之其具有生物质材料的轻质、可降解及可再生等特性,使其成为一种改善水性涂料机械、光学、耐水等性能的优异选择。本文综述了纳米纤维素制备和改性方法,详细论述了纤维素纳米纤丝（CNF）和纤维素纳米晶体（CNC）对水性聚氨酯和水性丙烯酸涂料的性能改善机理及其应用研究进展。最后总结了纳米纤维素复合水性涂料研究现存的问题,并总结了未来的研究方向。     

废纸基纤维素纳米晶的制备与表征

以废纸为原料,采用传统硫酸法制备纤维素纳米晶(CNCs),并优化其工艺条件;采用傅里叶变换红外光谱仪(FT-IR)、X射线衍射仪(XRD)、热重分析仪(TGA)、透射电子显微镜(TEM)及扫描电子显微镜(SEM)研究了废纸基纤维素纳米晶(SCNCs)的结构与性质。在最佳工艺条件(硫酸浓度60 wt%、水解温度50℃、水解时间90 min)下,SCNCs的得率为41. 2%,呈典型的纤维素Ⅰ型结构,结晶度为77. 6%;与原料相比,几乎不存在杂峰;SCNCs为棒状结构,长约142. 87 nm,直径约9. 67 nm。探讨了回收硫酸溶液再次用于制备CNCs;结果表明,首次回收硫酸制备的废纸基纤维素纳米晶(SCNCsH)得率为39. 9%,结晶度为78. 6%。     

酸水解法制备纤维素纳米晶体的研究进展

基于目前纤维素纳米晶体的制备研究现状,本文综述了酸水解法制备纤维素纳米晶体的研究进展,重点介绍了传统无机酸水解法的影响因素以及其他4种新兴酸水解制备方法,包括可回收的有机酸水解法、绿色环保的固体酸水解法、高效的混合酸水解法、金属盐催化酸水解法。并指出开发金属盐催化剂是酸水解法制备纤维素纳米晶体未来发展的一个重要方向。     

超低浓度酸水解制备纤维素纳米纤丝的初步研究

以漂白阔叶木浆为原料,通过控制浓度0.1%左右硫酸溶液(以下简称超低酸)水解温度和水解时间以及后续机械球磨时间制备不同特性的纤维素纳米纤丝(CNF),考察了不同过程参数对CNF得率的影响,并使用扫描电子显微镜(SEM)、X射线衍射仪(XRD)、热重分析仪(TGA)和纳米粒度仪分析了CNF的表面形貌、结晶度、热稳定性及粒度均一性变化。结果表明,水解温度由100℃增加到140℃,CNF得率降低了37.6个百分点,CNF的聚合物分散性指数(PDI)数值逐渐减小,CNF中长纤维和块状纤维逐渐减少,当水解温度达到140℃时,CNF长度约100 nm,分布均匀;而CNF的结晶度随水解温度的增加呈先升高后略微降低的趋势;水解时间由1 h增加到3 h,CNF得率从62.8%下降到49.8%,CNF的PDI数值和结晶度值均呈现先上升后下降规律,当水解时间达到3 h时才能获得直径约100 nm左右的CNF;球磨时间由8 h增加到24 h,CNF的直径均已达到100 nm,CNF马尔文粒度的PDI数值不断上升,CNF颗粒均一性下降。球磨16 h制备的CNF热稳定性提高。     

改性漆酶协同谷氨酸改善二次纤维微观结构及性能的研究

采用L-苯丙氨酸甲酯盐酸盐对漆酶氨基酸残基末端的羧基进行改性,研究改性漆酶-谷氨酸体系对旧瓦楞箱纸板(OCC)浆纤维微观结构及性能的影响。研究结果表明,与未改性漆酶-谷氨酸相比,经过改性漆酶-谷氨酸体系处理后OCC浆纤维表面呈层叠状紧密黏连,细纤维化程度更高;改性漆酶催化氧化木素,使纤维微孔结构瓦解并逐渐扩大为中孔,纤维BET比表面积和平均孔径增大;谷氨酸通过迈克尔加成反应嫁接到木素上使纤维羧基含量进一步提升,与OCC原浆相比纤维羧基含量提高了26.9%;显著改善纸浆的打浆性能,降低了打浆能耗;对纸浆的增强作用更加明显。     

