| Nanocellulose has many advantages,such as high aspect ratio,high specific surface area,good mechanical properties and reproducibility,which is usually used in the preparation of lightweight porous materials.Due to its unique nanostructure,nanocellulose lightweight porous materials(NCLPM)show excellent mechanical strength,flexibility,biodegradability,safety and non-toxicity,displaying great potential for application in food fields.The modification of nanocellulose can improve and endow NCLPM with better performances,such as mechanical properties,hydrophobicity and antibacterial properties.TEMPO oxidation and ball milling are currently commonly used methods for preparing cellulose nanofibrils(CNF).TEMPO oxidation can effectively promote cellulose defibrillation,which may enhance the efficiency and product performance of CNF prepared by ball milling.However,there are few studies on the effects of TEMPO-mediated oxidation on the structure and properties of CNF prepared by ball milling.Freeze-drying is a common method for NCLPM preparation,but it has the bottleneck problems of high energy consumption and long processing time.It is of great significance to develop a low cost,low energy consumption and green preparation method for NCLPM.Based on the above background,in this study,CNF(PP-TOCNF)was extracted by TEMPO oxidation combined with ball milling process using pineapple peel(PP),a typical fruit and vegetable by-product,as cellulose raw material.The effects of TEMPO oxidation degree on the structure and physicochemical properties of PP-TOCNF were studied.Then PP-TOCNF was preliminarily used in the preparation of NCLPM.Glutaraldehyde was used as a cross-linking agent to form covalent cross-linking between TOCNF and common food protein(gelatin).The TOCNF/gelatin composite lightweight porous material(TOCNF-G-LPM)was prepared by ice-template combined with atmospheric pressure drying.The effects of different gelatin addition on the structure and physicochemical properties of TOCNF-G-LPM were investigated,and the biosafety of TOCNF-G-LPM was evaluated.Finally,the porous structure and absorption properties of TOCNF-G-LPM were used to introduce typical plant active polyphenols(tannic acid,TA),endowing TOCNF-G-LPM with certain antioxidant and antibacterial properties,and the application of TOCNF-G-LPM as active packaging material in the preservation of refrigerated pork was studied.The specific research conclusions are as follows:(1)The structure and physicochemical properties of PP-TOCNF can be effectively regulated by adjusting the addition of Na Cl O(2.5 to 10 mmol)in TEMPO-mediated oxidation reaction with further ball milling.TEMPO-mediated oxidation endowed PP-TOCNF with excellent dispersion and suspension stability in water and good network building capabilities.With the increase of oxidation degree,the content of carboxyl group in PP-TOCNF gradually increased(0.218～0.550 mmol/g),the absolute value of Zeta potential gradually increased(-18～-34 m V),the average diameter gradually decreased(40～17 nm),and the viscosity gradually increased.The results of FTIR,XPS and XRD showed that the basic chemical structure of cellulose was not changed after TEMPO oxidation,but the thermal stability was decreased.The porous material obtained by freeze-drying PP-TOCNF suspension showed good light weight property.Tuning TEMPO oxidation level can effectively adjust its porosity(98.95%～99.35%),density(0.0097～0.0156 g/cm~3),water absorption(38.18%～71.71%),and mechanical properties(14.45～37.67 k Pa),showing good potential application as lightweight porous materials.(2)Using gelatin as auxiliary material and glutaraldehyde as crosslinking agent,TOCNF-G-LPM was prepared by using ice-template combined with atmospheric drying technology,and the effects of different gelatin addition(0%～1.0%)on the morphology,pore structure and physicochemical properties of NCLPM were investigated.The results of FTIR and XRD showed that TOCNF and gelatin could be connected by covalent cross-linking and physical hydrogen bonding.SEM and CLSM images showed that the appropriate amount of gelatin was conducive to the formation of more uniform pore structure and oriented network of TOCNF-G-LPM.The mechanical properties of TOCNF-G-LPM were significantly improved,the shape recovery ability and thermal stability were slightly improved,but its water and oil absorption ability decreased.In addition,the swelling process of TOCNF-G-LPM conformed to Schott’s second-order kinetic model.The experimental results of safety evaluation based on C.elegans model showed that TOCNF-G-LPM had no significant effect on the growth and reproduction of C.elegans with good biocompatibility.(3)Based on the porous structure and swelling adsorption properties of TOCNF-G-LPM,the TOCNF-G-LPM loaded with TA(TOCNF-G-LPM-TA)was prepared by direct immersion in TA solutions of different concentrations(0.5～2.5 g/L).The adsorption properties of TOCNF-G-LPM on TA,and antioxidant and antibacterial activities of TOCNF-G-LPM-TA and its preservation effect on refrigerated pork were investigated.The FTIR results showed that hydrogen bond interaction existed mainly between TOCNF-G-LPM and TA.The TOCNF-G-LPM showed excellent adsorption capacity for TA,with the maximum theoretical adsorption capacity of 230 mg/g,and the adsorption process fitted well with the second-order kinetic model.The isothermal adsorption process of TOCNF-G-LPM and TA was in accordance with Langmiur model.After the introduction of TA,the obtained TOCNF-G-LPM-TA showed excellent antioxidant and antibacterial activities,with a DPPH free radical scavenging rate of80.64%(TOCNF-G-LPM-2.5TA),and ABTS free radical scavenging rate of all samples was close to 100%,and also showed obvious antibacterial effect on Staphylococcus aureus.TOCNF-G-LPM-TA as fresh-keeping pad can significantly improve the preservation effect of refrigerated pork.When refrigerated at 4℃for 6 days,the experimental group significantly slowed down the p H growth rate of pork and the release of TVBN,and extended the shelf life of refrigerated pork. |
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