Citation: Taokaew, S.; Kriangkrai, W. Chitinase-Assisted Bioconversion of Chitinous Waste for Development of Value-Added Chito-Oligosaccharides Products. Biology 2023, 12, 87. https://doi.org/10.3390/ biology12010087 Academic Editors: Matthias Behr and Bernard Moussian Received: 29 November 2022 Revised: 25 December 2022 Accepted: 29 December 2022 Published: 5 January 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). biology Review Chitinase-Assisted Bioconversion of Chitinous Waste for Development of Value-Added Chito-Oligosaccharides Products Siriporn Taokaew 1, * and Worawut Kriangkrai 2, * 1 Department of Materials Science and Bioengineering, School of Engineering, Nagaoka University of Technology, Nagaoka, Niigata 940-2188, Japan 2 Department of Pharmaceutical Technology, Faculty of Pharmaceutical Sciences, Naresuan University, Phitsanulok 65000, Thailand * Correspondence: t.siriporn@mst.nagaokaut.ac.jp (S.T.); wg.kriangkrai@gmail.com (W.K.) Simple Summary: Bioconversion of chitinous waste to chito-oligosaccharides using chitinase is an attractive strategy for traditional waste management. Chito-oligosaccharides have a broad range of applications due to their water solubility and possess various biological properties. The different sources of chitinase provide different yields and physicochemical properties, e.g., the degree of polymerization of chito-oligosaccharides. This review discusses the potential of chitinase in chito- oligosaccharide production with a focus on the chitinase sources, chemo-enzymatic production of chito-oligosaccharides and their derivatives, applications of chito-oligosaccharides, and the route to industrialization, based on the academic studies published within the most recent decade. Abstract: Chito-oligosaccharides (COSs) are the partially hydrolyzed products of chitin, which is abundant in the shells of crustaceans, the cuticles of insects, and the cell walls of fungi. These oligosaccharides have received immense interest in the last few decades due to their highly promising bioactivities, such as their anti-microbial, anti-tumor, and anti-inflammatory properties. Regarding environmental concerns, COSs are obtained by enzymatic hydrolysis by chitinase under milder conditions compared to the typical chemical degradation. This review provides updated information about research on new chitinase derived from various sources, including bacteria, fungi, plants, and animals, employed for the efficient production of COSs. The route to industrialization of these chitinases and COS products is also described. Keywords: chitinase; chitin; waste; chitosan; chito-oligosaccharides; bioconversion; sustainability 1. Introduction Globally, about six to eight million tons of sea food waste is generated from crab, shrimp, and lobster shells every year [1]. The environmental concerns are caused by the disposal of this seafood waste accumulating along coastal areas since their natural digestibility is relatively low. In developed countries, disposal is costly—up to USD 150 per ton in Australia, for example [2]. Because such waste is a rich source of chitin (15–40% of the total weight of crustaceans), not only is the bioconversion of chitin food wastes to added-value products, an effective, eco-friendly form of waste management, but also those products are valuable from a market perspective [3,4]. For instance, dried shrimp shells are valued at USD 100–120 per ton. The ground shells can be used as an animal-feed supplement, as fertilizer, and in chitin production [2]. Chitin is the second most abundant polysaccharide. It is composed of repeated units of N-acetylglucosamine (GlcNAc) linked by β-(1,4)-glycosidic bonds for 100% degree of acetylation (DA), or the DA is lower due to the composition of D-glucosamine (GlcN) [5]. Predominantly, chitin is found in the cell walls of fungi [6–12] and algae [13], the ex- oskeletons of invertebrates, including insects [14–16], and the structural component of Biology 2023, 12, 87. https://doi.org/10.3390/biology12010087 https://www.mdpi.com/journal/biology