Available online freely at www.isisn.org Bioscience Research Print ISSN: 1811-9506 Online ISSN: 2218-3973 Journal by Innovative Scientific Information & Services Network RESEARCH ARTICLE BIOSCIENCE RESEARCH, 2021 18(SI-2): 323-333. OPEN ACCESS The effect of cellulase-hydrolyzed chitosan on the degree of deacetylation, solubility and viscosity of chitosan oligosaccharides Yusof Nurhayati 1* , Ezzat Mohamad Azman 2 , Asmaliza Abd. Ghani 1 , Norzaida Yusof 1 , John Yew Huat Tang 1 1 Faculty of Bioresources and Food Industry, Universiti Sultan Zainal Abidin, Besut Campus, 22200 Besut, Terengganu, Malaysia 2 Faculty Food Science and Technology, Universiti Putra Malaysia, 43400 UPM, Serdang, Selangor, Malaysia *Correspondence: nurhayatiyusof@unisza.edu.my Received 05-07-2021, Revised: 12-08-2021, Accepted: 15-08-2021 e- Published: 20-08-2021 Chitosan is a source of potential bioactive material with many uses in the food, health and agricultural sectors. However, the limitation to utilize the chitosan in biological applications, comprising poor solubility under physiological conditions. In order to overcome the limitations, chitosan is being partially hydrolysed to produce chitosan oligosaccharides (COS). The objective of this research was to determine the degree of deacetylation (DDA), solubility and viscosity of the chitosan and COS. In this study, chitosan was hydrolysed by the cellulase from Trichoderma reesei to produce COS. The DDA of chitosan and COS were determined by linear potentiometric titration. The physical characteristics including solubility and viscosity were assessed. The COS was characterized by the degree of polymerization (DP) and FTIR spectroscopy by examining the structural changes before and after the degradation of chitosan. COS showed a higher DDA (99.69 % ± 0.28) compared to chitosan obtained from Sigma Aldrich (77.54 % ±0.28). This enzymatic product, COS also showed high solubility in aqueous and acidic solutions as compared to the chitosan sample. The product of hydrolysis of chitosan mainly composed of COS, with the DP 1-2. The IR spectrum showed that there was no significant change of chitosan before and after the enzymatic hydrolysis confirming the conservation of the chemical phase of the chitosan. In conclusion, COS preparation using cellulase, a low-cost commercial enzyme could open a wide range of new potential applications to improve the quality of many foods. Keywords: chitosan, chitosan oligosaccharides, solubility, degree of polymerization, degree of deacetylation INTRODUCTION Chitosan is the major derivative of chitin, an abundant renewable natural resources and the main source of crustacean waste (Mincea et al. 2012). The amino group (NH2) is formed after an acetyl group (C2H3O) is being removed from the deacetylation process of chitin. The resulting copolymer of N-acetyl-glucosamines (GlcNAc) and glucosamine (GlcN) with the copolymer contain more than 50% GlcNAc units referred to as chitin. The degree of acetylation (DA) referred to the percentage of GlcNAc units in chitin polymers can vary from 50% to 100%. On the other hand, the copolymer contains more than 50% GlcN units is typically referred to as chitosan. For chitosan polymers, the degree of deacetylation (DDA) referred to as the percentage of GlcN units can vary from 50% to