Preparation And Characterization Of Pineapple Peel Cellulose Nanocrystals/Polysaccharide-based Composite Material And Its Preliminary Application

In this work,cellulose was extracted from pineapple peel residue,and cellulose nanocrystals was prepared from the pineapple peel cellulose.Pineapple peel cellulose nanocrystals（PPCNC）and polysaccharide（chitosan,sodium alginate）were prepared into hydrogel beads and films.The structures of PPCNC,hydrogel beads and films were characterized.Studies on bacteriostatic effect,enzyme immobilization and drug release based the mixtures of PPCNC and sodium alginate and chitosan were carried out.The main results of this work are concluded as follows:（1）PPCNC was prepared and isolated from pineapple peel by means of sulfuric acid hydrolysis,ammonium persulfate oxidation and enzymatic hydrolysis,respectively.The structures and morphological features of the prepared PPCNCs were characterized and compared.The results showed that the three types of PPCNC retained the main structure of cellulose as type I cellulose crystal type.The crystallinity of PPCNC prepared by ammonium persulfate oxidation and sulfuric acid hydrolysis reached 66.9%and 57.5%respectively,while the crystallinity of cellulose crystals prepared by enzymatic hydrolysis was 31.3%;all the prepared PPCNCs showed reduced thermal stability compared to pineapple peel cellulose.Both the PPCNCs prepared by ammonium persulfate oxidation and sulfuric acid hydrolysis were short-bar-shaped with an average particle size of 150.93 nm and 134.1 nm,respectively while the PPCNC prepared by enzymatic hydrolysis showed longer with an average particle size of 553.5 nm.The absolute value of the Zeta potential of all the PPCNCs was above 30 mW,and the yields of PPCNC prepared by sulfuric acid hydrolysis was the highest（43.2%）.（2）The S-PPCNC,chitosan,and tea polyphenol were blended to prepare a composite film,and the structure of the composite film was characterized.The structure of the composite film was characterized and the comprehensive properties of the film were measured.The antibacterial effect of the film was studied.The results showed that S-PPCNC,chitosan,and tea polyphenol could be uniformly mixed and interacted.With the increase of S-PPCNC content,The composite film showed the enhanced water vapor barrier property.The elongation at break of the film decreased remarkably,but the effect on the tensile strength was not obvious.When the concentration of S-PPCNC is 0.1%,the transparency of the composite film was the best.The effect of S-PPCNC on the antibacterial activity of the composite film was not obvious.While the addition of tea polyphenol enhanced the antibacterial performance of the prepared film with better antibacterial performance on Staphylococcus aureus than Escherichia coli.（3）Composite hydrogel beads and film based on S-PPCNC and SA were prepared to embed bovine serum albumin blended with sodium alginate and immobilize flavor protease,CaCl₂ and glutaraldehyde as crosslinking agent.The structure of hydrogel beads and composite films were characterized,and the immobilization process,enzymatic properties,mechanical properties and drug release properties of the composite films were studied.The results showed the addition of S-PPCNC can increase the tensile strength of the S-PPCNC/SA film.When the concentration of S-PPCNC is 0.05%,the tensile strength reaches the maximum and the effect on the elongation at break is not obvious.The S-PPCNC/SA film has a certain pH sensitivity.The water absorption rate in simulated intestinal juice is higher than that in simulated gastric juice.The drug release rate of the S-PPCNC/SA film is affected by the crosslinking time,the crosslinker concentration and the S-PPCNC concentration,which can be changed to realize drug controlled release.For the prepared S-PPCNC/SA beads,the optimal immobilization conditions were as followings:mass ratio of SA and PPCNC,at 100:1,1%of CaCl₂ concentration,enzyme dosage at 3 mg/mL,1%of glutaraldehyde concentration and 3 h of crosslinking time.After three times of repeated use,the immobilized enzyme still remained above 85%of its initial activity.The optimal reaction temperature of immobilized enzyme was increased and the storage stability improved.The optimal pH was shifted to acidity to 6.0.