Methods of Chitin Production a Short Review

Such characteristics, diverse applications in areas such as agriculture, food, environmental, and as two areas with greater focus: pharmaceutical and health [3,4]. Its structure consists of N-acetyl-d-glucosamine units with β- (1,4) bonds, having as main characteristic the insolubility in water and some organic acids [5]. Chitin belongs to the group of structural polysaccharides, together with cellulose, the second polymer being more abundant in the biosphere [6-9]. Due to its structural nature, a product release system was not found in any of the arthropod exoskeleton, in the structures of molluscs [10], in the cell wall of fungi [11,12], protozoa and bacteria, egg shells of nematodes [13,14], the shrimp fishery residue being the most widely used source [15].Throughout the decades of research and handling of this polymer, many methods of extraction have been developed, being the chemical method most found in the literature, being also used in the means of production of industrial chitin. The USA, Japan, India, Canada, China, South Korea, Russia and Norway generally use the reject of crustacean fishing for production. The use of strong acids and bases in the chitin extraction process generates critical points to the process, such as: high cost of the materials involved, generation of chemical effluent and final product with low levels of purity [16,17]. Biological processes become more attractive because they have an affordable cost of production, do not generate high risk effluent (such as the chemical process) and high-quality final product [18,19]. All the processes found in the literature are an objective: to obtain chitin by separating the proteins and minerals from the raw material used [20]. Chitin, besides having great biotechnological value, generates by-products (such as chitosan) that also have added value and even more relevant properties. In this paper we discuss the already known processes of obtaining chitin known and registered in the literature of 2010 up to the present moment: Chemical, enzymatic and biological processes relating the different methods of obtaining and with the objective to identify the particularities of each process regarding the industrial viability and economically balancing them so that the reader concludes the best process for their research, also the possibility of executing quality improvements in these processes. We will also discuss the polymorphic structures of α- and β-chitin and the different methods of obtaining each, since different processes are required in each of them due to their structures, properties and reactivity. The main objective of this review is to be able to relate the different processes of obtaining chitin with the most suitable applications for the method, based on such relation in aspects such as degree of purity and economic applicability.甲壳素（chitin）具备多样应用场景，覆盖农业、食品、环境等领域，其中医药与健康两大方向受关注度尤高[3,4]。其结构由以β-(1,4)键连接的N-乙酰-D-氨基葡萄糖（N-acetyl-d-glucosamine）单元构成，核心特征为不溶于水及部分有机酸[5]。 甲壳素隶属于结构多糖类群，与纤维素同属此类，后者是生物圈中含量第二丰富的聚合物[6-9]。鉴于其结构特性，在节肢动物外骨骼、软体动物组织[10]、真菌细胞壁[11,12]、原生动物与细菌以及线虫卵壳[13,14]中均未发现存在该聚合物的专属释放体系；而虾类渔业废弃物则是当前应用最广泛的甲壳素原料来源[15]。 历经数十年对该聚合物的研究与开发，现已衍生出多种提取工艺，其中化学法是文献中最常见的提取手段，同时也应用于工业级甲壳素的生产环节。 美国、日本、印度、加拿大、中国、韩国、俄罗斯与挪威等国普遍采用甲壳类捕捞废弃物作为甲壳素生产原料。但在甲壳素提取过程中使用强酸与强碱会带来诸多工艺痛点：原料成本高昂、产生化学废液，且最终产品纯度偏低[16,17]。相较而言，生物法更具应用吸引力：其生产成本可控、不会产生高风险废液（相较于化学法），且可获得高品质的最终产品[18,19]。现有文献记载的各类提取工艺，其核心目标均为从所用原料中分离蛋白质与矿物质，从而获取甲壳素[20]。 甲壳素不仅具备极高的生物技术应用价值，其衍生副产物（如壳聚糖（chitosan））同样具备附加价值，甚至拥有更为突出的特性。本文将讨论2010年至今文献中已公开并收录的甲壳素提取工艺：包括化学法、酶法与生物法，梳理各类提取方法的差异，并旨在明确各工艺在工业可行性与经济性层面的特性，帮助读者遴选适配自身研究的最优工艺，同时探讨对上述工艺进行质量优化的可能性。 此外，本文还将讨论α-甲壳素与β-甲壳素的多晶型结构，以及各自的获取方法——由于二者在结构、特性与反应活性上存在差异，因此需采用不同的提取工艺。本综述的核心目标为：基于纯度、经济适用性等维度的关联分析，将不同的甲壳素提取工艺与适配的应用场景进行匹配。