Toward Sustainable, Economic, and Tailored Production of Cellulose Nanomaterials

This paper introduces a concentrated di-carboxylic acid(DCA) hydrolysis process for the integrated production of thermally stable and carboxylated cellulose nanocrystals(CNCs) and cellulose nanofibrils(CNFs). The DCA hydrolysis process addressed several issues associated with mineral acid hydrolysis for CNC production, such as cellulose loss and acid recovery. The surface and morphological properties of the cellulose nanomaterials resulting from the DCA hydrolysis process can be tailored simply by controlling the severity of DCA hydrolysis. To further reduce cost, a lowtemperature(≤80℃) hydrotropic chemical process using p-toluenesulfonic acid(p-Ts OH) was also introduced to rapidly fractionate raw lignocelluloses for the production of lignin containing cellulose nanofibrils(LCNFs) and lignin nanoparticles(LNPs). The LCNF surface hydrophobicity and morphology can be tailored by controlling the fractionation severity, i.e., the extent of delignification. The lignin also improved the thermal stability of LCNFs. LNPs can be easily separated by diluting the spent acid liquor to below the p-Ts OH minimal hydrotropic concentration of approximately 10%. p-Ts OH can also be easily recovered by re-concentrating the diluted spent liquor after lignin precipitation. We believe that these two novel processes presented here have the potential to achieve true sustainable, economic, and tailored production of cellulose nanomaterials, suitable for a variety of applications.     

酶解辅助高压均质制备纳米纤维素及其性质表征

本研究以微晶纤维素为原料,经过超微粉碎预处理后,通过酶解辅助高压均质的方法制备纳米纤维素,研究纳米纤维素的结构和理化性质,并通过扫描电镜、透射电镜、红外光谱、X-射线衍射和热失重分析对纳米纤维素进行表征。结果表明,超微粉碎前处理能使微晶纤维素颗粒大小形状趋于均一化;所制备的纳米纤维素呈束状结构,颗粒直径为15⁴0 nm;纳米纤维素在制备过程中纤维素结构未遭到破坏;纳米纤维素的结晶度为58.1%,仍属于纤维素Ⅰ型;纳米纤维素的起始热分解温度比微晶纤维素的分解温度低,当温度达到500℃时,纳米纤维素的热失重率为82.9%。因此通过酶解辅助高压均质制备的纳米纤维素有望在可降解复合材料中得到应用。      

海藻酸钠-纳米纤维素胶粒对乳酸菌胃肠液耐受性的影响

为提高海藻酸钠胶粒对乳酸菌在胃肠液中的保护作用,分别利用豆渣纤维素纳米微纤丝与纤维素纳米微晶协同钙离子交联海藻酸钠包埋乳酸菌制备载菌海藻酸钠-纳米纤维素胶粒,并对海藻酸钠-纳米纤维素胶粒进行微观结构观察、傅里叶变换红外光谱分析、低频氢谱核磁共振分析,同时测定载菌海藻酸钠-纳米纤维素胶粒胃肠消化前后的活菌数量,研究海藻酸...     

纤维素纳米纤丝复合材料在药物缓释中的应用

纳米纤维素具有可再生、环境友好、可生物降解、比表面积大、弹性模量高、生物相容性好等优异特性。利用纤维素纳米纤丝开发药物载体材料,有助于促进农林生物质资源的高值化应用。本文系统地综述纤维素纳米纤丝复合水凝胶材料、复合气凝胶材料、复合膜材料在药物缓释领域中的研究现状,阐述其药物缓释机理,并展望纳米纤维素在药物缓释领域的发展方向。