DOI: 10.14457/tu.the.2019.523
title: Preparation of defatted rice bran cellulose nanocrystals and their applications in pickering emulsion stabilization

description: The biodegradability, remarkable physical properties and excellent biological properties of cellulose nanocrystals (CNCs) have made them an attractive material for design and development in many applications. Various sources of cellulose have been used as a raw material for the production of CNCs. In this work, an agricultural residue, defatted rice bran (DRB), was used as a cellulosic source for the isolation of cellulose nanocrystals (CNCs) by two different methods which were treated with NaOH/urea solution and hydrolyzed with 55% sulfuric acid. The morphologicalinvestigation of CNCs was performed by transmission electron microscopy (TEM), indicating a needle-like structure for CNCs which were isolated by sulfuric acid hydrolysis. The smaller particles size of those CNCs were demonstrated compared to CNCs which were treated by NaOH/urea solution. The rheological properties of CNCssuspensions were observed to understand the behavior of CNCs suspensions that are able to impact on processability. The zeta potential and sulfur content of hydrolyzed CNCs were also measured to investigate the colloidal stability and the surface charge density during the storage. In addition, the water adsorption property of CNCs was studied by near-infrared spectroscopy. It can be observed that CNCs have high rate of adsorption of water molecules. The surfaces of CNCs are often chemically modified to modulate their ability to form and stabilize emulsions. This approach, however, the chemical functionalization of CNCs can become the limitation in many applications. In this study, we investigated the possibility of tailoring the CNCs with surfactant through thephysical adsorption which could be much simpler and cost effective. Therefore, rice bran CNCs were applied as interfacial stabilizers in rice bran oil-in-water (o/w) Pickering emulsions, incorporated with a non-ionic surfactant (PG1.5SFR0.05) and gum arabic. The synergistic effect of PG1.5SFR0.05 and CNCs produced higher stability ofemulsion, with smaller mean diameter and monodisperse droplets compared to the incorporation of only gum arabic. The rheological data provided evidence of gel-like behavior in all emulsions. The emulsions were also tested with various NaCl concentrations due to the emulsion stability can be triggered by adjusting salt concentration. Furthermore, the interactions between rice bran CNCs and lauric arginate (LAE), a food-grade cationic surfactant was investigated. Complexes of anionic CNCs and cationic LAE (CNCs/LAE) were formed through electrostaticattraction which were confirmed using isothermal titration calorimetry (ITC), turbidity, and zeta-potential measurements. The complexes could be formed by 1:2 (w/w) CNCs-to- LAE at saturation. In addition, the physical and oxidative stability of oil-in-water emulsions containing lipid droplets coated by CNCs/LAE complexes was determined. Electrostatic complexes formed from 0.02% CNCs and 0.1% LAE produced high stable Pickering emulsions that were resistant to droplet coalescence. These emulsions also had relatively low lipid oxidation rates by presenting lower primary (lipid hydroperoxides) and secondary oxidation products (headspace hexanal) formationcompared to emulsions stabilized by LAE alone. The influence of emulsion stabilized by CNCs and non-ionic surfactant, Tween 20, to lipid oxidation was investigated as well. They presented the higher lipid oxidation rate compared to the emulsions stabilized by CNCs/LAE complexes. Furthermore, cold-pressed rice bran oil-in-wateremulsion indicated more stable against lipid oxidation compared to soybean oil-in-water emulsion. The developing of cold-pressed rice bran oil in emulsion system is thereby an alternative way for the utilization as a function ingredient in many products.